You should post this in the flooring forum. I think some of the tile pros will see it more quickly over there.

As for me, a guy who's done a fair amount of tile (but I'm not a full time pro), I think they steered you into some major work that may not have been necessary, not to mention these numbers seem high altogether. Using a couple small spots of mold as a means of coaxing you to pull up a floor is b.s in my humble opinion.

As for needing two layers, yes, sometimes it's needed to get a really solid floor so the tile doesn't crack. Same for the membrane, it isolates the tile layer from everything else, again, so it doesn't crack later on.

When you post in the flooring forum, please provide more details: type and size of the tile, spacing between your joists, any hints of a bouncy floor beforehand, etc. Good luck.

Here is a link that might be useful: Flooring Forum

Thanks homebound. I thought I looked for a flooring forum, but I obviously looked too fast ;) I appreciate the input too!

I am sorry to say that your story is very much like the ones we are trying to educate homeowners about. First and foremost, if he did not provide you with an allowance of the cost of the tile in his budget, then you should not be obligated to pay. The contractor discount is not the issue -- it's about his allowances. If the contract says "furnish and install at $1,540 then that is what you should pay. If there is other language in the contract that allows for changes, then he may have the right to charge extra -- though totally unethical if you did not approve those extra charges. The extra $650 for the "tile membrane" should also be included in the install price. If he did not add it in his original quote but is a needed part of the project, then he should eat that.

Overall, your expectations are reasonable. However, if your contract allows the contractor to bill for extras WITHOUT your approval, then you might be liable for the additional charges. If nothing is stated in the contract, it could go either way. I also recommend asking for receipts of additional materials he purchased without your approval.

Definitely check with the tile flooring forum for the particulars.

Finally, when we price out a job, small or large, we provide one fixed price. Period. The project includes installation and materials. If we miss materials, shame on us. Replacing the entire subfloor would depend on the age, tile, etc. Those are unknowns for any contractor until the area is exposed. When the types of changes you describe are required, we will issue a "change order" for final approval and signature. Nothing is done until the homeowner signs off.

Here is a link that might be useful: Hafer Construction, Inc.

The membrane is instead of hardi, not in addition to it.
Using the membrane made it easier on him.
It doesn't cost much and it's a breeze to install.

Two layers of ply is often done.
Questions to ask him are Which ply, How laid down, how screwed down.
Just to get him answering and defending his workmanship.

Yes he could have told you about the subfloor much earlier.

All his prices are too high, but whether you pay him all or only a portion of his bill is something I'll leave up to you to discuss.

All his work sounds like the right work, not overkill, not frivolous.

Since he takes himself so seriously (methods), let him give you a longer guarantee than he has ever given before. After all, he did spring a number of surprises on you instead of doing all the selling and explaining in advance, so let him stand by his work. He can at least guarantee that the tiles won't delaminate, for a longer time period than usual. Delaminating depends a lot on the workmanship, not the house (joists, bending floors). Web search to find out more.