Hi all!

Im new to this forum and am having problems with newly laid 3/4 maple solid 31/4 planks. The humidity is within limits in the living space and cupping has occured. The material was stored in a conditioned environment for thirty days along with 4 inch hickory. The maple cupped and the hickory did not. The RH is 45% in the living area and the crawlspace RH is 64%. My question is....did the differance in RH between the two areas cause the cupping? and.....why didnt the hickory cup? My plan of action is to install a crawlspace dehumidifier to reduce RH in that area to mirror the RH in the first floor area. Any ideas...and am I on the right track?

The RH difference can absolutely cause cupping. Greater moisture below the wood will move up through the flooring towards the drier air that is above the flooring.Is the hickory laid over the same crawl space or is there something different under the Hickory ? Also, is this pre finished flooring or unfinished ? Normally, with the difference in moisture , I would expect cupping of both species assuming that they are exposed to the same exact moisture conditions. But yes, Maple is one of the most diabolical woods as far as reacting to moisture.It tends to bow or cup more than most other species of hard woods.

As for acclimation, the trick isn't to let the wood sit for a long time, the trick is to get the flooring to absorb or release moisture so that it will be at equilibrium with whatever is below it. I say "below it" because the top of the wood is going to be sealed with something but the bottom of the wood is not. That is , unless you buy wood that is already sealed like Ten Oaks "sealed six side" flooring. This isn't always the case but when it is, I will try to store the wood in the area that is more moist so that it can absorb moisture and expand prior to installation. Sometimes , the exact opposite of this is what has to be done.

Now that you are in a bit of a pickle, I believe that dehumidifying your crawl space is only a temporary band aid.For the dehumidifier to work, you will have to run it constantly and it will have to be powerful and efficient enough to make the RH in the crawl space "lesser" than the RH that is in the living area.

In the future , one tip I can give you is to install some rows with spacers . This creates gaps between rows that will close up when the flooring expands . This wont always prevent cupping but in some instances will and in the event that it doesn't prevent cupping, it will help alleviate some of the tension that is created when flooring boards swell against each other and have no where to go but up or down.

Another tip , which isn't always practical is to spread the flooring out on the sub floor (loosely)without stapling / nailing it and let it acclimate that way .Then it can expand or shrink without having to cup,crown or twist .I hope your floor works out .

Thanks for your response! To clarify some things, the flooring was opened but not loosly laid out...but for a long period of time. The two species share the same crawlspace and were laid within a week of each other. I used 30# roofing felt over the subfloor but did not overlap.Today I checked RH again and it was 67% @ 72.5 degrees and 1st floor was 72 degrees and 47% RH. The vents got blocked off and am awaiting the Santa Fe advance dehumidifier. A bit of history, the structure was built in the spring of 2010 and just now being completed. That spring, the rain was overwhelming...I had to drill holes in the subfloor to allow the water to drain into the crawlspace. my guess is the moisture never did dissipate and is lingering in the floor gravel. The footings, walls and underside of the subfloor are not showing any moisture but the gravel is obviously wet two to three inches down. I know there is no moisture intrusion, the footing drain is in place, I am on a hill top and have a wrap around porch that is bone dry underneith, we havnt had three inches of rain all summer. When the hickory was installed, there were noticable gaps in areas ( only the installer could see ) that are still present, my thinking is once the RH has stabalized, the cupping will correct itself to a point and maybe need to be refinished. The flooring was all pre finished. Again, Thank you!

The only critical information left out is, What was the moisture content of the Maple, the Hickory and the Subfloor, prior to installation, when measured with a calibrated pin-type wood moisture meter?

ON another note, if the flooring flattens back out which is possible, great but you can re sand if it does not . This is unfortunate though.

I had done a BRazilian CHerry 4 inch floor in a home next to the ocean.Acclimated it nicely and installed it and then sanded and sealed it.Everything was great and I was awaiting the builder to then install his kitchen on top of the floor. Then the eccentric homeowner and decorator decided it would be good to dig under the house and make a new basement and pour a brand new concrete floor. Well, once they poured the new floor, all the moisture went up into the Brazilian cherry and cupped the heck out of it.

I told them I wouldn't do anything to the floor for 3 months which was when the dry winter changed to the super damp spring here in Connecticut. And in those 3 months , they ran some powerful de humidifiers to dry the basement. By the end of the 3 months, the house RH balanced out in that the basement became drier than the 1st floor .This caused the brazilian cherry to flatten out.I then re sanded it and re finished it for free.

Hello , the answer is...I am an amature with hardwood flooring. I have laid only about 6 to 7 thousand square feet in my life. Here is the amature response....I did not check the flooring moisture content or the subfloor moisture. I know, its my fault butbutbut I have never had this issue before and have only laid Oak. Dang...have I learned my lesson!

I hear that a lot. Finish guys doing lots of resanding for issues they are not responsible for. Makes me think I should never become a finish guy.

sounds like the maple was drier than the hickory when it was installed. You got to be careful when your are dealing with those floors that dont sell well. the longer it sits in storage the crispier it tends to become.

Hopefully it eventually straightens out, its not severe. The dehumidifier will pull the moisture out of the crawlspace but must be drier than the first floor for a long period of time to level back out. I hate to hear that finishers rework floors for nothing, I know its literally impossible to get anyone to admit they were at fault....so reputation and damage control take over. I did use a pnumatic nailer this time, the old manual one was much more difficult to operate. I picked one up online with good reviews and MAN that thing never skipped a beat! Anyone ever used a Freeman nailer? I was impressed!

Is there a vapor barrier on top of the ground under the crawl space?

It's only the 2nd time I re did one for free. But the problem is that I was subbing for another dude that wouldn't take responsibility for anything and the homeowners wouldn't' take responsibility and the builder wouldn't either. But it wont happen to me again.

On another note, I'm finding more profit in installation anyway which never used to be the case.Far less over head in installing.

I do not have a vapor barrier. I installed an exterior footing drain but not an internal footing drain. This structure literally is on the peak of a hill...the third highest peak in a 35 mile radius. My guess is the moisture present is from the flooding of the crawlspace two and one half years ago. Ill keep everyone posted as to how this all works out.

Hi again, the dehumidifier was installed as planned and RH has balanced between the living space and crawl space. The cupping hasnt noticibly receded but can see it has changed somewhat ( after three weeks ). I spoke with a friend in the commercial ( gymnasium floor ) business and she stated it may take up to 12 months to stabilize the maple. This person suggested leaving the floor alone for that period of time and sand/refinish then. She did snarl at the fact that it was pre finished and said it will be difficult to sand, not looking forward to that. Thanks again all!

You state the vents were closed off further up.
Building codes in most areas requires cross-ventilation in a crawl space equal to at least 1.5 percent of the square foot area within the crawl space. In addition, a ground cover of 6-mil polyethylene sheets (preferably black) should be placed over the
entire area of the crawl space soil, lapped at least 6 inches and held in place by bricks or other weights. (Black polyethylene works better than clear, because the black plastic slows the growth of plants, which can occur even in a relatively dark crawl space. In addition, some wood flooring manufacturers are now recommending 8-mil poly in lieu of 6-mil.) In cases where concrete is poured to create a floor in the crawl space, the 6- or 8-mil polyethylene cover is still required.
Crawl spaced should have 24" clearance or 18" minimum under girder.
Building codes in most areas requires cross-ventilation in a crawl space equal to at least 1.5 percent of the square foot area within the crawl space.
Most likely moisture content readings of the wood will show differently between the woods explaining why one does and another does not. I have seen different areas of a home exhibit different moisture readings that is why NWFA guidelines want upwards to 40 readings in subfloor and wood to evaluate moisture content in different areas of the home.

Simply cross ventilating may not be enough as condensation can develop on the underside of the subfloor and joists.