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 Post subject: Shellac over Lacquer?
PostPosted: Tue Jan 01, 2013 6:14 pm 
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Mahogany
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Location: Williamsburg Virginia 23188
Can I get some advice, please.
I have two beautiful fine-grained Carpathian spruce tops on guitars that I'm spraying
and I have developed the same problem with pitch disrupting the finish that was discussed in an earlier thread several weeks ago.
I sanded both tops with 220 grit and then first sprayed both with several coats of Seagrave Vinyl Sealer.
After several days I sanded and leveled both tops.
Then I sprayed two coats of Seagrave Gloss Lacquer and bubbles showed up in numerous spots on both tops along the grain lines.
So I sanded both tops down to bare wood and started over with three coats of dewaxed shellac per the thread.
Both tops looked great and I no longer saw any bubbles,
so I sanded both tops smooth and began to spray lacquer again.
One top looks great.
The second top has new bubbles in several spots.
Minor amount, but I don't believe more lacquer is going to solve the problem.
My suspicion is that I sanded through the shellac in several small areas and didn't know it and pitch is still exposed.

QUESTION. Now that I have one coat of lacquer over the shellac,
do I have to remove ALL the lacquer from this top before I spray a couple coats of additional shellac?
Or, can I just sand the affected areas, lightly sand the rest, and then spray the shellac?

First time I've ever had this happen. I would appreciate your advice.

Ken Grunst
Williamsburg, VA


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PostPosted: Tue Jan 01, 2013 6:39 pm 
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Brazilian Rosewood
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I suspect you have something else going on. What spray gun you using

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PostPosted: Tue Jan 01, 2013 6:59 pm 
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Mahogany
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Hi John:
I'm using the new Fuji HVLP gravity feed gun...and I've been very pleased with it.
I bought it based on Todd's recommendation on a separate thread.
it sprays beautifully and cleans easily, so I really like it better than my old Fuji gun.
The shellac I applied seemed to solve all the rest of the problems except for a couple of small spots on guitar #1.
Since I've pretty well sanded out the top (I hope down to the shellac) I don't know exactly where the blemishes were.
What do you think? I appreciate your expertise (and your terrific instructional videos on your website).
The backs (one koa...one cocobolo) are perfect.
Now...guitar #2 seems perfect.
I was hoping to solve the problem with #1 with a couple more coats of shellac,
but wasn't sure if I could re-spray the top without being absolutely sure there was no lacquer left...
hopefully without going back to bare wood again.

Ken Grunst
Williamsburg, VA


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PostPosted: Tue Jan 01, 2013 7:19 pm 
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Brazilian Rosewood
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I think you may need to adjust it a bit , What is your mix ratio? I like between 10 to 20% thinner and 10% retarder. That gives the bubbles time to float out.

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PostPosted: Tue Jan 01, 2013 7:48 pm 
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Mahogany
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I can do that.
Shall I continue spraying the top with lacquer,
or go back and seal with shellac first?
Ken


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PostPosted: Wed Jan 02, 2013 5:52 am 
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Brazilian Rosewood
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Are you sure this is related to something in/on the top and not solvent pops? If coats of finish dry to fast on the surface the solvents underneath will pop their way out leaving pinholes that can be a bugger to fill. This can be caused by to thick of a film, wrong speed thinner, drafts in the drying environment etc. Try wetting the finish down with some retarder and see if the spots will start to flow shut. If they do another couple of coats should fix it, you may have some drop fills to do on the worst ones.

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PostPosted: Wed Jan 02, 2013 10:03 pm 
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Mahogany
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Thanks, Brian:
I'm going to try one more time with thin lacquer with more retarder, and see if a couple of light coats will solve the problem.
If not, I'll strip it back down and start over.
I need a little better weather before I can spray again.
I have an enclosed outdoor spray booth.
Anyway...I appreciate your suggestions and I'll go to work.
Ken


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PostPosted: Thu Jan 03, 2013 5:35 am 
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Brazilian Rosewood
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Do not apply more lacquer until you can get the holes too start to flow closed. The lacquer will will not flow into the holes by itself. Re-wet the existing lacquer by spraying some straight retarder on it, the lacquer will reactivate and start to flow. The holes should start to flow closed. Be careful, you can wind up making some rather large runs by wetting out finish. If they start to flow wait until the lacquer dries and then apply more costs.

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