Sanding Sealer under Spar Varnish? - Woodworking Talk - Woodworkers Forum
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post #1 of 16 Old 04-10-2017, 09:59 AM Thread Starter
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Sanding Sealer under Spar Varnish?

I'm working on a project with quilted maple and plan to use Epifanes Spar Varnish as the finish. I'm thinning the varnish for spray and it lays down beautifully, but because the quilted maple is a mix of hard and soft grain, the varnish leaves a lot of uneven spots where the varnish gets absorbed unevenly and of course dries unevenly. I'd like to avoid too much sanding of these early coats because the quilted maple is dyed and I don't want to accidentally remove any dye. Does anyone think it's a bad idea to build up a couple of coats of shellac prior to starting the varnish coats.

Any thoughts?
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post #2 of 16 Old 04-10-2017, 12:37 PM
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A couple coats wouldn't hurt anything, and it probably will help
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post #3 of 16 Old 04-10-2017, 03:30 PM
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Quote:
Originally Posted by Quickstep View Post
I'm working on a project with quilted maple and plan to use Epifanes Spar Varnish as the finish. I'm thinning the varnish for spray and it lays down beautifully, but because the quilted maple is a mix of hard and soft grain, the varnish leaves a lot of uneven spots where the varnish gets absorbed unevenly and of course dries unevenly. I'd like to avoid too much sanding of these early coats because the quilted maple is dyed and I don't want to accidentally remove any dye. Does anyone think it's a bad idea to build up a couple of coats of shellac prior to starting the varnish coats.

Any thoughts?
You can apply a coat of varnish, wait until its tacky then apply another coat without sanding in between coats. After you apply the 2nd coat, sand lightly with 320 grit, then apply the 3rd coat. After that if you need another coat, you can sand with 240 and apply another coat.

From my experience, you can get a good build with only 3 coats on maple.
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post #4 of 16 Old 04-10-2017, 10:20 PM
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I wouldn't use a sanding sealer with a spar. I would just thin the first coat so it penetrates better and then use only the spar full thickness. A spar receives a lot of abuse from the elements and the sealer would just weaken it.
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post #5 of 16 Old 04-11-2017, 07:28 AM Thread Starter
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Steve,

The item in question won't be outside, in fact, it's a banjo, so the only abuse to suffered will be by the people who have to listen to me play. Does that change your opinion on using the sanding sealer?

Also, if using thinned varnish for the first coat, would you do just a light coat for the first coat and let it pretty much all get absorbed?
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post #6 of 16 Old 04-11-2017, 07:40 AM
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A spar varnish won't wear very good for a banjo, even Epifanes. A spar is an exterior finish deliberately made soft so it can expand and contract with the weather. For what you are doing it would be better to use an oil based polyurethane. It's a much harder finish. That is why someone has a deck on a boat with a wood finish they insist on you wearing very soft sole shoes.
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post #7 of 16 Old 04-11-2017, 07:51 AM Thread Starter
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Some luthiers worked with Epifanes to develop a formula suitable for musical instruments. Epifanes makes an additive that turns it in to a hard short oil varnish and these guys worked out ratios that make it dry hard. It looks great; much warmer than lacquer.
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post #8 of 16 Old 04-11-2017, 08:42 AM
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Originally Posted by Quickstep View Post
Steve,

The item in question won't be outside, in fact, it's a banjo, so the only abuse to suffered will be by the people who have to listen to me play. Does that change your opinion on using the sanding sealer?

Also, if using thinned varnish for the first coat, would you do just a light coat for the first coat and let it pretty much all get absorbed?
LOL!

Regardless of the use, you never want to put a softer finish under a harder finish. Eventually, it will crack.

If its going on an instrument, you can simply use a vinyl sealer and a couple of coats of lacquer and be ok. Gibson and Fender guitar uses lacquer coats on their guitars.

Matching colors on different substrates is easy. All it takes is patience and beer.

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post #9 of 16 Old 04-12-2017, 11:42 AM Thread Starter
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LOL!

Regardless of the use, you never want to put a softer finish under a harder finish. Eventually, it will crack.

If its going on an instrument, you can simply use a vinyl sealer and a couple of coats of lacquer and be ok. Gibson and Fender guitar uses lacquer coats on their guitars.

So, are you saying the shellac is the softer finish? I've heard of guys who use shellac under lacquer. Would you expect that to cause problems?
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post #10 of 16 Old 04-12-2017, 02:20 PM
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So, are you saying the shellac is the softer finish? I've heard of guys who use shellac under lacquer. Would you expect that to cause problems?
In your first post you were asking about applying shellac under a spar varnish. In that case, the shellac is softer than the spar varnish and would fail in less than a year if used out in the elements. Shellac < Spar Varnish

Since you later stated that it would be indoors, you can apply a shellac finish under a lacquer finish with no problems at all. Shellac > NC Lacquer If your finishing a banjo, you can use shellac or a vinyl sealer (2 coats), then simply apply lacquer coats to obtain the build you are looking for.

Gibson and Fender apply 2 sealer coats of a vinyl sealer, then apply up to 5 coats of lacquer, then sand and buff to the final sheen and look.
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post #11 of 16 Old 04-13-2017, 04:10 PM Thread Starter
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Thanks for the info. Of the two, I would have expected the varnish to be softer than shellac.
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post #12 of 16 Old 04-13-2017, 11:44 PM
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Thanks for the info. Of the two, I would have expected the varnish to be softer than shellac.
Spar varnish is often used on items that will be near or on the water, like a wood boat, decks, beach chairs, etc. Shellac will break down when exposed to water. So if you apply shellac then a spar varnish over it, and the piece is exposed to water or high humidity, the shellac will start to break down and cause the entire finish to fail. Where as if you used a spar varnish only in multiple coats, the finish will last longer when exposed to water, etc. Thats one way to look at it.
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post #13 of 16 Old 04-14-2017, 01:02 AM
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I think we should point out that varnish is different from polyurethane and anyone else reading this should be warned that polyurethane won't adhere to shellac where varnish will. For polyurethane a de-waxed shellac such as Zinsser Sealcoat should be used. Shellac has a natural wax which Sealcoat is refined more and has had this wax filtered out.
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post #14 of 16 Old 04-15-2017, 12:06 PM Thread Starter
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I think we should point out that varnish is different from polyurethane and anyone else reading this should be warned that polyurethane won't adhere to shellac where varnish will. For polyurethane a de-waxed shellac such as Zinsser Sealcoat should be used. Shellac has a natural wax which Sealcoat is refined more and has had this wax filtered out.

Interesting... I've never used "waxy" shellac, only seal coat or shellac mixed from dewaxed flakes. Just what is "waxy" shellac used for?

Going back to my original post: Is using dewaxed shellac as a sealer under spar vanish in an inside application an OK idea?
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post #15 of 16 Old 04-15-2017, 12:45 PM
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Interesting... I've never used "waxy" shellac, only seal coat or shellac mixed from dewaxed flakes. Just what is "waxy" shellac used for?

Going back to my original post: Is using dewaxed shellac as a sealer under spar vanish in an inside application an OK idea?
Shellac is a natural product which is produced from a lac bug. As is, it has a natural wax content. In the old days when painters finished knotty pine paneling they sealed the knots first with shellac so the sap wouldn't bleed through as bad and finished the walls with varnish. Then when polyurethane was developed they discovered it would not adhere to shellac so the manufacturers of shellac came up with a way to filter the wax out of the shellac which became Sealcoat. Without the wax content polyurethane would adhere.
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post #16 of 16 Old 04-15-2017, 02:43 PM
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Interesting... I've never used "waxy" shellac, only seal coat or shellac mixed from dewaxed flakes. Just what is "waxy" shellac used for?



Going back to my original post: Is using dewaxed shellac as a sealer under spar vanish in an inside application an OK idea?


"Waxy" shellac is used as a finish with nothing else being applied on top. I love using shellac, but not zinser shellac, I mix my own and not always flakes, you can also get raw shellac and button shellac (which is far more durable). Shellac is very forgiving and easy to use, it can be wiped on with rag, brushed on, foam brushed or sprayed. The pound cut isn't even that important. If it's too thick you notice when putting it on and add more alcohol, if it's too thin, you just apply more coats. You can also buy shellac in far more shades then amber and Garnett, it comes in shades from very clear to ruby red to black. It doesn't stink and dries fast.

Four years ago, as an experiment, I used button shellac on hard wood floors in my daughters small house. She has a dog, a cat, a husband and now a toddler. It has held up very well, but my daughter wanted to rejuvenate the floor so I mixed her up some button shellac just this week. Last night, with little more effort than washing the floor, she was able to wipe on a fresh coat and it looks great, no sanding, no sealing, no stripping, just wash the floor and wipe on a coat of shellac. Did the kitchen and living room in just a few hours.
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