Official Luthiers Forum!

Hello everyone:

I've been a “quiet” member of the forum for a while and trying soak in as much of this great information as possible. Today I ran into a finishing problem that has me stumped and hopefully one of you has seen this problem before and can give me some advice.

I'm finishing #5, a cherry OM, with EM6000 water-based lacquer. The previous four have all been finished the same way – three coats of Z-Poxy to pore fill on the back and sides and then 12 – 18 coats of EM6000 applied over three to four days. The previous four guitars all finished well. #5 has thrown me a curve.

Yesterday I started the spray finishing with six coats applied 1:15 to 2:00 hrs apart with the 6000 diluted 10% with water. I have always thinned, so I don't think this is the problem. These first six coats went on great and this morning I level sanded with P400 3M Fre-Cut gold – the same procedure I've used for past guitars. After I finished the leveling, I wiped down with DNA and started to shoot the next coats. After the fourth coat today I noticed a cloudy area on the back. On closer inspection, the area appeared to be saturated with thousands of tiny bubbles. All the other areas I shot, the top, sides and neck, were fine.

I've tried to capture the problem in the photos, but its really hard to get a quality shot.





I have never experienced this before and have no idea what might have caused it.

Any ideas?

Thanks.
Dean

Got water in your spray rig? Here's a related thread on Target's Luthier forum: http://www.targetcoatings.com/forum/viewtopic.php?t=2532

Tarhead:

I'm running an Apollo HVLP. No compressor and the air is typically warm, so I don't think that would be a problem. But I'll certainly check it out in the morning.

Thanks.
Dean

Where are you spraying? I can't say for sure since you are using a waterbourne finish but when I see bubbles, I think solvent pop. When I see cloudiness I think premature flashing.

If you are spraying outside and the sun hit that spot just the right way, it could have flashed off too quickly. Did you consider spraying another coat to see if it melts in?

I dont know if solvent pop is possible with waterbourne, but you did say that you wiped it down denatured alcohol prior to spraying. If the alcohol didn't gas out fully before you shot the last coat, it may have reacted unfavorably with the lacquer.

My disclaimer is that I only know solvent-based finishes so I could be way off base. It also kind of looks like overspray. Are you sure it was sprayed evenly, overlapping coats by 50%? I screw that up constantly.

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

absrec:
I was spraying in the basement.

I probably waited five minutes after the DNA wipe before I shot my first coat. Again, typical of what I normally do and it hasn't been a problem in the past. Do you think it should be longer?

Yes, I'm pretty sure its not an over-spray problem and I'm pretty careful about the 1/2 overlap. The coats have been going on pretty wet. One thing I noticed as I was taking taking the photos is that the bubbles are under the surface. If I rub my finger over the finish it all feels the same (smooth) - bubbles or not.

I'll try to sift through the Target forum today before I try sanding and shooting another coat.

Thanks.
Dean

Looks like classic solvent pop to me. Not quite enough dry time between coats perhaps. Or a draft on the area. Water Bourne finishes still have solvents in them, usually glycol ethers.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

WOW! You guys are good! Its seems that in some sense you're all correct. I found this with a picture that looks just like the issue I've run into over on the Target forum:


From Jeff Weiss:
It's caused by humidity/cosolvent flash. Ensure that you have the water mixed well into the EM6000 resin, then allow it to synergize. Do not "mix then go" right the spray gun. Give the water time to pick up the solvent package.

Also, the solvent pop is caused by high humidity reacting with the faster solvents within the formula. With all that extra water in the resin the solvent is flashing off faster, but wants to pull the water with it, however, the resin is flashing and drying but water is still trying to escape- the effect is a dull/gloss/dull pin hole effect....

Brian: I did turn on a fan in the basement to speed up the drying process (to help with runs). That may be what tipped the balance.

Thanks a bunch guys.
Dean

Just so you know, I shoot EM6000 straight. There is no need to add water. My shop is at 45-50% RH and 67-72 degrees and I can shoot dry coats about 30 minutes apart with no issues.

_________________
ELEVATE || Next Level Lutherie
http://elevatelutherie.com
&
http://ensorguitars.com

Chris:
I shot the EM6000 straight on my first guitar and wasn't pleased with the amount of orange peel. The 10% thinning helped a lot. But, if this issue is a result, I may have to go back. I just wasn't able to dial in the Apollo well enough to get a good leveling wet coat. Maybe I'll try 5% when I shoot on the final coats today.

Dean

Water born coatings can be tough with a turbine like an Apollo, the hot air does not do them any favors.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I have no experience at all with water based lacquer, but regular nitro lacquer does almost exactly the same thing sometimes if you spray too thick a coat.

Just a thought, but can you get a whip hose for the Apollo like the Fuji ones?
Cools the air at the gun around 10 deg. C, may help a bit with the finish layer.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Well today was experiment day. I started off by thinning the EM6000 5% instead of 10%. After level sanding to clean up yesterday's mess, I shot a fairly light coat on the guitar. I checked it out after a little over an hour and everything looked great. I next shot a heavy wet coat like I did yesterday. I check in on it 30 minutes later and there it was - the solvent pop just like yesterday.

So, I think the culprit has been identified - heavy wet coats with a 5% thinned EM6000. I'm not sure why this has never caught me before, but I'm pretty confident that's the issue.

Thanks everyone for weighing in, I really appreciate the help.

Dean

another possible culprit is moisture absorbed by your dna. all alcohols absorb ambient moisture. the more times the container is opened the wetter it will get. rh when open will affect how much is available to be absorbed. when you wipe down with it the alcohopevaporates faster than the water. you could have had resiual water from that.

i prefer to use naphta for this reason.

Yeah.. Solvent pop looks like hell. Sometimes you can let it gas off naturally. Other times, it's sealed in too far. I just had a problem yesterday when I shot a coat of black. Bubbles all over the back. This morning, I went down to the shop and looked and they were all gone. I said... " Sweet!".

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."