mazzlebizzle Posted March 10, 2021 Share Posted March 10, 2021 Hi Folks, Im wondering if this will become an issue. We need to insulate single skin concrete blocks (100mm thick 7.3N concrete blocks). We are going to flush the walls with the piers on all four sides with 3x2 stud attached to floor and ceiling. This will leave a gap of roughly 50m between the studwork and the concrete block. We were then going to compress 200mm rockwool into the stud work and compact it against the concrete blocks and fix mdf board to stud to stop rockwool falling into cavity etc but this will eliminate a lot of cavity space. Im then going to seal the blocks outside with something like bostik water seal. Is this going to be an issue or breed mould internally? Am I better using PIR between studs to keep it away from the wall completely? or maybe putting a breathable membrane on the internal wall and use rockwool? Ive used everbuild blackjack DPM to cover the concrete base internally, and covered up to 4 blocks high. Externally Ive painted 4 blocks up also. My plan is to have an electric dehumidifier in the winters. Thoughts? Link to comment Share on other sites More sharing options...
tonyshouse Posted March 11, 2021 Share Posted March 11, 2021 Disaster waiting to happen! Sorry, it will all go mouldy, best not to compress insulation, in fact use eps, MDF will get damp, change shape and eventually die what will it be for? 1 Link to comment Share on other sites More sharing options...
Moonshine Posted March 11, 2021 Share Posted March 11, 2021 2 hours ago, tonyshouse said: in fact use eps, Out of interest why not PIR? Link to comment Share on other sites More sharing options...
tonyshouse Posted March 11, 2021 Share Posted March 11, 2021 Eps is cheaper, breathable, less contraversial 1 Link to comment Share on other sites More sharing options...
PeterW Posted March 11, 2021 Share Posted March 11, 2021 EPS is also highly flammable ..! 1 Link to comment Share on other sites More sharing options...
mazzlebizzle Posted March 15, 2021 Author Share Posted March 15, 2021 On 11/03/2021 at 06:33, tonyshouse said: Disaster waiting to happen! Sorry, it will all go mouldy, best not to compress insulation, in fact use eps, MDF will get damp, change shape and eventually die what will it be for? Hi, So I've decided to water-seal the piers on which the wood will be closest using bostik water seal. The stud (3x2) and 75mm PIR Recticel will be around 50mm off the concrete block wall (about 5mm off piers). The whole outside of the building will be treated with bostik water-seal also then clad with wood slats. Were going to get ourselves an electric dehumidifier also. We decided against MDF in the end and went with 12mm structural Hardwood Plywood. Thats for the ceiling and walls because I hate plaster. Link to comment Share on other sites More sharing options...
tonyshouse Posted March 15, 2021 Share Posted March 15, 2021 Dehumidifier may not necessarily work, when the concrete walls are very cold as in frosty weather they may act as a more powerful dehumidifier than the one you buy, something to be aware of. Link to comment Share on other sites More sharing options...
SimonD Posted March 15, 2021 Share Posted March 15, 2021 Is EPS EWI either rendered or clad not an option? Link to comment Share on other sites More sharing options...
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