Is my floor going to be okay? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-02-2005, 06:12 PM
I'm building a house right now and made sure to let the engineers at the joist company know that I needed the floor to be over 720 for deflection. I've put in I joists on 16" centers. The engineers have indicated that the floor is almost 800. It was sheathed in 3/4" tongue and grove engineered OSB. I am planning to place DITRA over that and then install slate with Kerabond (unmodifed). I have checked the heights of the install and it works out perfectly for my 3/4" hardwood that borders the slate. I have been told that I need two layers of wood before the ditra from a friend of mine that does tile as well. I figure with a floor that solid that I would be okay. It is one of the most solid floor that I have ever felt in a house. I'm 240lbs and did the jump test and almost blew a disk cuz it was so stable. Anyway, your input would be appreciated. I have installed a lot of tile, but never a large 1200 sq/ft slate install.

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03-02-2005, 06:46 PM
Most stone installs will require an additional layer of 1/2" ( minimum)plywood. This addresses the deflection between the joists.


03-02-2005, 08:48 PM
What if I just use 1/2" Durock over the 3/4 OSB without the Ditra? I just don't want a huge step down from the slate to the hardwood...

03-02-2005, 09:06 PM
The pro's are gonna tell you that backerboard has no structural strength, so you must use plywood, and then the ditra to minimize height.

03-02-2005, 10:01 PM
I actually seem to remember them telling me that they were 14" on center, I'll check tomorrow, that might make the difference...(hopefully).

03-02-2005, 10:23 PM
You need the second layer not only for strengh, but for schluter to warrany your install. If you have any problems they will tell you, sorry no warranty, you did not follow our installation guidlines. It will only cost a couple hundred bucks for the additional plywood. You are already spending for the slate and ditra. seeing that it is 1200 sq ft thats a pretty good chunck of change. Im sure the I joists are more than strong enough to support that load. Its the span between the joist that is the weak point in your floor. Therefore the second layer of ply is needed. Requirements for natural stone are twice that of ceramic

03-02-2005, 10:26 PM
Hi Curtis. I have been told that I need two layers of wood before the ditra from a friend of mine that does tile as well. You would do well to listen to advice from this firend in future, methinks. :)

You do need the second layer of plywood. Even if you elect to use Ditra, although with the Ditra you can use 3/8ths inch - so sayeth Herr Schluter as I recall.

The 14 inch number migth well be the span between joists; some engineered wood joists have a 1 3/4 inch chord width. You still need the second layer.

It's not at all difficult to make a transition piece between a tile and wood floor, especially if you have the width of a door jamb for the reduction.

My opinion; worth price charged.