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here's some info...

Posted by jb on November 28th, 2001 01:01 PM
In reply to Hardwood floor cupping after instatllation by Terry on November 28th, 2001 10:27 AM [Go to top of thread]

If edges are cupping up then that means that the back side is expanding, This is likely to be from one or both of these reasons: 1. excessive moisture in your house/subfloor area and/or, 2. insufficient acclimation in your house prior to installation (with or without overdrying from previous storage).

From the Oak Flooring Institute

Oak Flooring is a quality product made from lumber that has been kiln-dried. To maintain the moisture level, don't truck or unload it in the rain, snow or other excessively humid conditions. Cover it with a tarpaulin or vinyl if the atmosphere is foggy or damp.

Kiln-dried flooring should be stored in an enclosed building that is well ventilated with weather proof windows and located in areas where similar fine millwork is stored. The storage area within the building should be clean and dry. Leave adequate room for good air circulation around stacks of flooring. Continual dry heat may over-dry flooring, which may later result in buckled floors when flooring is delivered to the job and installed without a proper acclimation or spacing."

See these pages, that are linked from the page shown above.

from the above:
"In-use" Moisture Content: Differences of more than 4% between the expected in-use average moisture content of flooring and the in-use average moisture content of underfloor construction are likely to cause problems such as cupping. The greater the difference the more severe the problems. A significant difference of 8% or more may result in buckling of the floor when the underfloor is the higher moisture content.


When job site conditions are satisfactory, have the flooring delivered and broken up into small lots and stored in the rooms where it will be installed. Allow 4 to 5 days or more, for the flooring to become acclimated to job site conditions. If flooring is packaged, open or remove packaging for acclimation.

Basically, if you have a humidity/moisture issue with your floor and crawl space then that is likely the culprit and you need to fix this problem first. If your floor is uninsulated then you could be getting condensation just below your wood floor and this alone could cause your problem. The problem could have also been caused by not letting the wood acclimate you the humidity level in your house for a week or two before being installed. If the wood was 'over dry" because of improper storage and just brought to the site and immediately installed and sealed, then even a normal home's humidity level could cause this problem. You need to try to figure out what the problem was, wet conditions in your house or improper acclimation. If it is ONLY the latter then you probably could have some recourse from your installer (if you have one, i.e. didn't install it yourself) In this case you could just tell him "fix it, whatever you have to do".

Whether your floor is junk or not, I don't know. Maybe if you had a really wet condition and you then fix it, then let everything dry out it might go down some. There might be some instance where you could sand the whole floor down again and re-finish, or you might have to just rip it all up and use it for (expensive) fire wood. I can't see it from here, so I don't know. I'm sure others will pitch in with opinions.

One side of the wood is sealed with your finish. It does not absorb ANY moisture. The other (bottom) side, and ends are unfinished and free to absorb moisture. When one side absorbs moisture it expands and gets larger. Effectively, this makes the bottom face larger (wider) than the front. When one side of something gets larger than the other side then it cups, be it bread, steel, or wood. I know in bathroom applications people seal the back side of hardwood before applying it, with one coat of poly, to prevent cupping from differential moisture conditions.

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