Damp proofing an old building usually means undoing what somebody else did to it. Roger is back with Robert from Tiffin, a restoration firm trading since 1695, at a 1906 school with damp all the way along one elevation.
The short answer is that the building was fine until people started helping it. Over the years, the ground outside was raised five brick courses without anyone excavating back down, which buried the damp-proof course completely. Then the walls were sprayed with a plastic coating that sealed the moisture in. Four or five weeks after the render came off, in the middle of a hot, dry summer, the brickwork was still saturated.
Robert walks Roger through the repair, including the AirDrain system he developed himself. It is a resin C-section channel fixed against the brickwork with the open side facing the wall, so air moves along its whole length and the masonry can evaporate instead of holding water. Below that sits a land drain about half a metre down in this case, and the existing air bricks now vent into the drain rather than into wet ground. Behind the render they also found a brick plinth built on edge about seventy years ago with no membrane, no ties and no damp proof course, which had gone completely live and had to come out. You never know what you will uncover when you start these jobs.
Eco Tiffin Air Drain 👇
https://go.skill-builder.uk/airdrain
KEY TAKEAWAYS
• Raising ground levels above the damp proof course makes it useless, and paving that falls towards the building makes it worse.
• Plastic spray coatings sold as maintenance-free trap moisture in the wall and cause internal condensation and timber decay.
• Rotten wall plates and joist ends are the hidden cost of a damp wall, so inspection holes are worth cutting.
• Render old brickwork in a weak sand and cement mix with no water-proofer, and keep it as vapour open as you can.
• Gutters, downpipes and gullies matter as much as anything else, because large roofs on small gutters overflow straight down the wall.
WATCH NEXT
Our first visit to a Tiffin site:
https://youtu.be/921lsmpwM3s
CHAPTERS
00:00 A restoration firm trading since 1695
00:38 The damp-proof course five courses down
01:13 Why the ground falls towards the building
01:53 Under the render: brick, sand and cement
02:20 What the plastic coating did to the wall
02:49 Rotten wall plates and suspended floors
03:23 What the air drain actually is
03:55 The land drain at the base of the wall
04:20 Surveying the rest of the school
04:46 Is damp work energy-related for VAT?
05:07 The hidden brick plinth
05:33 Rendering with no waterproofer
06:16 Gutters, roof runoff and new gullies
07:03 Brick on edge with no DPC behind it
07:24 The maintenance-free spray coating
08:28 Vegetation and vertical slate damp-proofing
09:17 What Robert would do instead
Have you seen a damp-proof course buried like this? Tell us what you found and how you dealt with it in the comments.
#Damp #DampProofing #Renovation #SkillBuilder
