Replies

1. 
   MGMaxwell | Jun 25, 2007 09:29pm | #1

   Q: Will one layer be enough? (Durock)

   A: CBU is not there for structural support so the number of layers or thickness is not important. It is there for adhesion.

   Q: Will it move too much?

   A: You can pose this question at JohnBridge.com and find the deflectometer that will give you the spans for natural stone. I think you are fine with that regard, but the more important question is: can you do this over PT framing? I doubt it. There will be too much movement. Natural stone requires more stability than ceramic. Plus, slate out of doors in a freezing environment is not a good choice. Plus, I don't believe any of the cement board products are rated for outside exposure. Doesn't mean you can't do it, but you will void any warrantees.

   If you proceed, then check the manufacturers suggestion for the correct thinset for outdoor freezing exposure.

2. 
   IdahoDon | Jun 28, 2007 05:50am | #2

   You'll want to keep water out of gaps and holes in the tile thinset so I can't imagine that happening without grout of some kind.  Also, slate may not be all that durable in freezing conditions since water can get into the layers, freeze, and split the stone.  If well sealed and a slate that either fake (ceramic that looks like slate) or a really solid slate with few weak layers it could work.

   As for what the tile is going on, you'll need to make sure water isn't going to get trapped between tile and wood, which is hard to do if a wood boarder is used.

   The framing can be screwed and glued enough I'd feel comfortable that it wouldn't move much, but it would be much better to add a layer of ply and durrock.

   I'd probably treat it like an outdoor shower and put a membrane under the tile with a bed sloped to the exterior so if water does get down in the tile it has somewhere to go and won't just sit, rotting wood of all kinds.

   Best of luck

    

   Beer was created so carpenters wouldn't rule the world.

3. 
   Piffin | Jun 28, 2007 05:25pm | #3

   This design is prone to become a maintainance nightmare! You can take two trains of thought. One is to change the design to be workable. The other is to say, "Heck,we'll want to change our minds in 7-8 years any way and maybe this will last that long...."

   Slate is a very slick surface when wet so consider that.

   You would need to grout and seal the grout because as you have it planned, you have a water trap. That water will freeze in the cement board which is not structural to begin with and destroy it from under the slates. Same water will blow the wood border right off the edges.

   What might possibly work is this -

   place PT Plywood on the joists, let it dry well, then run ice and water shield over that. Maybe a metal edge running under the I&W and over the fascia trim/skirt board.

   Use clamps and scrap wood to frame what will be the wood border. Or screw it in place and patch the holes later.

   Then nail in some expanded wire lathe and run a good dry packed mud bed. Then exterior grade thinset to lay the slate.
   Seal the slate, then grout, then seal it again.

   Now you take up the temp wood border and mill the permanent one to size. Add a lot of drainage dadoes on the bottom so that water that runs in behind it can find a way out. White oak would be the best choice for this. Now when you install the oak trim, seal it a couple coats of finish on all six sides first, let dry, then use a bead of caulk between it and the slate/grout to encourage most of the water to flow over the wood instead of under it.

   I'm hoping you have the framing pitched to let water run away from the house already too.

    

    

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4. 
   levelone | Jun 28, 2007 10:42pm | #4

   I'm not sure if this would work in your situation, or with slate, but I have seen decks with "floating" tiles.  They have plastic support pedestals under each corner of the stone.  One pedestal supports the corners of four tiles.  The stone, or stone look-alike is about 2" thick.

   You should be able to set these pedestals over a plywood deck that has some type of membrane or waterproofing on it.  The issue I see in your situation is the joists would need to be lowered to allow for the height of the pedestal and tile.

   Others here may be more familiar with this technique than I am.