Tile Gurus Exterior Porch Tile

olzo55

what membranes have you used on exterior tile work. my job is a covered screened porch outside of Chicago. the floor joists are ok for the span. the plywood was covered with a torched down roofing. (I know there should have been a preslope first but that depends on the membrane). My choices are Ditra or a Noble product. Ditra is more cost effective but the tile is a frostproof porcelain and I have never used an unmodified for exterior work (always keralastic/kerabond). Can this be done?
Also, what would be better for the slope under the membrane, concrete or sandmix?
Thanks,
olzo

angus242

What about Schluter Troba? It will allow any water penetration through the tile or mortar to drain without the worry of water freezing and then cracking your tile or grout from underneath. Of course, you'll need a slope to gravity drain the water....

genecarp

the correct job is to have pitch on the framing, in new york, in have the whole roof glassed, then tile directly over the fibreglass, can you rip roof.?

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olzo55

perhaps my description isn't making things clear. There is a roof over this porch. the plywood floor where the tile will be laid was covered with a torchdown roofing. I will build a sloped concrete or mud floor over that and cover it with either Ditra or a Noble product. Either product will be a surface membrane so no water will penetrate into the concrete. the torchdown was put down as an insurance. what i don't know is if unmodified will hold up in an exterior install. anyone use Ditra outside? I've talked with E3 about Nble and I could use modified with that membrane. It's just 3x what the Ditra costs.

genecarp

i understand the condition that you have, what i am saying is that there are simpler ways to execute an exterior tiled porch, i am not familiar with using ditra for outside, there is no reason to, why not use a proven system for exterior tile installation over a covered porch? that being said, if you walked into this job after the torchdown was installed and the customer said, they would like tile, ok, but if you designed it this way. you have made life difficult for yourself

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angus242

I won't claim to be a roofer but I'm assuming since they'd use torched down roofing on a roof, it's waterproof???? If that's the case, is it a good idea to use another membrane over it? Wouldn't you be trapping moisture between the roofing and the ditra? And if you are, in the Chicago winter climate, that's asking for a freeze/thaw condition that can affect your tile.
Or maybe I'm totally wrong....

olzo55

which proven system are you talking about? I had the Schluter rep out and we went over the troba system then concrete with the Ditra on top. came down to if water gets through the Ditra and freezes, even with the troba, you're toast.

So that's why I ask, which way would you do it? and, can unmodified work outdoors on porcelain in cold climate.

olzo55

Genecarp, I don't know anything about fiberglass as a roofing material. could you explain the method? What thinset is used? The Schluter rep, builder and I discussed the moisture sandwich issue. the thought was the cavities in the underside of ditra would allow the moisture to migrate out through whatever hole the water can in through should that situation occur.

genecarp

i am on long island, new york, cold winters, many waterfront homes, i spec alot of these covered balconies to take advantage of water views. when new construction i frame deck with pitch, sheath in 3/4 cdx, a day before my fibreglass guy comes in, i glue and screw 3/4 ac plywood. he comes in, bondos the screw holes, then proceeds to fibreglass the entire roof, runs up walls 6'', builds door pans, wrapps up and around any posts. first coat dries about 5 hrs, now if i spec tile, he comes back applies a second coat of resin, broadcasts granules, leaving me a grip surface to thinset tile to, i have been doing this for years, extreme conditions, no callbacks.

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angus242

I never used the word proven. I had read about Troba and thought I'd mention it so you could look into it. I've never used it so I can't say if it's truly a viable option. What I was suggesting is that it doesn't sound like a good idea to use 2 membranes. Even using Kerdi in a shower, you're not supposed to install it over an additional membrane.
What about removing the roofing material and putting down an exterior-grade CBU and then ditra over that?

genecarp

this is corner of fibreglass roofing system, notice up the wall, over the curb.

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