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I have been asked to remove Hanging tiles from approx 30 square metres of cavity wall. Then a plasterer will apply render for the customer to paint. The initial request was to install Kingspan ThermoKool K5 40 mm with eml over the top to take the Render. However the labour cost of drilling the 250+ holes and plugging and anchoring the material has prompted a request to consider using No nonsense expanding foam (Screwfix) :shock: in the cavity wall instead. Would this work?
I am concerned re type of foam and damp precautions/issues.

ab190162,
"consider using No nonsense expanding foam" not recommended.
Get a cavity insulation firm in to carry out the work to an approved spec.
end

About 20 odd years ago the Government of the day, recomended that cavity wall insulation should not be installed in homes in the west of the UK or in the central uplands as it causes more trouble than it is worth.

The problem being that most cavity walls are not waterproof.

The wind driven rain hits the wall, makes its way through the outer wall and runs down inside the cavity.

When you fill the cavity, often you create a bridge that moves the rain from the outer wall to the inner wall......and a wet wall lets heat escape at an incredible rate.

That is why the wall has hanging tiles to keep the rain out.

Taking them away will be a great mistake as they really do work.

Render is only a short time solution, before long it will develop cracks and the rain will get inside the wall.

There are two types of expanding foam, one with a lot of grab for the underneath of roofs, the other designed to be poured into a box, or indeed a cavity wall.

The problem with this is you need to drill through the wall at 18 inch centres and squirt the foam into the wall, put too much in at a time and it gets very hot, it also has a strong expansion that can push the wall out, the other problem is that over time it contracts by 15% leaving empty patches, that then become cold, attract condensation, then mould.

Keeping the tiles, adding cavity wall fill, like polystyrene balls will get a result. Drill from the inside.

For readers looking for related advice please see our DIY how to projects on cavity walls which have information and guides on damp issues and fixes, vertical Dpc, insulation of cavities and pumped cavity walls.