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

Finishing Problem
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=29008		 Page 1 of 1
Author:  ChuckG [ Sat Sep 11, 2010 10:31 am ]
Post subject:  Finishing Problem
I'm currently rubbing out the finish on my latest build - Mahogany -and I'm noticing some small patches - up to a couple of inches across - that look like an oil sheen on water. The shape of the patches is irregular and they look like I've rubbed through a layer of lacquer and the edges are translucent and colorful - like oil on water. You can only see them if you tilt the guitar and look at just the right angle.

This is my 21st guitar and I've always done my own finishing but I've never seen anything like this. I have always used McFadden's nitro lacquer, McFadden's vinly sealer, McFadden's retarder, and Crown thinner. I know I'm nowhere near through the finish as I've just done the initial leveling with P1000 wet/dry paper. I'm wondering if the coats of lacquer are not burning in to the previous coats properly. The only thing I've changed is the sandpaper I'm using which is now the Micro Finishing paper from Stew Mac (I used to use 3M wet.dry). I have always used water with a tiny drop of dishwashing liquid for a sanding lubricant.

Any help is very much appreciated.

Chuck
Author:  Wayne Clark [ Sat Sep 11, 2010 3:52 pm ]
Post subject:  Re: Finishing Problem
Can you post a picture? Hard to say otherwise.
Author:  woody b [ Sat Sep 11, 2010 4:46 pm ]
Post subject:  Re: Finishing Problem
I may not be understanding what you've got, but it could be blushing, or at least a mild set of blushing. Spraying a thinned coat may help get rid of it. Like Wayne said, a picture would be helpful. (but I may still not know what it is) Howard Klepper probably knows, maybe he'll read this.
Author:  Tom West [ Sat Sep 11, 2010 4:57 pm ]
Post subject:  Re: Finishing Problem
Chuck : Not much help here but I have never had a problem with burn in between coats of nitro.Hope you can solve your problem. Good luck.
Tom
Author:  ChuckG [ Sun Sep 12, 2010 7:54 am ]
Post subject:  Re: Finishing Problem
A picture is very difficult to get because you have to look at just the right angle into the light to see these patches. They are very faint, but I can see them and I know it's not right. It's definitely not blushing. It only showed up after I leveled the final coat of lacquer - 3 weeks cure time btw. I have gone through my polishing routine - level with P1000 then P1200, P1500, and 2000 grit Abralon pad - and most of the patches are now gone. I can still see one of them very faintly. The last step is to polish on the buffing wheel and I'll see if they go away or not today.

I'm wondering if it could be the thinner I'm using. I get it from the local hardware store and I've heard that cheap thinner can cause problems but I've never heard what kind of problems and I had no issues on the first 20 guitars with this same thinner. Perhaps it contains contaminants of some type that are causing this. Or could it be something in my compressor? I have a filter on it, but I haven't cleaned it in a VERY long time.

This is driving me crazy. [headinwall]
Author:  Matthew Jenkins [ Sun Sep 12, 2010 8:44 am ]
Post subject:  Re: Finishing Problem
Is it something like this Chuck?
Author:  ChuckG [ Sun Sep 12, 2010 1:30 pm ]
Post subject:  Re: Finishing Problem
Matthew,
No, it didn't look anything like your picture. After final polishing on the buffing wheel this morning, I can no longer see them so obviously I can't get a picture. The best way I can describe it is that it looked like I had sanded through a micro thin layer of lacquer into the layer beneath it and the edges, as they feathered from the top layer down into the layer underneath, were iridescent and colorful - just like an oil slick on water.

The final finish turned out OK, so no harm done at this point. I just finished spraying a Rosewood dred on Friday so I'll see in about 3 weeks if it happens again. I suspect that if it does, pictures will be easier to see because of the dark color of the Rosewood. One other observation - during the leveling process between coats (P320 sandpaper) I never saw this "phantom". Only during final leveling with P1000 wet/dry with the water/soap lubricant. Could the soap be getting into the lacquer somehow? idunno
Author:  Barry Daniels [ Sun Sep 12, 2010 4:11 pm ]
Post subject:  Re: Finishing Problem
I would expect oil contamination from your cheap thinner or dirty compressor. A small droplet of oil spit onto the wet finish would probably soak into the lacquer before it cures, and then create something like this. You must have sanded down through it during leveling or buffing so now its gone. But definitely get some better thinner (I like Sherwin Williams) and clean your compressor before your next finish.
Author:  ChuckG [ Mon Sep 13, 2010 8:31 am ]
Post subject:  Re: Finishing Problem
Thanks for the replies. I'll get some better thinner and I gave the compressor a good cleaning yesterday. We'll see. I can't help but think that oil would keep the lacquer from curing properly and to be softer in these areas - which wasn't the case. Barry, if it happens on the Rosewood dred, maybe I can bring it out to you to take a look at since we're neighbors.

Chuck
Author:  Barry Daniels [ Mon Sep 13, 2010 8:34 am ]
Post subject:  Re: Finishing Problem
I would be happy to look at it Chuck.
Author:  npalen [ Mon Sep 13, 2010 10:43 am ]
Post subject:  Re: Finishing Problem
I have seen witness lines show up in nitro when coats are sprayed several days or weeks apart as in a touchup.
They show up in the fine sanding but then disappear when buffing.
The buffing apparently "melts" the lines.
Nelson
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/