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Finish problem
https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=33248		 Page 1 of 2
Author:  Sondre [ Thu Aug 18, 2011 5:56 pm ]
Post subject:  Finish problem
Hi,

I am in the process of spraying nitro on my current build, but I am kinda new to this... I attached a picture of the problem

For some reason the finish doesn't flow well on a lot of the surface of the EIRW back/sides. Much worse than any orange peel I've had. I get a super smooth surface on both the entire neck and entire the spruce top. There is supposed to be a coat of z-poxy under there, but I suspect that the uneven areas are sand-throughs (is that a word?) to which the finish doesn't want to adhere. Because of oils in the wood maybe..?

Anyway, what do you suggest I do? I was hoping to get away with this without having to start the whole finish thing over...

Thanks!
Sondre
Author:  StevenWheeler [ Thu Aug 18, 2011 6:30 pm ]
Post subject:  Re: Finish problem
Sondre,

The oils from the EIR would not do that. It looks like the surface is contaminated with some sort of oily substance. I think your in for a do over. Better to start again now than to waste more time trying to work with what you have.

Steve
Author:  Tom West [ Thu Aug 18, 2011 7:01 pm ]
Post subject:  Re: Finish problem
Fish eye.....?? Did you get anything with silicon in it on the body? I use zpoxy as a fill with a seal coat and have never had anthing like that.Sorry,not sure what to say. Maybe one of the finish guys will show up.
Tom
Author:  Jim Watts [ Thu Aug 18, 2011 8:00 pm ]
Post subject:  Re: Finish problem
I'm thinking the same as Tom, contamination. If you have any silicone in your shop I would also suspect that, the stuff can get everywhere. I'd sand it off and reseal with shellac as a barrier coat before respraying.
Author:  B. Howard [ Thu Aug 18, 2011 8:00 pm ]
Post subject:  Re: Finish problem
Does the problem occur immediately as the coating is sprayed or does it develop as it dries? Did you use any kind of sealer like vinyl or shellac?

It would be very difficult to get some kind of airborne contaminant like oil or silicone only on the back and sides and none on the top or neck.
Author:  woody b [ Thu Aug 18, 2011 8:11 pm ]
Post subject:  Re: Finish problem
Is it the entire back, or just the area photographed? It's easy enough to get silicone, or some other type of oily contamination from your hand. I used to be a technician (mechanic) at a car dealership. I know a little bit about oily contamination from my hands. LOL I usually wear nitrile gloves anytime a guitar is getting close to ready to finish. Reguardless, I'd recommend sanding most of all of it off. Enough to get it smooth. Then wipe if with naphtha, let it dry, then wipe it with ammonia, and let it completely dry. This will usually get rid of silicone contamination. The oils in Rosewood won't cause problems like this with Nitro.
Author:  alan stassforth [ Thu Aug 18, 2011 8:18 pm ]
Post subject:  Re: Finish problem
Just a thought,
maybe the epoxy wasn't cured because of unequal portions?
I don't use epoxy, so I don't know how important the mix ratio is.
Looks like a compatability issue at first glance to me.
Did you epoxy fill the neck?
Author:  WudWerkr [ Thu Aug 18, 2011 8:29 pm ]
Post subject:  Re: Finish problem
are you sanding with silicon carbide sand paper it will look either dark gray or black, usally dark grey You do NOT want silicon carbide , it can and will cause fisheye . Your sandpaper should be Aluminum oxide ONLY !!
Author:  meddlingfool [ Fri Aug 19, 2011 12:49 am ]
Post subject:  Re: Finish problem
Hey Wud,
I think the silicon restriction/AO necessity applies to waterbornes...
Author:  Tai Fu [ Fri Aug 19, 2011 1:55 am ]
Post subject:  Re: Finish problem
What kind of nitro are you using? I found that some lacquer is more finicky than others. Real nitro doesn't seem to care if finger oils are on it, except for silicone oil. I have however used clear coats that would do this over any hard sealer.
Author:  Sondre [ Fri Aug 19, 2011 3:01 am ]
Post subject:  Re: Finish problem
Thanks for the replies.

I don't have any silicone in my shop (to my knowledge), so I would doubt it's that...

Brian, as far as I remember, it becomes visible a couple of seconds after spraying. Anyway, it is definitely not the gun or my spraying technique. I spray horizontally and some of the patterns are vertical. I did not use any sealer except for a coat of z-poxy that I know I sanded through quite a lot.

Woody, It is on the entire back, with variyng intensity, and on most of the sides. There are smooth spots/areas in between.

Alan, thanks, but I mixed the epoxy very thoroughly, and that doesn't explain the smooth spots...

Todd, thanks a lot. I'll spray some scrap just to be sure. Probably do it over

Tai Fu, it is a Swedish brand called "Saphir Polerlack". It is a cellulose lacquer. I don't know much more than that.

I forgot to mention a couple of things... The picture shows the third coat, and this happend on every coat. I scraped/sanded down until I got a smooth surface, which basically meant sanding down to bare wood. I'm not entirely sure, but the patterns may have appeared on the same places as the previous coat. I guess that kinda substantiates the sand-through theory. I wasn't expexting bare EIRW to be that repelling though....
Author:  Stuart Gort [ Fri Aug 19, 2011 3:18 am ]
Post subject:  Re: Finish problem
Did you wipe it down well with naptha prior to the first coat?

How long did you wait between coats? And what prep, if any, did you do between coats?
Author:  Sondre [ Fri Aug 19, 2011 5:31 am ]
Post subject:  Re: Finish problem
Stuart, I wiped the back/sides with alcohol prior to the first z-poxy coat. I waited for at least 90 minutes between the coats. Sanded with 400 grit between coats. No wiping in between
Author:  klooker [ Fri Aug 19, 2011 7:13 am ]
Post subject:  Re: Finish problem
That looks exactly what I experienced after spraying an area where I had sanded through the sealer to bare wood.

Kevin Looker
Author:  brenbrenCT [ Fri Aug 19, 2011 8:38 am ]
Post subject:  Re: Finish problem
kinda looks look too thick of a coat to me, but i'm just a guy trying to make his way in the world.

b
Author:  Tai Fu [ Fri Aug 19, 2011 9:09 am ]
Post subject:  Re: Finish problem
Does the finish adhere to the base coat at all? As in if you try and scratch it with a metal scraper, or try and damage the finish in any way, does it simply cause a finish dent or does a large chip come off?

If a large chip comes off, or if the finish chips in a way that suggest bad adhesion, then there's something keeping it from sticking, or that the epoxy isn't compatible with the nitro.

I would use a non-epoxy filler like normal oil (or water based if oil based is not available) based wood filler (darkened to match the color of the wood) rather than epoxy. Epoxy doesn't sand so well and there's alway the risk of allergic reaction when you work with it too much.

Something like Carpenter's wood filler (again darkened to match the wood) is actually not a bad product. Just spray a light coat of lacquer or shellac to seal it in before spraying on heavy coats of clear. I use them to fill the pores of swamp ash because oil based filler isn't available. Actually I don't even use Carpenter's, just a random no-name latex based filler.

To tell you the truth I usually don't fill EIR... the grain isn't so big, maybe I should in the future because the grain does become visible later on.
Author:  WudWerkr [ Fri Aug 19, 2011 9:24 am ]
Post subject:  Re: Finish problem
Quote:
Don't be ridiculous...silicon carbide (aka Wet or Dry) is DESIGNED and SOLD for level sanding finishes. It contains silicon, but does not contain silicone. Any wet sanding on a finish ends up being done with silicon carbide precisely because it cuts fast, does not load when properly prepared (soaked overnight), and does not leave any contaminants behind.


No offense taken Todd , However you should know I own White County ABRASIVE and industrial supply and we have sold sandpapers to wood working industry for 20 yrs . I sell approx 12 diffrent brands and I can take you to 100 diffrent shops that will tell you IT CAN and WILL cause a problem . Does it always do it . NO , however IT Does Happen! And NOT just with waterborn finish.

It is true that there are S/C based papers out there designed for the wet dry sanding , Mainly for autobody industry. I sell those also . There are wood working sheets and disc rolls that contain s/c for wood working and I do sell them . Yes the sterrate coating can be a problem , And some do use them , however they do run into this on occasion.

Thanks for tuning in , now back to our regularly scheduled program ! laughing6-hehe
Author:  B. Howard [ Fri Aug 19, 2011 7:43 pm ]
Post subject:  Re: Finish problem
I was thinking maybe oil/water contamination of the air supply. A very small amount of compressor oil atomized at the horn will cause an effect that looks very much like that. Water can do it too, but would not leave a lasting effect for trhe next two coats, oil would. Are you usining a good filter/seperator on your air supply? Is it as close to the gun as possible?
Author:  Mark Groza [ Sat Aug 20, 2011 8:26 am ]
Post subject:  Re: Finish problem
I've had the same problem when useing z-poxy for the first time. It's the z-poxy not being compatable with the nitro. That's why it's not on your top plate( you didn't put z-poxy there). A good couple coats of shellac before shooting the nitro will probably correct that issue in the future. To fix, you can sand back in that area and keep spraying nitro until level.It might take a few times doing that to get it right, but it will eventually level out from the build up/level sanding process. ;) Good luck with it.
Author:  Ken Franklin [ Sat Aug 20, 2011 9:43 am ]
Post subject:  Re: Finish problem
If there was any amine blush from the z-poxy that wasn't removed by water then that could leave a barrier like the one you show. I've also found that some finishes like to adhere to a rougher surface and 400 sandpaper might be too fine. I like to stop at 320. It doesn't affect the final clarity but it gives a little more tooth for better adhesion.
Author:  Howard Klepper [ Sat Aug 20, 2011 11:26 am ]
Post subject:  Re: Finish problem
woody b wrote:
Is it the entire back, or just the area photographed? It's easy enough to get silicone, or some other type of oily contamination from your hand. I used to be a technician (mechanic) at a car dealership. I know a little bit about oily contamination from my hands. LOL I usually wear nitrile gloves anytime a guitar is getting close to ready to finish. Reguardless, I'd recommend sanding most of all of it off. Enough to get it smooth. Then wipe if with naphtha, let it dry, then wipe it with ammonia, and let it completely dry. This will usually get rid of silicone contamination. The oils in Rosewood won't cause problems like this with Nitro.



Ammonia???

I don't get why so many people here finish over a layer of epoxy, or why the idea seems to be going around that there is only one brand of it. I use epoxy as a pore fill, not a base coat.
Author:  woody b [ Sat Aug 20, 2011 12:06 pm ]
Post subject:  Re: Finish problem
Howard Klepper wrote:
woody b wrote:
Is it the entire back, or just the area photographed? It's easy enough to get silicone, or some other type of oily contamination from your hand. I used to be a technician (mechanic) at a car dealership. I know a little bit about oily contamination from my hands. LOL I usually wear nitrile gloves anytime a guitar is getting close to ready to finish. Reguardless, I'd recommend sanding most of all of it off. Enough to get it smooth. Then wipe if with naphtha, let it dry, then wipe it with ammonia, and let it completely dry. This will usually get rid of silicone contamination. The oils in Rosewood won't cause problems like this with Nitro.



Ammonia???

I don't get why so many people here finish over a layer of epoxy, or why the idea seems to be going around that there is only one brand of it. I use epoxy as a pore fill, not a base coat.



An old cabinet builder/finisher told me years ago to use naphtha followed by ammonia to help prevent fisheyes. I had never done it, until a couple years ago. I was re finishing a 13 year old guitar, and having severe fisheyes on the neck. (fast fret, or fingerease I suspect) I remembered what he'd told me, so I done it, and the fisheye problem was gone.

I also think it's best to have whatever pore filler is used in the pores only.
Author:  runamuck [ Sat Aug 20, 2011 1:50 pm ]
Post subject:  Re: Finish problem
It looks like silicone contaminant to me.

Years ago I worked in a shop where a very small amount of silicone was sprayed
50 feet or so from the spray booth that was upstairs. We never did that again.
Author:  Sondre [ Sun Aug 21, 2011 10:04 am ]
Post subject:  Re: Finish problem
Thanks folks, I appreciate your help!

It is definitely not a compatibility issue with the epoxy or bad equipment/settings/technique, since both the neck and the top came out perfectly.

My intention was to leave a thin film of epoxy and spray the nitro directly on top of that. I know I sanded through on a lot of places though, but I didn't think it would matter. I am almost certain that the finish came out uneven at the areas where I sanded through.

Anyway, assuming that the problem is that the nitro doesn't adhere directly to the EIRW, I will probably strip the back/sides completely and do it over (I would like to hear it if there is another option though...). If I end up stripping it, how do you suggest I prep the body before starting to spray nitro?

Thanks!
Sondre
Author:  woody b [ Sun Aug 21, 2011 1:04 pm ]
Post subject:  Re: Finish problem
Nitro has no problem adhering to curing on EIRW. It's polymerizing finishes that need a barrier coat on oily woods. (Nitro's not polymerizing, it's evaporative) I didn't think about water/oil contamination in the air line until Brian mentioned it. It wouldn't take much to contaminate the back. Did you spray the back last? That could explain why there's no problem anywhere else. It could also be silicone contamination of the wood from a long time ago.
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