Oak Floor Buckling Up Because of High Equilibrium Moisture Content


My contractor recently installed a new select oak floor in new the new addtion for a kitchen. The boards are about 2 inches or so in width. They were stained and polyurethane applied. Subsequently my entire large kitchen was installed, cabinets, granite, appliances and then we noticed the floor was not flat but was wavy. Each board is buckling upward slightly at the intersection with the next board. It is nearly completely symmetrical with a subtle wave going thoughout the kitchen. My usually excellent contractor admits that this is a problem and is bringing in a wood flooring expect to look at it. The floor is constructed with sheets of plywood nailed to ceiling joists of the new garage below. On the plywood is 2×4’s about 6-12″ apart with an additional piece of wood on the 2X4 to increase height above the plywood. In between the 2×4’s, is tubing for radiant heat(which has not been turned on). The oak floor is then installed crosswise on the 2×4’s.

What could have caused this?

Is there any repair possible other then ripping out the entire wood floor which would be astronomical being that the central island alone is 6 ft by 8 ft with plumbing, granite and applicnaces installed not tomention the 600 lb range and 700 pound frig.



Dear Gary

Don’t start removing any floor YET, the problem may sort itself out, if you are really, really lucky.

The cupping of the wood was caused by excess moisture during the construction. The first thing the flooring expert will do, is a moisture test of the floor, with an electronic moisture meter (one without the pins). If the floor EMC (equilibrium moisture content) is above the average for your area, it still contains excess moisture in the wood. The floor will have to be allowed to dry out on it’s own.

Check first for any pin hole leaks in the pipes below the sink or the even the feed pipe to a ice maker on the fridge. This cause is doubtful as the result would be a localized bucking. Whereas you have a uniform cupping.

Most likely the mistake was made in installing the wood floor too early on in the construction process. If the hardwood was brought it at the proper EMC (check this from the supplier) and then was installed over air dried lumber, and drywall and concrete curing in the garage below. Well you can see that the wood flooring is hygroscopic and might have taken on the moisture from all these sources. It may even have developed a slight crowning just before the floor was sanded and finished. If the crowning was sanded off before the wood got a chance to correct itself, when the floor did flatten itself the cupping effect you see now then might have occurred. This is all a bit of a guess from where I’m sitting but it is a common occurrence on new construction.

It’s up to the hardwood flooring contractor to bring in the wood only when the job site is ready for it. The job site is ready only when the concrete slab below is has cured for a least 60 days. And the drywall has been taped and primed and dry for at least a week. All framing members under the floor including the plywood subfloor has to have a EMC about the same as the new hardwood floor. Air dried construction lumber really needs a month or more to dry out, and it’s better to wait until the AC or heating system is on to speed this drying process.

Also I should mention, now that you’ve read the Hydronics article, that it would have been wise to install the floor during the heating season. And using quarter sawn wood is just the thing in this situation. I commonly install my wood floors around existing kitchen cabinets, using the kick boards to cover the expansion space at the edge of the floor. In fact that is the ONLY way I will install a kitchen wood floor now. I’m just about to install such a floor starting Monday. It makes no sense to have the wood under the base cabinets. It traps the wood in a place where it has no room at all to expand. If it ever does buckle it may actually lift a base cabinet off the floor.

Sure installing the floor early on is easier for the installer. But given what you are now experiencing, it makes no sense to me.

So that’s the mistake. Now for the solution. Don’t do anything until the heating season starts. Follow my suggestions as to turning the heat on gradually and see what happens to the wood. If what happened is what I have mentioned before and the wood is now at the proper EMC turning the heat on this Fall will not help. So, if by Christmas the wood has not settled down flat, you can either sand it down flat again, or consider replacing it. Sanding it flat is a viable option, because if my guess is correct, the underside of the wood is now also flat. And now only the top is slightly cupped. Sanding the floor flat in the heating season will make both sides flat, and as long as the garage is heated also, both sides of the floor will have the same EMC, thus no more warping.

But if you want to replace the wood, this time follow my advice in the Hydronics article, using thicker plywood. The thicker plywood will keep summer time humidity from contacting the underside of the hardwood. You can see if you AC the space above, and have the garage hot and humid similar problems can occur again. In fact while I’m thinking about it, this may have had a factor in the cupping also. Especially if the kitchen was AC’d weeks before the sanding and finishing of the hardwood.

If you choose to replace the floor, there is a way to cut the hardwood out of these tight spots and remove it. We do it all the time on old kitchen floors. We use the Fein Supercut saw, to plunge cut easily and accurately right down next to a base cabinet. It won’t harm the base and the cuts are smooth and perfect. The new wood is installed (quarter sawn hardwood this time I hope) using proper expansion spaces. You may have to undercut parts of the base cabinet using the Supercut saw. The job will be laborious and difficult, but worth it in the end. Oh, and if a thicker plywood subfloor is not in the cards, under coat the hardwood as suggested in the article.

Sanding and finishing a job is no picnic either, but I do it all the time. We have methods and tools to sand floor smoothly in the tightest of spaces. This is a typical job for me in modern houses. But not cheap.

Well, I hope I have covered it all!