Vacuum chamber + polyurethane -- a hare-brained idea?

[Robert Marshall]

Before I give this a try, I thought I would see if anyone else has done so, and what the results were. Not much point repeating someone else's mistakes.

I use wipe-on poly to finish bowls, usually putting on quite a number of coats, to the point that the wood won't absorb any more. That could be as many as a dozen coats. Can get a bit tedious: apply, dry, steel wool rub, repeat.

I wonder what would happen if I immerse a bowl in polyurethane, in a vacuum chamber, and keep a vacuum on it until the bubbles stop, then let the vacuum off so it will absorb poly in place of the air previously in the wood. Then, take it out, let it dry, and proceed with what I hope be a much-shortened finishing process.

My assumption is that the polyurethane would be re-usable (the surplus not absorbed by the wood). I don't think being under a vacuum would change its working characteristics. I would weight the bowl with something to keep it immersed, not floating. I have the equipment, having used it for vacuum-resin stabilization with extremely spalted (and therefore very colorful) wood, so it shouldn't be a very costly experiment.

Any thoughts?

Robert

[Doug Herzberg]

I would worry that the poly would form a film and the finish under the film would dry very slowly or not at all. But I like to worry. Why not try on a piece of scrap wood and then slice it up and find out?

[Paul Williams]

I agree with Doug. Try it on scrap and let us know how it works. I think poly needs air to cure and therefore would not cure deep in the wood. BUT, if it works it would be a great way to stabilize slightly punky wood and would add strength to thin walled pieces.

[Jamie Buxton]

Or...you can start your finishing with full-strength varnish, applied with a brush. A couple of coats are the equivalent of a half dozen wiped-on coats. Sand to remove nits and brush tip marks. Then switch to wipe-on for the rest of the job.

[Peter Christensen]

Be aware that many of the solvents or the finish itself will boil off under vacuum and they can harm your vacuum pump as they pass through it.

[Steve Doerr]

I forget which turner I learned this from but he uses a similar process on his Norfolk Island Pine. After he turns the piece to finish he places it upside down on a craft foam covered board with a vacuum hole in the center. He then turns on the vacuum system and applies the finish to the outside. The vacuum pulls the finish thru the veins of the wood. He does this until the finish is pulled all the way thru the wood. By getting the finish thoroughly thru the wood and allowing it to become translucent.

[Brice Rogers]

I would have a concern that the large amount of poly in the wood would take quite a while to finally cure. If the OP can live with that, then perhaps his idea would work.

Once or twice I had applied several coats of poly to a piece. I typically waited 1/2 to 1 day between thin coatings. It was probably Minwax Wipe on. It was dry to the touch but I wanted to make sure that it was super dry before I re-sanded it. So I set it out in the hot sun to speed things up. When I check the piece an hour later, it looked like the uncured poly had been "sweated" out of the piece. There were hundreds and hundreds of little round sweat-balls.

If there was a 2-part poly, then the OP's idea might work very well.

[Marvin Hasenak]

I tried that process with BLO, I had BLO seeping out of the wood. I do a "urethane soak" by mixing it 50 50 with thinner, I apply a heavy soaking coat. Let it sit for a week or so and then apply the regular poly.

[Kyle Iwamoto]

I'm with Peter on this, the volatiles in the WOP could affect your pricey vacuum pump. Along those lines, the excess poly may not be re-usable.
There are "faster" alternatives, but I also use WOP almost exclusively. 12 coats minimum. Sanding between. YOU have to enjoy the process of the finish. Relish the road you're on to the end.
But if it does help, I'm all supportive for you doing a test run on this. It may work. I'd use a regular shop vac for the vacuum source. I don't think you'd need a "lot" of vacuum for this.
Enjoying the process is untrue. I hate finishing as much as you......

[JohnC Lucas]

I apply from.1.to.4.coats.of.wipe.on poly and simply buff with the Bealle system. I get.a.finish that always gets ciompliments from people. Not sure what your trying to accomplish with the soaking method.

[Sid Matheny]

When I used to turn a lot of pens I used poly in a vacuum pot with soft woods and corn cobs. Worked good but took a long time to dry. Don't remember how long but about a month I think.

[daryl moses]

I've found that if the piece has been sanded properly it will only require 2-3 coats of WOP to achieve a very good finish.
I sand to 600-1000 grit, then "burnish" the piece. It will already have a shine to it before any finish has been applied.
IMO, if it's taking more than 5 coats of finish you are just filling in sanding mistakes.

[Kyle Iwamoto]

I've found that if the piece has been sanded properly it will only require 2-3 coats of WOP to achieve a very good finish.
I sand to 600-1000 grit, then "burnish" the piece. It will already have a shine to it before any finish has been applied.
IMO, if it's taking more than 5 coats of finish you are just filling in sanding mistakes.

I agree with you completely, except sanding mistakes. The coats following 5 are pore filling. 2 - 3 coats gives just that, a very good finish. If you want the entire piece to be shiny without pores, that is what the extra coats are for. Some woods, require less pore filling coats. If a matte finish is desired, I do usually run 2-3 coats. I usually buff to high gloss shine though.

[daryl moses]

I agree with you completely, except sanding mistakes. The coats following 5 are pore filling. 2 - 3 coats gives just that, a very good finish. If you want the entire piece to be shiny without pores, that is what the extra coats are for. Some woods, require less pore filling coats. If a matte finish is desired, I do usually run 2-3 coats. I usually buff to high gloss shine though.
I suppose it depends on the wood species you are working with. I only use native wood that I harvest on my own property. I don't use "tropicals" so I don't have any experience with those. But I do use Black Walnut which is very open pored. I can still get a finish on Black Walnut using my technique which is shiny with no open pores.

[Rob Price]

Or...you can start your finishing with full-strength varnish, applied with a brush. A couple of coats are the equivalent of a half dozen wiped-on coats. Sand to remove nits and brush tip marks. Then switch to wipe-on for the rest of the job.

My vote. Using a foam brush a couple of brushed on coats will go way faster, then 1-2 wiped on coats. I do this on flat work as well.

[roger wiegand]

Perhaps use a catalyzed polyurethane to speed the curing process? Won't be reusable but in a vacuum bag you may not need so much. If the solvents are indeed volatile they should pass through your vacuum pump; it's corrosives like acids that do them in.

[robert baccus]

Yes. Liquid poly,s are solvent based and must have good air circulation to cure.

[Mike King]

It won’t cure in the vacuum bag. So, what are you trying to achieve by putting it in there?

[Dave Bunge]

What about using sanding sealer first?

I don't use wipe on poly very often. Mostly I use Minwax Antique oil, which is an oil/varnish/solvent blend that I wipe on then wipe off excess. But I've found that using sanding sealer greatly reduces the number of coats of AO required to get a good finish.

I use Zinsser Seal coat, which is dewaxed shellac in denatured alcohol, I believe a 2 lb cut. I dilute it 50% with more denatured alcohol. I sand my bowl to 320 grit, apply a coat of the diluted sealer, let it dry and apply a 2nd coat. If there is excess sealer (puddle in bottom of bowl), be sure to wipe it out and not let it dry. Too much shellac on the surface will gum up the sandpaper. Once the 2nd coat is dry, finish sanding and apply coats of Antique Oil.

This works well for me, doesn't change the appearance of the bowl from what I can tell. The sealer is much faster to apply, only takes a couple of hours to dry, and the DNA solvent is much friendlier to use indoors than the mineral spirits in the AO. Those are the reasons I like to use it.

Dave