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Oct 7, 2022 - 11:37:19 AM
400 posts since 4/15/2008

I have sprayed black lacquer on this peg head, then a couple coats of sander sealer, and then 6 coats of nitro lacquer. Please note the little hairline cracks in the finish that go from the top tuner holes. This has never happened to me before, so I don't know why this should happen, but I have sanded this thing down and started all over 2 or 3 times already.

Previously, the cracks didn't show up until I started final sanding, and I thought they might be forming when moisture from wet sanding worked under the lacquer via the tuner holes. This time, however, I have not begun to wet sand. I just leveled the lacquer with regular sand paper and was waiting for the lacquer to cure before proceeding. After doing that, I did not notice any cracks, but when woke up the next day, there they were.

Why is this happening?


Oct 7, 2022 - 12:25:21 PM
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181 posts since 8/31/2015
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I'm far from an expert on the finish process, but I've made a few new banjos and refin'd several guitars and I always followed the rule of sealer first, then color, then clear coat. Maybe the fact that you sprayed color first then sealer on top is causing some sort of problem? Just a guess. Others with more experience will hopefully chime in.
-TD

Edited by - TreyDBanjoKS on 10/07/2022 12:27:06

Oct 7, 2022 - 1:08:06 PM

211 posts since 5/27/2008

I've had similar cracks and I always though it was the moisture during wet sanding wicking into the wood. Since then I always seal inside the tuner hole with thin super glue on a Q tip before wet sanding. Seems to have solved my problem.

Edited by - notty pine on 10/07/2022 13:09:18

Oct 7, 2022 - 1:08:10 PM
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10134 posts since 8/28/2013

You may not be leaving enough drying time between the various steps (color, sealer, varnish).

Oct 7, 2022 - 5:02:32 PM
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13688 posts since 6/2/2008

I believe we're seeing scratches in the wood telegraphing through the black and all the finish coats.  If I'm right (and I could be wrong) I believe you need to take it down to wood again and re-sand to #150 or #180. Wipe the surface with mineral spirits: This will mimic what the wood will look like under sealer and will reveal if any scratches. If the wood doesn't look good, go back to sanding until it does.

Once it looks good, and after the mineral spirits evaporate, apply sanding sealer then clear coats of lacquer following whatever schedule or instructions you were using before.

Oct 7, 2022 - 5:28:24 PM

2674 posts since 9/18/2010

Finish checks can happen when a harder formulation is applied over a softer formulation. If your lacquer cures harder than the sanding sealer, checks can happen.
What info on compatibility do you have? Are all the products from the same manufacturer and are you following the manufacturers recommendation of thickness of film, cure time, order of application and so forth? Also, how old is the material, and are you stirring it up?
I've had older lacquer that's been in the shop for a while check, even though the same lacquer did not check when it was new. I assume the plasticizer in the lacquer degraded over time, but I've recently learned that lacquer plasticizers can sink to the bottom of the container, so even clear gloss lacquer should be stirred before use.

One of the things that I've learned in 35 years of finishing instruments is (in my best Roseanne Roseannadanna voice) 'it's always something'...

Oct 7, 2022 - 9:26:21 PM

Bill Rogers (Moderator)

USA

26468 posts since 6/25/2005

I agree with G E Porgie.

Oct 8, 2022 - 6:50:58 AM

heavy5

USA

2477 posts since 11/3/2016

Most probably know this , but just a comment about drying in direct sun light---- don't !
My brief experience taught me the direct UV rays will mess up a lacquer job & probably other coatings .

Oct 8, 2022 - 12:59:31 PM

400 posts since 4/15/2008

Thanks for the replies.

The problem has to be with the products I'm using. The lacquer is ColorTone from Stew-Mac. The sander sealer is Zinsser Bull's Eye (had trouble finding sander sealer anywhere), and the black paint is Krylon Fusion from Home Depot. The lacquer thinner is from Home Depot as well, and I've not had any problems in the past with it working well with the lacquer I'm using.

I suspect the problem is with the black paint, which I assumed is a lacquer, even though there is nothing on the spray can that says so. But it does say to clean it up with lacquer thinner. The photo shows another peg head using the same products but with the black script "Gibson" as the top coat. No problems at all with this application.


 

Oct 8, 2022 - 3:18:16 PM

rcc56

USA

4501 posts since 2/20/2016

Sealer on top of full strength lacquer sounds backwards to me.

Generally, we use sealer first, then full strength lacquer.
Spray the black until you get the color you want, then add 2-4 clear coats on top so you have something to level without sanding through the color coats.

If you want to, you can stain the bare wood before you seal. I prefer alcohol soluble aniline dyes or Fiebing's leather dye.

Edited by - rcc56 on 10/08/2022 15:18:37

Oct 8, 2022 - 3:57:21 PM

400 posts since 4/15/2008

quote:
Originally posted by rcc56

Sealer on top of full strength lacquer sounds backwards to me.

Generally, we use sealer first, then full strength lacquer.
Spray the black until you get the color you want, then add 2-4 clear coats on top so you have something to level without sanding through the color coats.

If you want to, you can stain the bare wood before you seal. I prefer alcohol soluble aniline dyes or Fiebing's leather dye.

I did not spray sealer over the lacquer - I sprayed lacquer over the sealer.  Here is a better photo of the cracks.



 

Oct 8, 2022 - 4:36:57 PM

2674 posts since 9/18/2010

I suspect that your clear is "floating" on the black paint. If it doesn't say "spray lacquer" on the can it is probably spray paint of some sort, and is probably softer than the clear lacquer above it. That can definitely cause checking.

Oct 8, 2022 - 4:52:16 PM

400 posts since 4/15/2008

quote:
Originally posted by sunburst

I suspect that your clear is "floating" on the black paint. If it doesn't say "spray lacquer" on the can it is probably spray paint of some sort, and is probably softer than the clear lacquer above it. That can definitely cause checking.


Thanks, John, that is the most reasonable explanation to me.

Oct 9, 2022 - 4:52:44 AM

2438 posts since 2/7/2008

By the way, Zinder Bullseye is waxed shellac and is not suitable as a sealer.

You could decant it in a clear and when you see the wax settle to the bottom, carefully take the shellac without wax off the top.

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