First of all, you still haven't specified whether your floor is "not flat" or "not level." Whatever else you have (or have not) done to get where you are, it would help a lot if you could say whether your problem is level or flat. Also, just to be sure here, if I am understanding you correctly, you installed the 2x4s ACROSS the 2x6s that make up the underside of the house? (Notice the very very NON-technical terms...so be aware that I'm not a builder or knowledgeable in this stuff like some of these people that post here...just sympathetic to rising note of panic in your posts....) The only reason I'm trying to clarify that is because I am wondering whether you installed the 2x4s "upright" (so the "4" dimension is vertical) or "laying down". I'm not trying to pile on to what you have *already* done, but I don't know what the proper distance for SPANNING that 2x4s have, and I don't know whether they can span two full feet if they are flat. This makes a difference because you want to install tile. If your subfloor is bouncy or bends ("deflects" I think is it), then all the tile you install will just crack and plague you and your heirs until the end of time...until you rip the whole floor and subfloor out again and re-do it. Or put in linoleum. Whichever comes first. You say in the top post that the cracks are like 1/4", but in your last post you write that they are up to 1". That's a big difference? Which is it? Does it vary from 1/4"-1"? Have you actually measure or are just eyeballing or going from memory? IF YOUR CRACKS ARE VERY SMALL: IF it were me (and it isn't), I'd probably just put down a very tight layer of Wedi board (thinset and screws/washers), seal the seams so it can hold the next layer, then put down a thin layer of self-leveling compound (though you still haven't said whether your floor is wavy or slanted), and then tile. IF YOUR CRACKS ARE 3/4'-1": Maybe use a layer of plywood (which would be cheaper but harder to cut), maybe tape and thinset the seams (ask someone on this board about this because I'm just brainstorming here), then use the SLC, then the tile. Only plywood will actually help form a floor (which I think you need to do with 1" gaps), not backerboard of any kind. Instead of Wedi, you could use probably any backer board (ask someone here what to do for the seams). But I only know about Wedi because that is what we went with, and I like it because it is light weight (good if you are a female working alone). I don't think your solution is in one step. It feels like you are going to have to create a tight subfloor, THEN level or flatten. I think you have a non-standard thing going on there, and that might not be addressed so easily with just one step before tile. One more thing, just out of curiousity, WHY do you think your floor must be level? Oh yeah, and I would start making your peace with a threshold. Given how non-standard your set-up is, AND the fact that this is DIY (or at least the subfloor), I'm not sure it is realistic to think you can get away with no threshold.

Some pics of DS's room (pardon the tween boy mess - I managed to avoid taking pics of the unmade bed). Horizon paint color - I forgot, his trim isn't stained, just beeswax and boiled linseed oil but it's somewhere b/t a "natural" pine and honey. Bunk beds (ignore the box spring underside) in sunlight bookcase - maybe darker pine than bed plus a shadow but I did use flash Desk cubby (dark) and edge of closet trim (beeswax) - I think the flash washed out the side of the closet a little though And, what you were waiting for - he has an oak dresser! This is next to a window, so the paint is under an east-facing window, no light but flash. Finally, here's BM Light Pewter with no stain, poly-only baseboard in bathroom. The colors are pretty true in this pic (a little bit of White Satin showing around the corner to the tub).

I took a LOT of my scrap strip pieces and just sewed them about 12 inches wide and the width varied as well as the prints/colors, etc. and I did not worry about the looks. I have maybe 6 strips about 4+ feet long. My idea is to cut the lengths of strips into 5 or 6 inch width, and have a solid panel to go between the strips. This might become the charity quilts that our club does every year for a women's shelter. In the past I have also taken my various sizes of leftover patches and sewed them however they fit together (thus making yardage of fabric), and this then is cut and made into the pieces for centers of blocks. Then I add a color around the blocks in a pattern and make larger blocks with them - sewed them into to charity quilts. They actually come out nice looking. I am one to NOT waste any fabric (after all, this is money you spent!), I just find a way to use it. Takes some thinking but this is my way to keep the old brain in working condition!

Thanks, all. Like budge said, it will dent, but it springs back. I would imagine a piano or other heavy item might permanently dent it, though. Also, we've been advised to put felt pads or the little slider pads on furniture to keep from gouging if something is dragged. Even though these planks are prefinished, a finish coat (or two) of poly is recommended to seal the seams. A spill should be gotten up quickly, but I think that goes for about any flooring. It is supposed to wear really well. This is solid cork, 3mm thick (the old-school cork tiles from the '50s and earlier were usually 1/4" thick, so this is slightly thinner). So as budge said, it can be sanded and refinished. There are some floating floor cork products out there, too, but I don't think they can be refinished. They also require a transition/threshhold at openings, and I wanted a cleaner look than that. If you've laid ceramic tile (or think you might be able to), you can do this. I dribbled the glue down onto the floor and measured and cut the tiles. DH was on the kneepads trowling out the glue and placing the tiles I handed him. We had a little trouble with some tiles "floating" prior to the adhesive fully curing, so we have some gaps. We used Bostick's Best adhesive, and probably should have allowed for a little longer "open" time for curing before placing each group of tile. But we got a bit impatient. I plan to source a different kind of adhesive for the next room. It will be a roll-on rather than a trowel-down, so won't have as much "play" in it and will be less tiring for DH to work with. Now, it's much easier than ceramic when it comes to cutting and trimming. A ruler, a box-cutter and a cutting mat is all you need. No saws, no tile nippers, etc. The fumes from the adhesive were strong for two days, but I didn't smell it when I got home this evening.