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Millertyme 03-26-2011 08:11 PM

porcelain tile over ditra
i will be laying tiles down soon and have the materials ready to go. Heres what I have. You guys tell me what you think. I have 3/4" plywood sub floor (I think just cdx). Over that I layed down 3/4" underlayment screwed down. This is over 2' oc trusses. I have Laticrete Mega Bond thinset and will be adding the liquid fortifier for laying the ditra to the wood floor. I will use a 1/4" x 3/16" v groove trowel. My Porcelain tiles are 13"x13" and I will be using 1/8" spacers between tiles. I will set tile down over the Ditra using the same mega bond, only without the fortifier. I will use the same trowel. Any advice or changes?

woodman58 03-27-2011 06:51 AM

The floor sounds stable enough. You need to use a 1/4" by 3/8" deep trowel to put the tile down. A 1/4" by 3/16" will not leave enough mortar to secure to tile.

Daniel Holzman 03-27-2011 09:29 AM

The Schluter website has detailed instructions for installation of the Ditra and tile. It sounds like the subfloor is OK, however you absolutely need to check the trusses for deflection (L/D). To do this you need to check the deflection rating of the truss with the manufacturer of the truss, which should be stamped on each truss. With any luck, they have a web site.

For 13 inch porcelain tile, you are going to need a minimum L/D rating of 480, 720 would be better since these are large format tiles, but check the Schluter site, it should give you the minimum requirements for your specific size tile. This is a pretty high stiffness factor, and it is possible your trusses do not make it, in which case you may want to consider using a smaller tile.

JazMan 03-27-2011 10:32 AM

I would add that you'd be better off also using a slightly larger trowel to install Ditra too. Take a side grinder and make those V's a little deeper, or if you can find a 3/16" square trowel.

I agree with Daniel that the stiffer the better, however the industry is coMfortable with L360 for tiles of that size, or even larger. The double 3/4" will take care of the between the joists (truss) deflection. Check with the manufacturer for your rating.


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