Monocouche render is everywhere now, on external wall insulation, blockwork and brickwork, and for good reason. It is a single-coat system; it is quicker to apply, and it needs less skill than a traditional two-coat render. But it has one very real weakness, and that is staining. Give it a few years on a north or west elevation, and you get that ugly green and black growth spreading across the wall.
The instinct is to reach for the pressure washer and blast it off. That is the worst thing you can do. Monocouche is a lime-based render, and it is relatively soft, soft enough to scratch with a fingernail. Hit it at full power and you will put grooves and dents in the surface, which holds more water and brings the growth back faster than before.
In this video Roger shows the method that actually works. Brush off the loose growth with a soft brush, apply Soluguard Multi Surface Biocide from Safeguard, leave it for at least 72 hours to kill the growth down in the coating, then rinse off with clean water. We used a Kärcher K4 Power Control Flex on its lowest setting to wash away the dead algae and lichen, letting the biocide do the hard work rather than the water pressure.
Once the wall is clean and dry we protected it with EWI Pro Render Shield, a clear breathable water repellent that sheds rain and dirt while still letting moisture trapped in the wall escape. It dries to a natural matt finish so it does not change the look of the render.
And before you touch any of it, check what is making the wall wet in the first place. Gutters, downpipes, joints, sill details, sealant around openings and vegetation shading the wall. If water keeps wetting that surface, you can clean it perfectly, and it will be green again next year.
PRODUCTS USED
🔗 Soluguard Multi Surface Biocide
https://go.skill-builder.uk/soluguard-biocide
🔗 EWI Pro Render Shield
https://go.skill-builder.uk/ewi-render-shield
Got EWI or monocouche render and you are fighting green staining? Tell us in the comments what finish it is, which elevation it is on and how old it is, and we will point you in the right direction.
KEY TAKEAWAYS
– Monocouche render is a soft lime based single coat system, so a pressure washer on full power will cut grooves and dents into the surface and make the staining come back faster.
– Green or dark green fluffy patches are usually algae, black spots in shaded areas are mould or lichen, and brown rusty streaks under sills or fixings are metal runoff or tannins.
– Find the water before you treat the wall. Check gutters, downpipes, joints, sill drip details, sealant around windows and doors, and any planting brushing or shading the wall.
– Soluguard Multi Surface Biocide is ready to use straight from the container with no mixing, applied with a garden sprayer, brush or roller on a dry day with no rain forecast for 24 hours.
– Leave the biocide to work for at least 72 hours before rinsing. That dwell time is what kills the growth deep in the textured coating rather than just on the surface.
– EWI Pro Render Shield is a clear breathable water repellent that becomes water resistant after about 4 hours, takes a second coat 2 to 4 hours after the first, and reaches full hydrophobic performance after around 7 days.
– The rules are simple. Do not blast it, kill the growth, fix the water that caused it, and expect maintenance rather than miracles.
#MonocoucheRender #RenderCleaning #ExternalWallInsulation #EWI #HomeMaintenance
