As I was laying out some pre-finished flooring last night, I got to thinking (never a good idea if one can help it): Why is it that finish is only placed on one side? My years of woodworking makes me squirm at the thought of having one side essentially waterproof, and the other completely open to the elements. And I can't imagine rosin or tar paper will significantly stop vapor changes.

I know this is essentially what has been done for ages with 'finish in place' flooring, but it just seems like an improvement could be made in terms of stability to at least place 1 or 2 coats on the bottom.

Just my ramblings, curious what others have to say.

--Brian

Some companies do. Woods of Distinction Bamboo comes to mind as a product that is finished on the bottom.

Out of the six or so prefinished floorings I'm familiar with, an engineered plank is the only one that has no finish on the bottom.

Don

Some installers will apply a sealer/finish to the backside if they suspect a moisture problem. This is normally only done with solid wood flooring. The idea is not to have any moisture vapor getting to the backside. That is why most, if not all, major flooring manufacturer's give very detailed instructions on keeping moisture away from the flooring to begin with. This is done with a polyethylene vapor barrier in crawl spaces and proper grading and venting. With concrete, a vapor barrier is suggested to be installed BEFORE the concrete is poured and this is code in some parts of the country. The concrete will sometimes also need a moisture barrier/sealer on top of it prior to the floor installation. With veneered/engineered flooring, it is much more stable and can resist moisture changes to a degree but only up to an average of 3.5 lbs. of vapor per 1000 sq.ft. in a 24 hour period. After that, a moisture barrier/sealer is required. Sealing the backside will help but is not a cure all for moist or damp subfloors.

A vented crawlspace is a problem, not a solution.

I agree with Chuck.


Once you get the ground moisture incheck and covered with a moisture barrier, why let exterior ambient conditions, into a cooler crawl space.


Take exterior ambient conditions, of say a summer day here, 90º @ 75%( in the mornings, it could be 75º @ 85-90%)

The crawl space is known to be at least 15º cooler. Cool 90º air containing 75% humidity, 15º and what does the humidity become?????

Now that it is figured, how is that going to effect the joists, and subfloor?

I have kicked this around a time or two myself and wonder why not more people have not gone to an enclosed crawlspace with some type of exaust fan? Then I think to myself if it caused a big enough problem almost every stinking new construction floor in town would cup up in the summer. hmmmn?