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What is this blemish? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=44888	Page 1 of 1

Author:	dnf777 [ Sat Jan 10, 2015 5:19 pm ]
Post subject:	What is this blemish?
Anyone recognize what this may be? It only appeared at buffing. My first thought was I was overzealous and burned through, but I doubt it. It appeared at first light buff, and I was much more aggressive on other places that are fine. It is mahogany filled with timbermate, and has 10 coats of KTM9, followed by a 10 day set. It looks like its something spilled on the bare wood level, but then again, everything looked fine until buffing. Unless anyone has a different suggestion, I'm just going to scratch my head a little more, then sand it down and refinish. Puzzling? I do admit that the pattern around the edge of the headstock really makes me think of overbuffing, but not the other patterns?

Author:	TonyKarol [ Sat Jan 10, 2015 5:25 pm ]
Post subject:	Re: What is this blemish?
looks to me like there is no finish left in those areas ...the lighter edges are a dead giveaway ...

Author:	Jim Watts [ Sat Jan 10, 2015 5:29 pm ]
Post subject:	Re: What is this blemish?
It looks to me like you buffed your finish off. Wipe some naptha on it and see if it blends back in, if it does you definitely buffed through.

Author:	johnparchem [ Sat Jan 10, 2015 5:33 pm ]
Post subject:	Re: What is this blemish?
Hard to see in the picture but if there is finish on those spots the finish is lifted from the wood.

Author:	Joe Beaver [ Sat Jan 10, 2015 5:45 pm ]
Post subject:	Re: What is this blemish?
I agree, probably sand through. If not then delamination of the finish from the pore filler. if I was a handicapper I'd put it at 95% chance of sand thru, 5% chance of delamination. (also a lot of sand thru on the head stock.) 10 coats of KTM 9 is on the light side unless they were very heavy coats. If they were that heavy you would most likely see a hazy, blue cast finish. But wait, that is good news!!! It is much easier to spray more coats than deal with delamination issues.

Author:	dnf777 [ Sat Jan 10, 2015 6:16 pm ]
Post subject:	Re: What is this blemish?
On closer inspection, I have to agree on the sand through. I thought it would be easier to tell, and probably is to more experienced eyes than mine. I guess I probably thinned things down with sanding, even though I thought my arms would be rubber before I sanded through with the fine wet sanding. Live and learn. Thanks for the comments--as always, this forum is a tremendous help! Dave

Author:	Parser [ Sat Jan 10, 2015 11:13 pm ]
Post subject:	Re: What is this blemish?
I spray waterborne and I have to do a lot more than 10 coats to get suitable thickness. I spray EM6000 and I get about .0003" (that's the right number of zeroes) per coat. I typically have to spray a couple dozen coats to get adequate thickness to wet sand and buff without burning through. I'd recommend making sure you build up at least .007" thick finish to get rid of burn thru... As for that neck...time to rough it up with 400 grit and build some more coats... I hope this helps! Trev

Author:	dnf777 [ Sun Jan 11, 2015 6:48 am ]
Post subject:	Re: What is this blemish?
Thanks, Trev. Yes, that is helpful, along with the other comments. I was led to believe that far fewer coats were necessary from the vendor's resources, but what you and JB say about the number of coats makes more sense now. I was wondering if you or others who use waterbased finishes could comment on sanding in preparation for buffing? Maybe my last coats were sprayed [edit, AAaagh!] "too" thin, but the surface seemed rougher (a VERY FINE orange peel) than what I thought it should be from descriptions, and so i flattened it with 400 wet sand. (that may be the beginning of my problem) I've read elsewhere that after a 1-2 week cure, you can start with 1000 grit. Wondering what you all recommend on that? Despite these troubles (teachable moments, lets call them) I really enjoy not having everyone yelling at me because the house smells like a nail salon after spraying nitro.

Author:	Herr Dalbergia [ Sun Jan 11, 2015 7:51 am ]
Post subject:	Re: What is this blemish?
nice aging...

Author:	Joe Beaver [ Thu Jan 15, 2015 1:00 am ]
Post subject:	Re: What is this blemish?
The coats should go on wet, right up to but not including runny. If I do spray a little heavy in spots I just rotate the piece for a few minutes until the finish no longer wants to sag. When that happens make sure you allow plenty of drying time before the next coat. (Drying time varies with heat and humidity. For a heavy coat it can be 1 hr 15 minutes to over two hours. If the coats are going on to dry it will look matte and feel rough, almost like fine sandpaper. You may need to adjust the spray gun or spray technique to get more finish on the wood. Also, KTM 9 is a high solids material and needs a fairly larger spray nozzle. I use something like a 1.8 on my conventional spray guy. Actually it is a pretty forgiving finish and will do a fine job for you with just a little practice.

Author:	Colin North [ Thu Jan 15, 2015 5:47 am ]
Post subject:	Re: What is this blemish?
That's shiny!

Author:	dnf777 [ Thu Jan 15, 2015 1:27 pm ]
Post subject:	Re: What is this blemish?
Thanks again, Joe. That's kind of what I figured, but its nice to hear it from somene more experienced. seems like there's a fine zone between too thin (rough) and too thick (runny). For the most part, I'm happy with the body's coverage and results. On the neck, I had thin coats, which were rough as you pointed out, and in flat sanding, I was a little too vigorous in parts. Well, back to the spray room....

Author:	johnparchem [ Thu Jan 15, 2015 3:21 pm ]
Post subject:	Re: What is this blemish?
I have sprayed a lot of EM6000 I found that if the coats are sprayed too thick you end up with a blue cast. Em6000 is great at leveling and it can be sprayed too thick (with regard to the blue cast) without running or sagging. I use a mill gauge when I set up the gun and spray 3-4 mill wet coats.

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