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Hi There.

I am a amateur builder from the U.K and have frequently used this forum for when I have had problems with a build and 99.9% of the time I have found the answer.

My current dilemma has to do with the finishing of guitar #5.

I wanted to use something which would give a harder finish than my previous french polished guitars. I decided to try Behlens ww spar restoration varnish.

I prepared the seal coat as per their instruction, applied the seal coat to the Indian rosewood back, sides and mahogany neck and waited for it to cure. I waited and waited and after 3 days the thing was still tacky. Worse still i notice through the sound hole the varnish had actually soaked through to the other side leaving blotchy spots on the inside of the back (not the sides though).

I proceeded to remove the finish as best i could, hours of scraping and sanding later i though i had done it. My reason for removing was from a strong sense that it was never going to cure.

Now to my question?

When I sand the back and sides the silicon carbide paper i use gums up as if it still has finish on it.

Could it be because the varnish has penetrated through to the other side this means there is varnish still in the pores of the wood?

It has been over a week since I removed the seal coat and further sanding is reaching the same result (gummed up paper).

Has any one had an experience like this and should i wait before going a different finishing route? (Thinking exterior grade french polish).

I Thought i may have used to much white spirit in thinning the varnish down so I brushed some varnish neat on some scrap and that took 24 hours to cure at room temperature not the stated 4 on the can.


Many thanks to any one who has taken the time to read this, as for a first post I have gone on a bit.

Regards.

Glenn.

The natural Oils in the Rosewood are preventing the varnish from drying. I once tried Behlens Rockhard straight on to Indian Rosewood and although it did appreciably slow down the drying I did get it to harden by placing it in a UV cabinet. Subsequent coats were fine. You really need a barrier coat of something like shellac, then put on Varnish coats.
I have my doubts that the spots on the inside are due to the varnish. If so it has gone a long way through the wood to cause that. Given that I can't get Dye to penetrate wood deeper than 0.3 mm's I think it highly unlikely.
I think your best course of action is to place the Guitar in natural light (window is fine) but NOT in direct sunlight. Give it a week and then sand a little. Some Varnishes will gum up even when it is truly dry, which is why we tend to wet sand.

Glenn,
Welcome! Sorry your first post has to be related to a problem. I've finished with varnishes over rosewood, mahogany, maple, walnut and ebony without any of the issues you describe. My first step has always been to apply a seal coat of wax-free shellac. I've heard of it being difficult to get a finish completely removed, but never that it was impossible. I would do as Michael suggests and let things sit as they are for a good long time--perhaps a couple of weeks--and then give it another try.

Good luck!

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George :-)

Thank you both for the good advice.

I guess i was asking for trouble by not practicing on scrap first.

I shall let it sit for a couple of weeks and see what happens.

Regards.

Glenn.

Another thought: I've never used the Behlens spar varnish, but some varnishes dry more thoroughly with air circulation. In addition to the natural light as Michael recommends, you may want to set up a fan to waft over the surface of the guitar as well. Maybe it will help.

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George :-)

I had similar results when I was testing with Tru-Oil, which is a wiping varnish. It wouldn't dry without a seal coat of either the Birchwood Casey sealer or a coat of shellac. Once the wood is sealed though, no problems. You might try wiping down the guitar with mineral spirits to remove the gunk, then let it dry, and seal with shellac. That process worked with the Tru-Oil.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Hi All.

If i may post an update to my progress with said problem above.

First of all I had left the guitar to sit for a couple of weeks as advised and began finish prep as before. I have decided instead of sticking with the varnish I instead reverted back to a Shellac based finish (exterior french polish).

I have finished the back and sides with said french polish and now i have a problem with the filled grain (I used a thixotropic grain filler) pushing through the surface leaving the finish bumpy like a frogs back. I have leveled the bumps and and reapplied polish and couple of times only for the grain to push up through. Its not actually braking through the finish, it's more like it is pushing it up.

I suspect there is still varnish in the pores which is seeping out.

I would like to be able to post a photo but it is impossible to capture with a camera.


I have attached a photo of the inside of the sound hole to which i refereed to in the original post that the oil had penetrated through to the other side.

Please if any one can offer an explanation to what is happening I would be most grateful.

Regards.

Glenn

Drying oils can have low molecular weight fractions that penetrate quite far. I've seen maple ribs of old violins that were wet down with linseed oil where the oil had gone right through a millimeter of wood. Rosewood has larger pores, some of which probably go through, and those were probably the conduit for the varnish.

Some oil varnishes do dry slowly on tropical woods. Often, as has been said, UV light will speed things up. So long as you can get that first coat to cure, the rest will be fine, but don't re-coat over a soft first coat. The upper layers may cure fine, but the first one won't, and, at some point, the whole thing, or parts of it, could peel like a bad sunburn.

I have not tried the Behlen's water white varnish. I used their 'Rock hard' varnish for years, until they stopped making it. Now I'm in the throes of finish trials to find a good replacement. *sigh*

One of the things I like about varnish is that it can have a refractive index that's close to that of the wood, so it gives a more saturated and 'deeper' look. Shellac doesn't quite make it, but you might be able to find another resin that's soluble in alcohol that would look better, and do as good a job as a seal coat. I made some 'terpene' resin some years ago that fills the bill, and I do use it on violins from time to time. If you want to make some, look up 'Fulton varnish' for the recipe. Kremer's pigment in New York sells lots of different resins that you could try.