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Need Help with Sunburst
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Author:  Goodin [ Mon Dec 02, 2013 7:04 pm ]
Post subject:  Need Help with Sunburst
I'm doing my first sunburst and I have come upon a problem that is puzzling me. I have the color down and am spraying on a few light coats of shellac to seal it. When I spray on the shellac the dark color starts to lighten up to gray. It only happens on one side. It looks like it's frosting over or blushing. It has done this once before when I sprayed shellac over color after about an hour of drying. I thought it might be because the color hasn't dried yet so I sprayed more color over the gray area to darken it back up and let it sit over night. Now, I just misted a light coat of shellac and it's starting to turn gray again, just on one side. Any thoughts?

Here is my process - sanded to 320, spray two coats of dewaxed shellac (Zinser seal coat) with an hour or so to dry, a few coats of vintage amber dye mixed with alcohol with the big gun over the whole top, sunbursted with tobacco brown and red mahogany dyes in alcohol and sprayed with an air brush, let sit an hour, sprayed three light coats of shellac and it started to turn gray, let sit an hour, sprayed tobacco brown/alcohol to darken back the gray area, let sit overnight, almost 24 hours. Sprayed one mist coat of shellac and it's starting to gray again. See pic. Lower bout on the bass side.

I'm puzzled on what is happening and what I can do to fix the issue. I'm wondering if it will darken up when I spray laquer over it?
Attachment:
20131202_183508 (Medium).jpg
Author:  Beth Mayer [ Mon Dec 02, 2013 7:21 pm ]
Post subject:  Re: Need Help with Sunburst
Goodin, I thought Sunbursts were done by doing the seal coat (shellac or whatever) then the color and then lacquer over the color. Hadn't heard of using Shellac over the color coats?
Author:  John Sonksen [ Mon Dec 02, 2013 7:31 pm ]
Post subject:  Re: Need Help with Sunburst
When you say mist coats, do you mean it's almost dry when it lands on the guitar? My first instinct is it's not wet enough when you're laying down shellac so the finish looks grey on top of the darker color underneath.
Author:  John Sonksen [ Mon Dec 02, 2013 7:32 pm ]
Post subject:  Re: Need Help with Sunburst
Beth, I'm not sure it will make any difference if shellac goes on over the color. Subsequent lacquer coats should stick to it fine, although it may be a unique approach
Author:  Goodin [ Mon Dec 02, 2013 7:36 pm ]
Post subject:  Re: Need Help with Sunburst
Hi John - I mean I just run the gun across it quick with the pressure turned down a little bit. Just trying to get a small amount of shellac on there and build it up gradually. Wonder if my shellac is bad? I'm using a 2-3 year old can of Zinsser seal coat. I knew better but totally spaced and used an old can of shellac.
Author:  nyazzip [ Mon Dec 02, 2013 7:52 pm ]
Post subject:  Re: Need Help with Sunburst
i have brushed Zinsser shellac of comparable vintage and it has been ok; i haven't sprayed it though
Author:  Alex Kleon [ Mon Dec 02, 2013 8:20 pm ]
Post subject:  Re: Need Help with Sunburst
I agree with John. Sounds like the shellac is hitting the guitar dry, giving a talc look to the finish. It may be better to spray a couple of wet coats, and sand back a bit, and repeat until you get to your desired thickness. Are you using conventional or hvlp spray?

Alex
Author:  Goodin [ Mon Dec 02, 2013 8:26 pm ]
Post subject:  Re: Need Help with Sunburst
HVLP spray. You guys may be right. Perhaps it's my technique. I'm spraying at about 35 psi with the air knob in about the medium range. Maybe I need to go slower or turn up the liquid feed? I might just go straight to laquer at this point.
Author:  B. Howard [ Tue Dec 03, 2013 6:16 am ]
Post subject:  Re: Need Help with Sunburst
You should have used a binder in your toners. The dye is just laying on the surface and reacting with the finish as it is applied. The gray areas are where the dye has formed a bridge or break in the film. The finish will likely lift or peel in these areas at some point.
Author:  Goodin [ Tue Dec 03, 2013 8:45 am ]
Post subject:  Re: Need Help with Sunburst
Thanks Brian. Any thoughts on what I could do to recover at this point?
Author:  B. Howard [ Tue Dec 03, 2013 10:53 am ]
Post subject:  Re: Need Help with Sunburst
Take it back down to the seal coat, removing all the dye that was put on. Mix your dye with some shellac to act as a binder and then spray the burst. You want more shellac than dye in the mix, it needs to form a coating in the end or it will likely delaminate.
Author:  Beth Mayer [ Tue Dec 03, 2013 11:26 am ]
Post subject:  Re: Need Help with Sunburst
B. Howard wrote:
Take it back down to the seal coat, removing all the dye that was put on. Mix your dye with some shellac to act as a binder and then spray the burst. You want more shellac than dye in the mix, it needs to form a coating in the end or it will likely delaminate.


Not to get off the OPs subject, but do you need to mix opaque dyes and transparent tints both with a binder? Is shellac the best binder to use?
Author:  John Sonksen [ Tue Dec 03, 2013 3:38 pm ]
Post subject:  Re: Need Help with Sunburst
Not trying to be a contrarian, Brian certainly knows his stuff, but at my shop our normal toning procedure has been to spray tinted lacquer thinner with no binder onto our seal coats for years. In my 18 years we have never had a de lamination problem directly attributable to that. We use pre-cat lacquer mainly, so I can't speak to shellacs qualities, but generally once the subsequent coats have laid down after the color, they've bonded with the sealer coats while assimilating the color into the matrix.

I suppose shellac dries faster than lacquer so you may have less time for this bond to take place, and I'm not saying you should go ahead and spray wet coats to try and do this. Just saying I've not had a problem doing this in the past.
Author:  Rodger Knox [ Tue Dec 03, 2013 5:00 pm ]
Post subject:  Re: Need Help with Sunburst
Beth Mayer wrote:
B. Howard wrote:
Take it back down to the seal coat, removing all the dye that was put on. Mix your dye with some shellac to act as a binder and then spray the burst. You want more shellac than dye in the mix, it needs to form a coating in the end or it will likely delaminate.


Not to get off the OPs subject, but do you need to mix opaque dyes and transparent tints both with a binder? Is shellac the best binder to use?


If the topcoat is going to be lacquer, why not use thinned lacquer as the binder? I think it might be a solvent interaction issue...
I've only done half a dozen or so sunburst, and none with lacquer, so my opinion is just a WAG. :D
Author:  Clay S. [ Tue Dec 03, 2013 5:29 pm ]
Post subject:  Re: Need Help with Sunburst
"Not trying to be a contrarian, Brian certainly knows his stuff, but at my shop our normal toning procedure has been to spray tinted lacquer thinner with no binder onto our seal coats for"

Lacquer thinner might burn in better than denatured alcohol, depending on what your seal coats are.

For the few bursts I've done I used dye, lacquer thinner and a small amount of lacquer as a binder. Then I top coat with the same lacquer. I don't like to mix up too many different layers of finish materials. It can make finish repairs that much harder.
Author:  RusRob [ Tue Dec 03, 2013 8:27 pm ]
Post subject:  Re: Need Help with Sunburst
I have been spraying lacquer for years and it has always been my practice to lay down a very smooth "base" before any custom finish is applied. So for a burst finish I seal it with vinyl sealer and prep it as if I was going to just put a clear finish on it. For me that would be about 6 to 8 coats of sealer sanded and blocked between every 2 coats.

Now when you spray your burst on it will be on a perfectly smooth finish. If for some reason you mess up spraying the burst you can easily wet sand it off and take it back down to the sealer.

This is a perfect example of what I mean. This is a Gibson I bought that needed a complete rebuild. The neck was off, it had broken and loose braces and the finish was falling off of it. I decided to put a burst on it and in the process I failed to wipe the outside of my spray gun and ended up with 2 quarter sized drips. They were about 2 inches below the pick guard. I quickly soaked up the drips with the tip of a rag. Let it dry and then wet sanded it down to the sealer and started over. I did have to re-seal it and block it out smooth. If you look really close you can see where the color bled into the sealer but you wouldn't have noticed it if I didn't point it out.


Image
Author:  Goodin [ Wed Dec 04, 2013 9:10 am ]
Post subject:  Re: Need Help with Sunburst
Thanks for the reply guys.

I touched up the gray areas with more color in alcohol and sprayed a wet coat of lacquer over top of it and didn't get any graying. So I'm thinking the shellac coat was sprayed too light and dried before it hit the finish causing it to frost over, or Brian is correct and the shellac is reacting with the alcohol, or a combination of both. I haven't completely decided yet but I'm leaning towards continuing to build the finish and see what happens. I'm not overly concerned if the finish starts flaking off in the future since this guitar is going to my best friend. I would welcome any finish issues because I want to get some experience with finish repair and refinishing. It's all a learning experience and I enjoy the challenges.

I have done some extensive research the past few days (and many thanks to you guys and the OLF archives), I think I will be able to do it "right" the next time. :).
Author:  Greg B [ Wed Dec 04, 2013 10:19 am ]
Post subject:  Re: Need Help with Sunburst
Goodin wrote:
HVLP spray. You guys may be right. Perhaps it's my technique. I'm spraying at about 35 psi with the air knob in about the medium range. Maybe I need to go slower or turn up the liquid feed? I might just go straight to laquer at this point.


35 pounds is high for an HVLP. I know lots of people are doing it, but it's still high.

Lots of good suggestions already. Why not use lacquer for a binder if you're using it for your topcoat?

I'd be extremely suspicious of a 2-3 year old can of Zinnser Seal Coat. Despite how magical and long lasting it is supposed to be, it does go bad IME. Fresh mixed shellac is still best.
Author:  Goodin [ Wed Dec 04, 2013 1:14 pm ]
Post subject:  Re: Need Help with Sunburst
Hey Greg - What PSI do you spray lacquer at (if you use an HVLP)? If I have to redo the current sunburst I plan to use lacquer for the binder. Yep, that can of Zinnser will be used for jigs and house projects only from now on. Next time I will use vinyl sealer for the seal coats since that's what I should be using with Behlen's instrument lacquer anyways.

Dang it, why does there have to be a "c" in lacquer? Seems unnecessary, and I keep forgetting it. Thanks spell check. ;)
Author:  Greg B [ Wed Dec 04, 2013 1:39 pm ]
Post subject:  Re: Need Help with Sunburst
Goodin wrote:
Hey Greg - What PSI do you spray lacquer at (if you use an HVLP)?


First a little qualification - most of my experience comes from spraying furniture professionally, which is a bit different than guitars. It's been a few years, but I think it was about 28 psi with a Devilbiss HVLP. That in itself was a little over pressure. Consult your manual, it differs from gun to gun. Frankly, I would have grabbed the conventional high pressure gun for a burst, but I think they are now banned in my area. (high pressure spray guns - not bursts... laughing6-hehe )

Now I happily FP in my apartment... :)
Author:  Goodin [ Wed Dec 04, 2013 1:53 pm ]
Post subject:  Re: Need Help with Sunburst
I think sunbursts should be banned!
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