QUESTIONWhat is the acceptable lippage of ceramic wall tile installed with less than 1/8" tile separation?
ANSWERANSWER - Tile lippage is the difference in height between two adjacent edges of tile, or of a crack or of a control joint in concrete.
ANSI A108.02-2013, section 4.3.7 Lippage states that a ceramic tile (porcelain is a type of ceramic tile) grout joint that is less than 1/4" in width cannot have any more lippage than 1/32" plus the actual warpage in the tile. The ceramic tile warpage cannot exceed the maximum amount of warpage allowed per ANSI A137.1. So in general, most tiles won't have more than about 1/32" of warpage; thus the maximum allowable lippage is generally at about 1/16" for most quality ceramic tiles.
Although, ANSI A137.1 shows that allowable warpage in a rectified porcelain tile (the tile has been ground down to a more precises size after being manufactured) is about 3/64". A a calibrated porcelain tile (one that was not ground down after being manufactured) will allow up to 3/32" of warpage along edges.
Although from a a standard of care point of view, good quality tile installations should not exceed about 1/16" of lippage and should be less if possible. If the tile is irregular in thickness and in its surface cleft, then the allowable lippage can be much greater.
According to the Marble Institute of American, stone should be installed so the lippage does not exceed 1/32" without any regard to warpage. If the tile is irregular in thickness and in its surface cleft, then the allowable lippage can be much greater.
If the tile does have a lot of warpage or there is excessive variation in the substrate or the tile itself, then if you widen the grout joint width, it will help reduce the lippage or the perceived lippage.
The standards warn that depending on the type and placement of lighting, natural or unnatural, it can accentuate the appearances of lippage. It could look like excessive lippage, but when measured it might be within the allowable tolerances. Wall washing lighting tends to accentuate tile lippage.