QUESTION

New tile just installed, 8" x 36" long, in house seems to have excessive lipping. What is acceptable? Installed with 1/4" gaps, most all pieces are bowed, tile has square edges, and I'm not sure if the installers used enough grout underneath.

ANSWER

ANSWER - The standards say that a tile with a grout joint of 1/4" or less is allowed to have tile lippage, where one edge is higher or lower than the edge of the adjacent tile, of 1/32" plus the actual warpage in the tile; assuming the warpage does not exceed the maximum allowable warpage.  So that could be up to 1/16" allowable warpage; about the thickness of a dime.

Large rectangular tiles tend to have warpage at their corners and at the center of the tile, so when two adjacent tiles are off-set from each other then you can get compounding warpage.  That is why standards say that you should not have more than a 33% off-set.

The wider the grout joint the more you can compensate for tile warpage and lippage.  Rectified porcelain tiles have been mechanical adjusted after they are produced to be more consistent in sizing.