What are the standards for grout joint widths and properly filling with grout?

QUESTION

We had marble tile installed with 1/16 inch grout lines and they vary from 1/16 to as much as 1/8. I am most concerned with the grout being very low, causing chips to the marble and also casting shadows so that the grout looks dirty. I have talked to the builder and he says everything is within standards and will not fix anything. All we are asking is to have the tile re-grouted to bring it up to the level of the marble and he refuses. I would like to have professional look at the tile and grout and give me an opinion as to whether the job was done properly.

ANSWER

ANSWER - The Natural Stone Institute (previously the Marble Institute of America) Dimensional Design manual state that the grout joint on a stone should never be less than 1/16"  wide and preferably 1/8" wide.  To achieve a uniform 1/16" grout joint width the stone tile has to be consistent in its facial dimensions.  When the tile isn't consistent in its dimensions then the grout joint has to be made wider to compensate for it.

Normally natural stone has a square edge with a slight arris or chamfer edge, which can make the grout joint seem wider than it is.  There are stones with a cushion edge that will require a wider grout joint width and the grout will result in a more recessed condition.  The ANSI A108.02 standards state that the nominal center of all grout joints shall be straight with due allowances for rustic tiles. The standards don't give a specific tolerance percentage of allowable variation in width.

ANSI A108-10 for Installation of Grout in Tilework states that all grout joins shall be uniformly finished.  Cushion edge tile shall be finished evenly to the depth of the cushion.

If you have a square edge stone without an arris edge the grout should be installed flush with the surface of the stone.  If your stone does have a slight arris then the grout could be installed to the depth of that arris. Either way the edge of the stone should not be chipping under normal use.

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