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| finish scratches/flash coat http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=38207 |
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| Author: | timn [ Fri Nov 09, 2012 12:23 pm ] |
| Post subject: | finish scratches/flash coat |
I'm spraying my 2nd shaded finish and began with a sealer of 1 part Seagrave lacquer 3 parts thinner then 2 coats 4 lacquer to 1 thinner. I gently leveled with 400 and sprayed a 1 lacquer / 1 thinner and sprayed the stained lacquer (3 to 1) to produce a reddish brown shading similar to an early 30s Martin. 2 days later I applied 3 coats 3/1. The finish measures around 3 mils and everything looked fine and after 4 weeks I wet sanded starting at 800 to 1500. I could still see sanding scratches but thought they might buff out but by the time I got to Menzerna medium paste (removes 800 sanding scratches) I began to buff through the shading, fortunately just at one edge that I can blend in. Areas of the finish still have fine scratches presumably from the 800 and hopefully not from the 400. Question is on a fresh finish, will a flash coat of 1 lacquer 4 thinner or even straight thinner melt in the scratches sufficiently that I may not have to wet sand and just go to a light buffing? I'm trying to get a very thin finish and its a real challenge particularly with shading. Its a gift for my daughter and I'd like it look good but not be too anal trying to getting it perfect. Thanks for any help. Tim |
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| Author: | B. Howard [ Fri Nov 09, 2012 12:50 pm ] |
| Post subject: | Re: finish scratches/flash coat |
I think 3 mils is a bit thin for a nitro finish, especially one with toners sandwiched in. When I consider all the extra solvents you add I would be looking for at least twice that on a green finish. To answer your other question about spraying solvents on to blend out scratches, unless you can get it to flow off the gun like glass you will need to do some more level sanding before heading back to buffing. |
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| Author: | Fred Tellier [ Fri Nov 09, 2012 6:38 pm ] |
| Post subject: | Re: finish scratches/flash coat |
If you have enough clear back up to the 800 and come back through the grits. I don't think there is enough finish from what you describe to do this. I spray more coats and after sanding and buffing have 3 to 4 mils. I often have to back up a couple grits if I see sanding marks and start sanding again, what I do when I think it is sanded enough is do a test buff and see how it looks. You can't see all the fine scratches until buffing. Try not to be too anal as in most cases no one but you will see the marks, at least a few sanding marks look better then a sand through and repair. Fred |
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| Author: | John Sonksen [ Fri Nov 09, 2012 8:23 pm ] |
| Post subject: | Re: finish scratches/flash coat |
I have a dumb question, how do you measure the mils of a finish? Does it require a special meter or is there some other more techno-ignorant way? |
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| Author: | John Sonksen [ Fri Nov 09, 2012 8:44 pm ] |
| Post subject: | Re: finish scratches/flash coat |
Thanks Todd |
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| Author: | B. Howard [ Sat Nov 10, 2012 8:23 am ] |
| Post subject: | Re: finish scratches/flash coat |
I always use a mill gauge and do the math as Todd said, but for you gadget guys there are these http://www.defelsko.com/p200/positector200.htm This is similar to what my coatings manufacturers rep uses to check finishes to help diagnose film failures and production problems. |
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| Author: | ChuckB [ Sat Nov 10, 2012 8:25 am ] |
| Post subject: | Re: finish scratches/flash coat |
John, if you use a plastic cover for the sound hole (like a small coffee can lid), you can peel the finish off the lid after it has dried and measure with calipers. Although it is after the fact, you'll know if you are ready to level sand. Chuck |
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| Author: | timn [ Sun Nov 11, 2012 7:46 am ] |
| Post subject: | Re: finish scratches/flash coat |
Thanks for the help. Decided to sand back the top coats with 400/600, partially respray the burst and this time add a few of more top coats before wet sanding. Considering there will be about 3/4 coats on top of the existing finish that has cured for one month, should I still wait 3-4 weeks before sanding/buffing? The anticipation of hearing her is very high and as a gift I'm presenting around Christmas, I'd like as much time to let it settle in and fine tune it before it goes to its new home on the left coast. Tim |
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| Author: | timn [ Sun Nov 11, 2012 7:46 am ] |
| Post subject: | Re: finish scratches/flash coat |
double post |
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