Floor underlayment and trowel size?

[Xenomorph]

I have a multipart question here:

1) I am installing porcelain tile on a concrete slab, but I am installing an electric radiant heat system on top of the concrete before I set the tile. Now after doing some reading, I have found that it is suggested to have some sort of thermal insulation down before I put my heating system down..and that cork board is suggested, but none of the tile installers I have talked to think that insulation needs to go down or that installing tile on cork board would be a very good idea. Can anyone give me a definative answer on the issue of whether insulation is necessary, and if so, what would be a good choice to use?

2) I am going to make a basketweave pattern for my floor where 3 1x5 tiles get butted against eachother. So I am wondering with this many small tiles, should I just go to a 1/8" or 3/16" (I can't remember the exact size) sized wall tile trowel so that the thinset doesn't come up through the edges of the mosaic, or will I be fine with a reguar 1/4" floor tile trowel?

thx for your time

[Xenomorph]

anyone have any ideas?

[Brian in San Diego]

Xenomorph,

I'd suggest you check with the manufacturer of your radiant heat system. I checked Warmly Yours installation guide and they said "if" you are using insulation, so it sounds like it is up to the customer. Perhaps you could request that a moderator change the title of your thread to something like "floor warming system questions". You may get more responses. As for your second question...it sounds like you aren't planning on having any grout lines. You said you are going to butt tiles together. Grout is the "glue" that holds a floor system together. I'd recommend you use at least 1/16" grout line. I would also use the smallest v-notch trowel I could find. I think 1/4x1/4 of 1/4x3/16 should work. just lift a tile to make sure your coverage is good.

Brian

[Xenomorph]

thx Brian