Why do I need grout line for expansion ? I have them in the field but on the side wall around a floor vent there is almost no room and the vent will virtually cover the joints.

  • Don't worry about it around a floor vent, that area will forgive any expansion. Commented Aug 8, 2015 at 23:34
  • FWIW, "expansion" is always shorthand for "differences in expansion"... i.e. tile expands by 1% per degree and the wood floor underneath, and the walls around, expand by 2% per degree. (Those are fake numbers). So expansion is always a consideration, but you have to think about the what the materials in question are. Also, how sturdy is the sub-floor? If it's concrete, movement of the subfloor is probably irrelevant, but if it's plywood over wooden joists in an older house... the floor is absolutely going to move.
    – pbristow
    Commented Jan 15, 2016 at 15:09

2 Answers 2


An article I read by a tile master said grout is for two reasons:

The first is the tiles are not perfectly uniform so the grout helps equalize size mismatch. To check this, put nine tiles in a 3 x 3 pattern tight up against each other and see if there are differences in measurements horizontally, vertically, and diagonally.

The second reason was expansion and slight movement could cause the edges of the tiles to chip or crack the tiles if they are butted right up against each other.

I don't know if I am completely convinced of the second reason since I have seen quite a few tile installations that have no grout lines, especially marble. The first reason makes sense especially with tile with looser dimensions like stone tiles. Otherwise your lines could be uneven.

Here is a link to a really good book by an actual tile master: http://www.amazon.com/Setting-Tile-Revised-Updated-Homebuilding/dp/1561580805/ref=sr_1_1?s=books&ie=UTF8&qid=1450267844&sr=1-1&keywords=setting+tile

  • Personally I feel like you can only discount expansion and movement of the subfloor if you're tiling on concrete. Then you can get away with no grout lines. Otherwise... that seems unwise. The thickness of your decoupling will make a difference too. If you use Ditra XL, for instance, I bet you could get away with smaller grout lines than if you use old-fashioned concrete backer board "glued" in place with thinset (as the former is plastic and has a lot more give then the latter, which is 3 layers of concrete).
    – pbristow
    Commented Jan 15, 2016 at 15:12

I would install tile and all granite and marble with no grout lines at all. I can’t do it. Even though it will look better initially, eventually it will ruin the tile. The best thing to do is use the smallest grout line your particular tile will allow and get a grout that closely matches the tile.

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