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I built a walnut shelf and finished it with 100%, grade A, straight from the nut, tung oil. I used just a single coat and was happy with the way it finished so ended things there.

That being said, I continued to take a clean rag to the shelf to wipe down the shelf and continued to be able to get a little oil on the rag up to ~4 or 5 days after oiling the board.

For a next project, I'm going to use the last bit of scrap walnut to make coasters.

Because of the expected abuse they'll take being coasters, I'm thinking it would be a good idea to apply multiple coats of tung oil.

The question is, when to apply subsequent coats? Am I right in assuming I should continue to wipe down the wood and then apply a subsequent coat only after the previous no longer leaves the rag brown?

  • Possible duplicate: woodworking.stackexchange.com/q/573/1646 - certainly lots of relevant looking information (not all of it consistent). I do wonder if it would be worth using a first coat of tung-oil + solvent to encourage it deep into the wood. (Would take longer for the solvent to evaporate and the oil to cure of course). – Martin Bonner supports Monica Jul 6 '18 at 8:38
  • My 2c is you'd be much better off not using tung oil for your coasters in the first place as there are much more waterproof choices available, every one of which dries more reliably and much faster than tung oil. But assuming you'll go ahead anyway, or just for the next time you want to use tung oil, many application guides suggest you lightly sand the wood surface prior to applying each subsequent coat after a nominal 'drying' time. – Graphus Jul 6 '18 at 14:00
  • @MartinBonner, different experiments have given different results about this but for all practical purposes diluting an oil doesn't actually increase penetration except possibly in end grain. There can be a minor improvement in long-grain absorption, but it's on the order of fractions of a mm, too little difference for almost all users to care about. As with varnish dilution actually speeds 'drying' time because less oil is deposited on the wood, and a thinner coat will always dry more quickly than a thicker one. – Graphus Jul 6 '18 at 14:06
  • @Graphus : Very interesting! Thank you. My comment about "drying" time was assuming that the thinner liquid might penetrate 2-4x deeper, when the time for solvent to diffuse out, and for oxygen to diffuse in would be significantly increased. – Martin Bonner supports Monica Jul 6 '18 at 14:12
  • @Graphus my technique for the shelf was to apply a thick coat, sand right away (created a little paste-like substance), and then push that around and wipe it off. Maybe that elongated the dry time? The only other thing I have on hand is some clear shellac. – user4781 Jul 6 '18 at 16:49

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