It is right by the shower. The shower is not leaking in any way. I think it is just where the former owners would exit the shower and whatever drips came off of them and were left on the floor make it right to the same spot. So im hoping by raising that area again that the water would pool away from the wall if left on the floor for any reason. Its not that I make a habit of leaving large amounts of water on the floor. I also thought of putting a bath matt at the shower entrance. But just in case the kids run out of the pool and leave water all over the floor (not like that would ever happen LOL) I would like to try and prevent it now while the tiles are being redone. One more thing it is a concrete subfloor. Thanks, Robert Robert

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.

Thanks for all the great responses. It's good to know from the variety of answers that there are many different ways to do it right (though I know that doesn't mean aren't many MORE ways to do it wrong :-). Another thing I've always wondered about with shims and EZ-levellers is that it would seem to concentrate the weight of the cabinets, counters, and contents into just a few spots vs. distributing the weight equally along the floor. Given that everyone uses some sort of shim, that technique must work fine, but it seems like it would make it more likely that some parts of the floor (those further away from a joist) would sink more over time than those directly over a joist. And it would put more stress on the cabinet (though if it's well-built that shouldn't be a problem). To make the cabinets fit together as smoothly possible, I was thinking I could join a run of three cabinets together (to each other) before installation. I've seen that suggested in forums and DIY videos. But if I do that, it doesn't seem like 4 shims/levellers at the 4 corners would be enough - the center cabinet would effectively be floating. But trying to shim that assembly at 8 points would be awfully tricky. Any thoughts on that?

You acted in haste, and unfortunately, the old adage is coming true for you. Quick decisions are usually not the best decisions. Your best solution at this point is if this unit will not work for you design wise, then sell it on Craigslist and buy a different one that will work within your design restrictions. Never violate the manufacturers installation instructions. Especially on something that can readily KILL you like a ventless gas fireplace! You also might investigate direct vent models while you are doing your research for a new unit. They don't have the hazards associated with ventless, especially the air quality issues.