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Well, we've gotten to the finishing stage on the three guitars that my students are building, and that's a good thing. But we've run into a rather bothersome snag... for some reason, we're getting some significant crazing in the topcoat (EM6000). I don't quite know what to do other than just go with it, and hope for the best, b/c we have a rather limited time frame.

But I am wondering what the cause might be. I've kind of narrowed it down to two possibilities: 1) the finish has gone bad (too old), or 2) we didn't wait long enough between the seal coats (shellac) and the top coats (just one day).

Whatever the cause, I'm pretty bummed about it. We've worked long and hard (as we all do) to get to this stage, and it's quite deflating to have to go ahead and finish the guitars with a significant flaw. But I don't think we have any other options.

Any guesses as to the most likeliy suspect?

Ken

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Ken Mitchell
Durham, NC

That picture is difficult to understand. However, I've dealt with significant orange peel with em 6000. I've found that the first 6 coats are almost sacrificial. Once you sand back level, not to wood, subsequent coats should go on fine. If this is true crazing, I dunno.

I spray EM6000 on shellac as my normal schedule. I am not sure I have even waited a whole day after shellac to spray my first coat.

What kind of shellac? WP lacquers like wax free shellac. Also EM6000 wants the wet coat to be around 3-4 mils. I sprayed heavier without crazing but you start to get a blue tint if the coats are too heavy.

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http://www.Harvestmoonguitars.com

Ah! John has a good point. Hopefully you used dewaxed shellac

I am no expert at finishing with water based finishes but I do know what crazing is and that is what you have. It is not orange peel.

Crazing is typically caused by a reaction of one finish attacking another, or in your case from the shellac not having enough time to gas off the alcohol before applying the water base over it.

You could sand it down but the chances of it showing up in the surface later on is probably about 100%. The only way I know that you can repair it is to sand it down to the shellac and start over which means probably sanding it down to the wood since the shellac coat is probably pretty thin.

This is one of the reasons I personally don't believe in using dis-similar finishes. In the auto painting business I would see this all the time when guys would use dis-similar sealers and finishes. It sometimes takes months to show up but checking, flaking, dulling or complete adhesion failure are usually the results.

Maybe someone more well versed in water based finishes over shellac will have an easier fix but that is my take on it.

Sorry to see that happen and it is even worse since you are teaching guys how to do it.

Bummer man...

Bob

I see there were a couple of posts after I started this one. I would think using a waxed shellac would cause fish eyes. That is where the finish separates away from the under coat usually in little bubbles that no finish will stick to. Adding silicone to your top coat is usually the remedy for that. (essentially adding wax to the finish so it will mix with the wax underneath). From the picture this looks just like crazing.

Thanks for all the thoughts... I think the problem is from the WB top coat reacting to the shellac (wax-free Zinsser) before it had dried/gassed off completely. We should have waited an extra day, probably. I've had this happen one time before, and now I think I know what the problem is, and how to avoid it in the future!

Argh! Hard lesson learned...

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Ken Mitchell
Durham, NC

I have always sprayed directly over the zpoxy or used em 1000 sanding sealer with no problems, I am thinking the shellac is the possible cause as well...bummer , sanding back down is a pain...don't ask me how I know , as far as orange peel goes, when I moved up to a better gun with a bigger needle...1.4mm and more powerful compressor that problem took care of itself for the most part

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MK5acoustics.com

No problems here with EM6000, or anything else, over shellac (I seal everything with shellac). Obviously it can happen but I haven't seen it. I use dewaxed shellac and mix it myself. After spraying the shellac, usually two coats, I wait overnight before spraying WB or nitro.

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Steve Smith
"Music is what feelings sound like"

How long did you wait between coats?
Did you use heavy(thick) coats?
Mike

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Mike Collins