# Marble Tiles Cracking



## joecaption (Nov 30, 2011)

Any real tile guy would have known this going in and should have built up the floor or floor joist to support it to prevent any movement.
Did he even use seam tape on the joints?
Real stone tiles need 50% less floor deflection then other forms of man made tile.


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## Daniel Holzman (Mar 10, 2009)

Normally when a professional tile installer undertakes an expensive project such as putting marble down, they perform (or hire out) a stiffness calculation for the underlying floor. The stiffness of the floor is critical in a natural stone installation, as an inadequately stiff floor can lead to cracking of the tile. Possibly this is your problem.

In order to calculate the stiffness of the floor, you need to know the size, span, species and grade, and spacing of the joists supporting the floor. The stiffness between the joists is a function of the type of subfloor used, and the method of attachment. There are on line calculators for floor stiffness, John Bridge has one, and the Schluter website has a lot of information on minimum allowable stiffness for various types of tile.

I suggest you have an in depth conversation with your installer regarding the exact method they used to determine the stiffness of your floor BEFORE they put down the marble. It is a bit hard to imagine, but I guess possible, that your contractor did not do the required computations first, but let's give them the benefit of the doubt and see what they came up with. By the way, the Tile Institute recommends a minimum stiffness of L/720 for natural stone I believe, meaning a maximum center of span deflection of 1/720 the length of the joists. For example, a 10 foot joist is 120 inches, so L/720 means a maximum allowable deflection of 1/6 inch at the center under design load. This generally requires large joists.


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## gshukert (May 7, 2012)

I don't see any seam tape on the joints and I doubt he did any kind of stiffness testing. At this point the bathroom is "done" except for the cracks. Recommendations now going forward?


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## joecaption (Nov 30, 2011)

Live with the way it is or the whole thing needs to be ripped out to fix it right.


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## ccarlisle (Jul 2, 2008)

Get a new contractor. Rip up the old floor, and subfloor, back to the joists. Stiffen the joists if necessary. Put down 5/8" T&G plywood, then another 5/8" layer perpendicular to the first layer, glued and screwed. Modified thinset. "Ditra". Unmodified thinset. Tiles.

Good luck. The old contractor messed this up for you.


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