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cyrguitars
 Post subject: KTM9 Over Lacquer?
PostPosted: Sat Dec 13, 2008 7:31 pm 
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Mahogany
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I have a bass body that has two coats of McFadden's Sanding Sealer on it so far. But I'd like to switch to KTM-9 waterborne lacquer now. Can I just apply it over the sanding sealer?

Thanks!

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Dave Fifield
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Sat Dec 13, 2008 7:48 pm 
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I'd slap on a coat of shellac first.

Dave F.

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Kent Chasson
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Sat Dec 13, 2008 10:08 pm 
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I've never tried it but conventional wisdom is that waterbourne under solvent based is OK but not the other way around. Solvent based finishes continue to off-gas for a long time. If you put an impervious film over it, the gas can't escape and problems arise.

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cyrguitars
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Sun Dec 14, 2008 1:56 am 
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So it sounds like I should strip off the sanding sealer, yes? I guess I'll attack it with some lacquer thinner tomorrow.

Thanks y'all!

--Steve in Roseville

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Dave Fifield
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Sun Dec 14, 2008 4:01 am 
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I would just sand it (220 grit) back to bare wood again, not strip it chemically. The little bit of sealer left in the pores of the wood isn't going to be an issue IMO. I would then seal it with shellac before moving on to finish.

Dave F.

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Robbie O'Brien
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Sun Dec 14, 2008 11:21 am 
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How about if you do a test piece on some scrap and see if it works. Then you could report your findings to help others in the future.
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cyrguitars
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Sun Dec 14, 2008 9:48 pm 
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Dave Fifield wrote:
I would just sand it (220 grit) back to bare wood again, not strip it chemically. The little bit of sealer left in the pores of the wood isn't going to be an issue IMO. I would then seal it with shellac before moving on to finish.

Dave F.


Sounds easier and less toxic than my lacquer thinner approach, so that's what I'll do. I don't have any shellac - is that a necessary step?

--Steve in Roseville

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Michael Dale Payne
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Wed Dec 17, 2008 11:50 am 
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the thought process is to seal the nitro and give a layer that the waterborn will adhere to . But frankly I too fear that the nitro is still gasing which will cause big issues.

If me I would finish out in nitro but if you really want to go to waterborne then I would remove all finish and start over if i was to put KTM9 on this guitar
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cyrguitars
 Post subject: Re: KTM9 Over Lacquer?
PostPosted: Fri Dec 19, 2008 3:10 am 
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Mahogany
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That's what I've done - sanded it down to bare wood. The next step is to seal it with epoxy in preparation for the KTM-9. I'll do that tomorrow, then start applying KTM-9 on Saturday.

Thanks again for the advice!

--Steve

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