Best finish: Tung oil, or Spar Varnish?

[MunichTaxi]

Wood refinishing of dash bows: Is Tung oil better than Spar Varnish?
I thought Spar Varnish would stand up better to UV deterioation?

[cbdo]

Tung oil is easier to apply prettily, but varnish is the original finish and you'll need to use it to get the gloss that it originally had. Varnish can be had with pretty good UV protection added. Applying it really well is indeed an art form.l

[psfred]

Spar varnish only. Tung oil will peel of in a couple years, it has essentially NO UV protection. The original finish was catalyzed nitrocellulose laquer. Use laqure thinner to remove the remnants after you use stripper.

Spar varnish is loaded with UV absorbants to protect the resin.

The trick to applying is to thin about 30% with thinner. This allows the coat to flatten properly. Rough each coat with ScochBrite until you have enough on there to sand flat (about 6-8 coats, no less!!!!). When you have a decent thickenss, sand to proper flatness with fine sandpaper between each coat until you have prefect flatness. This is easier to do than to describe, but what you want to do is sand off only the high spots, never removing all the finish. Each successive coat will fill in the "valleys" you leave until you get it completely flat.

Once flat, apply two or three more coats using only scotchbrite between. After the final coat (you want a total of 14 or so to duplicate the original thickenss and to protect the wood from fading), rub down to a completely flat finish with fine scotchbrite or 4F pumice poweder. Be careful not to gouge any spots out of flat, you only want to get it full matte. This removes uneveness, dust specs, cat hairs, etc.

Then rub up to whatever level of gloss you want with rottenstone or automotive polish and rubbing compound. I stopped just short of glossy because I don't want bright reflections off of it, and I think supergloss finish in a car doesn't look right. You can polish right up to mirror gloss if you want, and it will be perfect, no dust specs, no hairs, etc.

Finish off with a couple coats of plain carnauba wax, and wax again each time you wax the car.

Peter

[300SDog]

Why not use both?

Tung oil penetrates the wood and leaves practically no glossy surface at all. It's often used to restore wood stocks on military surplus WWII rifles where you dont want a high gloss varnish coating. The trick with Tung Oil is that you can rub it and refresh it, but it has no real surface coating and it's the best stuff in the world for treating old wood.

Marine spar varnish is like syrup. It yellows after awhile and is practically unworkable. I think you are better off with ordinary Formby's varnish instead, applied with several coats. I like satin finish better than high gloss, but thats personal preference. Formby's makes good varnish and refinishing products.

Forget about using sandpaper in between coats, #0000 steel wool is better and will not scratch the wood. Tack cloths are also a good idea for picking up dust. These come in packets and are sticky coated. Dust free environment is critical!! The best brush to use is a soft white china bristle or brown ox-hair brush that will leave no brush marks, pluck it for loose bristles first. Using a brush always does a better job at working varnish into the surface than spray cans do, i think.

And you will find your old wood to be very, very thirsty.... important to know if you use stain. When I refinished 220Sb wood trim going into a 190c, I used a helluva lot of linseed oil that penetrated into the back of the wood strips. Those were solid non-veneered wood bits on the 111, they probably could have been dipped and soaked in linseed oil without hurting them - they were bone dry.

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Last edited by 300SDog; 09-18-2004 at 12:32 AM.

[bikis]

I use lacquer for most house-hold wood finish - doors, cabinets, furniture.I don't know how good is UV protection, but here is how I work.First apply couple coats of sanding sealer. After that very light sanding with fine sandpaper.Surface becomes very smooth.Then whipe the dust and as many coats of lacquer as needed. The actual lacquer doesn't sand as good and is not suppose to be sanded.Sanding sealer does the trick.Different than varnishes (because usualy they are oil based), lacquer dries very fast so don't be afraid of dust getting on to the finish. Don't thin lacquer.It will be easier to reach desireable thickness. For big items I use airless sprayer, for small ones and touch ups spray can. It's Valspar brand and I buy it at Vista Paint stores.

[psfred]

The main point to remember is that the trim in the car is going to be exposed to huge amounts of UV radiation, especially the windshield bow (as is usually obvious by the finish degradation by now).

Tung oil wil permit very fast fading of the wood since it is quite thin unless you put on 20 coats or more, and it is NOT protected from UV degradation -- the wood will fade and the finish itself will decompose and peel.

Spar Varnish is indeed a thick, gooey stuff, that's why you need to thin it. The only "primer" you should use is one pound cut shellac, nothing else, or it will not stick, peeling up in a couple years, very ugly (to say nothing of way too much work!). Do not use stearated sandpaper (the non clogging stuff), just plain open coat for the same reason -- the coating on the stearated paper will prevent the varnish from sticking. ditto for "sanding sealers" -- all the woodwork in my house, finished in the late 1950s, is doing this inside, outside it would have peeled decades ago!

Formby's products are fine, just use exterior grade varnish. You will find it to be thick, yellowish, and hard to work with.

Steel wool can leave iron particles embedded in the finish. I prefer the scotchbrite. No visible residue, and it's faster.

Linseed oil will give you much less protection than any varnish, since again it will be a very thin coat. Looks very nice on interior light use objects, but the wood trim in the car needs protection from direct sunlight. It also takes months to properly polymerize, and slowly evaporates and needs to be renewed regularly. I suspect you will notice this over a couple years. Not considered a permanent finish in my mind, unless constantly applied. I also don't know how well varnish will stick to it on car trim -- one of the advanages of Marine varnish is that it is formulated for exposure to outside sunlight, inlcuding heat effects.

You certainly can spray appropriately thinned spar varnish, but brushing works just as well if you rub it out, as you should.

The point in sanding is to flatten the finish out. This eliminates the "ripple" effect from uneven coats of finish, variability in the actual wood surface, etc. A nice hardwood sanding block will render the surface dead flat, rubbing out the finish will make it then dead flat and flawless.

To look anywhere near factory, the finish must be very thick, and semigloss, I've seen new wood. Looks almost like plastic.

Peter

[300SDog]

And the point of using linseed oil is not to provide a surface coat to the wood at all. Try some on the dried out bare wood backs and it will penetrate and disappear.

Nobody applies "coats" of linseed oil and/or tung oil, expecting some kind of thick surface finish shell. You just wipe the stuff on with a rag and it penetrates into the wood, doing what varnish wont do to help preserve the wood.

Tung oil first, then high quality Formby varnish full strength is my recommendation. Exterior grade spar varnish syrup thinned to smitherines sounds ridiculous. And forget about "MB specs" in this case. It's one occasion where the home craftsman can do a better job than what the factory does.

[bikis]

Be carefull with linseed oil.Don't leave a rag that is soaked in linseed oil.It will catch on fire by itself.I know two cases when that happened.

[Arthur Dalton]

Originally Posted by bikis

Be carefull with linseed oil.Don't leave a rag that is soaked in linseed oil.It will catch on fire by itself.I know two cases when that happened.

Spontanious Combustion is the term...just in case you get on Jeopardy .
or stayed at a Holiday Inn last night...

[psfred]

Tung oil is just as bad. Spread any cloth, rag, or paper towel used to apply linseed oil, tung oil, or any other oxidizing liquid finish (including most high quality varnishes) out flat and allow to dry completely before disposing, and only put them in metal trash cans well isolated from flammable materials. I've known several woodworking shops to catch fire from this sort of thing. Not usually a problem at home, since you won't fill a trash can with oily rags, but you never know, and I have no desire to burn down the shop or the house!

Spar varnish is thick and sticky because it is loaded with UV absorbants that don't contribute much to the finish itself. You can overcome that by thinning 20-30% for brushing -- and you will find that if you read the container on just about any good varnish, thinning is recommened for good flattening and even coats. Pretty much standard for as long as I've been around.

Peter