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  1. #1

    what causes sweating in an oil finish

    Sweating is the clear drops that sometime form after an oil poly finish is applied. Where is sawduster when you need him?
    Last edited by Wisardd1; 03-02-2015 at 1:37 am.
    Charter Member of The Cody Colston WoodWorkers Benevolence Society
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  2. #2
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    Re: what causes sweating in an oil finish

    That's a new one on me ... i haven't experienced that myself.

    Maybe Mark knows?
    Jason Beam
    Sacramento, CA
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  3. #3
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    Re: what causes sweating in an oil finish

    Quote Originally Posted by Beamer View Post
    That's a new one on me ... i haven't experienced that myself.

    Maybe Mark knows?
    I've not experienced it either, but my first though would be contamination of some sort. Got a pic?
    Mark


    "Merely having an open mind is nothing; the object of opening the mind, as of opening the mouth, is to shut it again on something solid." G.K. Chesterton
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  4. #4

    Re: what causes sweating in an oil finish

    From the book "A Craftsman's Guide to Wood Finishing" by Jeffrey Greogory -

    Quote:

    Gloss varnish (finish) which has been rubbed to a dull finish will sometime change back to a greasy gloss and that is called sweating. The most common cause for this to happen is the application of varnish (finish) over under coats which are not sufficiently dry and hard. Sweating may occur over varnish under coats or over color and paint coats which are not (completely) dry. In some cases varnish (finish) will sweat, even when applied to properly dry and hard under coats, if it is rubbed too soon and before it is hard and dry. The long-oil varnishes, those which contain a large proportion of oil (poly oil finishes likely to fall into this category), are much more likely to sweat than short-oil hard-drying varnishes (finishes). The long-oil varnishes are, of course, the most durable type but are not intended for much rubbing. When they are rubbed they should be bone dry and hard. The very best quality finishing varnish is likely to sweat if rubbed as soon as a week or two after application. A much longer time must be allowed before rubbing such varnishes with safety.

    When it becomes necessary to rub finishing varnish of the long-oil type the job should be cleaned up after rubbing and be allowed to stand five to six hours in Summer (or over night in Winter), before another coat is applied. Usually, if sweating is going to occur it will show up in that time. And when sweating does occur allow the job to stand just as long as possible before brushing on the next coat. Also rub it again lightly with a very fine pumice or an old pumice rag before application of the next coat. When a job is so handled that sweating may occur it is well to use another precaution, that of applying the rubbing coats as carefully as finishing coats are put on, as to brushing, and rub as lightly as possible, using plenty of water. In this way the under coats are not cut deeply by the rubbing and a deeper lustre will finish on the job. If this procedire is not followed or if the job is finished too soon the finished too soon the finished surface may be specky or full of brush marks.

    Unquote.

    I know the instructions here is not easily understood, but this is what I gather:
    1. Keep under coats much lighter than the final coat
    2. Do not induce too much friction while rubbing
    3. Give plenty of time between coats to bone-dry and hard level.

    ere is the answer I found provided by my friend SR on another site:
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  5. #5

    Re: what causes sweating in an oil finish

    A friend of mine from another site provided the quote. His name is SR.
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  6. #6
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    Re: what causes sweating in an oil finish

    I've noticed it quite a bit but with Minwax Antique Oil Finish. I've been told that as the oil is absorbed by the wood and it generates heat as it cures. The heat causes the oil to bubble up out of the grain. The solution (At least with MAOF) is to continue to rub the oil out. Usually for about 2 or 3 hours after application and maybe 3 times after the initial rub out.

    A bit of a PITA but final results make it well worth it.

    Normally this happens only on the first coat.
    Rich
    Huntington Beach, California

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