Concrete floor and dampness

I've found some dampness under the vinyl flooring in the hallway of my late

60s concrete-floored house.

The concrete is still mostly covered with brittle brown tiles, and the concrete where exposed (missing bits of tiles) has some black stuff painted on it (or maybe it was the glue for the tiles).

The vinyl was put down temporarily a few months back (one day I'll put laminate down), but recently discovered a damp area underneath, together with white powdery stuff on the concrete, causing the floor to swell slightly.

What's the best way to deal with this? Someone I called out last year wanted to coat the entire ground floor for £400 (but I wasn't sure then if it was rising damp or a leak from somewhere). Would this work, or would any sort of coating just drive the moisture towards the walls?

Thanks.

Reply to
BartC
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Watch those - some possibility they might contain asbestos, so reasonable precautions when removing should be considered.

Bitumen compound most likely - probably tile glue and would have acted as a DPM (damp proof).

I had similar in a 50's built house with the sam efloor structure.

Concrete salts?

Good question. You could do it yourself (I did) - with an epoxy DPM. The stuff is not cheap, so it's going to cost a fair fraction of that just for the epoxy. But it is very easy to apply - roller on 2 coats at 90 degrees to each other (to avoid pinholes). Look for "F Ball" on google - they make the one I used and have all appplication details on their website.

What will be not so easy in your case is removing the bitumen. You cannot have *any* remaining before an epoxy DPM. Basically, it's floor grinder time if you go down that route and take the bitument and a couple of mm of screed off. Rather messy operation (I did it).

I bet your tradesman did not include that in his quote.

There are other options - which depend on what floor covering you want. The most obvious is to have another flooring that you can use *more* bitumen compound to stick down. Another is a floating floor (eg engineered wood, laminate - where you can loose lay a heavy plastic DPM under the whole lot.

Re walls: the floor was DPM'd via the bitumen before - if you were going to get any damp in the walls, I think it would have happened by now.

Cheers

Tim

Reply to
Tim Watts

yes, the asbestos will be bound in the vinyl though, making the risk as good as zero.

that seems to imply that water ingress into the slab is ongoing

It would cost you =A310-20 to it with bitumen gloop. It is slow setting, don't paint yourself into a corner :)

It would. Whether it would be a problem is another matter, each element of the building can evaporate a certain amount of water without harm.

Thats what I call making life difficult.

Another approach is to use a floor surface that lets the damp evaporate off. Then it just dries out.

NT

Reply to
NT

Indeed. That's why I said "reasonable" - taking them up with a spade or a bolster would be OK. Grinding them off would be bad.

My assumption with a floor of that age is that it is highly likely...

That depends on what sort of floor you want on top. I wanted slate - so no way was I going to leave a bitumen layer there.

For 400 quid, the OP's tradesman was either going to paint more bitumen on and rob the OP, or paint on epoxy without doing the necessary preparation and in a while it would fail, thus robbing the OP again.

This is another reasonable approach.

Reply to
Tim Watts

Pros won't lay floor coverings on a solid floor without latex screed. This invariably adds a day to the job but presumably solves the problem

Reply to
stuart noble

SLC (levelling compounds) will never bond correctly to bitumen - which is why I had to grind mine off. No real pro would do that, though there are plenty of cowboys who will.

There is a school of thought that more bitumen blinded with sand immediately is acceptable, but it's the sort of thing I'd want professional advice on - or at least well considered advice.

I have seen what happens to SLC on bitumen - it seems OK, then after a few heating/cooling cycles it shears the bond over large areas. My plasterer has also been a victim of this in a previous life when he worked in Germany on converting some old bunkers into habitation.

They had to take the SLC off again (bond shear set in so it was easy). A regime was worked out professionally for that one that involved drilling lots of small (1cm I guess) dia holes an inch or so into the screed at very regular and close intervals then pouring suitable rated SLC. The idea was the SLC would pour into the holes and peg itself in place, bypassing teh bitumen layer.

Apparantly that worked. You'd want to choose the SLC carefully too - not any old crap from B&Q. Also for pegging, the SLC thickness would matter as you are relying on its self strength to hold up between the "pegs" so a 3mm pour would probably not work. I suspect a 10mm pour of good stuff with holes every 6" may work quite well - and although that's a lot of holes, they are shallow and an SDS would make short work of it.

I would not want to guarantee that approach through unless the SLC manufacturer was consulted - or a professional flooring contractor.

Reply to
Tim Watts

Bitumen can be overlaid with cement etc if its blinded, and painting solvent bitumen on will dissolve the existing bitumen, so that approach is quite workable. The one downside is bitumen with solvent is very slow drying, so you'd want to not do it all at once if the house is occupied.

NT

Reply to
NT

The original solvent doesn't normally dissolve the hardened film e.g. white spirit has no effect on oil based paints

Reply to
stuart noble

How big - and what shape - is the damp area? Could there be a leaking pipe buried in the floor?

It's best to deal with the cause rather than the symptoms, if you can.

Reply to
Roger Mills

That is because most oil based paints polymerise as they dry so the resulting paint film is crosslinked. It may still soften with a solvent but it won't normally dissolve once it has fully cured to dryness.

Bitumen will dissolve in solvent although the solvent is smelly stuff and bad to breath (extremely high VOCs) and bitumen gets everywhere!

Reply to
Martin Brown

IIRC cellulose thinners softens bitumen but isn't a practical proposition because it evaporates too quickly and stinks to high heaven.

Reply to
stuart noble

Bitumen is after all merely a long chain hydrocarbon and should dissolve in any shorter one - petrol diesel, turpentine or white spirit..there is no need to get fancy and use the ketones!

Reply to
The Natural Philosopher

Interesting. Not a job I hope to encounter again, but I'll bear that in mind.

Reply to
stuart noble

Also bear in mind the flash point and fairly wide range of explosive concentrations if using the more volatile ones.

Reply to
Martin Brown

The worst damp spot had been at the bottom of a door-frame, which seemed to extend well into the concrete, if not beyond. The wood was soft, wet and rotten. But the nearest buried CH pipe runs past the frame on the other side, and that wood was sound. The only other possible pipe might be the incoming mains, but if there is a leak then it's not showing up on the water meter in the road; if the stop-c*ck is turned off under the sink, any residual flow stops, and usually no flow is shown most of the time.

The current area is perhaps 3x5" in the middle of the hallway, where there was a similar-size area of the brown tiles missing, but the dampness had permeated radially from there on the underside of the vinyl. The same floor had been used with no vinyl, just the tiles, for a month or so with no obvious damp.

There were a few other spots of damp, one in the middle of a laminated floor, causing it to swell and then split. But this was pretty much where a wall (between dining room/lounge) had once been, and was unlikely to be near a CH pipe. So it's possible any damp-proofing had been damaged.

Reply to
BartC

indeed. Always use the heaviest solvent that works - white spirit and diesel are the safest and least likely to poison you.

Reply to
The Natural Philosopher

I have a tee shirt relating to a combination of that and static electricity.....

Reply to
stuart noble

I know - I used one. Not recommended in an inhabeted house - you'd totally have to tape everything not related to the work area shut.

When I used one, the hosue was a building site and we had the windows open - from outside it looked like the building was on fire.

The "dust" was broomed up and taken out in many many buckets.

But it did the intended job and was quite controllable.

Reply to
Tim Watts

Sounds like the amount of water seeping in is very small, and evaporates without showing until you cover it with vinyl. It could well be the water main, because the amount of water involved wouldn't show up on a water meter.

Reply to
Roger Mills

Why would you want to get it off? What muck?

NT

Reply to
NT

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