Ground floor damp proof course or lack of.

What "compound" did you put on it? Did you do ant preparation/treatment apart from scabbling it off?

"The skim". What's that, the "compound"? The black stuff is hopefully bitumen emulsion.

If the surface is coherent, use bitumen emulsion again. If it's not, take it back until it is, or dig it out & replace.

Shouldn't be expensive. What's the "project"?

Your new membrance gcan go on top,it doesnt need to be 1" down. Salt only shows up when water evaporates, leaving the salts behind. Top the slab with a sealer and it wont dry, so no salts form. Concrete likes being wet, as long as its not wet & frozen.

NT

I've stuck some pics up as they make more sense than me. ;-)

Mark S.

The floor was breaking up when I'd taken the carpets and lino up. The top inch or so was hollow and crumbling and lifting off.

I took the this top inch off over the whole downstairs floor.

There's a concrete slab underneath except between the two was the bitumen type stuff which is what was the damp course.

I used self levelling compound over the whole floor to keep the dust down and make it less of a pain to keep swept etc.

Bits of this have lifted off leaving the salt deposits under them. If you put something on the floor and leave it there's a "damp" patch under it when you move it.

Do I repaint the floor with a bitumen paint and will that fix it or just dig the whole lot out and re-lay it in the normal way with proper layers, insulation etc.

The project is the house...

Mark S.

Mark - what you have is a concrete slab with a liquid damp-proof membrane, probably Synthaprufe or similar, applied on the top surface and then covered with 1" cement/sand screed. This used to be common practice years ago, but is never recommended these days as it always fails in the way yours has. The screed will never bond properly to the membrane and in time will break up. A reinforced screed at least 2½" thick is needed, but I guess you can't raise the floor level.

The salts tell me the membrane isn't effective - i.e. dampness is getting through it. Unless you do something about this the dampness will always be there to ruin any floor coverings you put down and give your house a damp smell and feel.

Your options are:

Peter

Is the floor slab a) coherent and b) flat and reasonably smooth?

Probably the damp-proofing was breached when you removed the screed.

I'd be inclined to remove the top (again), hire a multi-headed concrete floor scabbler, run that along, clean up, apply bitumen emulsion "as it says on the tin", and re-screed.

How long did the previous job last, I wonder? 50 years?