prepare for the tile basement bathroom

[diyfun]

We are finishing our 1950's poured concrete basement now. The walls and floors are good without cracks. Our basement has no water issue and a French drain/sum pump was added for double protection. Outside ground surface water is also guided away from the house perimeter.

We are thinking install engineered wood floor on the finished basement rooms. But for the bathroom, we are thinking use ceramic tiles or travertine tiles. We are preparing the basement floor with the following composition: plastic sheet + 1" rigid foam + AdvanTech subfloor. Then the engineered wood floor will be put on top of it. Plastic sheet here is to stop moisture from the ground.

I was thinking put the same composition on the bathroom as well. The ceramic tiles or travertine tiles will lay on top of that composition. But my friend thinks it is not necessary to have rigid foam and AdvanTech subfloor on the tile bathroom. He think just put the ceramic tiles or travertine tiles with thinset on the top of the plastic sheet is good enough and tiles will be cold anyway. Is that true? He also suggests use Schluter Ditra or backer board on top of the plastic sheet if I want to.

What's your opinions? no rigid foam and AdvanTech subfloor are necessary? tiles set on top of the plastic sheet will be stable enough?

[dlarrivee]

You're absolutely nuts for wanting to set tile on a plastic sheet like that.

Who suggested that would be an approved substrate for tile? I'd suggest ignoring their advice henceforth.

Read a TDS for any thinset, I've yet to see any of them suggest setting to a LOOSE wrinkly plastic vapor barrier.

[jadnashua]

No way thinset will adhere to a plastic sheet!

Given that the floor is fully supported, you should get away with using the foam and Advantec (Ditra would work over that) but you'd still need a decoupling layer - cbu or Ditra (or other) would work for ceramic. You might get away with that same sandwich if you went with natural stone, but industry standards call for two layers of ply. Since you'd have close to 100% support, you might not need the second layer, but it sure wouldn't hurt. Unless the floor is nice and flat, there still could be some deflection over a depression in the concrete.

You might want to consider electric heat mats or cable underneath the tile - it would enable you to make the bath floor warm when desired.

[dlarrivee]

I hope that isn't a load bearing wall shown in pic 1 and 2, with the giant gashes in it for small piping.

[zl700]

^ ^ obviously not with the steel beam columns shown in the pictures ^^

[big2bird]

Terry has a great forum, but honestly, ANY tile question has the best advice here:
http://www.johnbridge.com/vbulletin/index.php

[diyfun]

I hope that isn't a load bearing wall shown in pic 1 and 2, with the giant gashes in it for small piping.

it is not a load bearing wall.

[Dana]

Keep the plastic sheet and add the inch of foam + whatever substrate you need under the tiles. No, the floor won't exaxtly be warm, but with the foam it'll be at least 65F rather than 55F, and it will grow less mildew during the summer.