natural oil finish not curing properly


woodwright

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I've started using Sam Maloof's natural oil finishing mixture and have noticed white chaulk-like splotches here and there when I use it on walnut.  I use a homemade mixture of 1/3 pure tung, 1/3 boiled linseed and 1/3 spar urethane varnish for the first few coats and then 1/3 tung and 1/3 linseen plus some beeswax for the second few coats.   I sand up to 400 grit before I apply the finish and I wait a day in-between each coat.  I apply all coats liberally, let each coat sit few minutes, and then wipe off thoroughly before setting aside to dry.

 

When completed the pieces look real nice with a very smooth soft buttery feel.  But after a few weeks I notice that when viewed from a slight angle there are grayish-white chaulky looking spots here and there and the finish no longer looks uniform. 

 

What could be happening?  Any thoughts would be appreciated.

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Mike, thanks for the response. 

 

I've attached a photo for you to look at.  (It's not the best close-up photo but it captured the splotches OK.  The wood surface, by the way, although it looks grainy and rough in the photo, is extremely smooth.)  Your explanation sounds totally plausible.  It's definitely a curing issue.  Here's a related question.  Is it always best to wait until the previous coat of oil is thoroughly dry before applying the next coat?  I mean should it be bone dry or just 24 hours dry?  I wait 24 hours at which point the surface feels dry but with finger pressure still obviously not bone dry as oily fingerprints are detectable.  But I've been reapplying after 24 hours regardless. And should I be wiping off each new oil coat a couple times during that 24 hour drying period to make sure any oily film that rises to the surface keeps getting removed?

 

 

 

post-15559-0-30061900-1415375376_thumb.j

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It needs to feel dry to the touch before adding another coat.  It doesn't have to be fully cured...that takes days to weeks, depending on the finish, but it has to feel dry or you'll have problems.  If it's even the slightest bit tacky, hold off for a while.  Using a large ratio of oil in any finish is going to dramatically slow the drying and curing process.

 

My guess is that either you didn't wait long enough between coats, or the wax is causing the problem.  Never really understood why people feel the need to melt wax into finish.  Wax after the finish is cured if you just have to have wax.  I don't find it that great.  Maybe it's just me.

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Oil over varnish will slow curing for all of them. Oil alone is not durable and oil over varnish serves no purpose. I could give you a longer answer but there are books on finishing that explain better than I can. My recommendation is to use a strong solvent to remove all the oil and wax back to varnish, lightly sand and apply more varnish. I agree with Mike that a light coat of oil going down first is all you want then apply your film finish of choice (varnish, poly, shellac, lacquer). Usually if I use oil, I only topcoat with wax. I rarely use oil under a film finish anymore except for oil/shellac.

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I use spar mixed with BLO and mineral spirits quite a bit for outdoor stuff, I tend to give it 2-3 days between coats especially if it's cool or damp. but truly, if the piece is going to be indoors or otherwise not subject to wide climate changes then there's no reason to use spar at all. it tends to take longer to cure and doesn't harden the same way regular poly hardens.  that said if given enough time it will cure great and I would guess the same as Eric that the problem you're having may be with the wax.  arm r seal looks great on walnut, IMO no need to complicate it any  more than that.

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Thanks for all your responses.  This has been a good education in short order. I figured maybe the beeswax was the culprit but wasn't sure.  Looks like that's been confirmed.  Also, I've heard many good things about Arm R Seal so I think it's time I try it.  Looks like it's time to ditch the spar varnish and wax and do some experimenting.

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