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horizontal8 08-13-2009 09:17 AM

Can I lay natural stone (travertine) tiles directly on the subfloor?
The subfloor I have is the original 6" x 3/4" planks running at 45 degree angles and have a gap of about 1/4" between them. They are all in good shape. Do I need to lay a new level of plywood overtop of it before laying down the tiles? Thanks.

Just Bill 08-14-2009 05:52 AM

NO!! The fllor is not stiff enough to support the tile. Installing tile over that subfloor will result in cracked or loose tiles and grout. You at least need a layer of 1/2 tile backer set in thinset. Better would be a 1/2 plywood, glued/screwed, and then backer board.

RippySkippy 08-14-2009 07:23 AM

JB is LEAST add 1/2" plywood 5/8" would be better. You could put 1/4" backer board down rather than 1/2" as the backer board adds nothing to sub-floor stiffness.

Head on over to the John Bridge forum and plug your joist values into the Deflecto Meter, it will help you determine if your joist are adequate which is an additional factor in your equation.

Termite 08-14-2009 11:52 AM

Rippy Skippy and JB have this dead-on. Travertine and other natural stone tiles are incredibly unforgiving when it comes to weak or deflecting substrates and floor structures.

1/2" backerboard in unnecessary as stated. Put in as thick a piece of plywood as you can stand or consider replacing the 1x's with plywood. 1/4" backerboard set in thinset is all that is needed for floors. No, you cannot tile right over the wood unless you want the job to totally fail within months.

bjbatlanta 08-14-2009 08:00 PM

You ABSOLUTELY need another layer of subfloor(s) to apply tile. I would go to the mfgr'. website for the tile you plan to use to see exactly what is recommended so you don't void your warranty...

JazMan 08-15-2009 12:15 AM

WOW, a couple of you guys must not know about the requirements for tile installation and in particular natural stone tile installation. Or maybe you just missed the fact that it's stone.

First of all,

1. You can NOT install any backer board over dimensional lumber.

2. You need a subfloor plus an underlayment as the subfloor system to install natural stone tiles. Hopefully 3/4" ply + a 1/2" underlayment grade ply. Then you install the backer board or membrane such as Ditra or Noble CIS or?

3. You should check the deflection of your joists system. The recommendation for stone tiles is L720 or better, although Laticrete says their mortars only require L480. The standard home is built to meet L360, which is also the minimum requirement for ceramic and porcelain. This is for the joists, the subfloor has its own minimums as stated before.

Let us know the type, size and spacing of the joists. It would be helpful to also know the species and grade if you can find stampings. Also we need to know the unsupported span of the joists.


Termite 08-15-2009 01:08 AM


Originally Posted by JazMan (Post 314626)
WOW, a couple of you guys must not know about the requirements for tile installation and in particular natural stone tile installation.

Good info, but no need to belittle those of us that don't set tile for a living. Thanks for setting the record straight though.

Daniel Holzman 08-15-2009 08:43 AM

I suggest you check out the Ditra website ( for a full discussion on how to install tile over a wooden substrate. I installed stone tile over a wooden substrate about four months ago using the Ditra product (this is not a commercial endorsement by the way, I have no personal interest in Ditra other than to say it worked very well).

I followed the instructions on the website, and everything worked out fine. As previously noted, the Schluter site states that you need a minimum of 3/4" board (such as you have) overlain by at least 1/2 inch plywood, recommended 5/8 inch plywood. There is a minimum nailing pattern required as well. Then you place the Ditramat over the top layer in a mortar bed (full discussion on website about required type of mortar). You then place the tile over the Ditramat using a different type of mortar (see website for full discussion about required type of tile setting mortar).

As previously noted, you need a minimum stiffness of L/720, which means that the maximum deflection at the center of the floor should not exceed the span divided by 720. So for example, if the floor span is ten feet (120 inches), the maximum allowable deflection is 1/6 inch. To compute the deflection, go to the deflectometer web site as stated before. Good luck.

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