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Today I laid tile in a 25sq ft bathroom with a concrete subfloor. The concrete had a slight "bow" to it, meaning if you hold a straight edge across the 5' width, there is a gap of about 1/8" in the center. The tiles pretty much follow that slight curve. Will this cause any problems with cracking? If it matters, the tiles are 12" squares, inexpensive ceramic.

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What kind of load (traffic) do you expect there? – Peter Ivan Jul 15 '13 at 8:41
up vote 3 down vote accepted

Nah. You are good to go. Tiles will crack if they bear weight over an unsupported spot. The bow in itself is irrelevant.

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1/8" (c. 3mm) is small enough that you can even let the thinset mortar be thicker in the center of the room, eliminating the bow with the tile layer. – Tim B Jul 15 '13 at 11:49

Did you use comb to comb the mortar? The most important is to have the mortar under the whole tile surface. The bow is not a problem then.

Comb the mortar

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