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Tung oil plus...?

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May 8, 2019
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Two years ago I got a fair amount of Tung oil for next to nothing. According to the label, the stuff is pure 100% Tung and it looks, feels and smells as such.
I use it for my turned objects, but I have an outdoor project coming up. Last year a treated an oak plank twice with this oil (drying 10 days between first and second time).
This autumn the wood is still water repellant but black with mold.
My question: Can anyone here suggest an additive the will keep mold ect. at bay?

TIA, Lars
 
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Hi Lars, can't address the mold exactly (other than suggesting it may be a type of algae, too, like what you might see on the shady side if house roofs sometimes), but was that oak plank project in a shady location? Algae tends to grow on surfaces that have airborne organic dust settling, the moisture is right, and the sun shines directly on it very little. Like a north facing rooftop. The look is dark gray toward black. Mold would make me think more of a rot condition. Either way, the surface can be cleaned off with a simple soap and water solution, rinsing well. You could pre-treat with a mild bleach/water solution, but the internet has many differing statements about bleach products and wood. Either way, do some research, and you may need to be diligent about keeping those surfaces clean. The only other thing I can think of is some sort of zinc additive. Shingle manufacturers are applying zinc formulas right into roof shingles now to help them resist microbial growth. Zinc coated metal products on the surface of a roof (pipes, vents, etc) will always leave clean stripes down the surface of the roof if the rest of the roof has a gray surface film discoloring the shingles. Rain washes minuscule amounts of zinc down the roof, preventing the microbial growth.

As for pure tung oil outside, I would steer you toward a name brand, oil-based spar varnish rather than the pure tung oil. Spar marine varnish would be the best- if it's good for boats, it'll be good for your project. Best of luck.

Steve.
 
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Elsewhere on this forum it was suggested I use citric acid to eliminate mold on wet maple blanks I was drying. I made a solution of citric acid and water which I sprayed on the blanks to great effect. It’s been over a month I believe, and no mold has returned. I don’t know how it would work as an additive with tung oil, and how very long term it would perform, but in the relative short run it has solved my problem.
 

Roger Wiegand

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paint stores sell a mildew preventive additive. It would probably work in tung oil. I used it on a polyurethaned screen porch bead board ceiling and it has stayed mildew free for several years now where nearby surfaces have not.
 
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paint stores sell a mildew preventive additive. It would probably work in tung oil. I used it on a polyurethaned screen porch bead board ceiling and it has stayed mildew free for several years now where nearby surfaces have not.

Generally NOT for use on anything that may contact food.

Look at the ingredients.

Stu
 
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As for pure tung oil outside, I would steer you toward a name brand, oil-based spar varnish rather than the pure tung oil. Spar marine varnish would be the best- if it's good for boats, it'll be good for your project.
The last brand of pure tung oil I purchased was Corey's from the Skin Boat Store, where they sell it for treating skin shelled sea kayaks. Apparently, it's pretty water tolerant, at least in the version with pine resin included.
 
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Cupric Oxide or Copper Sulfate.

Both are used in multiple scenarios - from poured lab flooring which MUST be anti microbial, to preventing mold on plants. Mold is a plant. Now - as to how much to use per gallon of Tung oil...not sure how to recommend...I know it is water soluble but I do not know about how to integrate it in Tung oil. My guess would be that if you are going to thin the tung oil, you would add the CU to the thinner - and allow a few days for it to dissolve - if it will...intot he thinner - then add the thinner as usual, screening out any solids.
 
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Lars, if you discover the solution, please give an update down the road.

Good luck,
Steve.
 

Roger Wiegand

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Generally NOT for use on anything that may contact food.

Look at the ingredients.

Stu

I guess I assumed he wasn't eating off his outdoor project. Be assured I don't eat off my ceiling boards. I think that maybe if you have mildew on your eating and serving ware you might want to wash it more often.
 
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Dec 19, 2018
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You might try methanol(wood alcohol). Rubbing al, denatured, isopropyl, etc won't work. Other solvents like mineral spirits, ketones also won't work. You will probably get a ver low concentration, but that may be sufficient. I would dissolve as much as possible in some methanol, and then try to blend into some of your finish.
 
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