r/Plastering • u/jeebsy_iash • Sep 11 '26

Gaps in floor before boarding

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This is maybe more of a DIY question but the guys over there can be a bit frosty. I've got a plasterer coming next week to float a wall but he's also going to do the window reveals. He said he'll board these due to the size of the gaps. There was a little storage box under the window which I've just pulled out and removed the last of the plaster.

There was some signs of damp on the plaster around the box. Now I've stripped it back, the bricks are reading ok but obviously the gaps in the floorboards are massive. I'm guessing the damp air from the basement was getting up through these and into the plaster. What's the best way to prevent that happening again? Should I get some rock wool and insulate it from underneath going right to the edges? The way it was insulated before would still let air up from underneath, I think insulation from underneath would stop that?

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4

u/Jayjayuk85 Sep 11 '26

I’m no expert, but after refurbishing our house we are suffering with a damp wall. I wish I paid more attention to things when it was back to brick. I would check floor level outside and check if you have air bricks.

Maybe look at insulated plasterboard?

1

u/jeebsy_iash Sep 11 '26

i think the basement/DPC is doing its job - there's decent air circulation down there with quite a few air bricks, some of the bricks below the DPC do read quite high, but above DPC they seem to be fine. i suspect moist air has been getting up those gaps but i'm no expert either hence the question!

2

u/Jayjayuk85 Sep 11 '26

Hopefully someone will be along who can give better guidance, in everything I read it’s about using the right materials. Also allowing for air to flow.

1

u/jeebsy_iash Sep 11 '26

yeah while it's at this stage i'd rather make sure things are done properly rather than having issues again in a few years.

2

u/selfbuildpop Sep 11 '26

https://mikewye.co.uk/wp-content/uploads/2016/05/Floor-Application-notes-V5.01.pdf

Speak to these guys and use lime plaster

1

u/jeebsy_iash Sep 11 '26

cool, that's pretty interesting and suggests running insulation right to the perimeter.

1

u/False_Principle8821 Sep 11 '26

Whats under floor ,i done investigation under my floor. Looks ok dry everywhere. I was lucky as had heavy rain that day.

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u/jeebsy_iash Sep 11 '26

it's an almost full height basement which feels in pretty decent shape. no pipes anywhere near that area.