Latex screed + no DPM concrete = localised bond failure

[Tim S]

Hi,

Just been down to the Bunglow to gauge out the kitchen floor.

This started life as +/-15mm with significant bumps which would have made tiling impossible (unless I used mosaic!!!).

Anyway, whilst marking out the low spots that need more latex, I found a few areas where the bond had failed (cracking of the screed and hollow sounding noises when tapped). Worst area was about 1m x 40cm, and a few other areas were smaller. About 2-3m2 out of 19m2 had a problem, everywhere else the screed was sound.

This was a contracted out job, so obviously I'll be raising it with the chap who did it - he's coming down Thursday or so.

But, in order to be able to have an intelligent discussion with him, would anyone be prepared to pass an opinion on my theory, which is:

The latex compound didn't take properly due to the surface either being a bit damp or friable or both. In either case, chucking down some stabiliser might seem to be a good idea, before re-applying compound to the affected areas. I'm thinking a good soaking in SBR (as PVA won't be so good in damp conditions).

I plan to overseal the whole floor with AquaSeal "Aqua Stop" (on recommendation) before tiling, which will sort out any damp issues - so all I have to worry about is that the levelling compound maintains a decent bond to the substrate.

Cheers

Tim

[Stuart Noble]

IME 2 part latex floor screed is like shit to a blanket, which is why it's used to firm up friable surfaces. Existing dampness should make no difference, as the product is water based. However, it IS expensive, and there are cheaper one part, cement based floor screeds. I hope the contractor didn't cut corners.

[Tim S]

Stuart Noble coughed up some electrons that declared:

Hi Stuart,

I don't believe he would knowingly cut corners - we have a long standing association as his firm do lots of work where I work.

He's coming in tomorrow to have a look. He did mention that the product he bought, which used to be 2 part was now one part, with the "2nd part" mixed in dry to the 1st part. Seemed to be new to him. I'll get the brand tomorrow. Obviously it was a product variation that he didn't expect - maybe someone was telling him round objects.

Well, if he's used an inferior product it will be down to him to sort it out. He said he did put lots of stabiliser down.

Cheers

Tim

[Tim S]

BTW - forgot to say "Thanks Stuart".

That was exactly the sort of information that helps me look at this objectively...

[John Rumm]

All the latex ones I have used recently (typically Wickes) have been one part - just add water. They seem to bond pretty well IME. They do a cheaper one that does not include the "latex" in the title. I have not tried that, so don't know how it compares.

[Tim S]

John Rumm coughed up some electrons that declared:

Thanks John,

That sounds the same as the way he described. He did wonder if the bond failure might be one level down in the original screed, which apparantly is not very thick.

The key thing that matters is whether it will fall off or not. I'm sure, that if it turns out that we have 1.5cm of stable "skin" that's failed a bond lower down, then it's probably not going to fall off and with the weight of the floor covering on it, it's not going to lift off either.

If it's the latter, I'll drill and epoxy some 2" stainless stud in to lock it to the base slab. Bodge: possibly, but when the alternative is hack up

19m2 of floor and pour 2 tons of concrete into the room plus a ton of screed, then needs must. It's very easy to be a perfectionist, in which case, might as well knock the house down and start again. What matters is whether it works, rather than how :->>>

Shall see what tomorrow brings...

Thanks chaps!

Tim

[Stuart Noble]

I somehow doubt that there is any dry form of SBR because it's basically a type of rubber.

Also, the 2 part stuff I've used isn't cement based. The powder is the same colour, but it behaves very differently, and there appears to be no chemical reaction with water. It seems to be some kind of inert mineral that is bonded by the polymer, but there is no "cure" as such. Don't know how relevant that is to your problem, but it might be interesting to see what your contractor thinks.

[Stuart Noble]

No need :-)

[Tim S]

Stuart Noble coughed up some electrons that declared:

They used this (Cementone Cempolatex 1 pack)

after some discussion this morning, we think the hollow sounds are coming from lower down (ie the next level of original screed is dodgey). I think that's far enough down that it's not likely that the screed will collapse or flake. I'll leave it alone, probably. The floor will be bare for a couple of months so plenty of time to see how it goes. A degree of "carefully engineered bodgery" is acceptable, as long as it is basically sound.

Thanks to my efforts in marking out the contours, they primed the areas with PVA and dropped a fair amount of extra compound bang in the middle of the 3 remaining hollows and feathered them in. That should be good enough to lay insulation on (subject to a further check when it's dry). Also they showed me how to mix and apply the screed so I'm set up to make any minor alterations and repairs later (they're helpful like that).

Cheers

Tim

[Tim S]

While we're on the subject and I was searching for Cempolatex, I noticed:

which tells me Cempolatex 1 pack is 17.35 inc VAT.

Whereas Travis Perkins website tells me it's 29.98 PLUS VAT.

Hmm - suggestions involving barge poles and orificial insertion come to mind. Pity Beers are only Liverpool way - but it does give a very good indication of how much to negotiate the local supplier down to.

My builder paid about 20 quid per bag ex VAT, so the Liverpool to SouthEastern compensating factor seems to be Beers plus about 30%.

Very useful information, to me at least (and hopefully someone else). I'll use them as a guage for all general materials...

Cheers

Tim

[A.Lee]

TP are comical in their pricing. I avoid them now. Last time I went to the local one, I needed 2 18" plain slabs. I pay £1.34 inc. vat for these at the other merchants. Now TP have a loading sytem, where you load up, take a ticket into the office, then pay. The yardsman does not know the prices.

So, loaded the 2 slabs, went to pay, was told they are £2+ vat. each. I said they were £1.34 down the road - "go there then" I was told. So I got the slabs out and havent been back since. Alan

[Stuart Noble]

According to the COSHH sheets, the one pack contains cement, and the dry part of the two pack is 60% alpha quartz/30 % cement. I'll stick with the idea that the 2 pack (sbr) is used where there's a danger of damp, and the one part (or just a pva mortar) is fine for everything else.

[Tim S]

Stuart Noble coughed up some electrons that declared:

Good call Stuart.

I've followed that up. Makes it the same as the 2 part "Part A Powder". Odd though: I can't get the data sheet for the "Part B" liquid for the 2 pack...

Also makes the name a bit of a con: "Cempolatex", if there is no "latex" in it. I checked the COSHH sheet for the Arditex equivalent "2 part" and the liquid is "High ammonia preserved natural rubber latex concentrate" and "methanol".

I'm not sure if I should be saying "oh bugger" at this point :(((

Well I know what not to buy...

I suppose, given the applied stuff seems OK over all bar perhaps 2m2 of the

19m2 floor, that if push comes to shove, I might trim out the dodgey patches and infill with some proper 2 part and stabilise the substrate with SBR first.

The patches are small (worst is 1m x 30cm) and isolated, so it will be an almost trivial job for me now I've got vaguely level edges to work too. I need to get a few bags of compound anyway as I've to make good the bit by the fireplace when I take the fire hearth out in April, and some of the other floors need patching and smoothing. I'll just need another bag or two, not a disaster...

Anyone want to tell me if the above is a bad idea?

Now where's me anglegrinder...

Cheers

Tim

[Tim S]

Tim S coughed up some electrons that declared:

states:

"Latex modified self-levelling sub-floor compound"

Something's talking round objects... Perhaps I shouldn't worry after all.

I'd have to admit, Arditex's website is a hell of a lot more informative than Bostik's. Arditex say, of their 2 pack, that it's suitable with damp crappy substrates. I'm sincerely hoping the same applies to Bostik's stuff...

This is very confusing.

Cheers

Tim

[John Rumm]

As I mentioned before - you can certainly get latex products that don't have a separate latex liquid. The price seems to be in the right ballpark for that sort of product.