Hello - the short answer to this is no doubt no floor should be laid over damp concrete sub floor, but having contacted Ardex about the suitability of Arditex NA / DPM 1 coat / Arditex NA sandwich on a concrete sub floor, they have told me not to do this over bitumen adhesive residue, despite a reputable flooing company advising it would be OK. Our Karndean is lifting and after gleaning information from this site and my own research, given our house was built in 1973, the marley tiles and bitumen we removed (leaving a residue in places), could have removed what was acting as the DPM. As heating pipes are below (not very deep), the expansion and contraction could have caused one area to lift (powdery, cracked, pitting underneath), which became apparent 5 years ago, but the newest area lifting was measured at 36 in the lifting corners by the flooring company 6 months ago and my worry is that ventilating until its acceptable dampness wise and doing the sandwich will either push the damp up the walls, or push it into the rest of the downstairs, which also had the tiles and bitumen removed 15 years ago? My husband's solution is to remove the latex / slc and then put down vapour barrier underlay and waterproof laminate, but surely the damp problem will rear its head again at some point? Plus the bitumen residue has presumably prevented proper bonding to the latex or slc? Is grinding this off the only option? Or given we want to be able to access the concrete floor for future leaks, is another flooring type a better way forward? Your suggestions would be much appreciated. I can't attach pictures of the floor under both areas, but under the heating pipes was cracked, dusty, powdery (orange colour) and under the new area you can see dark bitumen residue and the slc broke off easily from the floor. It looks damp but doesn't feel it. There could also be a slow leak, as a plastic pipe repair was put on an imperial pipe (damaged by wall being taken down) and the water mains pipe across it looked very corroded when that was done 15 years ago and seemed to be surrounded by concrete. Is that best left alone? Your advice on the best prep and flooring in this sutuation would be appreciated, as we can't afford for it to go wrong again..many thanks
Wow. I think you should break it all out and have a new sand cement screed put in with a proper dpm sheet underneath! Im surprised Ardex have said that. The Ardex na dpm sandwich is a go to for that type of subfloor. What was the reason and the limitation for them saying no? Personally I wouldn’t want to bond to a subfloor like that. If you want access laminate is a good option. Normally I would level that with a latex levelling compound. Wouldn’t want to grind it as it can contain asbestos. Maybe test it first at least. Look at a company called Triton. They make a really good dpm sheet that has dimples beneath so the subfloor can breath. Then underlay, then laminate
Yeah as Dan said it’s surprising ardex have said that. I’ve done that system for 20 years and not had it fail.
Any pipe in concrete that’s not lagged is a burst pipe waiting to happen. I’d be digging that screed up and sorting from the base up. New dpm, new screed, new pipes. New floor
Wow indeed. Thank you both for your responses. The reason this has came to the top of our list is that we need a new boiler and plumbers want to put a combi in but I was worried about the pipes being old. Now I'm really worried! Was going to check the flooring company would remove the bitumen residue before latex sandwich, but from what you've said above, you wouldn't want to grind it either. The kitchen is in good condition and the corroded mains water pipe that looks to be surrounded by concrete goes under the oven etc in to the hall (also karndean covered ) and to the stopcock in the toilet. It's been hard enough to get my husband to consider checking and replacing the plastic pipe repair and connectors, but the thought of digging everything up is too depressing for words. Dan - you say you are surprised ardex have said that, but also say you wouldn't want to bond to a floor like that - is that not why they have said the bitumen residue has to go? Can it be done another way, like sanding? And if we did the sandwich which everyone seems to do, would the lack of DPM 1 coat on the rest of the downstairs, end up pushing more damp in to the hall and lounge which are adjacent? And how on earth do we know if there is a leak or how to find it? This is a total nightmare. Not sleeping as it is. Even the thought of a plumber digging to the corroded pipe is worrying, as they may well cause a leak in the process. My husband wants to remove latex, put underlay and laminate on top, but he doesn't get the lack of bitumen could be a massive problem and laminate in a damp area would rot - hence your suggestion of more DPM. How can we get the concrete tested? Is screed the same as concrete? Sorry, all these terms are new to me. And can laminate be uplifted then, as the flooring company (karndean is really there thing), said you couldn't repair.
How do you know you have a leaking pipe? You can get leak detection companies. Or you can ask your insurance company. If I don’t trust a floor than I won’t bond to it. But NA will go over all sorts of bitumen and crap. I’ve even put it over a old fireplace hearth that was practically soil once lifted. You can sandwich a dpm to protect the new floor. The Ardex NA is moisture tolerant so you can use a sheet dpm on top of it. I prefer one that can breath or your going to start a mushroom farm beneath your floor. Dpms control moisture and some level of rising damp but if you have water from a burts pipe or hydrostatic pressure from damp it will blow through the dpm or go up the walls. Maybe you should employe a damp specialist first to find out the exact cause
