Damp proofing a concrete floor repair

My workshop was a miners cottage once. At some point in the past the row of cottages were converted into small industrial units and a that point a concrete floor screed was poured. At some point after that a brick partition wall was removed and replaced with a low stud wall counter. Ive now removed that and its revealed a gap in the floor where the brickwork used to be.

Theres a plastic membrane under the screed – but theres a gap in that membrane now that the wall is gone – and materials in that gap , beneath the level of the plastic, is fairly damp.

I want to fill the gap but don’t want it to be a source of damp – what would your trick to fix that gap in the plastic before I fill it? Or should a use an additive in the concrete? Or use something other than concrete

Clean up all the dust and chunks of concrete. Vacuum it too. You’ll need to ideally tape* the membrane together but hard to determine with all the debris there as how wide the gap is. If the gap is quite wide then a membrane laid in the gap and tape that to the existing and fill the gap in between.

*Use an appropriate membrane tape.

Could try and expose more of the membrane and try n glue a patch in.

If its just a workshop id concrete it with an additive n try it

Was the stud wall floor plate damp when you pulled it up? And how critical is lack of dampness to your workshop?

I’d be tempted by a tanking slurry poured into the gap and then once it’s dry level up with screed. I’m not a builder though so take that with a pinch of salt

When do I add the pinch of salt ? 🙂

There was a bit of damp under the floor plate – the debris in the gap in the floor is plasterboard, not concrete so the grey-ness indicates how moist it is (and the wall was taken down a few weeks ago)

It’s an unheated workshop mainly for joinery – the less inherent damp the better just to minimise stored materials being spoiled – stuff like birch suffers in damp conditions.

So the less damp comimg up the better – Its a 6ft long repair and the bottom of the cut is one brick wide so not a huge breach in the floor

Remove detritus thoroughly.
Tape a roll of flashband and in there. Buy the one with the adhesive.
Then add a waterproofer like sbr to your concrete mix .
If you really want to go for it paint with Thompson water seal afterwards

Ooh – flash band – good call – because the plastic is a bit scrapy and cockled I was trying to thing what would stick to it well and something quite gooy like flashband sounds just the job (and I think Ive got some somewhere)

Flash band sticky side up. Plastic pressed down onto it. Taking from above to seal any holes left.

Flash band sticky side up

Like your thinking

When are we going to see your bunker?

Thoroughly clean it out and use some kind of bitumen or tar based product? They used to use bitumen as a damp course in years gone by.

When are we going to see your bunker?

No-one ever sees it – thats the point!.

🙂

that project is sort of on a back burner at present. Been working away from home too much.

Remove all loose stuff, dust, apply liquid DPC product to seal and bind in the existing membranes and finish with a suitable concrete repair compound

that project is sort of on a back burner at present. Been working away from home too much.

That’s some back burner… How long have you had it 😁