Suitable substrate for 3/4″ travertine

QUESTION

I have a customer that wants to install 3/4″ travertine on their floor. Do I still need to add 1/2″ to the substrate, since the stone is 3/4″?

ANSWER

The answer to your question is yes. A stone is considered a “tile” until it is thicker than 3/4″ and larger than 24″x24″. Therefore, F250 (Stone) in the TCNA Handbook applies and requires the second layer of wood to help ensure the correct deflection ratings for the floor system.

If the stone is larger than 3/4″x24″x24″, I would be extremely cautious setting it on a wood structure. Deflection is critical. Deflection is measured not only across the entire span of the floor, but between spans of load-bearing structures (i.e. floor joists). It is common for deflection to result in cracking along the tops of joists, rather than between joists. Calculating for the weight of the tile assembly, dead load, live loads and forecasted/planned use is also critical. Determining the suitability of the wood structure to properly support such an installation is typically beyond the requirements of a tile contractor’s ability/knowledge. I suggest that a structural engineer or architect is consulted to determine whether the structure is suitable for this installation. – Mark Heinlein, NTCA Training Director