Hi, we are having a house build and have had the builder install interlocking floating bamboo flooring. The board are 5 or 6 inches wide. The install looks great and he seemed to leave enough around the edges for expansion and contraction, however there are several areas where are lifted just a little from the subfloor. When you walk on them they go back down but when you leave the area they pop back up. We aren't talking a lot,... maybe 1/8 inch but it is noticable. The builder told us that they will settle down over time. He did use the felt underneath but did not put 1/4" plywood subfloor in. It was put right over the OSB plywood which probably had some seams that don't exactly line up.

Is he right? Will it settle down? Should we withhold some of his final payment until we find out? Or is this just normal for this kind of floor?

After reading some of the other posts on here, I guess I should say a few more things. The floor is not cupping, but it is lifting in a few areas. As for moisture, I have no idea. The house was the furnace on for more than two months while it was under construction. The subfloor was definitely not wet. The humidity in the house was around 35% when the floor was put in. The house does have a full basement. The bamboo was brought and and allowed to acclimate for some time before he put it in.

Kinda have to be there and see. But couple things can do that. The floor could not be flat, depression in that area or it could also be that they installed a few bowed planks that keep the section lifted. Then theres the underlayment. The ends of the rolls are often bunched up thus giving the impression of a low spot untill it flattens out. I usually throw out the last 3 or 4 feet on underlayment if it is bunched up to much.

Acclimation to the lower spectrum of the humidity scale, can have weird effects as the flooring tries to get to the coming 45-50% rH levels of a wet spring time.

Acclimation to me is not a time thing to me, it is a moisture content deal.

Regardless if it is subfloor flatness or locked in related, movement of a click-loc T&G design, is a separation problem waiting to happen, as the lock wears down from the movement.

Well this is kind of put me in a pickle. It is the snap lock type floor. I can't wait and see as we will be closing on the house soon. Could be noted as an item and reason to withhold some money, but I'm not sure at what point we'd know for sure if things are ok or not.

Is this likely something that might settle if some weight in put in these areas for some time?

If it is from the substrate, no.

If it is because all the expansion space that was originally left at the time of install has been used up as the flooring swelled, yes & no. It will just move the problem over to a different location.

I would have to guess if anything the bamboo has dried since it was put in the place as it is winter here in Michigan and the furnace has been running a lot and there is no humidifier. The humidity has been below 35% for some time. I don't think it is expanding by picking up a lot of humidity from the house or the floor.

You mentioned that you have a floating floor. And one common issue with floating floors is that there is up and down movement anywhere that the sub floor has a low spot next to a high spot. Or think of it as a valley in the sub floor .IF there is no other problem with the floor such as cupping or crowning and there is no evidence of the locking system failing anywhere, then you should pay your contractor.Floating floors almost always have problems with feeling spongy which is why many people opt not to use them.

Thank you. That was the advice I was looking for.

Wood, exotics and bamboo in particular need moisture. Get a humidifier. I'd bet the manufacturer even calls for it.

Won't that make the floor swell and lift more?

Even domestic woods distort when they are out of the comfort zone, let alone an exotic like bamboo that was grown in a jungle. I have pulled engineered out of a box to check planks when it was to dry and you can actually observe them bowing right before your eyes as the exterior plys dry down.

What Stephen is saying is that getting moisture back into the room and floor will get it back to the state it was in when it was installed.If it shrank a little, it will return to where it was and perhaps regain a bit of stability and flex less.

Thank you Paul. Well put.