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  #1  
Old 02-13-2020, 12:22 PM
jrodriguezcros jrodriguezcros is offline
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Default Nitro over shellac

Hi all,

I am just about to start the finish process of a guitar that I built. I will finish it with nitro, but I thought about using shellac as a sealer first, mostly on the top because I like the color that it adds to the spruce. I know you can spray nitro over shellac with no problem, but when I have applied shellac before I have always used a lubricant oil (just a few drops) to the cloth. Will this little of oil cause any problem later with the nitro?
I normally finish the top, then remove the finish where the bridge goes, then glue the bridge on it. Can the shellac + lubricant oil applied be a problem for gluing the bridge later?

Thanks in advance,
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  #2  
Old 02-13-2020, 01:30 PM
JonWint JonWint is offline
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I only buy de-waxed shellac. For a seal coat(s) I use a 1 pound/gallon mix without oil. You just want a continuous barrier coat.

Only use oil if you are finishing with French-polished shellac.

Under the bridge you will be removing down to the wood so all oil should be gone. I always wipe the surface with naphtha before gluing.
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Old 02-13-2020, 01:34 PM
Howard Klepper Howard Klepper is offline
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If you are spraying the nitro, then just spray the shellac, at about a 1.5-2 lb. cut.
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Old 02-13-2020, 01:42 PM
redir redir is offline
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It should not be an issue for gluing the bridge since you are scraping the finish down to wood but I would hesitate to use oil for a seal coat of shellac. If you must pad it on then do it dry and just make long straight strokes. When I seal with shellac I make a dilute solution and brush it on with a good Hake brush.
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Old 02-13-2020, 01:50 PM
jrodriguezcros jrodriguezcros is offline
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Thanks for all your replies! They are very heplful.
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Old 02-13-2020, 04:40 PM
M Hayden M Hayden is offline
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This brings up a question: who masks off most of the bridge area with tape vs scraping entirely after finishing? I’ve always done the latter bc bridge placement can move a mm here or there, so I figure out where it belongs, scribe, and place, but I’m considering doing a smaller area that falls within the overall bridge boundaries that reduces the amount of footprint to scrape.

Thoughts?
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  #7  
Old 02-13-2020, 10:20 PM
nikpearson nikpearson is offline
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Default Limited experience but...

On the guitars I’ve finished to date I masked off around the unglued bridge precisely, then made a Sellotape mask of the bridge footprint. With this Sellotape mask in place the surrounding tape can be removed leaving just the Sellotape. This gives very clean results when French polishing. Not so sure about other finishing methods.
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Old 02-14-2020, 08:39 AM
redir redir is offline
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Quote:
Originally Posted by M Hayden View Post
This brings up a question: who masks off most of the bridge area with tape vs scraping entirely after finishing? I’ve always done the latter bc bridge placement can move a mm here or there, so I figure out where it belongs, scribe, and place, but I’m considering doing a smaller area that falls within the overall bridge boundaries that reduces the amount of footprint to scrape.

Thoughts?
Why would the bridge placement move at all? I like to tape it off and make the tape foot print smaller as you suggested. That way you get now rise in finish to the edge of the bridge foot print, it tends to collect there a bit more and makes a better transition when polishing out. Then you can scrape it away and not have to deal with scraping away the entire foot print. Works for me.
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  #9  
Old 02-14-2020, 09:01 AM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by nikpearson View Post
a Sellotape mask..
For those of us not in the UK: https://en.wikipedia.org/wiki/Sellotape. It appears to be what we'd call "Scotch tape".

Although I have yet to try it, a while back, someone here suggested using Frisket film, suggesting that it worked very well: https://www.grafixarts.com/products/frisket-film/
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  #10  
Old 02-15-2020, 02:52 AM
nikpearson nikpearson is offline
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Default Thanks Charles...

I forgot these things have different names across the pond.
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  #11  
Old 02-18-2020, 01:18 PM
Alan Carruth Alan Carruth is offline
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In theory nitro over shellac violates the painter's rule of 'fat over lean'. Shellac is a softer and more flexible coating than nitro, and this can cause crazing as the nitro tries to hold onto the softer substrate. Many people get away with this, but I have seen instances where they didn't. Keep the shellac layer thin.
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