Hello, I am a contractor in Florida. A customer purchased some Mesquite. I hired an English finish carpenter to do the work, and he installed the wood perfectly. About six months after the installation it began to cup in an area about 4 feet in a circle and I though maybe they dropped some water or something. So I got a moisture meter and the floor read 8 to 10%. About 25% of the floor has cupping.
Now as the rainy season in Florida has begun the floor is cupping. It is down well - not lifting - but in some places the moisture has risen to 12%.
I have tried everything to seal the exterior of the building and I think the moisture is beginning to abate. I put in a dehumidifier which is pulling out a gallon of water a day. Should I check the moisture in the air? I can't figure out how the moistrue is getting into the flooring - yes I put plastic and a layer of house wrap - on concrete floor and used 3/4 inch tongue and groove backer board - best I could find at 34.00 dollars a sheet.
I told my customers that I would pay to have the floor sanded and refinished, but the customer thinks refinishing will void their 50 year warranty. In fifty years the floor will need to be refinised a number of times, I should think?
Any ideas how to solve this problem? After reading the advice you guys give, I see that you think that if anything goes wrong the installer is a jerk, but I did this thing by the book and took every precaution just to avoid a call back. I think it's Florida. I just think Florida has too much humidity for wooden floors...
My question - any ideas on how to solve this situation? Does anyone have any experience with Brazilian Mesquite? Is it a reasonable product for Florida? Does it stay down well? If I sand the floor and refinish it, does that sound like the correct solution?

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Lots of questions here. I'll try to help.
1st. Did you build this house from the ground up? Foundation and all? It's a concrete slab, yes? If yes to these questions, then common sense dictates that a 6 to 10 mil polyethylene vapor barrier be installed UNDER the concrete and over a sand or gravel base, to help prevent the concrete from naturally wicking up ground water. THis MAY be the problem. I don't know. You say you put down plastic OVER the slab, then put down 3/4" T&G backer board? What the hell is that? NOFMA and NWFA specs call for 3/4" CDX plywood as an underlayment for nailing. How was the "backer board" installed? Nailed? Screwed? Glued? Tapcons? What? Also, are you sure the wood is truly AMERICAN Mesquite? American mesquite is a VERY stable wood, one of the best for stability. However, buying from LL is suspect as it MAY be some weird asian import called "mesquite" when in fact, it is far removed from true mesquite botanically. You need to check that first, IMO. Got to know EXACTLY what you are dealing with! Another thing to check is RELATIVE HUMIDITY. American Mesquite is from TEXAS and you are in FLORIDA. Quite a swing in humidity ranges. That flooring was probably milled and dried for the local market and you aren't it so it may be that it was not properly acclimated to the conditions it was to be installed in. Also, is this floor a solid or an engineered, multiple ply floor? If it's a solid, and I suspect it is, they are typically nailed down. How was your floor installed? I like the part where you mention you hired a "English" carpenter to install the flooring, like they have something over us Americans. I can tell you, I've forgotten more about flooring than ANY "English" carpenter ever knew. AS to how to fix it, let it sit for 6 months and see what happens. If if doesn't get better, then you'll need to rip it out and get some QUALITY flooring from a reputable distributor and hire a real hardwood flooring contractor to install it.

No you didn't. You don't even own "the book"so how can you say you did it by the book. I, and many other NWFA members, own "the book", called the NWFA Technical Reference Manual and if you had done it by the book, you would not be experiencing the problems you are facing now. OK, lecture over. Sorry, but lots of folks come here and tell us pros how "correct" their installation was and what's wrong with the wood they bought at a discount somewhere. Most of the time, and the inspectors will back this up, it is installer error.

What is the actual species? Brazillian Mesquite is a made up name to make it marketable, by a broker of cheap flooring.

Sounds like concrete moisture to me. But I'm not there to see it myself. A circle? Might be a plumbing leak inside the slab.