Expanding foam between wall and skirting?

20 Feb 2007
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United Kingdom
Hi. I have an old house built with lime mortar and render. Inside, the lime plaster has been painted and papered over the years, before my ownership. The internal plaster has crumbled and come off the brick across the whole front bay leaving a gap behind the skirting of over an inch, allowing cold and moist air from the floor void into the room. Given there doesnt appear to be a damp course (built C.1880) and the wall has lime mortar, will it be ok just to squirt expanding foam down behind the skirting to hopeful fill the gap, stop the draft, or will this suck moisture from the wall onto the back of the skirting, slowing rotting it? (even though original plaster must have been in contact with the wood) I dont plan to replace the plaster.
Many thanks to anyone who has long term experience or knowledge on expanding foam and moisture. Cheers


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I doubt the gap behind the skirting was ever plastered. I can see the wooden grounds it was fixed to. I think a better method to block the draught is to stuff mineral wool into the gap.

if you can put a wooden batten behind the skirting, with its top level with the top of the skirting, this will give you a nice edge to plaster against, and will hide any remaining gap. It is easier to do this if you can take the skirting off without damage.
don’t put wool in there, its a ludicrous suggestion and will retain and transport moisture in to the skirting.
the gap behind the skirting is there for a reason . it vents from the subfloor and dries out moisture at the bottom of the wall as it enters.
if you must fill the gap concentrate solely on the top edge with expanding foam only then trim it back.
although this may push the top of the skirting outwards.
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ROCKWOOL insulation products will not absorb water by capillary action and can be used in situations where it bridges the DPC in walls.
Thank you for the replies. My concern was that the rockwool insulation might get damp over time and hold the moisture but it is much easier to stuff in than the foam, which would have needed me to life off the radiator. Ive stuffed in some rockwool. not too much, enough to stop the draft. If it gets wet, the air flow below, and the radiator above should dry it as its only a couple of inches thick. Thanks again for the suggestions.

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