Varnish question

I had been slowly shaping my Bending Branches Sun Shadow ST over the past year, slimming it an quieting the catch and giving it a better balance. As it was a work in progress I simply used Watco Exterior Oil on it, assumig the I would sand it some more in a week or two.

But the time came to put the oil aside and apply varnish. I had a quart of Helmsman Spar Polyurethane (solvent-based) that was about two years old, and had about 1 inch of headspace on top. When I opened the can and stirred it I found quite a bit of goo at the bottom of the can, which disappeared with several minutes of gentle stirring.

Seemed a bit thick going on, but I used it anyway. It turned out that it WAS too thick, and would not “sheet” after I tipped the surface with the foam brush. Dried ugly with brush marks and heavy runs, but it dried.

After sanding deeply I discarded about a third of the remaining varnish and stirred in turpentine to thin it. I just brushed on a coat, and it is much more acceptable looking. Brush marks are gone, although there may be some runs (Hint: a 250 W HPS lamp is NOT the light source of choice for finishing wood!).

So, tomorrow will tell if I was successful.

Question is: Can solvent-based varnish be resurrected by thinning? Or should I have discarded it and bought fresh?


PS: This is not a work of fine furniture art: Just a canoe paddle.

Contact BB
Give Bending Branches a call. Great folks, always happy to talk to you.


– Last Updated: Sep-24-08 5:31 PM EST –

Jim, I'm gonna defer to Cockney's superior knowledge of these things but, it's possible that your old varnish did begin to polymerize in the can. Being a cheap yankee myself, I've thinned many leftover cans of paint, varnish, etc. over the years with mixed results. I'd recommend letting this one sit for a week to see if if it really hardens like it should. If yes, no harm. If no, you've got a messy refinishing job on your hands! And yes, warm sunlight isn't the place to apply spar varnish either.

Edit: HPS lamp=high-pressure sodium? Residential? Why?

Oil based varnish
can be thinned with Mineral Spirits or Turpentine. For a good article on varnishing look here:

Yes you can revive varnish
with turpentine. If it has lumps or dried chunks in it you can strain it through an old cotton tee shirt. And if it goes on too thick and heavy like yours did you can dip the brush in turpentine and run it over the paddle to flatten the brush marks. I usually sand at least three times to fill in the grain depressions. It is important that the last coat goes on smooth and not heavy if you want a truly high gloss plastic look.

Also I would advise that you let the paddle sit for at least two days and thoroughly dry between sanding, unless you can leave it out in the sunshine which seems to cut drying time to hours instead of days.

Try not to purchase “quarts” …
… if at all possible , unless you need that much for a job. Better to get “pints” , especially for small jobs like paddles . A pint goes a long way , even with three coats , there’s quite a bit left over …

HPS = High Pressure Sodium
In my shop at work, where I occasionally play.


Good article on varnish.
Thanks for the link.

The thick varnish dried OK, and was sndable, so I assume that tomorrow morning I will find a dry, nicely coated paddle. Ready for another (thinned) coat.

N.T. - great idea for overbrushing with turp. It would have saved me a heavy sanding.


McMaster-Carr to the rescue! page 1658

4, 8, 16 oz cans available. Cases of 12.

Mike and Dave, if you guys want I can order a case and we can split it 3 ways or 4 if N.T. wants in. Delivery at Raystown?


No thanks…
I was surprised to find quarts of oil based Cabot spar varnish at the local Lowe’s. I’ve gone through a quart in a month and like the results. It is somewhat slow drying, but worth the wait. They also now have Watco Teak oil. Pretty unusual to find this stuff at Lowe’s.

Does wonders for preserving unused varnish. I’ve had one too many 1/2 full cans of varnish polymerize on me. I especially recommended for tung oil based varnishes that seem to polymerize quicker than I can use them.

That’s been my experience, too
I’ve had really good results with Bloxygen.

No, you really can’t “revive” varnish…
…that’s begun to cure in the can. Varnish doesn’t dry, it cures by combining with oxygen, which is why having air in a varnish container causes it to partially cure. The problem is that cured varnish is chemically different than uncured varnish and is will not dissolve in the same thinners. You can thin it, stir it and disperse the partially cured portion into the rest, but as you found, you end up with a thicker, gloppy varnish that doesn’t flow well. When varnish gets to that point, it’s best to toss it. I hate doing that for several reasons, but it beats having it ruin a finishing job or having to sand it endlessly.

Good news and bad news
Good news is that the thinned varnish did dry overnight. Bad news is that it still didn’t flow properly, and even with the very runny appearance it didn’t tip-out well. Guess I will be chucking it.

The paddle is still quite usable, but all of the other kids will probably point to me and laugh. But then, they already do that.

Live and learn.


Can size?
What is the consensus on size?

16 oz?

8 oz?

I can order either.


Purge the can with an inert gas?
Could you fill the empty area of the can with something other than air to get the oxygen out of the can before sealing it?

We use argon and nitrogen at work, I have no idea what’s available to the average citizen.

How old is your turpentine?
Turpentine may lose some of its potential as a solvent if it’s stored in an oversized container for long periods. These issues involving less-than-fresh finishes really only apply to hobbyists, as any pro would never consider using anything that’s been allowed to sit for long.

Old-Timey painter’s trick
was to take a breath and exhale into the top of the can of oil-based paint before sealing the lid.


Sounds to me like you may have a can of satin varnish which has solids in it that sink to the bottom. These solids are what make the varnish satin. If you stirred it and the goo disappeared, I would suspect there is nothing wrong with the varnish, it’s just not a gloss varnish.

Well, varnishing season
is rapidly ending (temps below 60-65) and I have no other projects on the horizon. I will wait until spring and then buy a new can. ANd decant it into smaller cans.