Natural stone flooring has cracks in it. Is floor heating to blame?
The following has been taken from a Schluter Install manual, not for distribution:
There are three principle reasons a stone product has cracked:
1) Most stone products have a minimum flexural strength that is substantially lower than what is typical for ceramic tile;
2) Stones are products of nature and complex heterogeneous materials with naturally occurring regions of discontinuity, such as veins and fissures. Such features can be weaker than the surrounding stone fabric and act as “stress risers,” concentrating bending stresses within the region of discontinuity;
3) When wood floor assemblies are subjected to forces such as loading – both live and dead loads – they produce flexural stresses in the surface covering which can cause weak and brittle materials to break or crack.
Engineering mechanics as well as field observations show that the location of maximum flexural stresses in the floor assembly is directly over the floor joists and at seams in the subfloor panels. Therefore, a double-layer wood installation is recommended when installing natural stone in order to increase the stiffness of the sheathing assembly and position underlayment seams away from the joists to minimize flexural stresses in the stone covering directly above the joists and at seams.