QUESTIONWe have concerns about the installation of our limestone flooring. What would be the industry standard for acceptable lippage for installed 18” x 18” (Dorado) Limestone High Honed. This is a high quality limestone. We had approximately 1,150 sqft installed mainly on a concrete slab with 2 bathrooms upstairs. In our dining area alone we counted 64 tiles and 24 had lippage ranging from 1/32” to 3/16” this lippage is throughout the entire 1,150 sqft of installed limestone with a 1/16” grout line. We have measured several with calipers the readings were .092, .089, .188, .210 What is the industry standard for lippage for our limestone floor and who sets these standards. Thank you.
ANSWERANSWER - According to the Marble Institute of America (MIA), on smooth surface stones, lippage should be limited to +/- 1/32". Further more they state that allowable lippage is an installation tolerance, and is additive to the inherent warpage of the stone unit. Inherent warpage means the warpage of the stone that is being installed. Lippage is the measurement of the vertical displacement between the edges of two adjacent stones.
Most quality polished or honed tile stones have very little warpage, although some could be present depending on how the stone is cut and depending on the condition of saw that is used for cutting. There are no quantitative standards for warpage in marble tiles, but from a standard-of-care point of view, I would not expect a polished or honed stone tile to have more than 1/32" warpage.
So according to MIA, if you have 1/32" (0.03125") of warpage in the tile then allowable lippage is 1/16" (0.0625"). Although MIA states that stone tiles installed on interior stone flooring should have a minimum 1/16" wide grout joint and preferably 1/8" wide. Having a 1/16" wide grout joint requires the tile to be very consistent in its various dimensions. The more narrow the grout joint, the more difficult it is to avoid tile lippage, and the more the tile lippage will be accentuated. If the grout joint width is 1/16" wide, then I would expect that the tile being used should not have more than 1/64" of warpage; thus the allowable lippage would be 3/64" (0.04688") per MIA standards.
Fortunately, with natural stone tiles you can grind the entire floor to remove the tile lippage and then re-polish or re-hone the stone. This work should be performed by a professional stone restoration company. In some cases, stone installers plan for grinding and re-polishing the stone floors in anticipation that there will be lippage, and they include the cost for that work in their price to their client.