Help with unlevel self leveling cement [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-25-2008, 07:05 PM
Hi All - I recently poured Bostick SL 150 self leveling cement over an electric heat mat, which was attached to 2 layers of plywood. I used Bostik primer as well. I am planing on using a Ditra mat and then tiling with marble tile; room is aobut 75 sq ft.

The problem is, the floor came out both not level, and lumpy. Probably out of level by 1/4 or so in some spots. I am guessing the best idea is to try to take some of the bumps out with a grinder and try the self leveling route again...making sure it flows better and is mixed better. If anyone has any other ideas, or tips, i would really appreciate it. Thanks very much !!

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02-25-2008, 11:19 PM
sounds to me like you didn't make it lose enough and it wasn't able to level out like a liquid would.

02-26-2008, 02:16 AM
I've used a couple of different SLC's and found they won't self level if mixed exactly to the manufacturers directions - they're too thick. Had to add extra water to get them to flow properly. That's been my experience at least.


02-26-2008, 08:47 AM
Sounds like a few possibilities here
1: Did you dam the peremeter of the room and prime the floor?
2: Lumps, Add material to water gradually. Mix for 2 minutes at the recommended speed after you have added all the powder.
3: Some applications require a second pour. Prime over the existing slu.

I recommend getting a couple hands to help as the quicker it is poured the more effective the product is as far as leveling. The flow time is generally 20 minutes.

02-26-2008, 11:40 AM
I saw this post on FHB too!

I like the idea of grinding down the high spots better than trying to correct yourself by adding even more material.

I just used Laticrete 86 on my 25sq' bath floor. There was an occasional bubble or lump here and there, but they came off with a metal paint scraper. SLC is not like concrete, you can scratch your name in it with your fingernail.

Get a straightedge and map out exactly where your highspots are, I'll bet you can knock them down in fairly short order.

What size tile will you be using?

02-29-2008, 08:25 AM
SLC is not hard like normal concrete right away, but it can get that way with time. On one of my projects I had no problem scraping during the first couple days, but two weeks later I discovered a 1/4" high spot that I hadn't noticed early on. The SLC was hard enough that the grinder didn't even work very well, though I did eventually get it down to what I needed.

02-29-2008, 06:04 PM
Thanks very much for all of the advice. The problem is, not only are there lumps, that i could possibly grind, there are bigger waves. Highest point is about 3/4 from low....but...i am not so sure the floor is underneath is exactly level.

I am pretty sure it would be impossible to grind down all the high spots. So i can either dig up the current pour, and risk ruining the heat mat, or pour more SLC. Seems like more SLC would be easier.

I guess the big question is how do you guys 1) mix to the right consistency, and then spread what will be like 100+ lbs of this stuff in the 10 min or so it takes to start setting up ??

Thanks again !

02-29-2008, 06:17 PM
The biggest problem people make with slc is to try to pour too thin a layer. You can do a thin layer, but it takes more skill and understanding. If it is thick enough, you wet the whole area, and there is enough material, it will level itself. If it is too thin, it is quite easy to end up with an uneven surface. Depending on the configuration you use, it is starting to set in minutes after you pour it. There are some configurations that can give you up to say 1/2-hour, but literally, some are setting in less than 10-minutes. If you try to move them aroud at that point, you'll end up with chunks sort of like a puddle that has just started to ice over. The stuff is much more fluid than concrete, but less than water...more like honey or pancake batter. Pancake batter doesn't lay flat like a crepe, but if you filled the pan, it would be pretty level (discounting the bubbles from the baking soda).

03-01-2008, 02:12 PM
I'm having the same exact problem with my kitchen right now. I've been going at it with a belt sander and 36 grit belts. But like you I have waves, more than lumps, undoubtedly from trying to rake it out for coverage. I used an ardex product. My plan, after talking with the Ardex tech. support was to fill in with Feather Edge or a similar type product that can be troweled on. Product is good for up to 1/2". Additionally it's ready to cover in 1-3 hours instead of 2-4 days., But you have to re-prime.

This is the second time I've used SLC and have been disappointed each time. If I ever have to use it again, I'm calling in the pros.

Good luck.