Use rockwool and solid PIR on same wall? 36cm/ 14" solid wall with external render

17 Oct 2008
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United Kingdom
Hi all

So just rechecked and the 3.5metre high ground floor solid wall (1780's wall) I want to internally insulate is 36cm/ 14" thick, that includes c2cm of external render someone put on c30 years ago. Wall in good condition.

The wall is lime mortar, at least inside is, so render stops it's breathing I read, but no issues we have with damp ever. Celotex or rockwool?

As wall uneven in one area, thinking rockwool for top 1metre of the wall withn bumps, and celotex where walls no bumps.
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Think I remember seeing a rough test for render, squizz a bit of vinegar on it, if it foams it suggests the presence of lime.

Perhaps other can say if this is correct or not.

If there is lime in your render, it should be breathable.

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