I have few small areas around my floor slab and original solid wall that could do with a bit of paint-on DPM, just to be sure. Some areas will be behind skirting board, one small area under carpet. The bit under carpet is the top of a small internal wall where a suspended timber floor meets a new solid floor. I need a product that dries fully (does not stay sticky etc), and that has no long-term smell. I got some generic bitumen paint from B&Q, but just thought it may not fit the above spec. Should I got for something more expensive like synthaprufe / liquid rubber etc ? Or will the bitumen paint be fine ? Thanks, Simon.
Bitumen / rubber emulsions are a lot better for this (particularly where they're weather from the outside) and worth the small amount extra. Shop around though, as they vary enormously in price.
Cromar's Cromaprufe is one. Bitubond do one too, but I can't remember the product name (which is odd, as I've just been through about 6 of them).
=A325 / 5 litres is typical, looking around should find something at just under =A310 / 5 litres.
It's water cleanup, but IMHO while you can rinse the brush enough to keep it for the next day's painting, it's knackered afterwards. Also either shave your arms, or wear disposable gloves and long sleeves when applying.
I agree for the skirting. This doesn't sound like a critical application
- any old bitumen scunge would be all I'd use - couple of coats.
The area under the carpet - not so sure.
I'd be concerned about either the bitumen wearing off or bleeding into the carpet.
I'd soak the area in dilute SBR but that's because I have it lying around. Not a DPM, but I have observed that slowing damp progression.
For the OP, I might be more inclined to purchase a small pot of floor paint from B&Q - it's not really a DPM but it will reduce the transmission rate and the carpet presumably will allow the area to breathe.
The other option would be to soak the area in a bit of cheap Halfords fibreglass repair resin - that stuff soaks into cement quite well (I know - I tried to repair a crack in a concrete pond with it once - didn't gap fill the crack but it did soak in quite well to the cement. This could be classed as the mother of all bodges, but it's cheap and won't be any the worse.
I could have done. But when I laid the floor, this wall was holding up a temp wall and door keeping the elements out of the house, and also the air ducts to vent the suspended floor were too high to lay the concrete over. So I layed the floor up to the wall. Then, I could have removed the top course and screeded over, but part of the top course is a couple of lintels spanning ducts to vent the suspended floor to outside. And I didn't fancy just screed over them since they are flexible plastic air brick type vents which convert to 4" drainage pipe outside the wall.
In retrospect, I could have put in the air ducts lower down when I built the wall. But I didn't ;)
Oh, I did relay the top course with SBR-laden mortar to help with the waterproof aspect. A top source over a DPM would have had no strength.
The top of the wall is not damp at all at present. One side is open to the area under the timber floor (although I may put some celotex against it), and the other is against the concrete slab. Its about 4 courses high and the bottom is on the original subfloor concrete (like the sleeper walls). The wall is built with blue engineering bricks and the top course is built with SBR mortar so not really sure I need the paint-on layer at all - its just an extra protection. I have some SBR so I could give it an extra soak with that. However, I may give it a go with liquid rubber and just see how durable it is. If it wears off eventually, so be it ! Cheers, Simon.
With the engineering bricks and SBR mortar (which is quite a good block)
- if the carpet and its underlay can breathe, I don't think I'd worry - I would expect a very slow vapour movement there and if it can escape upwards I don't think you'll notice it.
I'd only worry for vinyl or a wooden floor over the top where there is a
100% impervious layer.
The other option, of course, with carpet, is you can loose lay a plastic DPM (eg that stuff that's sold for use with laminate flooring) over the entire floor under the underlay - as long as it doesn't give you any problems with the carpet sliding.
Story time...
My floors all leak moisture to some degree - this was evident when I took up some old vinyl and found much black mould under patches. For thos parts that were to be covered with wood, I used marmox plus a vapour barrier underlay - but I think the vapour ingress was slight - probably never have noticed with carpet, because it dried out fast once uncovered and never remained visibly damp.
The kitchen was terrible though - after I ground the old bitumen floor adhesive off, it hit you right in the face - a real damp cellar musty earth smell that never went away even in summer.
Room humidity went sky high and stayed there (70%).
After I soaked the floor in as much SBR as it could absorb (we're talking until it pooled - about 10l SBR diluted 1:4 over 20m2) and after that dried out, the humidity fell right back.
It wasn't perfect but it was a lot better.
But because the floor was in such a bad way, I levelled it and used a
2-part epoxy DPM (not cheap at about 300 quid, but a lot cheaper than ripping the slab out) and the room is absolutely dry now.
One other room that I had to screed, I used 30mm SBR screed and that floor (which is shortly to get wood on it) is pretty dry with just the screed alone - I do not believe that slab has any DPM under it. It was back in the days where the DPM (if they could be bothered) was some bitumen painted over the slab before screeding - I've seen it in other parts of the house where I've had to angle grind a hole in the floor for drains. For some reason, the kitchen didn't get that treatment AFAICS and it's obviously not perfect even where it does exist.
Well, vapour can escape sideways into the underfloor void on the suspended floor side, so it would even be OK with a non-breathable covering. That was sort of the plan - paint the top and solid floor side (down the side of the screed where it meets the main slab DPM), and then all damp will escape to the underfloor void.
By the way, Tim, I've nearly finished the main SBR screed (half- strength SBR mix) over my 25m^2 floor using my aluminium screed "rails", and in approx 3m^2 sections, and its worked pretty well. I had the mix like a stiff mortar as I found the dry mix too hard. As you leveled it bits pulled up since there was not enough water to bind it properly. I think for that method to work, it has to be even dryer, so it spreads almost like a powder (which matches the youtube videos I've watched), but such a dry mix would not disperse the sand and cement sufficiently in my belle mini-mix. Anyway, my method has worked, but its annoying when you have to abandon the "professional" method ;-) Cheers, Simon.
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