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

  1. #1
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    Vacuum chamber + polyurethane -- a hare-brained idea?

    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

  2. #2
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    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?
    "Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert Heinlein

    "[H]e had at home a lathe, and amused himself by turning napkin rings, with which he filled up his house, with the jealousy of an artist and the egotism of a bourgeois."
    Gustave Flaubert, Madame Bovary

  3. #3
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    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.

  4. #4
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    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.

  5. #5
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    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.

  6. #6
    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.

  7. #7
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    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.

  8. #8
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    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.

  9. #9
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    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......

  10. #10
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    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.

  11. #11
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    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.
    Sid Matheny
    McMinnville, TN

  12. #12
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    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.

  13. #13
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    Quote Originally Posted by daryl moses View Post
    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.

  14. #14
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    Quote Originally Posted by Kyle Iwamoto View Post
    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.

  15. #15
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    Quote Originally Posted by Jamie Buxton View Post
    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.
    Where did I put that?

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