Hi all:
I have a question about finishing a tabletop I just completed. First the background:
It is solid cherry, 1 3/4″ thick. It has hefty breadboard ends, and will be mounted on a trestle. I sanded it to 220, then rubbed in some linseed oil, and padded on 2 coats of 2 lb. cut shellac, top and bottom. Next, it will get 3 or 4 coats of Behlen’s Rock Hard tabletop varnish.
Before I varnish, here is my question:
I know that in general, what you do to one side of a slab of any kind should also be done to the other side, to prevent warping. Do I need to varnish the underside of the tabletop also? Or does that shellac that already covers the bottom side offer enough of a seal that I don’t need to worry?
Getting under there with a varnish brush seems like a major pain, which I will avoid if I can.
Thank you for any input you might have.
Alex
Replies
Not sealed. Is still a semi permeable barrier.
One side , with the finish, may move slower than the other side but it will equalize eventually.
You could rag on the under side coats.
I have intentionally left the under side of this table completely un coated just to see what would happen.
I put finish on it a year ago in December it is still flat enough for me. We have never noticed any change that was discernible with out a straight edge. Notice no bread board ends.
I just checked it while I was writing this. I used a Starrett 48 " straight edge. I could see a little light under the straight edge here and there but could not fit the corner of a sheet of printer paper .003 " under any where along its length. By the look of it it is very flat. I bet it is on the order of .002 ".
I am in Colorado. This is well acclimated bubinga that I had in the house for years before I worked it. The finish is Maloof with french polished shellac over it. I don't necessarily recommend that but it is an experiment for me.
The humidity outside right now is 80% ( normally much lower ) for what that is worth. I don't know what it is indoors. We have forced air central heating by gas and do not use a fire place.
Soooooo . . .
there you go.
that is pretty high humidity
for that climate, is it not..
it also depends on how you have that top bolted down as to cupping. it never hurts to seal the bottom with the same finish as the top
shellac can cause grief at times. I went to seal the bottom of a top oncewith shellac before I had and finish on the top. I brushed on a generous coat and turned it over. I had about 140 hours invested in this this. within about 5 minutes it had a curl all the way down the 14' of it like a bobsled shute. I won't repeat what I said but collected my thoughts and pulled out a gallon of methol hydrates and washed the top down generously and within about another 5 minutes it was back to normal. alcohol holds water
We are on the edge of the desert here. In so many ways.
>bolted down<
Bolted Down ?
As in . . . m e t a l . . . bolts ?
Parish the thought.
I am hurt. Yes I am. No faith. You just have no faith in me.
bolted down . . . P A A A L E E E Z Z Z.
: )
OK I'm done. Nah dude nah . . . the top is just sitting there on top of the frame. Nary a dowel peg let alone those unmentionable things . . . well we will just forget you even said anything about those.
PS: I would like to see the structure that could resist that bubinga if it did set its mind to move. Nah . . . it would just move and take the structure with it. Note the thickness.
PPS: WHOA ! That is a very cool counter you made! ! ! Way to go !
PPPS: I wonder what would have happened if you had gone at the bobsled run the same amount of finish on both sides if it would have balanced and become flat.
For once some one ( you ) have told me why I would ever want to buy anhydrite denatured alcohol. THANKS !
Until now I had been buying the good stuff but didn't understand why.
sorry
should have used the term fastened
what ever is ,anhydrite denatured alcohol?.. I use a better grade of alcohl to dissolve shellac and then methyl hydrates to thin it. alcohol has the capacity to absorb water. methyl hydrates is also used as gasline antifreeze.
Oops
>anhydrite<
I ment anhydrous denatured alcohol
We will blame it on my beleaguered spell check.
I had a stock of Ron Hock's solvent but that is no longer available. Lately I wound up with some more commonly available stuff that is full of chemicals I am not liking to breath.
Maybe I will go with this stuff next
http://www.toolsforworkingwood.com/indextool.mvc?prodid=MS-ALCHO
I was so desperate I was going to get 190 proof from the liquor store and pay the tax. I still may do that.
both sides
IMO if you don't balance it will get funky on you. Why spend all the effort to make such a wonderful piece to have it screwed by the finish. My rule of thumb finish the bottom the same as the top, However I'm not as carefull on the botom with runs drips errors but its the same and I finish the hard to's prior to attachment. Especially if your brushing.
Thanks for the input, everyone. I realize that, in the whole scheme of things, considering all the time I needed to build, I should just shut up and start varnishing. I will thin it out a bit and wipe it on, and I'll do a couple of coats.
Alex
Many professionals and factories do not finish the underside except for surfaces that can be seen or felt. For example a tabletop that will have skirt will be finished from the edge to the skirt.
If the tabletop is for a table that does not have a skirt such as a trestle table, the whole bottom will get the same clear coat as applied to the top surface. This is becaues there is little support to keep the tabletop flat. Breadboard ends are only marginally effective and only for the first 12" from where the breadboard is attached.
please note though
that Howard said most, but not all. most factories are not dealing with solid wood construction so perhaps that is a moot consideration.
if you have pride in what you do and want the best longevity for your project, don't be afraid to do that little extra. preventive applications always make one sleep better.
ron
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