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Unread 02-05-2019, 06:43 PM   #1
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Self leveler - Floor Flattening Questions

Hi everyone,

I'm a new here, and seeking advice! I plan on pouring SLC, and want to make sure that I have my ducks in a row before doing so.

I am installing 6x24" ceramic tile on a concrete floor. I need to first flatten the floor. I mapped out the topography of the floor using a laser level, and found the deviations, in 1/16" increments and 1' apart from each other.

Here are my results:
The standard deviation is about 3.7/16" The average is .63"

The top five frequency is

0 38
-3 31
1 29
-2 20
-1 19

I have a few questions.

1) Should I grind off the high spots? If so, how much should I grind off? I was thinking up to the -3 points, because those are the second highest in frequency?

2) What's the standard procedure in figuring out which number/area I should try to get everything to? I was thinking to the -3 points, because those are the second highest in frequency?

3) The goal is to get the floors flat. Getting every area to the same level is expensive. Should I consider slope instead of trying to aim to level everything to a certain number/area?

4) Maybe I should pour SLC and then start tiling in the high spots? That way I can just compensate with thinset if I don't pour enough?

Thanks guys for helping out a newbie.
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Last edited by jgleason; 02-11-2019 at 07:10 PM.
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Unread 02-05-2019, 07:10 PM   #2
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Welcome, CK.

The ceramic tile industry standard for flatness of the substrate for tiles the size you have is no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in two feet. That's measured from the high points in your floor.

You'll do better with a ten-foot straight edge when deciding how to achieve the desired flatness.

Commonly one would grind down the excessive high points and fill the lowest points with an appropriate patching compound.

Your tiles don't give a rat's patooti whether the floor in question is level, they care only that it's flat enough.

My opinion; worth price charged.

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Unread 02-05-2019, 07:26 PM   #3
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If I’m understanding your diagram correctly, it looks like you have a 20+ft x 20+ft area with a tad over an inch slope from one corner to what I’m guessing is a patio area or something outside of what you want to tile. From the numbers, it appears to be somewhat of an even slope rate. Have you checked the degree of out of flatness with a long (like 6 or 8’ or more) straight edge? If you’re OK with the slope, you may not be all to far out of flat.
1- grinding is dusty work even with a vacuum shroud. Unless you take a lot of care, you’ll wind up with divots and waves that may be more of a headache.
2- not sure what you’re asking here
3- an inch over 20+ feet is noticeable (at least to me). Our living room slopes that much and the kids used to play marble races. That’s up to you.
4- with SLC, most don’t like a feathered edge, and need some nudging to get leveled (they’re loose, but not watery). If you only do a portion, you’ll wind up with an edge that will be more of a pain in the neck. Consider SLC as a “do it all, or go home” kind of thing.

Cx beat me to most of it. See what happens when you take a call while posting?
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