# Does an oil finish take longer to dry in a humid environment?



## nostrildamus (Feb 24, 2009)

I just applied a coat of Watco Danish Oil (which I believe is an oil/varnish blend), and I'm waiting for it to dry thoroughly before applying shellac.
It's been awfully soggy here in the northeast lately, and I was wondering, do I need to wait longer because of the higher humidity? Or is humidity not a factor with a non-water based finish?
And yes, I'm running a dehumidifier down in the shop!


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## cabinetman (Jul 5, 2007)

nostrildamus said:


> I just applied a coat of Watco Danish Oil (which I believe is an oil/varnish blend), and I'm waiting for it to dry thoroughly before applying shellac.
> It's been awfully soggy here in the northeast lately, and I was wondering, do I need to wait longer because of the higher humidity? Or is humidity not a factor with a non-water based finish?
> And yes, I'm running a dehumidifier down in the shop!



Why would you put shellac over Watco Danish Oil?








 







.


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## nostrildamus (Feb 24, 2009)

I am going to build up the shellac to a high polish, also, for durability. I'm building a harpsichord and this finish is for panels of marquetry, walnut in curly maple. I used a dye first, to highlight the curls, but it's hard to get a glossy finish due to pores in the curly part of the maple. I don't want to fill the pores with anything opaque; shellac ought to work.

The oil was just to add a little extra warmth to the color. Looks good on some test pieces.


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## SeniorSitizen (May 2, 2012)

Do this test and by tomorrow at this time you'll be more knowledgeable about the oil finish and you can more than likely advise us.:laughing:

Just for fun, put about a quarter inch of water in a container that you have a lid for and suspend a throw away brush or cheeeep sponge applicator containing the finish within the container. With one in the container and one at atmosphere, report back so we all will know if one dried more than the other. Inquiring minds would like to know.


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## jigs-n-fixtures (Apr 28, 2012)

Humidity effects how quickly any evaporitive finish dries. 

The air can only hold so many molecules of anything in suspension at a given temperature. Relatively humidity is the percentage of water vapor in suspension, as compared to the maximum the air can hold at that temperature. The lower the relative humidity the more "room" there is for other vapors to fill. And, the more readily other aromatic solvents can evaporate. 

There is a difference between how long it takes the solvent in the Danish oil to evaporate, and how long it takes the oil portion to oxidize. Which can take several weeks, or months. 

That said, the shellac can be applied a few days after the Danish oil.

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## nostrildamus (Feb 24, 2009)

jigs-n-fixtures said:


> Humidity effects how quickly any evaporitive finish dries.
> 
> The air can only hold so many molecules of anything in suspension at a given temperature. Relatively humidity is the percentage of water vapor in suspension, as compared to the maximum the air can hold at that temperature. The lower the relative humidity the more "room" there is for other vapors to fill. And, the more readily other aromatic solvents can evaporate.
> 
> ...


That makes sense, thanks! Oxidation isn't the problem, it's avoiding solvents trapped under the shellac.
BTW Cabinetman, this process was recommended in Flexner's book as the best way to finish curly maple


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## cabinetman (Jul 5, 2007)

nostrildamus said:


> BTW Cabinetman, this process was recommended in Flexner's book as the best way to finish curly maple


Watco can be a stand alone finish needing no topcoat. IMO it's a more durable finish than shellac. 









 







.


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## Steve Neul (Sep 2, 2011)

Humidity effects the drying time of any finish. From where you are I would keep putting the watco finish on and rub it down with a gray scotchbrite pad when dry. I think shellac will adversely affect the color as it gives a amber cast to the finish. If you want to put a chemical coating on it I would use a water clear product.


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## Improv (Aug 13, 2008)

jigs-n-fixtures said:


> Humidity effects how quickly any evaporitive finish dries.


Actually, incorrect. The humidity affects the curing rate of the finish, not the rate the solvent evaporates*. The amount of free volume in the air vs a liquid is tremendous and all the solvent can easily fit into the air.

*The issue at play here is 'partial pressure' which states that its vapor pressure is mitigated by its molar percentage in the condensed state. This results is two key points: (1) If water dissolves in the finish, then it will have an affect on its dry time and (2) As more and more solvent evaporates, it becomes harder and harder to remove the solvent ... think about that one for a while.

Regards,
Steve


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## jigs-n-fixtures (Apr 28, 2012)

I did when I was taking chemistry and physics. But I try not to talk like a chem prof, and I use simplified analogies on news groups. Getting too technical, even if it is highly accurate, frequently alienates other users, and results in them not reading your posts.

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## Improv (Aug 13, 2008)

jigs-n-fixtures said:


> I did when I was taking chemistry and physics. But I try not to talk like a chem prof, and I use simplified analogies on news groups. Getting too technical, even if it is highly accurate, frequently alienates other users, and results in them not reading your posts.
> 
> Sent from my iPhone using Wood Forum


Three sentences is far cry from a technical description. I just added enough terms in a footnote that interested parties can quickly search out information on the subject if it interests them. I just felt your description was so far off base, it required and extremely brief and pointed correction.


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## HowardAcheson (Nov 25, 2011)

As CM states, Watco is a standalone finish that does not require or benefit from a shellac top coat. As far are "building" shellac, be aware that shellac does not respond well the high numbers of applications. Because of its hardness, it will crack and craze. Shellac should only be applied as a thin film.


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## jlintott (May 28, 2012)

*japan drier*

Watco, traditional varnish, linseed oil, tung oil, oil paint :

All of these products harden from the inside-out.
Oxygen in the air must go into the material to achieve a hardened film. 
Metallic Driers are factory mixed into these products, and the driers sort of "kick start" the oxidation process.

Air Humidity slows down the hardening process.
Cold Temperatures can slow it down too.

So what can be done to dry your Watco finish during soggy weather?


Best Solution: 
Turn up the thermostat, get the air moving a little bit.

Other Solution:
Japan Drier is a metallic drier. When all else fails. it may be added in very small amounts to an oil based finish. (home depot has it)

Caution should be used when disposing of any rags used with oil finishes, because heat is created during oxidation. 

I used to soak oily cloths in lye, then machine wash. one time in the clothes dryer, a batch of rags caught fire. 
my wife never knew.
Oh Baby, the troubles i have seen!


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