Official Luthiers Forum!
http://luthiersforum.com/forum/

Finish issues
http://luthiersforum.com/forum/viewtopic.php?f=10123&t=51785		 Page 1 of 2
Author:  Borg [ Sun Apr 07, 2019 12:31 pm ]
Post subject:  Finish issues
I have built several solid body electric guitars. My recent build is a somewhat transparent blue strat burst. When I was buffing out the finish I noticed what looked like embedded dust or tiny tiny specks as the buffing proceeded. I had this problem before and was advised by the Mohawk tech rep to make sure my compressed air was dry. I did that and the next build, solid red, was better but the contamination was still there. On my recent build, the blue one, I took every precaution I could think of including tack cloths, superfine strainers, calm warm conditions ect. It's the worst one yet. You cant see it if you are not looking for it but I CAN. Driving me nuts. I'm now thinking it might be in the tint I'm using which is Mixol.

Thanks in advance to anyone that has any suggestions or similar experience. I could post a pic but I don't think it will show the issue.
Author:  Glen H [ Sun Apr 07, 2019 2:26 pm ]
Post subject:  Re: Finish issues
What type of finish are you using? Nitro? Do you have a spray booth or working outdoors?
Author:  Borg [ Sun Apr 07, 2019 3:01 pm ]
Post subject:  Re: Finish issues
Nitro. Sort of outdoors. I open my garage door and spray just inside the door.
Author:  Glen H [ Sun Apr 07, 2019 4:31 pm ]
Post subject:  Re: Finish issues
I would mix up a small batch of finish with that tint in it just like you did when you sprayed. Small amount like a baby food jar amount. I’d put it in glass and let it sit and see what it looks like in a few minutes or an hour . See if that blue stays in solution or falls out.
Author:  Borg [ Sun Apr 07, 2019 4:39 pm ]
Post subject:  Re: Finish issues
It does settle out some but not completely. I think you are on to something here. Mixol is less expensive than other tints. Maybe because it's inferior. I think I will run that by the tech at Mohawk.
BTW, do I need an online host for posting pics? I read the FAQ and that's kind of what it sounded like.
Author:  Glen H [ Sun Apr 07, 2019 6:13 pm ]
Post subject:  Re: Finish issues
I’ve uploaded pictures before here without using a host, so I don’t think so.give it a try.
Author:  Borg [ Sun Apr 07, 2019 8:47 pm ]
Post subject:  Re: Finish issues
It said the files are too big. Don't really know how to fix that. The issues don't show in pics anyway.
Author:  B. Howard [ Mon Apr 08, 2019 5:52 am ]
Post subject:  Re: Finish issues
I use mixol colorants without issue and have for a decade in all types of finish materials. And if it was the issue you should only be buffing the clear and never touching the colored base coat....

I quit using track rags, especially the cheap yellow ones from home depot etc, many years ago due to contamination issues. I don't even trust the blue ones from the body shop supplier any,more.

Sounds to me like small particles of airborne dirt being picked up in your booth air stream. What is your booth like? how well is it sealed? And is your intake air filtered?
Author:  Freeman [ Mon Apr 08, 2019 10:57 am ]
Post subject:  Re: Finish issues
Borg wrote:
It said the files are too big. Don't really know how to fix that. The issues don't show in pics anyway.


Open the picture file with Paint (plain old MS Paint, not 3D). Click the resize button, change one of the settings from 100 to something smaller (I use 25), the other will change at the same time, click OK. Save the file. The size should have dropped dramatically (you want it 250K or smaller I think). Try uploading it into the forum software. It might take a couple of tries to figure out how big your camera makes the files and how much to reduce them, and yes, its a hassle but other than hosting site its about the only way I know to do it.

I'll be interested in your pictures and the responses. I shoot nitro basically the same way, open my garage door, put the guitar just outside, worry about dust and everything else. I do drain my water filter every couple of times I spray and I try to make sure both the temp and RH are reasonable, and I probably reduce the lacquer a bit more than recommended (4 or 5:1). I am absolutely anal about cleaning the gun every time I spray, I know it isn't necessary but it takes five minutes. The only dye that I have added is Colortone and those have worked fine.
Author:  Borg [ Tue Apr 09, 2019 11:49 am ]
Post subject:  Re: Finish issues
This is the best pic I can get. It's very close up and it sure looks like tiny pits to me. At first they were white. Then I washed the surface, now they are pits. Must have been the polishing compound that made them look white.

Attachment:
Close2.jpg
Author:  Borg [ Tue Apr 09, 2019 11:51 am ]
Post subject:  Re: Finish issues
Sorry. Not sure what I am doing posting pics. Kind of blew up the screen for me.
Author:  Conor_Searl [ Tue Apr 09, 2019 1:14 pm ]
Post subject:  Re: Finish issues
Are they air bubbles?
Author:  Glen H [ Tue Apr 09, 2019 5:58 pm ]
Post subject:  Re: Finish issues
Not what I was thinking. From the pic it looks like you’re pores were not filled completely.
Author:  Barry Daniels [ Tue Apr 09, 2019 5:59 pm ]
Post subject:  Re: Finish issues
Search for "solvent pop".
Author:  Chris Pile [ Tue Apr 09, 2019 6:35 pm ]
Post subject:  Re: Finish issues
Mixing your finish too hot, perhaps?
Author:  Borg [ Tue Apr 09, 2019 7:53 pm ]
Post subject:  Re: Finish issues
Glen H: There are 10 coats on that basswood and basswood fills and seals easily.

The Mohawk rep did mention solvent pop. So yes, it could be air bubbles. This really seemed to become an issue after I switched to a compliant thinner. (I'm in California, I'm lucky I can get nitro). I use Mohawk Piano Lacquer thinned about 15% with a thinner that I get from the supplier that also sells Mohawk. The thinner has no manufacturers label. I will be ordering some Mohawk 2255 reducer and only using the other to clean the gun.
BTW, that pic is really magnified. My son has a Nikon D3300. It's amazing what those things can do.

B. Howard: I ran an experiment where I determined it was not the Mixol. I'm glad it's not the Mixol. I like it.

It's either the lacquer, the thinner and or solvent pop. That much dust contamination isn't really possible as careful as I am. I know I get some but not that much.

Will try to scale down a pic so I can show what I am working on.
Author:  Borg [ Tue Apr 09, 2019 8:22 pm ]
Post subject:  Re: Finish issues
This is the model but not the same body. I'm building a new one because I moved some controls.
Attachment:
Shrunk.jpg
Author:  Mike_P [ Tue Apr 09, 2019 9:00 pm ]
Post subject:  Re: Finish issues
I've seen that exact same thing involving 2 different scenarios:

Solvent pop

a brand new Binks Mach1SL that had bad gaskets and had to be rebuilt straight out of the box...

I'm betting on solvent pop as in the case of the Binks it was rather apparent upon spraying as bubbles immediately formed during the spraying process (which I can only assume unless you were toasted off your butt you would have noticed while spraying)
Author:  B. Howard [ Wed Apr 10, 2019 6:21 am ]
Post subject:  Re: Finish issues
That is solvent pop, really bad solvent pop. See my chart for help. https://howardguitars.blogspot.com/2015/05/spray-finish-problem-solving-chart_18.html
Author:  Borg [ Wed Apr 10, 2019 8:53 am ]
Post subject:  Re: Finish issues
I really appreciate the help. This issue is driving me nuts.
Like I mentioned, the issue seems to have developed when I switched to the "compliant" thinner. It may be that I have just noticed it too. I will check some older guitar bodies.

Right now it's very dry here and warming up. Humidity is in the 30's at 75 degrees. Mohawk says that the lacquer does not need thinning under normal conditions. In case it's not apparent, I am not a seasoned luthier. Especially in the finishing department. I have tried spraying without thinning and was not happy with the appearance. (Rough, orange peely). Maybe I shouldn't be so picky there since I will be level sanding anyway. Add 1 more coat and start with 400 instead of 600 or 800 what's the big deal?
If I do need to thin I'm going to try to get some of Mohawk's 2255 reducer. May have to smuggle it in.

My setup:
5 cfm compressor w/8gal tank.
Large capacity filter/separator then inline dessicant mounted at compressor.
Hose, 50' 3/8 pvc.
Pressure regulator mounted at gun. Maintain about 30 psi while spraying.
Spray gun, Husky (Home Depot) HVLP
Mohawk piano lacquer
I have a very small garage and no room for a separate booth. I spray right at or just outside of the garage door. I try to spray when there is no wind at about 50% humidity. I use a stick mounted in the neck pocket to hold and rotate the body. It goes immediately back to a hook well inside the garage hanging vertically to avoid settling particles on the front or back surface. No more than 2 coats in a day and 1 hour apart min. I repair any issues the next morning and drop in lacquer if req before next coat.

This is my typical process:
Bare wood dry sanded to 320.
Pore/grain fill mostly with Timbermate or Aquacoat.
Stain if required. May grain fill after staining, depends on colors.
2 to 3 seal coats. Lacquer.
Lightly dry sand with 400.
Tint/burst/solid color at this point. Usually 3 to 5 coats.
Blend burst layers by wet sanding 600-800 grit.
4 to 5 top coats. Lacquer.
Hang for 3weeks/summer, 4 weeks/winter.
Level sand wet 600,800,1000,1200
Buff with Turtlewax rubbing compound, power buffer with foam pad.
Buff with Turtlewax polishing compound, power buffer with foam pad. Separate pad.

If any of you guys have issues with my setup and process please advise. I obviously need the help.
Thanks again.
Author:  Chris Pile [ Wed Apr 10, 2019 9:08 am ]
Post subject:  Re: Finish issues
Using a reducer usually slows drying time a bit, and might allow the finish to lay out....
Author:  Mike_P [ Wed Apr 10, 2019 4:59 pm ]
Post subject:  Re: Finish issues
the times I've had solvent pop issues where when I was putting lots of layers and not allowing enough time between coats...lots of (thick) layers = lots of solvent, not enough time between coats = solvents still in lower layers because they hadn't flashed off enough.

after I learned the "lesson" I haven't had one issue with solvent pops...simply allow more time between coats (remember it's lacquer and it burns into itself so there's not a great worry with adhesion, well there is and that's why is pretty much necessary to at least scuff up the surface before you start shooting again after 2 weeks!)

you note use of a "compliant" reducer...well that may certainly be part of the issue...I can say with confidence you usually get what you pay for with reducers and perhaps this particular product (while satisfying commifornia's rules) is lacking in other areas no matter what it's cost
Author:  B. Howard [ Thu Apr 11, 2019 6:29 am ]
Post subject:  Re: Finish issues
Drafts in the drying area... Direct sunlight.... both can cause this issue under otherwise normal conditions. You make no mention of coating weight per wet coat and this has a big effect on drying characteristics as well and lead to solvent pops.

To help you fix this you need to understand what is actually happening., The top of the wet coat is drying too fast. The top of the film skins but the wet underneath is still out gassing so the bubbles form and are trapped under the very top of the coat. So it looks flat on top but when you sand to buff you open up all the tiny bubbles. Matching reducer evaporation speed to environmental conditions can be factor in this as well but temp graded lacquer thinners are pretty much a thing of the past even from good industrial suppliers. Retarder may help but may not depending on the actual cause. If it is sunlight or severe drafts then retarder will not do much and you must correct the environmental condition causing it. Retarder will also increase times between coats and time to final buff considerably with all modern nitro formulas.
Author:  Borg [ Thu Apr 11, 2019 2:53 pm ]
Post subject:  Re: Finish issues
Mike_P: I mentioned that I do 2 coats per day max and 1 hour between coats. What schedule would you recommend? I will also try spraying without thinning.

B. Howard: No sunlight but circulating air could be an issue. I spray in the doorway and return the body to a hook well back inside. I don't have a way to measure coating weight. I simply hold the body at an angle that allows me to see that the coat is wet. I rarely if ever see any sags or runs which is my sign that the coat is not too heavy.

I may try spraying with the door closed. I have never used retarder as I have never had any blushing.
Author:  Chris Pile [ Thu Apr 11, 2019 3:26 pm ]
Post subject:  Re: Finish issues
Quote:
I have never used retarder as I have never had any blushing.


Retarder is added to slow the drying time to smooth out the finish, so it flows. You can use it to fix blush (there are other techniques, too), but that's not what reducer is for.
Page 1 of 2 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/