Rendering Tips for Patch and Repair Work

Ernie Cook, the master bricklayer, who I had the pleasure of working for in my teens used to say “The worst thing that has happened to the building industry is cement”. It was a bit of an exaggeration but we spent a lot of time travelling around London and the South East putting right the work of bricklayers who were born into the cement age and knew nothing of working on buildings built with sand and lime.

The results were cracks appearing where they had never been before and spalling brick faces caused by moisture trying to find an escape route. All this because the brickie had the wrong mix for the job.

“If only they would use a bit of lime” said Ernie.

“If only they would use a bit of lime we would be out of work” I replied.

Lime is a magical material that has the ability to move and reconstitute itself in mortar, render and plaster. It is said that during the Blitz many of the buildings built with lime would jump minutely to absorb the impact of a nearby explosion whereas the sand and cement buildings would crack apart and stay cracked.

It is a golden rule of bricklaying that the mortar should be no stronger than the material it is joining together. That, in a nutshell, is the reason that Ernie Cook had such a poor regard for cement mortar. It wasn’t the fault of the cement so much as the lack of knowledge of those using it.

Nowhere is this more evident than in modern building with lightweight aircrete blocks. The mortar used to build block walls should be around 1 part cement to 8 parts of soft sand but it is rare to see bricklayers changing the mix (gauge) between the blocks and brickwork which is typically laid 1 part cement and 4 or 5 parts sand.

Limey mix for rendering

The result is that the blockwork moves at the weakest point which is the block itself and not the mortar. This produces cracks at the place where the blocks are most free to move, which is usually directly under windows. The cure, according to some builders, is to use an even stronger sand and cement render mix as a base coat for plaster. I have seen this done on so many occasions that I have lost count. Of course now the use of dot and dab plasterboard hides the cracks from view.

Another common problem is a strong mix of sand and cement render on exterior walls. Some plasterers think this stops cracking but sand and cement will always shrink and it pulls the brick or block with it producing hairline cracks. Until you’ve seen it you won’t believe how much water can run down a wall and track in along horizontal hairline cracks.

The capillary action sucks it in to soak internal faces. I have seen walls covered with the white web of dry rot simply because water has tracked in through cracks that you would hardly notice with the naked eye. Even worse is when well-meaning builders rake those cracks out and fill them with even stronger sand and cement or resin thinking that it will stick the building together. What then happens is the seasonal movement in the building causes the cracks to push upon the hard repair and lever the cracks open even more.

So faced with all this grief, why are brickies and plasterers still so anti-lime and pro-cement?

The reason that many won’t kick the habit or at least cut down is because putting in less cement makes the mix difficult to work with. It loses moisture into the bricks and won’t stay on the trowel. The simple answer is to use an equal part of hydrated lime and cement but this means ordering two different materials and mixing them together.

The modern answer is to use plasticiser which mimics lime by putting lots of tiny balls of air into the mix to help it flow. While plasticiser introduces air to increase workability and help frost resistance it doesn’t have the same stickability as lime. It does, however, allow the brickie to use less water which helps reduce shrinkage so it is a good second best.

The same effects can now be achieved by using enhanced cement which has plasticisers in a powder form but, in my experience, it still isn’t the same as putting hydrated lime in. The ratio of hydrated lime to cement is important. The lime should not exceed the cement. If you use more lime than mortar it is likely to fail if the frost gets to it. A typical mix is 1cement 1 lime 6 soft sand for bricklaying or sharp sand for rendering. If you want an even weaker mix for internal blockwork then a 1.1.9 can be used.

Not only does the hydrated lime help the workability and adhesion of the mortar it also retains the moisture during the initial set to assist hydration. The set takes place before the mortar has fully shrunk which means it is less likely to crack.

Even if it does crack, say with building movement, the lime helps the mortar to self-repair by leaching lime into cracks. The lime then reacts with the atmosphere to form limestone in much the same way that stalactites are formed. This makes it the ideal material for repointing brickwork.

The most important thing you have to get to grips with is that hydrated lime is different to hydraulic lime.

Many people confuse hydraulic and hydrated lime. The use of hydraulic lime in bricklaying, rendering and re-pointing is old school but is now largely confined to historic buildings. Hydraulic lime sets in days, sometimes weeks and is much too slow for most builders looking for fast track solutions.

Hydrated lime mixed with cement is far quicker to set. It is the reaction between the hydrated lime and the cement which makes it set, if you leave out the cement it simply won’t set. Although hydrated isn’t a direct substitute for hydraulic lime, it does give some of the benefits.

If you are extending an old building for example and want a good colour match but don’t want to go to the trouble of using hydraulic lime then hydrated lime is the next best thing.

If all this has started your head spinning just retain one thing. Next time you are doing a bit of above ground bricklaying or rendering buy a bag of hydrated lime from the merchants and add it to the mix in equal quantities to the cement. The instructions should be on the back of the bag. If you do this you will never go back to straight sand and cement.

We would very much welcome your comments below.

About Roger Bisby

Roger Bisby is an English television presenter and journalist, known for his expertise in the British building industry.

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  1. Hi Roger, I think all your tips are brilliant. I am self building but my plasterers are making an awful job of the external render, so I ‘ve decided to have a go. I have multicem cement from Hanson mixed at 6:1:1. What is the situation with adding water proofer and fibres ? and also is this enhanced cement okay to use or do I need ordinary cement.
    Your advice will be gratefully received,
    Thank you.

    • That is fine. That cement has lime in it so it will work well. Fibres are only good in the base coat. Better still is fibreglass mesh in the base coat. You can buy it and push it into the scratch coat. It is available from Teco Products in Shoreham and it will stop cracking

      • Thank you very much. There are too many cowboys out there and it is appreciated that you spend time helping others with good solid sound advice. Thanks again.

      • Hi Roger.

        Iv been watching your YouTube video online and i think there fantastic how you explain everything in detail.

        I’m a self DIY beginner. Just wanted to ask you, what are the ratios of mixing lime render for internal walls??? Also do u need to PVA the walls first???



        • Thanks Moe. I wish YouTube had been around when I was starting out and making so many mistakes. I am happy to pass it all on now.
          The render mix for internal walls depends on the strength of the masonry. If it is Celcon or Thermalite then something along the lines of 6 to 1 lime and 1 cement will be strong enough. I would say you could go to 8 sand to 1 cement 1 lime but it is hard to get it to stick. If you put a good dose of PVA in the water then it will hang together and be easy to spread.
          If you paint PVA on the walls you need to get the mix on while it is tacky. The way to do it is just keep a 6 inch brush in a bucker and slosh it on as you move along the wall.

    • I forgot to use lime when rendering recently, so it’s great to get your advice. I was shown that adding detergent helps with the workability but you havn’t mentioned it. I’m rendering the cement blocks, below my weather boards, so perhaps I should make a slightly stronger mix, say 5:1:1?

  2. Hi im a bricky by trade and am looking to render dormer window cheeks,which are already plyed and felted with the beads on and coverd in eml what would be the best sand and cement mix for the scratch coat and the top coat and also what coat do i put the waterproofer in.

    Thanks dave

    • Hi Dave

      I am assuming that you are using a breather membrane under the eml to stop any damp getting into the plywood. If so then the water proofer isn’t so critical. If you use a 5-1-1 sand cement and hydrated lime that will be good. I would put on the scratch coat and then put a little SBR in the finish coat and that will act as a waterproofer.
      You can use the same mix on both coats but the top coat will be thinner.

      • Hi thanks for the reply,
        yes its breathable felt and do you recommend sbr instead of a liquid water proofer additive for example opti-mix ?

        Thanks dave

  3. Hello Roger

    Thanks for your great Rendering Tips. This explains why I have been having so much trouble trying to get a decent finish. I do have a couple of questions if you would be kind enough to help.

    You recommend a mix of
    1 cement, 1 Lime to 6 sand for block work. Does this apply to all block work regardless of the density. I am using Dense 7 nm blocks for a retaining wall.

    Where can I buy the Round Bonnet Sponge you recommend in the video.

    • You can use a stronger mix on dense blocks. The mix should never be stronger than the block so you could even go for 3 to 1 lime, 1 cement but really that is a below ground mix so maybe go 4-1-1.
      The sponge is called a drywall sponge. They come from Gyproc tools and Refina. Good builders merchants should be able to get them next day through Toolbank or try William Way Godstone Surrey. Ask the boys and tell them I sent you. They will post you one out.
      Address: 38-42 High St, Godstone RH9 8LW
      Phone:01883 742757

  4. Hello Roger

    Thanks for your great Rendering Tips. This explains why I have been having so much trouble trying to get a decent finish. I do have a couple of questions if you would be kind enough to help.

    You recommend a mix of
    1 cement, 1 Lime to 6 sand for block work. Does this apply to all block work regardless of the density. I am using Dense 7 nm blocks for a retaining wall.

    Where can I buy the Round Bonnet Sponge you recommend in the video.

  5. Hi Roger. Recently put a scratch coat on consisting of 4-1 sand and cement with waterproofer. I SBR’D the red brick wall prior to scratch coat. Then decided on using lime on final coat. Consisting of 4-1-1 with SBR in mix. Went on a dream and then when drying it has developed “Hairline cracks” they just look like fine lines. Any idea what may have caused this. I used plasterers sand in the final skim.

    • Hi James
      It might have helped if you had used the lime in both coats so you had uniform movement. The cracks are shrinkage of the top coat, sometimes the sand is a bit sharp and a little building sand mixed in gives it a bit of body but they are nothing to worry about. If you are masonry painting them the paint will fill them. If they are left bare the lime will leach into them. If you tap the wall there shouldn’t be a hollow sound and that is what matters.

  6. Thanks Roger, did the job for a family member and he said they seem to dissappear when rubbing the wall.

  7. Hi Roger,
    I have a 1.5m brick wall between my property and next door. It retains about 1m of earth, on their side.

    It is fairly old and showing signs of spalling (crumbling bricks and some vertical cracks). A BC officer who was inspecting some other works we were having done suggested that I could use a mesh and rnder (or resin?) over the wall to give it a few more years.

    Could you recommend a mesh product (I’m assuming it’s a fibreglass mesh?) and would you recommend resin or render – like your video above?

    Do you need to attach the mesh to the wall first (somehow?) or do you render, push mesh in, then skim over?

    I was going to drill some weep holes and insert a (probably copper water pipe) through at variuos points along length to assist water release, as I think this is part of reason for damage. Sound sensible?


    • I would start with the drain pipes to get rid of the water behind it. Then I would stitch the cracks with helical ties. That will put the strength back in it. Then put on a slurry coat of sand cement and SBR. Then apply a thicker coat of render and press glass fibre mesh into it. You can get this from Teco in Shoreham Sussex. Press the mesh into the base coat and scratch the surface for you top coat which can go on thinner. You can use SBR in this coat to aid adhesion but it will probably be fine as it is.

  8. Hi Roger,
    Reluctamt DIY learner OAP here. This is short notice I know but I’m half way through a 7′ high (approx) party wall wall render repair, up against a conservatory. Am having to re-render behind glazing also. Have done an “inadequately deep” scratch coat & have to “try” a top coat tmrw. Have used 4:1 building sand & cement with SBR prepared surface & in mix but found huge problems in keeping required depth of render to stay in place. Trowelled it in for hours & eventually had to remove an area & apply again.
    It is an uneven level to finish. Deeper one side than the other. 3/4″ & 3/8″ (very approximately) about 4′ wide, narrowing to half that for half the height.
    Because of above problem & having to hand mix, I found it impossible to make scratch coat deep enough on deep side but ok on thinner side.
    Is it feasible to effectively do two scratch coats please, as I don’t think it will take all that depth in one go, on that deeper side?
    Sorry this is a bit confusing.
    Many thanks

    • Hi Lee
      It sounds like you are having a nightmare there. A bit of lime in the mix will help it hang and hold together and give you something nice and fatty to scratch up. You can put the scratch coat on in as many coats and patches as you like. If a bit falls out of the middle leave it until the rest is set and then fill in the patch it is way eaiser. Sometimes we put up wooden battens and rule off to them and then when the rest is set take the battens out and fill in the grooves, then apply a thin top coat all over. Whatever works.

      • Many thanks for those insightful tips Roger.
        It certainly merited being called a nightmare yesterday but today was easier. The mistake I made yesterday, was making the mix too wet. My theory was that it would help it access the fine surface fluctuations on the base but .. it was more problem than help.
        Contrary to my expectations, I’ve actually done a very good job & sponged off to a very acceptable finish in one go today …but … I didn’t have any Lime handy & no time or vehicle to get any. As a result, even before it has properly set, there are already signs of fine cracks appearing in a few places.
        Funnily enough, the larger, deeper area at the top was easier than the thinner narrower area below. I thought, with a narrower area at the bottom, the moisture from the larger area above maybe seeped down & made it too wet. Anyway, I removed the section, let it dry off for a while & re-applied & all is OK, so far.
        If you have any miracle tips about how to overcome fine cracks as mentioned, I’d be very grateful but I guess a good dollop of masonry paint is perhaps all one can do.
        Yourl website was very helpful in my achieving success as far as it has been.
        Thank you very much indeed for your kind help.

  9. Hi Roger

    Firstly, thanks for all the advice you give freely it is much appreciated.

    I might need to render over some “Heritage” Cotswold style cast concrete blocks on our “new” 60s house. There are 4 panels of “stonework” directly below some downstairs windows. The vertical sides are bordered by normal brickwork piers standing about 70mm proud of the blocks. Do I go to the trouble of cutting the dressed faces of the blocks to give a more uniform surface level (very labour intensive as the windows are 2.4m wide) or bring the level flush by putting an initial coat of render on to fill in the imperfections? Will the latter method need mesh or metal lath to prevent cracking due to non-uniformity of depth? Can the render finish tight against the brick work piers? Presumably as this is going on fairly dense concrete I need a 4:1:1 or stronger mix.

    Many thanks again


    • Hi Steve

      You can render directly onto the blocks. Use some SBR in the 4.1 cement mix and make up a slurry coat to gain a key then prick that up as it dries to make it spikey.

      You can then make up a mix of 1.1.4 again with a small amount of SBR in the water. Press some fibreglass mesh (from builders merchants or TECO Building Products into the mortar and let that go off. Apply a scratch key on the render as it dries.
      You can use fine chopped fibres for render (Selco) in the next scratch coat to bind it and again a little SBR. You should then be able to apply your final coat of render.
      The important thing is that each coat is slightly thinner than the last. Ignore the thin slurry coat that is for adhesion.

  10. Many thanks for the reply Roger that’s saved me quite a bit of labour and mess over my initial thoughts.

    You’re a gent.



  11. The black arts of true masonry are always difficult to discover! A google search of ‘aggregate void ratio’ will open many people’s minds to these lost secrets. My personal favourite mix for laying brick is 1:2:9 (OPC:Hydrated lime:Aggregate) also 1:3:9. Ensure the powders are carefully measured (by volume) & thoroughly mixed before addition of water. Water should contain an admix of Sika or Feb plasticiser at 5ml per litre. Most everyday builders don’t use hydrated lime; yes partly due to poor education but mainly because of cost (arguably a function of poor education). A bag of hydrated lime is 5x & sometimes 7x more expensive than the cheaper Aluminosilicate ‘clinker’ based cement. Good quality sand or sharp sand of known water content with an acceptable void ratio is necessary for these mix ratios to work effectively in the associated application. OPC is still a valuable component to the overall mix because it increases durability & surface hardness. Rendered surfaces should avoid being painted as this can affect the breathability of the substrate; cladding is a significantly preferable option for unsightly exposed weathered brickwork.

    Bricklayers & Masons in the good old days were highly respected craftsmen:

    • I was told that hydrated lime will not set without cement so you should always have equal parts of lime and cement. A 1.1.6 mix is common and gives weather resistance and flexibility.

  12. Addition of lime extends usability of OPC.
    Give it a try using a trial batch measured accurately using a small volume vessel.

    Thanks for all the excellent work you do for the community.

  13. Hi, great stuff here.

    I’m going to be rendering my old French farm house on the INSIDE with sand and cement render – 1 scratch coat and 1 top coat. I’m going for a ‘not perfect’ finish to reflect the ambiance of the house.

    The house is quite damp in places as it’s stone built and i read that sand and cement render was good at holding back damp.

    I’m going to use a plasticiser with my mix and was planning on around about 5:1 sand and cement.

    Have you got any advice for me?

    Thanks, Phil

    • If you are going to hold back the damp then don’t use a plasticiser because that provides lots of tiny holes.
      The best approach is to use Sika 1 and follow the manufacturers guide lines.

      alternatively you can let the wall dry out by using a lime renovation plaster which allows the moisture to evaporate into the building. The advantage of the renovation plaster is that you don’t get condensation forming on it because it absorbs and then dries out. With waterproof render any airborne moisture will form condensation.

  14. liked your YouTube rendering vid, it looked like a dogs dinner at one stage but you brought it back to a good finish.

    Have you ever rendered over a timber framed extension ? I can’t find any info. The osb board is covered is breather paper. Battens are then nailed over this and another layer of breather paper and then eml. (expanded metal lath) The second layer of breather paper to stop render filling up the cavity I have ascertained this much but cannot find how the created cavity is closed at the bottom to stop rodent and insect ingress but also retaining air circulation. I notice that the Americans put mesh direct onto the breather paper omitting the battens, second layer of breather paper and not creating the cavity.

    I have tried plastering sand from various retailers and one stood out as being much better than the others presumably because it had silicon added. I was told that they used to sell internal and external rendering sand the difference being the external had the silicon added but for logistical reasons they added silicon to all their rendering sand to simplify things. Sadly now their sand seems no different to the others presumably because the silicon is now absent. Do you know of any silicon additives.

    A reply would be very much appreciated. Regards Rick

    • Hi Rick

      I am not sure what you have done and what you are planning to do. If you were starting with a blank canvas I would not bother with the eml. The quicker easier method is to screw cement board onto the timber frame and then use a renders primer from Weber with a fibreglass mesh embedded in it. Then before it sets prick this up. I use a wood float to suck it up slightly. You only have to dab it and lift it and it makes a fantastic keyed surface. Then you can go over it with a bagged product such as monocouche or a sand and cement mix with 6 sand 1 cement 1 lime. If you put a small amount of SBR in the mix it will be there for life.

      If you have already started with the mesh then by all means continue.

      Another great thing to do is to use the boards and some mesh in primer then instead of pricking it up trowel it smooth and then use an acrylic product. You can get this in tubs again from Weber. It is often used on loft conversion dormer cheeks to create a render finish rather than tile hanging.

      • I am approaching this stage too. I have got my timber frame up. I am planning on skinning with OSB and then putting house wrap over that. Are you saying I don’t need to do that and just do cement board directly on the studs and then render over that?

  15. Roger
    Have you ever rendered over a timber framed extension ? I can’t find any info. The osb board is covered is breather paper. Battens are then nailed over this and another layer of breather paper and then eml. (expanded metal lath) The second layer of breather paper to stop render filling up the cavity I have ascertained this much but cannot find how the created cavity is closed at the bottom to stop rodent and insect ingress but also retaining air circulation. I notice that the Americans put mesh direct onto the breather paper omitting the battens, second layer of breather paper and not creating the cavity.

    A reply would be very much appreciated. Regards Rick

  16. liked your YouTube rendering vid, it looked like a dogs dinner at one stage but you brought it back to a good finish.

    I have tried plastering sand from various retailers and one stood out as being much better than the others presumably because it had silicon added. I was told that they used to sell internal and external rendering sand the difference being the external had the silicon added but for logistical reasons they added silicon to all their rendering sand to simplify things. Sadly now their sand seems no different to the others presumably because the silicon is now absent. Do you know of any silicon additives.

    A reply would be very much appreciated. Regards Rick

    p.s. comment broken into two parts as it kept saying duplicate comment

    • Ha! thanks Rick. I like that dog’s dinner comment. It highlights a problem that many novices have and that is that they try and get a finish before they have the sand and cement on the wall.

      I can see there is more below. I am not sure about the silicon. There is silica sand which is sometimes used in high end work to match in with Portland stone but I don’t know about silicon. I don’t always trust merchants, they sell stuff that the often know little about.

  17. Hi Roger,

    Having watched the rendering video and read most of the great tips you have given, I have recently bought a bungalow which is rendered on 3 sides, but unfortunately is a mess, cracks, blisters and damp to say the least.
    I am about to remove it all and have a go at re-rendering it myself, in battened stages.
    Can you just confirm that I should use 1 Lime 1 Cement and 6 Sharp sand for the render, could you also tell me the depth at which I should apply it ?

    Thanks for your help in advance.

  18. Hello Roger – I’ve watched many of your videos and think they’re excellent, so thanks for sharing your knowledge. I need to re-render part of the facade of our Regency townhouse in Brighton but am unsure about whether to use waterproofer in the mix. I planned to mix the scratch coat 5.1.1 sand.lime.cement and the float 6.1.1 but having read far too many forums all I see is conflicting advice. Could you steer me in the right direction please?

    • Sorry, Simon, I missed this one. I tend to use SBR in the scratchcoat for adhesion and provided you have a really good key the top thinner coat will stay on with no problem. Most people advise against waterproofer as such because it traps moisture. However, SBR is a waterproofer as well as an adehesive hence the reason I use it only in the scratchcoat. That way the top coat can absorb water and evaporate. That said if you are painting the render you are applying a water resistant coating but it doesn’t seem to trap moisture. I think that water vapour gets through but water droplets are repelled.

  19. Hi Roger, Great advise and tips in your rendering video.I use lime in my mix all the time and mesh the scratch coat before top coat is applied.
    I have a north facing gable end to render which is rather exposed and at times catches the wind.
    Scratch coat dryed to quick for my liking but seems nice and solid.
    I will cover scaffolding to protect from weather but how can i slow the set time down to give me more time on the wall ?.
    Dave south coast

    • There are commercial retardants that are used in silo mixes etc Mostly these are used for bricklaying mortar so you have to be careful that they don’t cause an unwanted effect in rendering. Mostly they have one of the following ingredients.
      • Unrefined lignosulfonates containing sugars
      • Hydroxycarboxylic acids and their salts (i.e. sugars)
      • Carbohydrates including sugars
      • Gelatin (Sodium Heptonates – animal or fish fats)
      • Hydroxylated polymers
      An important sub group of retarders are those used in the production of ready to use ready
      mortar, they are covered by BS EN 934 -3: (Admixtures for concrete mortar and grout: Part
      3 -Admixtures for masonry mortar). Their use enables mortar delivered to site to be used
      for up to seventy- two hours after manufacture. Conventional retarders are used at a high
      dosage rate in combination with air entraining/plasticizing admixtures. The air entrainment
      assists in the retention of workability and the minimisation of bleeding.

      You might get better information from Cemex technical department but my approach is as follows.
      If you protect the wall from sun and the wind and you hose down the scratch coat the day before and again on the day and make sure your mix water is cold then you will increase the open time. Even storing the cement in a cool environment can help because the setting is aided by heat.

      • Thanks roger,dont want to start adding chemicals to mix ,will do as you say at the end of your reply.
        Would it help to brush on a cementone waterproof pva ?
        Around a 3.1 mix ratio.or a diluted sbr ?

      • Hi Roger, we were badly let down by our builder/renderer on a small job. Forced to finish off the rendering ourselves. Used 1 to 5 mix, cement and sand with SBR mixed in, didn’t use plasticiser. Now dried and has been painted. But a good 30% has visible signs of the surface is flaking and when rubbed comes away as white powder. Please advise how we can rectify this problem

  20. Hi Roger, thanks for clearing up a load of questions with you’re videos, I’ve been asked to render my next-door neighbours outbuilding which has been built in two parts. The first section is brick built which is no problem but the second section is timber frame and I’m not sure what product to use as a base for me to render to, it is literally timber frame with kingspan in-between. Any suggestions greatly received thanks Jim..

    • Hi Jim

      The modern material to render onto is cement board. You have to prime it with a key coat of Rendaid from Weber and then you can apply the sand and cement. The joints need to be covered with fibreglass mesh.
      In days gone by people used stainless steel expanded metal but you waste a lot of material and it is prone to cracking.

  21. Hi there,

    Thank you very much for doing the article on me!

    Please follow me bk,

    I’m extremely interested in doing product testing video in the future, is there any advice you could give me and point me in the right direction to get involved?

    Any help would be very much appreciated

    Thanks again guys,


  22. Hi,
    my builder is close to completion of our new home and i have noticed 2 vertical hairline cracks under windows running down to the bottom of the external render and these are both along created “expansion” joints. This render is upstairs and was applied on boarding. When I pointed this out to the site supervisor he simply said that it is natural for it to run along the joins – nothing more to see here. I am concerned about water ingress, he tells me that the crack depths would only be superficial and therefore not a danger as far as water goes. Any comments regards this would be most appreciated.

    • Can you send us some pictures. It would seem that cracks on rendered boards would be hard to avoid but I would have joined the boards with Sika flex to allow this kind of movement.

      • Thanks so much for the reply, I’ll tray and get a couple of photos to you, my concern is really whether the hairline cracks are just surface type of cracks that don’t allow water to penetrate through to the inside of house, or whether they do indeed provide opportunity for internal dampness and mould. The boarding it is rendered on is about 20 mm thick of a cement type of material. Thanks again

  23. Hi Roger I’m a DIY’r and I’ve recently had an old alarm box removed from my pebble dash wall which has now revealed a dirty looking square mark and a cable entry hole from the old alarm box. Would the dirty mark clean up no bother when I get access to the area and what would be best to use for this? And what would be the best way of going about repairing the hole that is in the wall? The hole is obviously round with small bits of further damage around the hole in a circle shape, the render is white and the pebble dash is white. It seems a straight forward repair but everywhere I look there seems to be so much different information.


    • I can only suggest some sort of detergent and warm water to cleaan it up initially, then maybe some bleach. Give it a scrub. As for the hole a bit of white exterior filler and a few pebbles pushed into the wet mix should do it. You should be able to find some pebbles lying around the bottom of the wall.

  24. Hello Roger

    I would be very happy if you could advise me what to do with some cracks in cement render on the back of my house. They are not wide, the widest perhaps only being 3 to 4mm….. What could I use to fill these before repainting the wall? Something flexible and ‘breathable’ would be ideal but how would you get the stuff in there??
    There is also a hole that needs filling too, about 50mm deep, from an old fixing that held a previous soil stack. Could I use the same filler as above?
    I plan to paint the wall afterwards with Graphenstone primer and paint which looks like very good stuff.


    • Hi Dave
      Sorry for the delay. I carried out a repair to a building with just such a crack which went from the footings to the roof plate. It has not opened up in 32 years and is almost impossible to detect. I did it using a flexible mastic from a tube. I gunned it in and then threw fine playpit sand onto it and rubbed it slightly with a damp sponge and then left it to dry. When it was dry I ran a sharp Stanley blade scraper up it to take off any excess and painted it a couple of times.

      As for the hole a deeep filler will be fine. There are lots to chose from and they all do the same thing. Again throw find sand on it and when it is nearly dry use a damp sponge to feather it in.

      Had I used sand and cement or esin I am sure it would have cracked. If the house is on clay then the crack will open and close with the seasons and any attempt to put hard cement in there would cause it to ratchet open and it becomes wider and wider.

      • Hi Roger, many thanks for taking the time to reply, I appreciate it a lot and for your advise. I found a casin filler by Earthborn which contains lime, white cement and clay amongst other things and this promises to be breathable and flexible. I might get an empty mastic tube and see it I can apply it in the cracks/hole using that. Interesting to hear what you say about houses built on clay, which this one is likely to be. Will do some reading around that. Best regards. Dave

  25. Hi Roger
    Can you sugest a Hydrated lime/sand/cemnt mix for repairis to cracked sand/cement render.
    House is old timber framed Circa 1700 Which over the years has been iced over with sand/cemnt render.

    • I hestitate to suggest anything that has cement in it since the house was built with hydraulic lime and sand. Hydrated lime doesn’t add much to the flexibility since it is mixed with equal measures of cement. What is does is to spread the cement/lime mix more evenly through the mix and add air to the mix. If the building moves and the render cracks it will also shift lime into the cracks and form a little bit of autogenusus self sealing. The real benefit of the hydraulic lime is to allow you to use less cement so a 1.1. 6 lime/cement/sand will form a good workable mix. If you tried a 6 to 1 sand and cement mix it would not handle well and maybe difficult to use. I would suggest contacting a specialist lime company or asking about bagged products. It is for repairs yu won’t need that many bags.

      • Thanks Ill caontinue looking for bagged products but nothing yet.Yes the original build would be Hydraulic lime. Love to take all sand/cement render off. but thats not on the menu. So looking to makeover 20th centry mistakes.

  26. Hi Roger Id like to know your thoughts on the Lidl range of parkside power tools, I’ve always bought Bosch tools it’s just what I’m happy with but I’ve thought about getting a radial chop saw but Bosch ones are big money and I’m thinking about buying the Parkside radial slide chop saw it’s only €100 but can it be any good, bear in mind it would only come out of the van once a month maybe.. any chance of a youtube video on the Lidl saw as most are not in English thanks for all your videos and keep up the great work cheers Kevin Scully The Fireplace Factory Scully Stoves

  27. Hi Roger
    My parents live in a timber framed farm house that was extended in the 70’s and re rendered with a hard mortar. Over the years it has developed cracks which have been repaired using various fillers.
    A builder friend said he had repaired a customers house with the same problem using a lime mortar and it is still good today.
    Have you any advise for me using a lime mortar. The cracks when racked out are between 3 to 8mm wide.
    The house will be repainted once repaired using a Dulux or Sandtex paint.

    • Hi Dave
      Not sure if the cracks are in masonry walls but assume they are. Lime will do a good job if the cracks are shrinkage but if they are due to movement and will continue to move I favour a mastic gunned in the crack. You can throw some sand on it and wipe it down with some sacking or a piece of wood to help it match in. I did this on a house I owned 30 years ago and when I walk past it the cracks have not re-appeared. Fingers crossed they never will


  28. Hello Roger,
    My parents house was built in the late 30’s and is pebble dashed so I am assuming it is a lime render.
    Cracks have appeared over the years, mainly hairline, and they have had a leak in the kitchen coming through from the outside wall where the old full height of the house chimney is. A builder came and said the leak was coming from the roof so they re-tiled the “problem area”. Come the rain and it still leaked. The builder came back out and has now said it’s the render. They pointed to the cracks and the chunk of render they said “fell off”! They quoted removing all the render from the side of the house ( which gets the full force of the weather) and replacing with sand and cement at a cost of £5k plus vat!
    The parents cannot afford this and now the piece of render that “fell off” on the slope of the chimney is causing a small waterfall when it rains.
    I have no diy skills at all and my parents are elderly, any ideas as to what I can do to fix this problem, albeit temporarily?
    I’m concerned that with the winter weather approaching this problem is going to be exacerbated.
    Many thanks

    • Hi Leigh

      If the builder said it was the roof and it turned out not to be then they jumped to conclusions. If the pebble dash has just fallen off in one place it might not be necessary to hack it all off. I am assuming it has never been painted.
      I think you should call in another builder and get a second opinion. If you send photographs I can probably give you a better idea of what is required. I am assuming the chimney is no long used. What area do they live in. If it is on my route I might be able to have a closer look at the problem.

      • Hi Roger,
        Thanks for replying.
        No, it has never been painted and the chimney is no longer in use, it was capped off years ago and when the builders came they re-tiled the area and replaced the lead.
        My parents live in Gloucestershire.
        I’m unable to attach photos for some reason to this site, can I send them somewhere else?
        Many thanks

  29. Hi Roger have purchased a old Victorian house built in 1899 the stone facias and window surrounds are in a rotten state of repairs . What would you advise for trying to render them back ? I intend to paint them a sand stone colour upon completion. What do I seal the remaining stone with and what mix for the render ? any help much appreciated I have been told they are millstone and not sandstone .


  30. Hi Roger you may know the unswere. I would like to render the side of my two store house which ad moment are bricks, the problem is that the wall is right on the edge of my neighbour property, do you think i can exid few cm to do so?

  31. Hi Roger, you are very good helping us all like this. Really enjoy your videos. I need to fix the smooth render between the wood cladding on a mock tudor external wall. On the render part, what looks like a thin skim (that has been painted over) has blown in parts and has cracked and the render skim is coming off leaving the underneath render coat. What would be the best way to proceed? The underneath render is in good nick so I don’t want to remove that. Can I just scrape/bolster off the blown skim and then try to scratch into the underneath render to make a key for a new skim or just use pva on it to get the new skim to stick? I don’t want to have to redo the entire skim coat so can I just do the patches that have blown? Would I use of 6:1:1 mix with sbr for the skim? Could I get away with just external polyfiller? Would really value any advice but understand if you are too busy. Thanks once again.

  32. My house in Cornwall is built of Copper slag blocks, scoria blocks, and I want to repair one of the large hearth openings prior to getting a wood burning stove fitted. There is a lot of mortar missing, but because of its age and history it is really beautiful so i want to take care to repair it properly. Can you suggest a mortar mixture that will be workable for a decent time? The existing mortar alternates between an orangey colour and a more usual cream colour. Thanks in advance.

  33. Hello Roger,

    Really appreciate your well thought out videos and the good advice.

    I am doing a self build in the Dominican Republic where we have high heat and humidity. Will this affect the type of mix I need to use?

  34. Hi Roger,

    Wow – thank you so much for so many useful videos and sharing your knowledge! Reckon lots of us would like to buy you a pint or two!

    I’m going to render the top half of my house soon – typical 1930’s red brick in south yorkshire.

    What do you think about the cements that have lime already mixed in? eg I like to use the blue-circle mastercrete cement (yellow bag). I’m thinking to just do 4:1 with sharp sand for the base coat. I’ve used that on concrete blocks for a standalone garage before and seemed ok.

    For the top coat I’m considering using a coloured silicon sand, perhaps one of the K-rend products so I dont have to paint it. …I’ve never used anything like this before.

    Would really appreciate your thoughts and comments on this.


  35. Hi Roger

    I could do with some advice.

    Early 1930s single (solid) brick construction detached property. Brick facing on front BUT Spar dash in a sand and cement render on 3 walls. Not lime render as I would have thought and many plasterers insist it is not… . property undergone extensive refurbishment work, therefore a good amount of render repair work subsequently required, following steel beam work and window replacement.

    Question 1) Regards render – ive come to conclusion there are 2 options:

    a) patch repair with sand and cement render and then decorator paint with exterior masonry paint eg Keim paints


    b) render remedial repair followed by External weather coating such as Weathertex medium texture

    Problem is I have had 4 render people quote –
    two builders recommended option (a). One quoted 850£, another quoted £4500 for same remedial work only (EXCLUDES painting).
    Another 2 companies quoted or are in process of quoting for remedial work followed by EWC application of Weathertex, 1 price come through to date at 13K. 2nd one AWd

    Its too late for me to go down EWI avenue: New windows in now and when I got a quote for this before any building work had started, 2 yrs ago – quotes were in region of 21K; I decided at time not to pursue due to cost. Now in hindsight considering render repair and EWC Weathertex decoration is almost 13K – beginning to think I made wrong mistake and should have planned for EWI from outset…

    What should I pursue now? option a or b. I don’t know … EWC firms say traditional paint will leave pinholes appearance over time due to sharp Canterbury stones and therefore painter does not give warranty, not to mention walls will consume lots of paint…. and build up of damp behind paint

    What should I pursue?? option a or b. I want to do what is right by property rather than solely focus on cost. In terms of EWC coatings – so many companies out there – alot of which I presume subcontract.

    Standard render repair, then traditionally paint trader would say EWC sounds fancy but don’t believe all you read online – theyre dressing it up like saying a felt roof is a 3 layer roof system (latter sounding better but at end of the day its just felt)

    Whereas one EWC firm has proposed:
    Hack off any blown sections of render.
    Apply render scratch coat to removed sections.
    Apply finishing coat of render over scratch coat in keeping with the existing render.
    Remove any moss, mould, algae etc and treat with a Biocide.
    Grind open any cracks and fill with high quality 2 part Epoxy.
    Apply SBR Bagging coat as required to provide excellent adhesion.
    Mask all windows, doors and any other areas that require protection.
    Apply bonding primer.
    Spray apply long life coating in your chosen colour and finish.
    Remove all masking and leave site in good order.

    Also QUESTION 2:

    The rear sliding glass patio door (steel box frame is boxed in standard plywood, Not marine grade). This needs to be made waterproof and then rendered over! Is plywood made waterproof with application of PVA prior to use of EML mesh and render, or is there a different product/method to make sure the plywood boxing my steel frame remains waterproof indefinitely beneath the render. What is a good method? I understand EML may reduce render risk of cracking; as ply and render are not good marriage one firm says so using EML would reduce risk, another firm says they would use a (slurry coat) render texture with fibreglass fibres (instead of sand/cement mix for remedial repairs), hence EML not needed as fibreglass product.

    I do have photos if needed

    Any advice to dissipate confusion and facilitate my decision making as to what is correct method/approach would help!

    Many Thanks!!!

    • Hi Shamira

      It is going to be difficult to make those patch repairs blend in even with an EWC sprayed on. Canterbury spar is usually left unpainted and, even though you might not get an exact match it might be acceptable to find a close match and blend it.

      The best option is to render the whole wall with a self-coloured smooth render but if the walls are not really seen then the patch up and paint is probably fine. I am sure the EWC will be done right but I have seen it peel off in huge sheets before and then it all has to come off.

      As for cladding the steel with ply, don’t do it. There are purpose made cement boards made for this job which can be rendered or texture painted with acrylics. It is done all the time and There is no need for EML.

      I think the steels are best wrapped in a breather membrane first and then the cement board is fixed on a frame in the same way as roofing.

      • Thanks Dylan for your reply. Appreciated. The problem is :

        1) the steel box frame has already been boxed in plywood. The sliding glass door company advised this to the builder before they came to install their floor to ceiling sliding glass doors. In hindsight, I’m now aware this wasn’t best material choice; but it’s done. What if any steps can now be taken to ensure the plywood is made waterproof and stands the test of time of decades and does not warp beneath the render?

        Regards visibility of the walls – they are very visible. The property has no garden, more a rear patio 2.5 m deep. And when you sit there at the back- the view is the walls of the house!

        By a self coloured smooth render- I presume you mean K-rend. Nobody has quoted for this yet – I think due to cost, they’ve veered more towards weathertex EWC. They said K rend is an option but more costly.

        Given the potential outlay in cost now – I wish I had chosen to go for EWI from the outset before the build began! but it’s all creeping up to that price with the benefit of aesethics only without insulation. Knowledge gained- albeit the hard way!!!

  36. Hi, I am hoping you may be able to offer me some advice as I live by the coast in a 1920’s house of cavity wall brick construction with a tyrolean render finish that appears to be of sharp sand and lime etc. The top coat has blown and I am stripping it all off but the base coat appears very sound and is like iron and will not come off.

    My dilemma is that a plaster is proposing to put on a scratch coat before applying peppledash but I question the need for a second scratch coat because if that will stick to the existing then why not go straight for a final coat that ought to stick just as well and avoid all that extra weight. I have been unable to find anyone who does tyrolean rendering but the modern stuff comes in a bag and I am considering applying that myself with a flicker box to the exposed render. I have read however that the modern throlean render should be applied to a smooth finish whereas the exposed render is rough. What would you do?

    • Hi
      If the scratch coat is sound then you can just apply the second coat to it. Like you say no need for the scratch but the plasterer is looking to add some waterproofer so the final coat for the pebble dash hangs around longer. If it goes off too fast he won’t be able to put a pebbledash on it.
      They way around it is a bonding aid such as Rend Aid to reduce suction but still give a good key. This can be brushed onto the existing scratch coat them you are ready to go with the butter coat.
      The thin acrylic coats need a really flat sub-base.

  37. Hi Roger, loving your work.
    I’m just a DIYer who has bought an old house. I’ve got a couple of small outside walls, not part of the house structure, the surface of which are crumbling away, possibly due to dampness and previous ivy attack. I’m hoping to arrest the damage by simply rendering thickly over the surface. So three questions really, 1) is this a good idea? 2) is there a good ready-mixed product I can buy? and 3) do I need to seal the crumbling dusty brickwork first (if so, what with)?
    Cheers mate, keep up the great work,

  38. Hi mate thanks for all of your useful videos.
    I’ve got rendering between the upstairs and downstairs front windows. Where the render overhangs by about 4 or 5 inches the render is cracking and look ls like it’s going to fall out.
    Any suggestions for products to buy to patch it up?
    A ready mix product would be preferable.

    Many thanks

    • you could try a bagged render. There are lots on offer at EWI store Chessington.
      Any lime based render will do the job.

      • Thanks mate.I’m in Liverpool so if do a search for ready mix lime based render I should be able to order online or get it from a builders yard.
        Thanks again,

  39. Hi mate thanks for all of your useful videos.
    I’ve got rendering between the upstairs and downstairs front windows. Where the render overhangs by about 4 or 5 inches the render is cracking and look ls like it’s going to fall out.
    Any suggestions for products to buy to patch it up?
    A ready mix product would be preferable.

    Many thanks

  40. Sir, I have watched lots of your video’s and the advice has been sound and well received for modern buildings. Unfortunately your advice for most pre 20th century buildings is liable to do more harm than good.
    My 1860 Victorian house was built using stone, wood, bricks and lime and i’ve had to spend 10 years stripping modern building materials inside and out and replacing them with traditional lime mortar, plaster and render. It thankfully has allowed the building fabric, bricks, wood and mortar to dry out and every single problem they caused is now gone, why because I trusted the experts at Lime Mortar Scotland and Historic Building Scotland and refused to employ builders that didn’t have the certification of the experts.
    You see the previous owners had fell for every “damp and building scam” possible and often just bad workmanship completed by builders that didn’t know the properties of Victorian and Edwardian buildings. Modern products and plasters should not be used to fill internal lime plaster cracks, damp proofing instead of removing rotting or old drain pipe brackets, the “rising damp and damp bull” that was simply walls plastered in modern plaster, render and cement all the way to the floor and covered over vents and outside raised cement patios, pathways and driveways.
    The outside wall of my 150 year old house cellar (my daughters bedroom) in Belgium is a canal and there was not an inch of damp so I learned many years ago “rising damp” is a very British con trick. maybe you should make it clear your building advice is not suitable for old buildings and then those of us that had to fix the problems bad builders cause will respect you for it, unless your sponsors wish differently obviously. !!

  41. Hi Roger.
    I have read your post and all the comments and helpful replies that you have provided. I have tried to distil an approach for my rendering issues, but I am still struggling a little to understand what my best approaches will be.

    I need to fix the render damage caused by extending the doors and windows and removing the terrace on my 1975 breeze block house. The house has white coloured render. I am going to paint on top of the repaired render so colour match is not an issue. I am a bit unsure how to proceed and would really appreciate some advice on what my priorities should be and whether spot rendering is the answer in all cases.

    The main cases with the render as I see it are:
    around all windows and doors there is a small gap between windows and door frames and existing rendered blockwork. The size of the gap varies, at the front door it is about 5cm, around the terrace door it is about 1cm.
    In some places there is more extensive damage to the render caused by new aluminium window and door fitting. This goes all the way back to the breeze block and has in some cases been filled with foam. This is typically around the corners. The depth of the render is 15-20mm.
    There is a large area of unrendered blockwork revealed when the terrace was removed.
    Smaller areas where there is surface damage to the render such as where cables have been clamped to the surface.

    Do you have any top tips on how to approach this? I have bought Toupret Touprelith F Exterior Masonry Repair Filler 1.5kg (7626H), but I am not sure if this is appropriate for all the cases. I also have some buckets of rapid set cement mixes that may be relevant. Finally I have SBR which I think could be used both as a primer and as an additive.

    My best guess approach outline below is based on no experience, just web research and reading product labels.
    I wonder if these regular gaps around the windows and doors are best filled with a flexible compound such as a suitable silicone or mastic. Is that fair and would you be able to recommend a suitable product? Or is there a gap width at which one would fill the gap with render?
    For the more extensive repairs on the corners I am very unsure. Can I render on top of the foam? If not, what do I do with the foam? I presume I would prime the whole area to be repaired with diluted SBR (1:4?) immediately before applying the Touprelith F? I assume I would not add SBR to the Touprelith as it probably already contains it? I think the Touprelith can be applied just as one coat and finished with a sponge or some sand brushed into it to match the surrounding area?
    As this will be mainly below the deck that is yet to be built I guess I will just aint the breeze block to match what has been done elsewhere on the house. Any areas not covered by deck I think the approach would be similar to case 2?
    The smaller areas with surface damage I presume I would prime with SBR and repair with Touprelith, again finish with sand or sponge?

    By the way – I have been warned to make sure the windows are properly covered. I guess that also applies to aluminium framing?

    Finally – is there any role for the rapid set cement in this? I guess I would add SBR to this?

    Apologies for a long list of questions. Fingers crossed you can help my refine this into a workable set of approaches.



    • Hi Tom
      There is a lot to consider there. If the blocks are aircrete then a slurry coat of cement with SBR will be needed on the bare block. Prick it up with a sponge and let it dry for 12 hours.
      The foam needs to go into all voils around the windows and doors. You can then render over it with a 4.1. 1/2 sand cement and hydrated lime.
      Yes you must protect glass and frame from splashes or hose them down immediately.
      I would not add anything to the Toupret and I would also avoid any quick set product.
      If you live near me in Surrey I will come and give you a hand for a day just to get the video footage.

      • Thanks Roger for a very speedy response. Unfortunately I am up on the lovely Isle of Arran off the west coast of Scotland.

        I see the numbering of each case disappeared in my post. I have therefore repeated part of my post for clarity:

        1) around all windows and doors there is a small gap between windows and door frames and existing rendered blockwork. The size of the gap varies, at the front door it is about 5cm, around the terrace door it is about 1cm.
        – My suggested approach is to fill with suitable mastic or silicone.

        2) In some places there is more extensive damage to the render caused by new aluminium window and door fitting. This goes all the way back to the breeze block and has in some cases been filled with foam. This is typically around the corners. The depth of the render is 15-20mm.
        – My updated approach based on your response is to first prime with SBR on the bare block and foam, then do a slurry coat of cement. Finally prick it up with a sponge and let it dry for 12 hours.
        – Finally render over it with a mix of 4 parts sand, 1 part cement and .5 parts hydrated lime.

        3) There is a large area of unrendered blockwork revealed when the terrace was removed.
        – My updated approach for the areas not covered by the deck will be to follow approach outline in 2)
        – For the area under the deck I will paint to match rest of house.

        4) Smaller areas where there is surface damage to the render such as where cables have been clamped to the surface.
        – My updated approach here would be to prime with SBR, then render over with a 4.1.½ sand, cement and hydrated lime mixture.



      • Roger, being quite inexperienced in the art of rendering I also have a question on the makeup of the slurry coat. Is it just cement and SBR?



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