After reading many posts in this forum regarding installation and subsequent cupping of various types of flooring, I gave some thought to this. Most of the cupping probems are related to the solids and to a lesser degree, the engineered types(moisture gain).As a cabinetmaker (and amateur flooring installer) I'm quite familiar with wood movement. One of the basics in that regard is that ALL sides of a wood part are sealed. In fact the cardinal rule of veneering is what you do to one side, you must do to all others. Why don't flooring mfgs. coat the whole piece of flooring? Even the engineered types could be sealed since obviously it would be a waste to veneer the backside! With the technology in today's adhesives, a coating on the bottom surely could be formulated to accept these glues. In your pros' opinions, would something like this fly? Just wondering.

Maybe that is why flooring has relief channels moulded into the bottom of each piece and precise spacing in the toung and groove and reliefs on the bottom portion of the groove?

That is unless you buy cheap flooring not milled very well ... try tellin customers the diffrence between the brands .. (I'd name a few for comparrison but not sure how cool that would be on Ken's site).

I have seen bamboo that was sealed all round and it resisted even the expensive adhesive. (just a note)

Not to mention I wonder how much that would add to an allready competative cost margin.....

Short answer -- it doesn't work.

In his excellent book Understanding Wood Finishing, Bob Flexner shows through testing that coating all sides of a piece of wood with finish will NOT prevent wood movement problems such as warping, cupping, cracking, etc. That is, wood finished on all sides performs no better than wood coated only on the top. This is because finishes never completely seal the wood; the wood still absorbs water vapor and liquid. Finishes only slow the rate of absorption. Slowing the rate is inconsequential for moisture that is constantly present, like with ambient humidity or subfloor moisture content.

I'd be willing to bet that manufacturers have tried and abandoned the strategy of finishing all sides. It would be very cheap and easy to do, and if it prevented more cupping problems for the end user or allowed more installation possibilities, it would be a huge win for them. But it doesn't work; that's why they don't do it.

The issue of veneering both sides of a board is a different one. Finishing does not prevent movement in a board, but a glued-on piece of veneer WILL move differently from the board underneath. You don't want movement forces on one side of a board but not the other; the force acting on only one side will warp or distort the board. Veneering both sides will cause equal forces from both sides, a much better result.

Bottom line, when making cabinets, you DO have to veneer both sides of a board, but coating all surfaces with finish is a waste of time (for surfaces that won't be seen or stained from handling).

I used an unfinished wood that was coated on all 4 sides, after they dried the wood they sprayed all of it with a sealer. It was kind of sticky to the touch. They claimed it would hold up to moisture issues better because it was sealed.
I installed it went to sand it and the sealer on the boards would prevent them from going as tight as the regular unfinished flooring I normally used. So when I sanded it the butt ends mainly had sealer in them and wouldnt take stain as the rest of the floor., needless to say I removed the flooring and reinstalled/sanded. I will never use that product again.

At one time, applying finish/sealer to the backside of unfinished solid wood flooring was a generally accepted method of helping the flooring from absorbing excess moisture from below, in a "less than perfect" install scenario. Your post debunks this "myth". Although I do believe it will would slow the transmission of moisture in the same way a vapor retarder would.
Personally, I only did it once a long time ago. And it took up way too much time. I'm not sure if it even helped that much. I have noticed some solids coming from China are finished all over, top and bottom. I don't know what the reasoning is. Control moisture absorption during voyage? Sloppy application methods? Moisture control for solids in lieu of wrapping cartons in plastic? All of the above? Anyone know for sure?

I've seen the six sided sealed unfinished floor your talking about and have my doubts about it's usefullness. If there is a underlying problem with moisture sure it will slow down the effects but if the problem is not addresed it's still going to swell and cup like any other floor its just going to take a little longer. There are lots of mountain cabins in this area that I have seen with cupping problems due just to the fact they have the windows open all the time and there is a constant fog that sits up there like 6 days a week. No moisture from below the floors, its getting wicked in from the top thats got three coats of finish on them.