Concrete floor flat enough for tiling?

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Old 06-14-16, 08:37 AM
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Concrete floor flat enough for tiling?

My intention is to lay 1' x 2' tiles over a concrete basement floor. I thought I had a flat concrete floor but I've now found a high spot that rises up about 1/8" from the rest of the floor in a sort of slight hump. As I understand it, using a very straight board 10' long you should have no more than 1/4" gap anywhere. (Please correct me if I'm wrong on this.)

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As seen in the image, with the hump in the middle I look okay, but the lower image shows I'm not. The floor looks pretty good everywhere else I check with my stud although there are some areas that have 1/8" valley.

Can someone explain to me how to measure correctly?

Thanks
 
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Old 06-14-16, 09:59 AM
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Nice drawing!

Not a tile pro, but I don't think a 1/8" hump will be a problem; you will just compensate a bit with the thinset so the tiles end up nice and flat.

You could have it ground down, but I really don't think it's necessary. Let's see what the pros here say.
 
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Old 06-14-16, 12:46 PM
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The problem is not necessarily in the small hump, it is in the large oversized tile. The size dictates the needs for flatness of the floor. If you scaled it back tosay 12"x12" or 8"x8" you would not have as much of an issue. Then use a 1/4"x3/8" trowel to give you a little more cushion in the thinset for slight variations.
 
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Old 06-14-16, 03:11 PM
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Czizzi,

Well, I'm trying to keep the wife happy. The other tile she liked was a 6" x 24" but if I understand your reasoning then that would probably be no better and maybe worse than the 12" x 24". So, no floor leveler needed if I do a 12 x 12 with a 1/4" x 3/8 trowel? But anything bigger than that and I should use floor leveler?

Any ball park idea how much it would cost to have that hump ground down? I'd say it's approximately 3' x 1', 1/8" high.

Thanks for your advice!



Carbide Tip,

For the drawing, I used "Paint.net", a free but powerful photoshop-lite style editor easy to find with a google.
 
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Old 06-14-16, 04:49 PM
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I can rent a single disk grinder for about $80 a day. A hump that small should take less than an hour. Cleaning up the mess will be a bigger job.

You could even score it with a diamond blade in an angle grinder and then chip it off, but that would make a *real* mess.
 
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Old 06-14-16, 07:31 PM
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What I might be concerned about is the origins of the hump or bump. I can't believe that it was poured that way. So is it still rising or is it very stable and not rising ever again? I've seen a few basements that the concrete has heaved over the years.
 
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Old 06-15-16, 06:21 AM
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Carbide Tip,

Ug, your postscript really does apply to this job. You say the grinding is messy. I think I know what you mean. Not so much just dust, but clouds of room filling fine dust that coat everything? The wife is already quite unhappy about it, but it seems easier to just get a smaller tile and as long as this project has dragged out we both just want it to be over so long as it isn't done "wrong". I even started looking into what carpet would cost.

Anyway, thanks for your advice and feedback.



Norm201,

The house is about 65 years old. I don't see any cracking anywhere near the hump. I've lived here over 15 years but it's always been under carpet so I don't know if it's changed. While I know very little about concrete, and I do appreciate your feedback, I don't really have any good reason to think there's a larger problem.
 
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Old 06-15-16, 07:17 AM
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The larger floor grinders are used wet, so they don't generate dust, just a wet, messy, slurry.

Doing it with a dry diamond cup in an angle grinder would generate lots of dust.

Not that bad of a job for such a little area. Plenty of Youtube videos if you want to see.
 
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Old 06-16-16, 06:07 AM
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Carbide Tip,

I found a place that rents the grinders. After I do my best to seal off the room for dust I'm gonna go get it.

Thanks for the help.
 
 

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