TruOil not setting up for some reason

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lonepine

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May 7, 2010
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My cousin sent me a box of assorted exotic woods to use for making handles. I know that some of them can be quite oily and I've been wiping them down with alcohol before gluing them to a knife tang. I've used four of the various woods and two of them accepted a finish of TruOil, but on two others it seems like the TruOil either will not harden or is hardening extrreeeeeemly slow. Why is this happening? Has this happened to anyone else? Is there a solution to it?

I thought that perhaps the oil in the wood was interfering with the TruOil so I wiped the finished scales with alcohol also to remove surface oils and let the TruOil do its thing. It didn't seem to help.

One of the troublesome woods is Pau Ferro.

According to Wikipedia
"Pao ferro" or "pau ferro" (Caesalpinia ferrea or Machaerium scleroxylum Tul.) is an exotic tree found in Brazil and Bolivia... It is also known by the names morado, palo santos, caviuna, Brazilian ironwood, and Bolivian rosewood, though it is not actually rosewood.
Pao ferro,... is a strong sensitizer capable of causing acute outbreaks of allergic and irritant dermatitis in workers not previously exposed to it. This, however, has not prevented furniture factories from using the product. Apparently, most workers develop tolerance to the wood. The allergen is (R)-3,4-dimethoxydalbergion, a strong skin sensitizer.

LonePine
AKA Paul Meske, Wisconsin
 
Two things here.
One is that woods like cocobola, rosewoods, ebony, and ironwood don't take oils well. The finish may not absorb right.
Second, tru-oil needs to be rubbed in and the excess wiped off ( IIRC). Leaving on a thicker layer will lead to a sticky and non-drying surface. The woods mentioned don't absorb the oils from the finish, so it sits on the surface and becomes tacky, but never quite dries hard.
Another source of poor hardening is humidity.
The woodworking pros use several tricks to deal with difficult woods and high humidity. Thinning the finish and adding driers are common.
 
Here are some additional comments.

You may need to try liberal amounts of acetone instead of rubbing alcohol to dry the wood.

How much time are you giving the Tru-oil to dry? On walnut gunstocks I allow to dry a minimum of 2 days between coats. After the final coat I will let them dry for 2 weeks.

You can speed up the drying time if you expose Tru-oil to UV light--sunlight, or a grow-bulb for plants.

Finally, how thick of a coat are you applying? I finish bare wood to 400 grit, then rub in the Tru-oil either by hand, or with 0000 steel wool. For a typical knife handle I might use 2-4 drops the size of a pencil eraser. You are better off applying several thin coats than a thick layer.
 
You might have a old bottle of tru oil. The stuff does not keep forever. It has hardeners in it that will harden in the bottle leaving behind the "oil" with not enough hardner. So if your bottle has a thick crust/skin on the liquid that would be most of your hardner and it is time for a new bottle.
Cheers Ron.
 
Wow! Thanks for the feedback.

Quote "Second, tru-oil needs to be rubbed in and the excess wiped off ( IIRC). Leaving on a thicker layer will lead to a sticky and non-drying surface. The woods mentioned don't absorb the oils from the finish, so it sits on the surface and becomes tacky, but never quite dries hard."

And,
Quote: "Finally, how thick of a coat are you applying? I finish bare wood to 400 grit, then rub in the Tru-oil either by hand, or with 0000 steel wool. For a typical knife handle I might use 2-4 drops the size of a pencil eraser. You are better off applying several thin coats than a thick layer."

I didn't apply any more than I had done on other handles but I will try putting very light coats on in the future.


Quote: "Thinning the finish and adding driers are common."

What is used to thin TruOil? What is used as a drier (or hardener)?


Quote: "How much time are you giving the Tru-oil to dry? On walnut gunstocks I allow to dry a minimum of 2 days between coats. After the final coat I will let them dry for 2 weeks."

NORMALLY handles cure enough over eight hours that I can sand is lightly for another coat. Two days seems an extremely long time but I'm certain you get great results with it.


Quote: "You might have a old bottle of truoil. The stuff does not keep forever."

I bought this bottle of finish this spring and don't leave the top off any more than I have to. I've used it on over a dozen handles, most recently last night, and the finish was hard to the touch this morning though I'm certain it will continue to cure and harden as NStricker implies.

When I opened the bottle I didn't remove the entire safety seal. rather I made a hole about the size of pencil to wet my finger with. Three reasons for this, one is that if I were to accidentally tip it over there would be a smaller hole to spill from. Second is to restrict the amount of air that can get in it to dry it out, and third is that I don't use but a wet finger tip worth of it at a time and a big opening is just not needed.


Quote: "You may need to try liberal amounts of acetone instead of rubbing alcohol to dry the wood."

I don't have regular acetone on hand but can "borrow" some of my daughter's fingernail polish remover. I think I'll still wipe it down with alcohol in case the polish remover left anything on the surface.


Quote: "You can speed up the drying time if you expose Tru-oil to UV light--sunlight, or a grow-bulb for plants."

I seem to remember reading that somewhere and I placed the two knives outside one day, and though they were still tacky they had seemed to have made progress. I'm gonna put them out again and see what happens.

Great ideas and suggestions. Thanks. Has this happened to others or am I just super "lucky" and "special" to have this happen to me?

LonePine
AKA Paul Meske, Wisconsin
 
If the natural oils in the wood are interfering with the curing of the truoil, then they need to be removed from the surface. Alcohol alone is probably not going to be sufficient to remove the natural oils from the wood surface. You need an "oil-based" solvent. Acetone is pretty "tried and true" for this. Nail polish remover probably does have something else in it besides acetone that you don't want left behind on the wood, and alcohol may not remove it. Other possible degreasing solvents would be toluene, trichloroethane, naptha, lacquer thinner or very light mineral spirits.

I would suggest using acetone or mineral spirits to remove the gummy truoil, degreasing the wood with more solvent, and starting over with the truoil. One thing to beware of, acetone can dissolve some epoxies.

After you degrease, try thinning the first couple coats of truoil with about 50-60% mineral spirits (paint thinner, turpentine)

If you were making furniture, you could apply a seal coat of shellac to the wood and then build the oil finish. But this prevents the development of the chatoyance (shimmer) that is unique to penetrating oil finishes on wood, and shellac is not a very durable base for a finish for a handle on a using knife
 
Mineral spirits will work fine as a thinner. Get the best and purest grade from a paint shop..

I don't use dryers now, but used to use japan dryer. (Lead used to be the standard dryer in paint and varnish, BTW) Metallic compounds are what accelerates the drying. I think zinc has replaced lead, and recall cadmium and cobalt as being used ,too.

Here is a good gun stock finishing tutorial that should work well on knife handles. It deals with all the issues.
http://www.outdoors.net/site/features/feature.aspx?rn=80919&Forum=Firearms&ArticleCode=3037&V=False
 
UPDATE

I've been putting the knives outside in the sun (and heat!) and it certainly does speed up the curing/hardening process. I've even been able to put a couple more coats of TruOil on but I'm not seeing the "chatoyance (shimmer) that is unique to penetrating oil finishes on wood." (I LOVE that word Mahony)

If I can't get a decent finish curing it in the sun I may yet have to strip them and start over.

Digging around under the workbench looking for a file that disappeared I discovered that I had about a half gallon of mineral spirits and a half-can of Water-Lox. The Water-Lox had a pretty thick skin. I put about a quarter to half a cup of mineral spirits in the can and am hoping that it is still usable. I'm testing it on a piece of oak even as I type. I'm not sure what type of water-lox this is.

Does Water-Lox make a good knife handle finish? Does anyone use it? What's good and bad about it? Are there any "secrets" to getting a good finish with it?

- LonePine
AKA Paul Meske, Wisconsin
 
It isn't the finish type, it is the surface. If you want to get a 3-D finish with chatoyance ( literally -the look of a cat's eye), you don't want a thick finish. It is the light playing on the surface and the difference between the smooth looking, but microscopically lined wood surface and the glassy surface of the finish. The finish must be very clear and dry hard.
Start by wet sanding to fill all pores and grain,that is a must. On each layer, use steel wool to rub the finish off. Repeat many times. Each time you build a minute layer of finish..... with micro scratches. The final result is a rolling band of light across to the surface. It is the principle of a diffraction grating.
 
Huh,... Stacy, you just explained chatoyance exactly opposite of what I thought. I was working with the totally unfounded premise that it was due to a THICK layer of finish and the shimmer was due to refraction through the finish (like a spoon appearing to bend in a glass of water). Exactly how this worked out in my special personal reality was a mystery to me, but heck, as long as it looks good I didn't care.

LonePine
AKA Paul Meske
 
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