Cavity wall questions

MichaelR

Hello,

I am renting a 1950s cottage with a later (60s? early 70s?) flat roof extension. The cottage is apparently monolithic concrete, but the extension seems to have a cavity wall. At least, when a hole was drilled through the wall, it goes concrete-empty space-concrete. This was for a drain that was later moved; the plumber, despite my request to seal both sides of the hole, only sealed the outside part with cement.

So I have the wall (not too big, it's about 20 sq. m. in all), and one relatively big (about 4 or 5 cm diameter) hole. And my questions are:

- How do I find out if this is a cavity wall, or a wall of cavity blocks? (As I understand, insulating the cavities in the blocks is not a good idea?)

- Is there any sense in the idea of using usual shop expanding foam to fill the cavity? In B&Q, I saw "7pur foam" which is fire rated and the bottle says it is good for "cavity walls" among other things. But the sellers of special foams for the purpose (way too expensive for consideration in a rented house) claim that one needs 2 component foam there and single-component just won't work.

starbelgrade

The extension was probably built with hollow block, hence the concrete - hollow - cavity.

It can be drylined from the inside, or filled with foam insulation. Either way, I wouldn't attempt a DIY job on it.

Get your landlord to either pay for a professional remedy, or move out. It's not really your problem, so why pay for or worry about it?

MichaelR

I did find the reason why shop foam should not be used. Apparently it can expand for a long time after being put in - so can put pressure onthe wall, in the worst case breaking it.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2806&page=1