Self Levelling and Tiling Failure

[GarryC]

Hi All,

Sorry for the long post but i'm in the middle of a tiling a disaster on my kitchen floor. The kitchen is in a 1970's extension with a concrete slab floor. I removed two layers of different lino before levelling it with Bostik Cempolay deep after priming with acrylic primer. The SLC was varying in thickness from about 35mm to 10mm.

Over this I laid 60x60 porcelain tiles which looked fab for around 2 days before before I could see them starting to lift up in the corner of the room. After a month or so patch about 2m2 had started cracking and lifting. In the end I bit the bullet and pulled up the offending area to find that the SLC had completely delaminated from the concrete.

After pulling up all the loose SLC I cleaned and reprimed the area with SBR and relevelled it to match up with the surrounding sound areas, this time in two goes each half thickness. After leaving it for about 3 weeks I noticed it starting to crack in roughly the same area and after about a month again it had completely buckled and delaminated again.

So having wasted a few hundred pounds of materials and hours of my life I had to rip up the failed SLC again and scratch my head as to what to do. I've checked the concrete, there are a few small cracks maybe 2mm across but none of them have any vertical height difference and the concrete slab has been down for many years. I checked with a polythene sheet and moisture meter and there doesn't seem to be any damp coming through although I can't say for certain if the DPM is intact. There are some hollow sounding areas of the slab but no obvious signs of movement

The lino was well stuck down so in some areas there's a cream coloured residue (possibly adhesive) which is almost impossible to get rid of, although the SLC didn't really adhere to the bear concrete patches either.

I'm really at a loss as to what to do next, I've a few ideas but don't really have the heart to waste more time and money ad have to rip it up for a thid time, to make matters worse my 6 month old will be crawling soon and missus wants this sorted ASAP. My options?

- Liquid DPM, resin inject cracks and use a different levelling compound?
- Laying plywood over packers and screw down, tile over with Ditra mat? I'd be a bit worried about how to get the ply level and also the washing machine and dishwasher sit on this area so it would need to be pretty solid.
- Tile directly onto concrete with thick bed adhesive?
- Dig out concrete floor and start again? Not really an option as the kitchen is already fitted!!

None of these sound like good ideas but need to give something a shot.

Any words of advice much appreciated, thanks!!

Garry

 

[chappers]

it seems strange that the rest of the floor is Ok, assuming that had the lino residue over it too. you could try the tile addy direct to the floor. do a test run. or try an SLC suitable for use over asphalt. Failing that you could get a grinder on it and try and get the lino adhesive off.

 

[Doggit]

How much water did you use with the Bostic Cempolay, and was it to the pack recommendations. Was the pack within date (normally only 6 months)

Having had a quick look on the Bostic website, I suspect the problems lies with the primer you used, how did you apply it.

 

[GarryC]

Thanks for the replies,

I didn't check the date on the packs but I used it straight from the store and mixed it with the recommended amount of water, ended up quite thick but I guess that's necessary for the deepbase stuff.. The primer was the cemetone SBR (expensive stuff) and dilluted as recommended and brushed on.

If I could guarantee it sticking I could use SLC again but I can't be sure the surface will adhesre unless I grind off the any residue etc?

 

[Doggit]

I've heard of problems before with not using fresh Bostic, but I think it's the SBR that's caused the problem. From the pictures, the SLC went solid, but came away from the substrate, which being old tiles, has no porosity. SBR is highly rated, but I tend to avoid it as it has to be used properly.

If you check the SBR data sheet, it says key the substrate first, and then mix it with water and cement to make a slurry, but the SLC tech sheet tells you to lay it down before the SBR goes dry. If you use an acrylic primer (such as Setcrete), then you'd use it at 1:4 on a permeable surface, but neat on a non permeable one such as the tiles.

Bostic tech support is 01785 272625, so it might be worth contacting them to be doubly safe.

 

[vinn]

Why not go to johnbridge.com & show them what you've shown us. They are the most professional and friendly site on the web. Believe me you will learn much.

My first glance assumption is that its a moisture problem - something is causing the primer, SLC and Tile to lift & pop off. That something is usually moisture penetration.

An alternative would be mechanical pressure from the tile touching abutments with no room to expand.
Or the slab itself rising/moving due to ground pressure(s).

How do you know that you have a membrane(DPM)?
Have you seen the membrane flopped up at all kitchen walls? The same coloured sheet?
Is the kitchen FFL higher or lower than the outside ground level?
Has the kit fitting work revealed any damp in the walls?

Laying matting would be your best bet but there might be further difficulties.

 

[GarryC]

Hi Doggit - The first time I used the acrylic primer mixed 1:4 as you say as it was painted over the exposed concrete. Second time I used the SBR, the instructions were a little bit unclear but I laid the SLC when it was still tacky.

I've contacted Bostic, not super helpful as they suggested laying a DPM and 50mm sand cement screed over the top, not exactly possible now that the kitchen is installed, also 2/3rds of the kitchen is tiled and holding on fine also the kitchen transitions into an engineered wood lounge area so I can't exactly have a 50mm step!

I suspected moisture may be the problem, there's no obvious sign of a DPM as this part of the house was built in 1974, no signs of a membrane at the walls anyway. In terms of FFL it's definately higher than ground level and no obvious signs of damp in the walls. I've laid Correx down temporarily and haven't seen any condensation build up.

Thanks for the suggestion about John Bridge, I'll give that a go

Garry

 

[Doggit]

I don't think moisture would cause such a problem, but you could check by taping a foot square piece of polythene to the floor for 24 hours, and see if there's any water droplets underneath it after 24 hours. But if it is moisture, then you'd need something like drybase liquid dpm, and then throw some sharp sand on it before it dries, then you vaccum the excess sand off before you apply SLC.

I would have just used the acrylic primer, and then put the SLC down, but it can still fail. I've just had to take up some tiles, and about 2 sqft of the second coat of SLC didn't hold to the primed first coat, but having lifted that section, the rest is solid.

 

[Stevedore]

Sorry to interrupt the thread but I've had a similar problem with that Acrylic primer with my floor...

Old uneven concrete floor slab with cracks & joins in it. I painted on a polyurethane dpm (G4 damp seal) which I primed with that same Setcrete Acrylic primer before laying deep base SLC at 10-50mm depths. It was finished with a 3mm top coat and vinyl tiles.
Within 3 weeks a 1ft sq patch had risen up and over the past 9months various other patches and an edge have bulged up, as high as 50mm! It appears areas have curled up where the SLC is above irregularities in the concrete slab. The flat half of the kitchen where SLC is thinner has no issues and doesn't sound hollow.

I've taken up some of the SLC to find it has debonded from the polyurethane. The SLC appears to have green primer stuck to the bottom of it so assuming it's the acrylic primer that didn't stick to the polyurethane. No signs of damp and polyurethane layer appears intact.

I'm planning on trying again but with FBalls P131 neoprene primer, I might even sand the polyurethane lightly to give it a key.
Is Neoprene more suitable than Arylic? Any thoughts??

 

[Doggit]

Having had a quick read of the G4 Damp seal, it looks as though you should have thrown sharp sand on to the 3rd coat, and then brushed off the loose sand before you laid the SLC.

Did you use the Setcrete neat, or diluted.

 

[Stevedore]

Thanks Doggit, I used the Setcrete Acrylic neat...
Ok so if I sand lightly, apply another coat of polyurethane and sand blind it that would give a mechanical key.
You think I should then prime that or just put SLC straight on?

 

[Doggit]

Just put the SLC straight on. Putting it on neat was the right way t do it, but as the SLC has come up with a green coat on it, it obviously hadn't taken to the Poly.

I brush off the excess sand, and then use the vacuum cleaner (mine not hers) to take the excess off first. And run the Poly up the wall a bit as well so it dries evenly.

 

[GarryC]

What do you all think would be the best combination of liquid damp proof membrane and self levelling compound to build up the level by 10-35mm? I think I'll grind clean the concrete and give it another go

Cheers

 

[Doggit]

I tend to use safeguard drybase, but if used properly, most damp proofer will do. As to SLC, I've been using Setcrete lately, and had no problems with it.

 

[L95]

Sure the residue wasn't bitumen? If so then that's your problem.

Secondly, I've been advised by various people before (manufacturers) that polyurethane isn't suitable for tiling as it can't bond to anything so in that section I would rip out the polyurethane and put down PTB Fibre with AD1 built up to 25 mm if that can make up the difference. Never heard of the brands mentioned above personally so give BAL technical a ring and see if they have anything to advise you with.

Just my 2 cents.