Finishing Top & Bottom

[Ed Gibbons]

Is it really necessary to finish both top and bottom as a method of dealing with wood movement? I can’t recall who but I remember one of the top finishers say there is no evidence that by also finishing the bottom of a table top makes any difference.

[Jeff Roltgen]

I am in that camp, but I've always sealed the bottom of dining tables. Got in the habit when doing finishing work for a local unpainted furniture store. The clients just thought it wasn't right if not stained and sealed on underside. I got in the habit, and always do so now.
Personal preference, IMHO, not a hard/fast rule either way.

[Steve Jenkins]

Makes it easier to remove gum.

[Lee Schierer]

I seal top and bottom, inside and out as a normal process. To me it makes sense that the finish on all sides would make moisture changes more equal on table tops and such. I've had box lids warp that were only finished on one side. I've never had anything warp when it was finished on all sides.

[Stan Calow]

I remember reading that article by (I think) Bob Flexner. His conclusion was that wood will cup on the side that is getting wet. For example, a table top getting periodically wiped down. He pointed out that you rarely see a wood deck where the boards don't cup concavely on the top, regardless of the grain orientation. When I read that, I went out and looked at my deck and confirmed what he said. I noted at the time that musical instruments, for which warping would be death, are not finished on the inside.

I still do it, because it looks neater, but I dont give the underside all the coats and attention that I give the top.

[Jim Becker]

I noted at the time that musical instruments, for which warping would be death, are not finished on the inside.


It's true that most acoustic musical instruments are not finished on the inside, but they are also really well supported by construction method so warping would be difficult. Some luthiers do do a wash coat of shellac on the insteriors; depends on the maker.

[Kevin Jenness]

An unrestrained panel finished on one side will tend to cup due to different rates of moisture exchange. A tabletop held down to a framework will be restrained from cupping, but it is still good practice to at least seal the underside.

[Jim Becker]

I agree with Kevin...even a single coat of "whatever" on the underside to seal is a good practice for a table top.

[Ed Gibbons]

Article on finishing top & bottom:

https://www.popularwoodworking.com/article/finish_both_sides_not_necessary/

[Stan Calow]

Ed, yeah that's the article I remembered - wow - from 2007!

[roger wiegand]

I'm not sure why you wouldn't. I can see that if you are Ikea making 10 million of something that the few cents worth of finish saved on each would add up, but for most of making a few pieces a month it doesn't seem worth thinking about. Finishing all surfaces eliminates worrying about where the dividing line should be and how to make it neat.

Open to question I guess as to doing as a method of dealing with wood movement. I'd be surprised if it makes a big difference on something thick like a tabletop, finishing only one side of unsupported 1-2 mm aircraft plywood makes it curl up like a potato chip.

[Lee Schierer]

Article on finishing top & bottom:

https://www.popularwoodworking.com/article/finish_both_sides_not_necessary/

I disagree with their claim on decks always cupping up. The problem with decks is sun exposure. The deck gets soaked with rain and then the sun comes out. You don't have to guess which side of the deck boards are going to dry out first. When wood dries out, it shrinks, hence the cupping on top. The shady side or bottom of a deck will always have a higher moisture content than the top surface.

[Warren Lake]

finish both sides the same. If you want to do it more correct you cut slots on the underside which take away the strength to warp. Its called breaking the back and its what the old guys were taught, same with the guys that taught them and on and on. Even If i checked an end table and looked inside the top had cuts in the bottom side. Hall table the same.

[Danny Nevala]

finish both sides the same. If you want to do it more correct you cut slots on the underside which take away the strength to warp. Its called breaking the back and its what the old guys were taught, same with the guys that taught them and on and on. Even If i checked an end table and looked inside the top had cuts in the bottom side. Hall table the same.


Could you expand on this a little bit Warren? I haven't heard of this before, and am intrigued. Some questions I have are:

Would the slots be with or across the grain?

How wide and how deep?

How long?

It's always fun to explore a new technique. Thanks for mentioning it.

[Warren Lake]

slots cut in the boards for their length stopped before the ends. From a saw blade to a dadoe. Depth and width decided when you do it. Ive seen on the small side just a saw blade. You have seen it done in some flooring then its usually sort of a round front dadoe and several of them. Here are a few flooring offcuts, The white piece is home siding maybe Maybac


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