cracks in self-levelled floor, should I be worried?

[The Night Tripper]

Hi All Last night I just had my first go at using self-levelling compound. This is on a concrete floor around 5sq.m. in area, prior to laying ceramic floor tiles. I used two 25kg bags of B&Q (sorry) self-levelling compound, so there was a reasonable thickness (~5mm) of compound. Prior to this I primed the whole floor with dilute PVA BTW, and left it for 12 hrs or so to dry.

In the morning I now see that:

(i) the final surface is not as level as I'd hoped. I guess I have been warned eg. by this NG that 'it doesn't self-level' This may not be a problem, it's not too bad and I assume the tile adhesive can take up some of the discrepancy. However:

(ii) There are some fine cracks in the surface. Not too many, it's not 'crazed', but in some areas, 3 to 4 per sq. foot., each a few inches long.

Should I be worried?

Thanks Jon N

[Tim Watts]

Next time, go with Stopgap 300 - that flows almost like water once it's been pushed around to wet the substrate.

Tile adhesive can correct descpencies but it makes for a slightly more involved job. If there is a definate hollow, you can level it with some cementious tile adhesive the night before using a straight edge - that's what the pros do. Then tile normally over the top.

As to the cracks - probably shrinkage on drying. What matters most is that the bond is good. Go around and tap it with a plastic screwdriver handle or with the edge of a medium ring spanner and see if any of it rings hollow. If not, I would guess things will be OK.

Cheers,

Tim

[The Natural Philosopher]

+1

[The Night Tripper]

[...]

OK, will have a look at that.

The bond seems fine - I would have been really worried if not. So I'll probably go ahead with your first suggestion.

Thanks a lot J^n

[Tim Watts]

I had two areas where our bloke did this:

1) Where I had used assloads of F Ball Stopgap products dealing with a ropey kitchen floor, I had the subfloor about 1cm higher than the alley past the side stairs (floor here was flat and level and sound), but wanted the tiles taken through. Using a real tile adhesive (not a tub - don't do that!) he put about 1/2 bucket's worth down and trowelled it into a ramp about 3 feet long and left it until the next day. After tiling over the lot, you cannot tell short of measuring with a level that anything is amiss.

2) Where a short wall had been removed, I had a step in the screed (the old screed rode up 1/2" one side of the wall). I SDS chiselled it mostly off (it was bloody hard screed) and left him with a bumpy lumpy patch but mostly level overall. He spatted a couple of pints worth of adhesive over and trowelled it into a featheredge. Again, absolutely cannot tell afterwards.

What he said he wanted to avoid was trying to put a couple of tiles on a bed that was significantly thicker than the rest as it would be harder to level and more likely to settle out wrong. Certainly been my experience of tiling that getting the substrate flat makes things a lot easier. Cement based adhesive does not mind going on in a couple of layers - particularly if it is a decent make like Mapei or Ardex with the magic extra stuff they include in the mix.

That would not worry me then. The only time I've had a disaster was having some fool splat that stuff on top of bitumen where most of the bond failed in short order (PVA did not save the day).

Cheers

Tim