Woodworking Finish: both sides?

[toolsForCharlie]

1) Do you finish both sides of panels?
2) If yes, would it be bad to use a different type of finish for the underside/inside?
3) Should both sides be equal in number of coats?

So I'm halfway through one of the bigger projects in my young woodworking journey. After foolishly saying "I can build it better for less," several months later I'm nearing the final assembly / finish prep stage of a dining table and bench for the lady. We don't have a huge dining area, so the table top is going to be roughly 4'x3', but the particular style she wanted meant a few other panels in addition to the top, and it's all out of 4/4 white ash.

I've been reading mixed opinions on whether or not to finish both sides of panels. The humidity in our area ranges from 30% to 100%, often indoors as well because we like to leave the windows open. Anything mounted is via slotted holes or z-clips. I'm leaning towards yes on finishing both sides, but that also means an extra ~30 sq.ft. of finishing to do. Is this unnecessary? Going to be using General Finishes Arm-r-seal for the top and sides. Is it a bad idea to use a polyurethane (oil-based) for the underside/inside?

 

[BigMike782]

I typically seal all sides to keep humidity change to a minimum.

 

[bdbecker]

For this application, yes, you'll want to finish both sides.

Be sure to post some pics of the project once you get it done!

 

[Jehannum]

1) Do you finish both sides of panels?
2) If yes, would it be bad to use a different type of finish for the underside/inside?
3) Should both sides be equal in number of coats?

So I'm halfway through one of the bigger projects in my young woodworking journey. After foolishly saying "I can build it better for less," several months later I'm nearing the final assembly / finish prep stage of a dining table and bench for the lady. We don't have a huge dining area, so the table top is going to be roughly 4'x3', but the particular style she wanted meant a few other panels in addition to the top, and it's all out of 4/4 white ash.

I've been reading mixed opinions on whether or not to finish both sides of panels. The humidity in our area ranges from 30% to 100%, often indoors as well because we like to leave the windows open. Anything mounted is via slotted holes or z-clips. I'm leaning towards yes on finishing both sides, but that also means an extra ~30 sq.ft. of finishing to do. Is this unnecessary? Going to be using General Finishes Arm-r-seal for the top and sides. Is it a bad idea to use a polyurethane (oil-based) for the underside/inside?

If you don't finish both sides, you run the risk of cupping because of uneven moisture takeup.

 

[MoonRise]

Short answer: Yes.

Longer answer : Yes, you need/want to apply type of finish and the same number of coats of finish to both sides of the wood to minimize humidity-differential induced cupping or warping. And to make the piece 'finished' all around.

You don't necessarily have to sand/polish the back/inside to the same level as the exposed visible 'good' side(s), but you should apply the same number of coats.

It also thus protects the underside/back and makes it more visually appealing, especially if using a finish that can/will tint or color the wood. Oil-based polyurethane varnishes (including Arm-R-Seal) usually add a (to me anyway) pleasing amber tone to woods such as ash or oak. A nice amber tone on the top and sides of your table and then a plain bare unfinished bottom of the table would look unfinished to me, no pun intended.

Be safe with oil-based finishes! Spontaneous combustion of rags or brushes from oil-based finishes is real. Read up on it (or ask here) if you are not sure what that is and how to avoid it when using oil-based finishes.

 

[jar944]

For a table top or bench tops, there is no need to finish both sides.

 

[strutaeng]

I usually try to finish every exposed or accessible surface of my woodworking projects. Mostly so I don't have any raw wood.

I used to think like every else about finishing all sides "seals" out the moisture. However, in Flexner's book called, Understanding Wood Finishes" he says this is a myth.

I now think moisture eventually reaches an in-service equilibrium moisture content (M.C.) regardless. And the equilibrium M.C. actually can vary slightly based on geographical location and time of year.

 

[PugetDude]

Why risk ruining all that hard work?
A quick coat or two on the underside is cheap insurance against uneven moisture absorbtion.

 

[rharman]

Regardless of the moisture issues, I think this project needs to be finished on all sides. You'll feel better about it when you get a glimpse of the bottom side when it's in use.