I'm planning to tile the floor of a ground floor utility room. It's L-shaped and about 2m along each longest side. One section is inside an alcove and houses the washing machine.

The floor is concrete, and was previously covered with lino, which I removed and scaped off the remaining adhesive.

I then laid a coat of Wickes High Performance self-levelling compound to an average depth of about 7-8mm.

Unfortunately it doesn't seem to have 'levelled' itself as much as I would have liked. The floor wasn't particularly level beforehand. There's a definite linear 'bulge' which runs along the line of the level in this photo, between where the main room meets the alcove:




The SLC seems to have 'rounded off' the ridge somewhat, but there's still quite a difference in level across the room. You can see in the image beloe where there's an 8mm drill holding the level at a level across from the toilet side to the ridge in the middle. Luckily, the floor is pretty level front to back. It's just across its width that I have the problem.



The tiles I'm planning to lay are 10mm thick ceramic 60 x 40 floor tiles (see below). Obviously, being quite large, conforming them to differences in level like this while getting edges butting nicely is quite a challenge.

I guess the question is - should I lay more SLC on top of this to try to even up the level, or will I be OK laying the tiles on a thick bed of flexi adhesive (my preferred brand is Bal).

I'm not too worried about the floor not being perfectly level, but I want to avoid having the tiles come loose or cracking.

Incidentally, if I do need to pour more SLC - do I need to seal the first lot beforehand?

Many thanks.

The easiest way would be to add some more slc and bring it up to level. Personally I always prime the previous coat before doing so. It is possible to run the tiles through level by skimming the back of the tiles with more and more as the floor drops awayadhesive but I'd say that option was more for the experienced tiler.

Yes, I think I'll pour a second coat. It says that it can be feathered, so I think I'll tie my level onto a batten and use that as a float to get it as level as I can with the high point.

I'm going to buy some Prime APD anyway for the tiling, so I guess that will make a suitable intermediate surface for the SLC.

Slc dos'nt self level on it's own, self smoothing is what it should called..

i've had similar problems with cheap/poor slc. i only use mapei renovation screed now, it's the dogs danglies. i would go over that again for a good finish

I'm mapping out the contours with a level, so at least I'll know where to pour the stuff this time.

OK, so in the end I came up with a slightly different - and perhaps not perfect solution - but it seems to have worked out for me at least.

First I found the highest spot in the floor. Then I got a couple of lengths of 8mm square wood moulding and stuck them flat to the first layer of SLC following the floor profile.

Then I planed them until they were exactly level with the high point and level along their length from end to end. This is actually a lot easier than it sounds. I just started at the high point and planed the rest down until it was level, checking for high spots with some pencil black scrubbed onto the bottom of the level.

Once I had my guide, I cut a length of skirting the width of the room from wall to wall to use as a float, poured the SLC at one end and drew the float along on top of the wood moulding to spread the SLC to the correct depth and level from side to side. Perfect first time!

One issue you might run into is that if you run out of SLC before you get to the end of the stroke, it can't run across from one channel to the next through the wood, but just pour some more SLC into whichever section needs to be built up and start the float from the last level point. Easy!

If it was a bathroom or somewhere which got really wet, I might be concerned about the embedded wood mouldings swelling up a little, however unlikely, but as this is essentially a dry room, I'm not expecting any problems like that. Being only 8mm square, there's a limit to how much they'd swell anyway. If you were really concerned, you could always chase the mouldings out with a narrow wood chisel and fill the cavity with SLC or tile addy.

There are thin metal strips from wickes about 5mm thick which could have been used and bedded onto a spf then leveled..

Phil hobson is the man for this method, sure he will be on later to explain what he does! I usually just do it over 2 layers, mixing the slc to its most watery consistency to give it a better chance of finding its level!