I have completed my install of plywood rips and heat transfer plates and will finish placing the pex tubing today.You said earlier you used Ditra under you tile for uncoupling but did you use anything on top of the rips and plates first like 1/4" of dura rock or some other cement board or did you use thinset directly on top of the plates and rips? We will be using slate. Thanks, Tom

Howdy;
I used latex modified directly on top of the rips and plates, it will take a little more than you normally would expect as you are filling in the top of the tubes. Then the Ditra on top, I found a 2x4 works well to bed the Ditra and level it out. I did this way because the stackup height was almost identical to the engineered floor I used elsewhere. It also minimized the material between the tubes and the room, I'm getting about 15 Btu/sqft-hr out of it. I have also had no problems with it, although I did have my wife back butter all of the tiles as we set them.

Thanks for the reply. I guess my concern is I used double wide plates and kept them fairly close together so that's a lot of metal to cover with thinset but maybe the vinyl modified stuff will do the trick. Tom

Are the centers of your plates supported on rips? If yes I would go ahead and place the thinset on it, the modified sticks to most things.

Yes six inch rips on the sides and up the middle. I like the idea because I wouldn't have to screw down Dura Rock and worry about my tubing being punctured. Thanks again for your input. Thankfully the rest of the rooms will be engineered wood. Tom

Are the plates compatible with cement products?

They are aluminum, however to quote a Reynolds study: "...aluminum is not affected beyond a slight surface attack by concrete...". They note that this attack is on the order of 1 mil, and that as long as the interface does not suffer repeated wetting and drying the effect is gone after 4 or 5 days. So if you are going to attach aluminum windows to a concrete wall outside it would be a bad idea, however indoors under tile not much of an issue. It should be noted that if you are worried you could roll a coat of paint down before you set the tile.