Dining table

[msajeep]

When finishing a dining table and benches is it common practice to stain and finish the bottom of the tops and back of the aprons or leave them unfinished?

[KC]

Stain and finish as you do everywhere else. I never spent as much time sanding the underside/inside as I did the parts that show, but for sure finish it.

[Doug_H]

Dear MSA,

It is important that moisture exchange with the atmosphere be roughly the same on both sides of any panel. Otherwise, the unfinished side may expand (during humid conditions) and contract (during dry conditions) more than the finished side. That cupping and bowing action does not have to be very great on a large panel to be noticeable and to strain the joints and fasteners.

That said, finishing the bottom extends the time required to complete the finishing process. Personally, I seldom apply more than three coats of varnish or shellac to the underside of a table and I have never had a problem with unequal moisture exchange.

Staining is mainly an aesthetic decision because the stain is not a significant moisture barrier. I would choose to stain both sides, especially if the contrast is great between the original wood color and the finished wood color.

Doug

[ianab]

I agree with Doug.

The stain doesn't matter, and the quality and exact number of coats that you put on the underside isn't critical. But you want at least a similar finish on the bottom. But you can skip the fine sanding and 2 or 3 coats is "close enough".

Reason is that the table top is going to gain and loose moisture with the seasons. This happens much faster if the wood isn't varnished. So if the unfinished bottom gains moisture and expands faster than the top, you get cupping. Then when it dries out faster it cups the other way. By having a similar finish on both sides the change is both slower, and even. Probably not so important with the aprons as they are much smaller. If a 6" apron gets a slight cup, you don't notice. Not like the cup that can form in a 3ft wide top.

[bhh]

Point; counter-point:


article on the subject

[KC]

ianab said:

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I agree with Doug.

The stain doesn't matter...

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If it's a table for yourself, I'll agree that stain doesn't matter. If it's a table for sale, it's going to matter to almost anyone that crawls under there to see it. And my experience at 9 or 10 shows says it's not just the woodworkers that look.

[ianab]

bhh said:

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Point; counter-point:


article on the subject

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The 3 points he makes are totally correct, but they relate to reasons for a permanent cup to develop. He's missed the 4th reason for cupping to happen temporarily. Uneven gain or loss of moisture. if you want to experiment with that, go and lay a wide board on the lawn on a sunny day. Give it couple of hours, and it will be a banana. The sun dries one side, the moisture from the grass dampens the other, and it will cup like crazy.

Now you wont get that extreme in your kitchen, but unfinished wood gains / looses water about 10X faster than varnished. So a wide board with one side unfinished "could" temporarily cup. Until the other side caught up.

Maybe your apron and fastenings will hold it down? Maybe you don't get crazy swings in humidity? So maybe you can get away with it. But I slap a couple of coats on the underside just to make sure.

[Pink Floyd]

I was told early on when I started woodworking that whatever you do to one side, do to the other. I've followed that advice and while I can't say that it is the sole reason for no moisture-movement problems, I haven't had any on the furniture I've built.

The old adage, "an ounce of prevention is worth a pound of cure" applies here. Finishing the bottom side isn't a lot of time or labor and might just pay dividends later on.

[Doug_H]

I agree with ianab. I generally respect Bob Flexner's opinion, but I was speaking about transient moisture changes, e.g., from humid summertime to dry indoor wintertime. A hard film finish (varnish, etc) slows down moisture exchange. Eventually the wood reaches equilibrium with the ambient humidity. But if the bottom changes moisture content faster than the top, it will expand or contract faster than the top.

Doug