Finishing Question: Can I put polyutherane on top of Tung oil?

cacu · 02-23-2004, 10:31 AM

I would like to finish my Eros with Tung oil, but I also want the toughness of polyutherane. So I'm thinking of putting 1 coat of Tung oil and then a few coats of polyutherane on top.

Is there anything wrong with doing this?

The cabinet exterior is of 1/8 pre-veneer mdf which I got from Lowes. It's call Lauan door skin.

ThomasW · 02-23-2004, 10:45 AM

If you want the golden glow of the Tung oil, just use the solvent based poly instead of the water based. The solvent based poly does turn yellow/amber over time.

Dan Wesnor · 02-23-2004, 11:44 AM

Yes - chances are pretty good that the poly already contains either tung oil or linseed oil. If it's a water based poly, wait a week for the oil to thoroughly dry.

cacu · 02-23-2004, 10:53 PM

Dan,
I'm not sure I follow your answer. Yes, I can put poly over tung oil?

Dan Wesnor said:
... chances are pretty good that the poly already contains either tung oil or linseed oil. If it's a water based poly.

This contradicts with what ThomasW said. ThomasW said use solvent for the Tung oil affect. I'm confused.

Dan Wesnor said:
wait a week for the oil to thoroughly dry

This is if I do the Tung oil and poly separately right?

Thanks. Just want to make everything clear before I do it. I've made too many oops on this project already. Don't want any more mistakes.

Allen Ross · 02-23-2004, 11:46 PM

i think dan was reiterating what tom said in that poly has tung oil or linseed oil in it, so if you want that yellow color poly will be all that you need.

But if you really want the tung oil finish, (i personally think is darker then poly) then let it dry for a week and then top coat it with polycrilic poly so it won't color the tung oil that you so desired.

Either way you do it, always test on scrap wood and see what you like.

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Bruce Jackson · 02-24-2004, 12:12 AM

A true oil finish unless mixed with a dryer takes a long time to “dry” (oxidize). The more dryer added the more unstable and volatile the finish becomes. Do not attempt to add or mix chemicals unless you understand what you are creating.

Visit an industrial finisher for detailed information on finishing or stick with suggestions from your retail finish supplier, local hardware, or big box store.

Are you using true tung oil? Tung oil originally was made from the nut of the China Wood tree. Oil based finishes do not dry through evaporation but dry through oxidation. Think of an oil spill on your driveway versus gas spilled. Gas evaporates, oil oxidizes. How long does it take for the oil to “dry” versus how long for the gas?

A true oil finish is designed as a stand alone finish and needs no topcoat since topcoats did not exist when it was first produced centuries ago. The oil finish is a “high” maintenance finish since it eventually oxidizes and is gone. Yearly recoating is required. During the oxidizing process the finish is always tacky and picks up and retains oil, soot, perspiration, and any other airborne particulates. This causes black or dirty looking areas on the wood.

A poly finish is a “cover” over the a stain or the “whitewood” (unfinished wood). Any clear coats that have an oil base, from poly to varnish, will yellow with age as the oil base (solids) oxidizes and yellow.

True clear industrial finishes are refered to as "water-white". If you are staining then the next step is a sealer for leveling purposes. Sand the sealer and apply a topcoat which is the hardest of all the finish steps.

Stains color, sealers level, and topcoats protect.

If you are looking for that "funiture finish" look then many additional steps are required. There are several good books out on the subject. Check with your local library.

ThomasW · 02-24-2004, 12:22 AM

Quote:

ThomasW said use solvent for the Tung oil affect.

No, I said instead of using Tung oil; use the standard solvent based polyurethane. That will get you the effect of Tung oil, with the protection of polyurethane.

Michael.Hoffman · 02-24-2004, 06:57 AM

I think what Dan was communicating is that if you use tung oil and want to coat it with a water based poly, then wait a week for it to dry before coating it with the water based poly. I've had problems with doing it like that before and used the advice of Jeff Jewitt and did the following;

1. tung oil
2. wait until dry and seal with clear shellac
3. wait 48 hours and use water based poly.

If you decide to use oil base poly, then either skip step 2 or do as ThomasW said (which is the easiest) as oil based poly does eventually leave you with an amber hue. Hope this helps you out with some of the confusion.

Mike

cacu · 02-24-2004, 01:39 PM

Thank you all for your inputs. I think will try this procedure as described:

1. tung oil (probably Minwax Tung Oil)
2. wait (1 week) until dry and seal with clear shellac
3. wait 48 hours and use water based poly.

Dan Wesnor · 02-24-2004, 04:14 PM

After putting the first coat of oil on, wait 2 days and sand to 320 grit. The oil may "raise the grain", which makes the wood look and feel a little fuzzy. After sanding, wipe them down with a tack cloth, and decide if you need to re-oil.

Pete Mazz · 02-24-2004, 08:02 PM

I agree that if you really want a poly finish, to just use poly and forget about tung oil and shellac. The finished product will look identical and you'll have a better finished product. Thin the poly down about 10% and use a rag to wipe it on for that hand rubbed finish.

Pete