AlexRex Posted January 31, 2023 Share Posted January 31, 2023 Plasterboard on external solid wall has a musty smell when removing skirting and smelling under it.. it has a foilback, black vapour sheet barrier and polystyrene.. I thought to remove it and put new plasterboard.. however plasterboard onto external wall may cause damp. Do I leave as it is? I’m thinking vapour barrier isn’t breathable so it will always have a musty smell? Thanks Link to comment Share on other sites More sharing options...
Radian Posted February 1, 2023 Share Posted February 1, 2023 How is the PB attached to the wall? If there's a vapour barrier I guess it must be on battens - which might imply it has been boarded to mask a penetrating damp issue. How thick is the polystyrene? What your senses are detecting is probably the flourishing micro-environment in the gap between insulation and masonry. But with a vapour tight membrane between it and the inside atmosphere, the only issue is what ventilation is available to the inside of the masonry. Link to comment Share on other sites More sharing options...
JohnMo Posted February 1, 2023 Share Posted February 1, 2023 I had mould in our ensuite, started as a musty smell. Tracked it down to a very minor leak in a water pipe joint behind the plasterboard, which over a number of days resulted in damp plasterboard. Link to comment Share on other sites More sharing options...
Radian Posted February 1, 2023 Share Posted February 1, 2023 19 minutes ago, JohnMo said: I had mould in our ensuite, started as a musty smell. Tracked it down to a very minor leak in a water pipe joint behind the plasterboard, which over a number of days resulted in damp plasterboard. You remind me of a TV program where a woman tells George Clark she doesn't like en-suite bathrooms because they have a 'water smell'. George was quite taken aback, but the woman's experience was probably based on living in a series of poorly built houses where such leaks are common. Also, the grout and sealant on tiles always gives up eventually and the widespread (bad) practice of tiling straight onto regular plasterboard means mould is flourishing in all kinds of unseen places. I've got recurring issues in my own shower room to take care of again now.🙄 Link to comment Share on other sites More sharing options...
AlexRex Posted February 1, 2023 Author Share Posted February 1, 2023 (edited) Thanks! Edited February 1, 2023 by AlexRex Link to comment Share on other sites More sharing options...
AlexRex Posted February 1, 2023 Author Share Posted February 1, 2023 (edited) 2 hours ago, Radian said: How is the PB attached to the wall? If there's a vapour barrier I guess it must be on battens - which might imply it has been boarded to mask a penetrating damp issue. How thick is the polystyrene? What your senses are detecting is probably the flourishing micro-environment in the gap between insulation and masonry. But with a vapour tight membrane between it and the inside atmosphere, the only issue is what ventilation is available to the inside of the masonry. Thanks! Yes battens, the next bedroom along same wall just has PB as far as I can see. Suggesting they just wanted to insulate the main room and no penetrating damp issue. Suggesting it’s self inflicted with use of non breathable products? Couple of cm the polyestene Edited February 1, 2023 by AlexRex Link to comment Share on other sites More sharing options...
Radian Posted February 1, 2023 Share Posted February 1, 2023 The wall may indeed need to breath in both directions. That's the problem with insulation retrofit in what is presumably a single skin masonry wall. Either a breathable insulation and surface finish (difficult) or non-breathable finish and insulation with a well ventilated gap to the masonry (compromise) or best of all, Exterior Wall Insulation. Then you can leave the inside as it is. Link to comment Share on other sites More sharing options...
AlexRex Posted February 1, 2023 Author Share Posted February 1, 2023 (edited) 24 minutes ago, Radian said: The wall may indeed need to breath in both directions. That's the problem with insulation retrofit in what is presumably a single skin masonry wall. Either a breathable insulation and surface finish (difficult) or non-breathable finish and insulation with a well ventilated gap to the masonry (compromise) or best of all, Exterior Wall Insulation. Then you can leave the inside as it is. Yeah tricky, appreciate your input. Older homes always tricky.. what about Battons with rockwool rolls inbetween them with plasterboard to finish? Rockwool is breathable. Otherwise plaster it again (no PB) hearing ventilation issues with old walls and gypsum plaster Edited February 1, 2023 by AlexRex Link to comment Share on other sites More sharing options...
Radian Posted February 1, 2023 Share Posted February 1, 2023 Lime plaster is breathable but no insulation means you might still have condensation problems unless the room is very well ventilated. To be honest, very old buildings are not my speciality. You do seem to be very aware of the pitfalls - which is a good start. Hopefully you will get some more advice along the way. Link to comment Share on other sites More sharing options...
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