RC ! got you, I agree, A person can use the " ditra drain" but not the "kerdie" because there is no proper tile substrate for the kerdi since this deck is plywood. My only question is, has any tile expert and installer ever installed tile at an area that was not by the book ?, and it worked. I still maintain that installing kerdi over plywood using say " laticrete 253 " works just fine even though its not by the book. If all tile experts go by the book and thats all where are we as forward looking contractors ? If I can't prove a certain installation method because it's not by the book, does that make it wrong. Just a note, the schluter rep, off the books says that installing kerdi over plwood and than the ditra drain, probably is acceptable. The only drawback would be " the guarentee ". I will still give my opinions based on my knowledge and can only hope this helps to provide answers to questions in the future. Thak You to the senior members on this.........

What is "ditra drain" ?

I can't see how installing Kerdi over plywood can possibly work. There's too much potential for movement in the plywood for Kerdi to be able to compensate. Kerdi is strictly a waterproofing membrane that must be applied to stable substrates. Plywood is not one of them.

Your Schluter rep should be fired for making those statements.

This exterior deck is 1" 1/8" plywood, what if I used redguard then seamed than the ditra drain mat over ? Also ditra drain mat is somewhat like schluters troba mat. I am trying to get another layer of waterproofing underneath the ditra as back up.

I think we need to clarify terminologies.

To my knowledge Schluter Ditra Drain was or is only available in the UK.

As far as I know there are only two types of Ditra available in North America, regular Ditra and Ditra XL. Both are uncoupling membranes only.

Here in this part of the world there are only two mats classified for drainage and they are Troba and Troba Plus.Each with their own characteristics.

Please correct me if I'm wrong on the availability of Ditra Drain in North America.

It would be your call Rick if you want to use a liquid membrane in your hybrid assembly. You and you only are the one who has to warranty the system your creating.

Whether it may or may not work is anybodies guess. We on this forum try to keep all answers to questions inline with manufacturers specifications and industry guidelines as specified by the TCNA and TTMAC

I don't think anyone is going to go out on a limb and tell you what you want to here.

According to one of my tile suppliers I can get " Ditra Drain Mat" after August of this year, I actually have a quote on this product.I better call again and check. Looks like a good product. I actually quoted an outdoor balcony based on the fact that I could aquire this product. Good luck I guess. Thankx