Several years ago I had about 1500 sq. ft. of 3/4 white oak flooring installed. About 2 weeks afer he finished I started to see a little cupping. After a couple mo. it was very noticeable. If I lay a straight edge on the floor I can see 1/16 inch gap. I have talked to several installers lately about sanding and re-finishing. Problem? Each has a differant answer. One says I have correct the moisture problem first or the cupping will come back. Another says once it has cupped it won’t cup again. What say the experts here? One thing I have noticed is the floor seems to have stablized. I see no difference summer or winter. It seems to me that if the moisture remains the same the floor could be sanded flat and it would stay flat. Am I right or Wrong?
Thanks, Bill
Replies
The floor is cupping because the moisture content of the timber is now higher than when it was first laid.
This can happen if the timber wasn't properly acclimatised to the area before laying or if the humidity in the space below the floor has changed since installation.
You don't give details of the crawl space but the first thing I'd do would be to ensure it has adequate ventilation. As a rule it's not good to sand the floor while it's cupped in case it does flatten out later.
IanDG
Yes the floor is over a crawl space. The vents are all open and not obstructed. Eves are all clean and downspouts drain away from the house.
Plastic is covering the dirt all though the contractor done shi$$y job putting it down. So if the moisture remains the same can I sand the floor flat and will it remain relatively flat.Bill
The fact that the cupping started shortly after installation and has remained stable for a long time suggests to me that the timber was insufficiently acclimatised BUT if that isn't the cause then sanding it can result in more trouble later if the correct cause is identified and cured.
Can you remember any details of the acclimatisation of the timber? Was the weather particularly dry, for example, and for how long was the timber allowed to remain unpacked and stacked within the area where it was to be laid before installation?
IanDG
Can you remember any details of the acclimatisation of the timber? Was the weather particularly dry, for example, and for how long was the timber allowed to remain unpacked and stacked within the area where it was to be laid before installation?I floor was installed in August. The wood was delivered the day before the install started. Nailing, sanding, staining, 4 coats finish all done within 10 days. I have always though that he should have waited several weeks after nail down before proceding with the finishing. By the way I live in Nashville Tn.Mojoman: 3"1/2 white oak select or better. The quality of the wood is excellant. Other than the cupping the floor is beautiful.
Edited 1/20/2005 9:29 am ET by Jake
The facts that the cupping hasn't worsened over time and that it started very soon after the floor was laid plus a total failure to acclimatise all point toward a situation that can be cured by re-sanding.
It's obviously too late now but the contractor deserves to be hung out to dry.
IanDG
Thanks IanDG. All my research has led me to the same conclusion but I wanted to put them to the test. AS far as the contractor. We are members of the same church. The wife and I decided rather than cause bitter feelings we would just live with the floor. He knows about the cupping but has chosen to do nothing. My background includes 12 years as a masonry contractor. I have hand finished hundreds of concrete floor so I think I have the mechanical skills to sand and finish this floor myself. Anyway I don't think I will make it look worse.Kind Regards
Bill
Bill,
If you need it, here's a link to my site and an instruction sheet on DIY floor-sanding using rental equipment -- it might come in handy.
IanDG
Much appreciated. Thanks for your help.Regards, Bill
you havehad a moisture problem.
can you help us out with some background as to where the moisture came is coming from ?
we need:
age of house, subfloor material, basement,crawlspace, slab, did the subfloor get wet, is it a new home, type of heating system........etc.
carpenter in transition
You also have to take into account the seasonal variation in humidity. 20% relative humidity in the winter gives you a board with 4.5 % moisture content. When in the summer and the relative humidity is 84% the board has 17% moisture content.The change in size will vary depending on the wood, but if it was laid in the dead of winter, even if it equalized, and then grew in size in the summer, it would probably cause it to cup.
If a sanding will heal it, I don't know.
You also have to take into account the seasonal variation in humidity.
He did say that there was no apparent difference between the seasons.
IanDG
<<He did say that there was no apparent difference between the seasons.
Ian, Unless he is in a tropical type climate the humididy changes substantially summer /winter. A Dew point of 20F in winter to 40 or 50 F in summer is substantial,and not uncommon where you have a cold winter. If you live in places like the eastern U.S. or the U.K. I am sure the swing of dew point is from 20F or so winter to 70F in the summer. That will give you the humidity swings I was speaking of. If the floor was laid at the dead of winter and the average dew point was 20F or so and then it got to 6oF or so in the summer the floor would have grown substantially,probably enough to cup it...If he is in Florida or some such place it may not change that much..
He's the guy on the spot -- if he says the cupping doesn't alter from summer to winter, why should I disbelieve him?
IanDG
Ian, Dont think anyone is "on the spot"...
If you lay a floor,attached to a sub floor, at its smallest (driest) point and then it gets more moisture content it will swell, and associated pressures will cup the boards.Most likely they will stay cupped because the wood cells will be crushed. Once they are crushed it will probably not re-cup if you sand it off level.Once it is cupped it wont change summer/winter.Does not mean the moisture levels don't change summer/winter.
Most likely they will stay cupped because the wood cells will be crushed
It's not been my experience that the timber stays cupped after it has dried out to the original moisture content it had when it was laid, in fact the standard advice in cases of water damage is 'Do nothing until the timber has dried because it may flatten out'
Sanding the timber while it is cupped will give you more problems if it does eventually flatten out -- you'll be left with a cobble-stone appearance with the edges lower than the middle of the board.
IanDG
How wide are the boards? Around here, 2 1/4" oak is very common, but once I had a 5 1/4" hickory floor installed. It cupped both ways: Once in the humidity of the summer, and then the other way as it dried out when the heat came on.
If the humidity in your house swings wildly, I think your floor will continure to move. If it was a problem with the wood initially being much drier or wetter than your conditions allow, it may have now stabilized.
Maybe the best approach is to get a moisture meter and see what's going on. Then you can determinine if you have an environmental problem with large variations in humidity, or find out that the wood is now stable and you can safely refinish.
Al Mollitor, Sharon MA