We put in bamboo flooring two years ago. Now, there’s perceptible cupping over the entire floor–not enough to notice unless you are looking for it–but enough to be mentioned by two flooring contractors who were here to bid on another job. The flooring went over cement, and we don’t know if sealers were used. One contractor mentioned sanding and sealing over the surface. Would this actually fix the problem?
Sanding and coating the floor will fix the cupping, but I would want to know for sure that there isn't going to be future problems in regards to moisture. Why fix it if there is going to be a recurrent problem?
Who says it's a problem? Wood floors move. Bamboo moves. Contractors like to drum up business. That urethane glue they use to put the bamboo down is a vapor barrier by itself.
It sounds like you had another type of flooring down before. If it didn't have water problems, you probably don't have water problems.
Bamboo is not wood flooring, but actually a grass. I suspect it may behave in a similar fashion to wood floors with humidity, of which I'm familiar.
Check the manufacturer's website and see if they recommend an expansion space around the perimeter. Natural materials are subject to swelling with high moisture and wood floor manufacturers recommend leaving room to accomodate the natural movement that occurs with higher moisture/humidity levels. That is typically the cause of the cupping you mention. If it is possible to pull back a small piece of the trim and you see the floor is pushing against the wall.
If the installation was not in keeping with the manufacturer's recommendations, you may have recourse by going back to hopefully the seller, or the installer.
Also, on concrete or below-grade, a moisture check should be done for wood flooring prior to installation. If you have a damp slab or hydrostatic pressure, that could also contribute. If the cupping resolves in dry conditions, either of the above could possibly be an issue.
In my opinion, the problem has to be identified and corrected first. Sanding and sealing does not prevent moisture from below and may worsen the problem. You may want to contact the retailer and ask them to come inspect the problem as they are trained to identify issues, and often they bring a manufacturer's representative along. If improperly installed, there is the solution in this newer installation. If it is a manufacturing defect, which I doubt, your warranty should cover it - unless improperly installed. Catch-22.
On a side note, I did buy a bamboo "rug" for the screened porch which is subject to all weather conditions. The construction, however, does allow for movement, so I haven't seen cupping. It is over raised wood decking, but still open to the elements and I've hosed it, mopped it, etc.
One last thought, be sure there is good drainage around the slab and the gutters are clear. Sometimes that can raise the humidity in the slab. Good luck to you!
You may be experiencing a form of vapor drive from the concrete floor. Bamboo is beautiful material for a floor but will still cup and move like any other wood flooring product. If the concrete floor was not sealed or did not receive a vapor barrier prior to the wood floor instalation, this problem will repeat itself after you sand and finish the floor.