Finishing with Tung Oil

[Sam777]

Hello all,

I think I saw some talk about using Tung oil but I could not find the thread.

I bought a can from Home Depot and last night I saturated (as much as possible with a brush) a piece I made from 1/2 oak. Today the piece is dry. Was I supposed to have mixed this with mineral spirit?

Would polyurethane stick to tung oil, even it is dry? I guess oil doesn't really dry specially on an oak piece?

I would appreciate your comments and advice.

Thank you

Sam

[DWSUDEKUM]

Sam 

I use a lot of tung oil to do my finishes.  The can of "Tung Oil" that you purchased at Home Depot bears little resemblance to the pure tung oil that is available.  The product in the can that you purchased all ready has been thinned and has dryers added.  What I use is the pure tung oil which I get from my local WoodCraft store.  I make a mixture of 70 / 30 Tung Oil to Mineral Spirits.  Tung OIl is one of the few "drying oils"  What it does is penetrate the pores of the wood and get below the surface then when the air hits it the oil starts to congeal.  Most finishes such as Lacquer, Shellac, Polyurethane sit on the top layer of the woods surface where it becomes cured. The Tung Oil because it sits below the surface helps prevent the top coat finish from soaking into the wood.  Most finishes are fine as a top coat on top of Tung Oil.  Please be aware that the rags that you apply the oil with and the rags that you wipe off the excess with should never be left crumpled in a ball as they can spontaneously combust and burn your shop down.  Hope this helped a bit Sam.  Feel free to ask questions if you have more.

 

 

DW

[amazingkevin]

Sam 

I use a lot of tung oil to do my finishes.  The can of "Tung Oil" that you purchased at Home Depot bears little resemblance to the pure tung oil that is available.  The product in the can that you purchased all ready has been thinned and has dryers added.  What I use is the pure tung oil which I get from my local WoodCraft store.  I make a mixture of 70 / 30 Tung Oil to Mineral Spirits.  Tung OIl is one of the few "drying oils"  What it does is penetrate the pores of the wood and get below the surface then when the air hits it the oil starts to congeal.  Most finishes such as Lacquer, Shellac, Polyurethane sit on the top layer of the woods surface where it becomes cured. The Tung Oil because it sits below the surface helps prevent the top coat finish from soaking into the wood.  Most finishes are fine as a top coat on top of Tung Oil.  Please be aware that the rags that you apply the oil with and the rags that you wipe off the excess with should never be left crumpled in a ball as they can spontaneously combust and burn your shop down.  Hope this helped a bit Sam.  Feel free to ask questions if you have more.

 

 

DW

Thanks for the info DW !

[orangeman]

I recently toured a shop that makes furniture. The gentleman uses a 50-50 mixture of pure tung oil/mineral spirits and then adds 20% of Behlen's varnish to the mixture. I haven't tried it yet but intend to do so.

 

bb

[Bill WIlson]

Chances are what you used was actually a blend of oil, varnish (or polyurethane) and thinner.  The oil used in these blends is likely linseed oil and not tung oil, but the differences are somewhat subtle.  Finish manufacturers use descriptions like "Tung Oil Finish" mostly as a marketing tool.  They may be the oil/varnish/thinner blend or they may be simply a thinned wiping varnish.  These products are intended to give the wood a hand rubbed look and feel.  They aren't necessarily intended to achieve a high gloss build, like a straight polyurethane varnish.  If you want a higher build, glossy finish, you can overcoat the "tung oil" finish you used, but let it cure for several days.  The can should have guidelines for how long it needs to cure before applying any topcoat.  If not, a general rule of thumb is to let it dry until it no longer off-gasses any odor.

 

There are differences between oil/varnish/thinner blends and wiping varnish.  The manufacturers confuse the issue by using similar sounding names and descriptions, but the key distinction should be found in the application instructions on the can.  Oil/varnish blends are usually applied, allowed to set for several minutes to soak in, then the excess is wiped off.  Typically no more than a couple coats are recommended because the oil content will keep the finish soft and any build up on the surface, from too many coats will tend to stay gummy.  A wiping varnish (or poly) is applied in thin coats that are left to dry, without wiping off the excess.  You can apply as many coats as you want to get a high build finish.  If a hand rubbed, satin look is desired, then one would usually stop at 2 or 3 coats.  To get a more protective, full build finish, up to 6-8 coats may be required.

 

If, by chance, the oil you applied was actual un-thinned, raw tung oil, the drying time may be significantly longer.  The product should say Pure or 100% Tung Oil, if that is what it is.  If it says "Tung Oil Finish" or something like that, it is likely not tung oil.

 

Hope this helps.

[CharleyL]

The Tung Oil that is available in many stores will dry to the touch in about 24 hours, if there isn't any thick build-up anywhere, but it seems to take weeks to completely dry. When it loses it's distinctive odor, it's finally really dry. I like oil finishes, because they make the visual appearance of the wood grain "Pop", but I have gotten away from Tung oil because I don't like the smell and the long time that it takes for this smell to go away.

 

I now prefer "mixes" of BLO (Boiled Linseed Oil), MS (Mineral Spirits) and POLY (Polyurethane), and usually a mix of about 1/3 of each. This will create a thin and easy to apply finish that dries to the touch in less than 24 hours that has a more pleasing smell, however this smell will still last several days. For thicker coats, I reduce the amount of MS in the mix.

 

Be careful when using BLO and oil finishes. Bunching rags with BLO on them in a pile as they are drying can produce enough heat from this reaction to cause a fire. The drying BLO absorbs oxygen from the air as it dries, which creates a chemical reaction that gives off heat. Always spread rags that have BLO on them so that both sides can release this heat into the air easily so the air cools them and they don't overheat. I used to drape mine over a chain link fence, but now use a better second method, which is to soak them in a pail of water for 24 hours before discarding them. NEVER leave them in your shop after you have used them, and don't go to lunch with one bunched up on the corner of your bench, or your shop might burn down. Other oils and oil type finishes can do this too, but BLO is one of the worst for this.

 

 Charley

Edited March 16, 2016 by CharleyL

[Sam777]

Thank you all for the comments and advice.

I will sure I don't leave any piled up / bunched up rags around. this is scary.

Thanks again.

Sam