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Discussion Starter · #1 ·
Recently delivered 2 cartons of 5" pre-finished red oak "cabin grade" hardwood to a job site to allow acclimation. Only 2 cartons because we were planning on replacing some boards that had been damaged as a result of cupping. All indications were that the original floor was not properly acclimated prior to installation. I'm aware of what normally causes cupping and although we disputed the proper acclimation finding, we couldn't prove otherwise. The house is infrequently occupied, air heat and cooling, timber frame with insulated panel exterior. Super tight home, HRV set to run intermittently and vent the baths.

The bands were removed from the carton and the boxes cut open. 2 weeks later I returned to take moisture readings and discovered every board cupped, throughout the box. Moisture read 8-10%, as did all the other wood in the house. Returning the wood to a super dry environment has all but eliminated the cup, still is slight. Less than 6% moisture content, lowest reading on my meter.

RH in the house is elevated, but not extreme, 50-60%.

Original floor remains cupped, but acceptable to the Owner, thankfully with the exception of a few boards.

Basically, unless I dry the house to what I would consider an unhealthy level, I am unable to acclimate this wood.

Anyone have any thoughts on this? I'm beginning to question the reasoning for the initial cupping.

Could the wood be too dry before the finish was applied?

Thanks in advance.
 

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Discussion Starter · #3 ·
What was the MC of the subfloor?

Were the cartons sitting on the subfloor?

Sounds like the crawl space/cellar is really damp.
Thanks for the reply. MC of the subfloor is the same 8-10%. Cartons were sitting on the existing prefinished oak floor. Basement is finsihed conditioned space, hardly "really damp", maybe elevated but within normal. Like I stated, the existing floor is cupped as well, including the second floor, well above the basement.

I'm going to bring in another sample of similar but different manufacturer and see what happens.

Have you ever seen hardwood cup prior to installation?

Thanks again.
 

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Maker of Fine Sawdust
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It's wood. It can do anything it pleases. If it becomes unbalanced within it will change shape. It is possible that it came form the factory over dried less than 6% and bringing it back to normal home conditions has caused it to change shape.
 

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Lots of variables at play here..If you have cupping on 2 above grade levels and the cupping is everywhere,this is in part probably due to the house being vacant at times and there is a source of moist air from the basement.Is the basement HVAC operating full time?Is there a dehumidifier in the basement?Houses that are not occupied full time can hold more humidity due to lack of air movement, and most people do not set the temps at the same comfort levels as the would if they lived there full time...Seen this many many times over the years...
 

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Discussion Starter · #6 ·
Lots of variables at play here..If you have cupping on 2 above grade levels and the cupping is everywhere,this is in part probably due to the house being vacant at times and there is a source of moist air from the basement.Is the basement HVAC operating full time?Is there a dehumidifier in the basement?Houses that are not occupied full time can hold more humidity due to lack of air movement, and most people do not set the temps at the same comfort levels as the would if they lived there full time...Seen this many many times over the years...
Absolutely correct, the house is certainly vacant at times. The HVAC doesn't run all that often because you're right the owners set the temp higher when they leave and also because the house has a very low air exchange rate, it's quite efficient. A small dehumidifier does run in the basement. Again, Rh measures 50-60% throughout.

Also at play is an HRV that runs with bath exhausts, and intermittently. I'm suspecting in the summer months it brings in quite a bit of moist air.
 

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I've installed a lot of unfinished flooring in every extreme. Houses under construction in the winter where humidity levels were very high, and I've never seen flooring start cupping before it's installed. There has to be something going on with the environment that it's in. There is a moisture problem somewhere. There must be some piece of information that you're not getting.
 

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solar guy
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You answered your own question.
When you brought the wood in it was at a low MC
Since it was prefinished it only picked up moisture on the unfinished side causing it to cup. When dried out it straightened up.
Try applying a finish to the back and edges and re aclimate it. It should pick up moisture more evenly and the cupping should be eliminated or at least less severe.
 

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Absolutely correct, the house is certainly vacant at times. The HVAC doesn't run all that often because you're right the owners set the temp higher when they leave and also because the house has a very low air exchange rate, it's quite efficient. A small dehumidifier does run in the basement. Again, Rh measures 50-60% throughout.

It is called "greenhousing" Pretty common with rentals and snowbirds.
 

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Going back to Leo, wood does what it does. Cupping means that the moisture content is higher underneath. Was a vapor barrier installed?
 

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just a question, but isn't cupping going to move the wood in the direction of the growth rings regardless which side of the flooring has the higher MC?
 

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just a question, but isn't cupping going to move the wood in the direction of the growth rings regardless which side of the flooring has the higher MC?
No.
Vessels/cells of all wood are hygroscopic. As they absorb moisture, they swell. The bottom of the board with higher moisture content, swells more than the top, which has less moisture content.
 
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