moisture and wood movement

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Forum topic by jpc posted 11-27-2010 10:33 AM 1613 views 0 times favorited 8 replies Add to Favorites Watch
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139 posts in 3176 days

11-27-2010 10:33 AM

ive been doing woodoworking for about two years now as a hobbiest, ive learned alot and made some really nice things around house, now on to my question, as a woodworker i know that most things you have to finish both sides equally to make sure that moisture will come and go equally to help stabilize the peice, and as some of you know i had a disaster in my house and since have been doing home refurb, and have decided to do hardwood floors in two rooms instead of just replacing the carpet, and doing research and lookin in flooring forums, and the most frequent thing talked about is floor buckleing, movement, letting the wood aclimate bla bla bla,,,but as i start this new venture , i find that hardwood flooring, prefinished that is, only comes finished on the face, to me,...alll the effort and tidious stuff done to prevent floor problems, how could this major bit of info that we woodworkers adhere to be overlooked, or has it, any of you know if there is a logical reason for this, i was thinking maybe to allow the flooring and subfloor to breath as one, i dont know

8 replies so far

View crank49's profile


4030 posts in 2966 days

#1 posted 11-27-2010 10:52 AM

My dad was a hardwood floor finisher for over 50 years. He never taught me any way to finish anything more than just the top of the floor. I’ve never heard of anyone finishing the bottom of the floor. There must be a proper vapor barrier on the subfloor, below the hardwood.

Also, I have a house full of antique furniture and no piece of it has finish on anything other than the outside surfaces. Some of this stuff is 100 years old and nothing has buckled or warped.

View jpc's profile


139 posts in 3176 days

#2 posted 11-27-2010 12:01 PM

and ive never heard of anyone finishing the bottom of flooring either, but like table tops, any thing where edge joining or what not ive always been told do the top and bottom equal, it sounds like you have some quality made stuff.believe me i followed all the vapor barrier suggestions and every step the way they said, i cant afford to buy that flooring again, just thought that it the bottom was finished it would fend off some of the moisture issues that cause issues

View Tim Dahn's profile

Tim Dahn

1567 posts in 3560 days

#3 posted 11-27-2010 01:40 PM

Does the fact that the underside of the flooring is not exposed play into this?

We have pre-finished hardwood floors throughout our house and had a flood from a pipe burst, the entire master bedroom floor buckled, it looked terrible. I chose to let it dry out before replacing to see if it would, it has been almost two years now…you can’t tell it had ever been wet.

-- Good judgement comes from experience and experience comes from poor judgement.

View helluvawreck's profile


31044 posts in 2862 days

#4 posted 11-27-2010 02:47 PM

I have never seen anyone finish the bottom surface of flooring either nor have I seen anyone finish the backside of paneling. If it is all installed properly and moisture is kept outside of the home there shouldn’t be any problems.

-- helluvawreck aka Charles,

View Gregn's profile


1642 posts in 2979 days

#5 posted 11-27-2010 04:07 PM

The reason table tops, benches, and shelves are sealed on both sides is because of the ambient humidity changes in the air. For flooring you first have the sub floor and then a vapor barrier and then your hardwood flooring. The hardwood flooring is protected from ambient air changes by the vapor barrier and sub floor. The sub floor is what will be affected by the humidity changes first, which is why so many local codes have gone to plywood sub floors because of the stability of plywood being limited in its amount of movement.
The old plank style sub floors where laid down on the floor joists at an angle to even out the wood movement to prevent as much buckling as possible in the flooring. So your sub floor and vapor barrier acts as it you sealed the flooring on both sides.

-- I don't make mistakes, I have great learning lessons, Greg

View wisno's profile


88 posts in 3007 days

#6 posted 12-01-2010 08:07 AM

The finish for both side is recommended especially for the big and wide surface. The wood will always try to adjusting his MC according to the humidity of its air environment. It will shrink and swell according to its MC. But the coefficient of wood movement is depend on the type of wood, the size of the wood, and also the humidify changes in the air. When you deal with flooring with small panels, or the wood that has small coefficient movement, it may be okay. But if you deal with big and wide panels and porous wood with high coefficient movement, then you will get wood problem such as checking, bending and warping.

Good luck



View jpc's profile


139 posts in 3176 days

#7 posted 12-01-2010 05:21 PM

thanks everyone

View dbray45's profile


3320 posts in 2772 days

#8 posted 12-01-2010 05:42 PM

A lot depends upon the flooring material and how it is cut. I have a 3/4” cherry floor, I finished one side, and it moves a fair amount – I left a 3/4” on all sides, moldings are 1.5”. Almost all of the boards are flat sawn. I once put in a floor that was all quartersawn red oak and you could probably submerge it and it wouldn’t buckle. The movement was verticle – installing was a pain because it is prone to splitting with round nails and staples, had to pre-drill everything.

I made a couple of tables 3’x5’ with glued mitered edges and they never cracked or split but every board was quartersawn and each center board was finished 3/4” thick and 7” wide and hand picked. One was cherry and one was maple – Walnut can be touchy because it tends to have a lot of stress in it.

-- David in Damascus, MD

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