Grout line 1/8" unsanded grout. My first reaction was nope-- use sanded. But if you mix the grout super thick, you might just get away with using unsanded. My recommendation would still be to use sanded with a joint that size, though. As for the basement floor, you're taking a big chance. If you're going to do this at all, use the Ditra, but even then, I can't guarantee you there won't be problems. You say the crack is virtually flat. Either it is, or it isn't (not meaning to sound flip), and if it isn't, there's not a membrane in the world that'll protect against vertical movement, not even Ditra, which is considered by many (including myself) to be about the best in the world. THe ONLY way I'd consider tiling over that would be to do a mud job over a slipsheet (tar paper or polyethlene) and wire. That way, the floor would be completely independent of the structure. Anything short of that, though, I'd be very reluctant to warranty it.

You shouldn't tile directly on Dricore because you need a tile underlayment. But you can put Ditra on top of the Dricore and tile over that. That's what I'd do in your bathroom, to keep the floors level throughout your basement. Oh, and Ditra does nothing to warm up the tile.

Varnish (aka polyurethane) is MUCH too thin to be anything but a finish. It doesn't block a darn thing. Glue down cork tiles (which I believe you are using the term 'cork mosaic' because they are tiles) are KNOWN for their warmth, their slip resistance and their comfort underfoot. A glue down cork tile job (all costs lumped together) *should cost roughly the same amount as a regular ceramic/porcelain tile install. This should be $12 - $15/sf (total job cost). If you require subfloor preparation then you will pay a bit more for that service. I've sold cork - both glue down 'mosaic tiles' and floating flooring (click together) - for many years. I have helped people 'winterize' their RVs (Alaska, Northern Canada), their cabins (N. Dakota, North West Territories, Yukon, N. Quebec, N. Ontario, N. BC, N. Alberta, etc) their ice fishing huts, etc. Trust me, the warmth is REAL. The finish on top does NOTHING to change that. www.icorkfloor.com My former colleague, Anne, has sold thousands of glue down floors. She can help you find what you need.

Hi robin, You are welcome to float the WISE cork flooring. The issue with the centre board (traditionally High Density Fibreboard = HDF) is not an issue with WISE. The WISE has a mineral core. This makes it truly water proof. You will need to have a FLAT subfloor. The rigid core makes the click system brittle. And bit of 'wonky' movement in the subfloor could mean the breakage of the edges is possible. I'm a traditionalist. I prefer the glue down product. With a little bit of subfloor prep (same prep as the floating type) you can glue down a cork tile floor quite easily. You would required 2 packages of 4mm or 6mm cork glue down tiles from iCork Floor LLC (roughly 40sf). You can purchase a quart of Roberts water based contact cement adhesive (Low or no-VOC) and a quart of Loba 2K Supra AT (from iCork) to finish the installation.