Number of Coats

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nehsgolfer
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Joined: Tue Mar 11, 2008 9:09 am

Number of Coats

Post by nehsgolfer »

I'd like some opinions on what you guys think is the FEWEST number of coats of lacquer that may be put on the top of a guitar and still make it through years of playing. The guitar will probably seldom leave my bedroom/den and be handled very gently.
Ben-Had
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Re: Number of Coats

Post by Ben-Had »

As John Hall likes to say, "It's not what you put on, it's what you leave on." Depending on the type of finish you're looking for can determine how many coats you will need. If you are looking for a high gloss finish you need to put on enough coats so that you can remove all the "pits" and get a perfectly level finish. If you go with a more semi-gloss or a satin finish where some of the "pits" are still visible you won't need as much build up and can therefore use fewer coats. I never really closely measure my final thickness but it is around .005 to .007" as best I can measure. I put on around nine coats for a semi-gloss/satin finish and that is of course with my gun and how I have it set up, yours may vary. That being said, when I build with a student I put on 2 coats of sealer and 3 coats of finish and call it done. I have done that to one of my guitars that is 5 years old now and holding up fine (sounds great too):)
Tim Benware
nehsgolfer
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Re: Number of Coats

Post by nehsgolfer »

Thanks. I plan to use rattle cans if that makes much difference.
tippie53
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Re: Number of Coats

Post by tippie53 »

when I used rattle cans I didn't realize just how thinned this material is. I used to use about 6 cans for a guitar.
Here is what I found out. I used Behlen top coat or stringed instrument lacquer along with the vinyl sealer. Gloss on the headstock and body and satin on the neck
Once the guitar was prepped I use a pint deli cup and foam rubber in the sound hole to seal it off and a business card to see how much of a build I was getting.
The key was to spray a coat about every 45 min for 8 to 10 coats. I was looking for about .016 to .020 green build. This shrinks down a good bit in the 2 to 3 week cure time. At this point I would start to level sand. You know your on too fast if the sandpaper blocks up right away.
Use a block at all time. and light pressure. Don't get hoggy , take your time.
I start with 600 grit to cut through the the orange peel . Once I was about 1/2 way I would sway to 800 to just about the bottom , then go to 1200 . once I was level I would start wet sanding with a mix of 1 table spoon of dawn to a qt of water. You need to keep a close look so you don't cut through. Once I was about ready to polish I would lay out where the bridge would go and see how think I was at that point. I look for about .006 to .008 in thick. You can also mic around the sound hole before you spray , so if you know it is .115 to start and you have .120 you have a good .005 build.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
B. Howard
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Re: Number of Coats

Post by B. Howard »

Number of coats is directly relative to a few things. First the actual solids content of the lacquer. This is something you probably will not know if using spray cans. Second is the thickness of the wet coat. this can be measured with a mil gauge. With this info one can calculate the dry film build left per coat and then target the desired final dry film thickness. Most lacquers will not survive below 3-4 mils dry film, and that will be after leveling and buffing.
You never know what you are capable of until you actually try....

Brian Howard
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Brian howard's guitar building & repair blog
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phavriluk
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Re: Number of Coats

Post by phavriluk »

John, I need a lesson in how I can measure the thickness of a finish after it's hardened. I'm at a loss. Thanks!
peter havriluk
tippie53
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Re: Number of Coats

Post by tippie53 »

I use a business card under a deli cup at the sound hole you can tape it there also. As I spray I just let the card collect finish. I measure it first usually between .008 and .011 in thick. As the finish builds at the end of about 8 to 10 coats you should see .016 to .020 build
This will be soft as the finish may be dry to the touch but it is still green. It will take about 14 to 20 days to cure depending on air exchange. As the finish cures it will shrink. 20 to 30% is not uncommon. You will often see a smooth finish on day one to a finish with with lots of pore sinks as it cures. The finish will harden and will develop some orange peel.
You can also use a micrometer and measure around the sound hole. That way you can measure the top build of finish. You can also measure after wet sanding so you have an idea of the final thickness.

when you remove finish off the top at the bridge you can see and measure the finish thickness at that point.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
phavriluk
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Re: Number of Coats

Post by phavriluk »

John, thanks for the details on thickness determination. Makes sense, now.
peter havriluk
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