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I've recently built a standing desk out of sandply with a mahogany veneer.

I have stained it, and 2 weeks ago added a polyurethane clear coat to protect the stain. However, after doing this, the desk is slightly tacky, and things don't slide very well on it. What can I do to reduce this "stickiness"?

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3 Answers

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The poly simply needs to cure for a while. Even after it "dries" and is safe to work on, the solvents that keep the polymers in suspension aren't all gone; they'll continue to evaporate, and the clear coat will fully harden in time. Check the can for your particular product; it should have a full cure time. It could take up to a month if you laid on a really thick coat and it's humid in your area.

Contrary to intuition, you can wax furniture that has a poly coat, much like you can wax a car that has a clearcoat. Just pick up a can of Minwax, apply and buff, then let dry overnight. This additional protective coating will be temporary, but hard, water-repellent and slick.

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I finished the desk about two weeks ago. –  Malfist Aug 5 '11 at 15:42
    
If it's been humid or you put on a thick coat or the poly wasn't well mixed, that still might not be enough time. –  Alex Feinman Aug 5 '11 at 15:45
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Then I would try the wax. You may also try sanding the poly with an ultra-fine-grit paper (320 or finer), then painting on a second coat. Tack-rag the surface after sanding before putting on the second coat. –  KeithS Aug 5 '11 at 15:46
    
I did put on a thick coat. How often would I have to wax it? –  Malfist Aug 5 '11 at 15:48
    
Depends on how often you used it and how much contact and friction the surfaces see. The top surface will need waxing more often, and special attention paid to the front of the desk. If you had only waxed it, I'd say about once a year, but since you have a poly undercoat you should be able to let it go longer. –  KeithS Aug 5 '11 at 15:57
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Oil based polyurethane "dries" in two stages. First the solvents evaporate leaving the resin behind. This normally takes on the order of hours, but as others have mentioned it depends on the temperature, humidity, and thickness of the finish. When the solvent has evaporated the finish will still be sticky. The second stage of drying is cross-linking, where the molecules react in the presence of oxygen to bond with one another. Cross-linking is what makes polyurethane finishes more durable than other finishes. It takes a little longer, but it should not take weeks if the finish was good and properly mixed.

I don't think you have much to lose by trying to seal it with shellac, or even wax, but if that doesn't work then you are left with stripping or sanding back to the wood and refinishing - or put a sheet of glass over it.

Checklist for the refinishing:

  • Is the polyurethane compatible with earlier stain?
  • Are the temperature and humidity within the recommendations?
  • Is it a new can of finish? (check the expiration date before you buy)
  • Stir the can of finish well.
  • Use multiple thin coats instead of one heavy coat.
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Poly has a naturally rubbery texture especially if you have a thick coat. You might try sanding with high grit sandpaper to break it up.

Alternately you can put another layer of finish on--something that dries to a hard coat, like shellac.

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Yea agree - your top coat need to be hard. You might have to apply a 3-5 layers - don't overdo it all at once or you get uneven finish. Patience is a virtue. Layer- wait 30 minutes, next layer.. the more layers the nicer the finish at the end of the day. –  ppumkin Aug 5 '11 at 15:57
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