Official Luthiers Forum!

Ok, so let's forget for a second that I need to avoid getting air bubbles in my finish to begin with. Do I need to sand back to wood to get rid of them or can I just keep over coating and level when the finish is thick enough? I'm brushing KTM-SV with a foam brush. I'll likely head out and get a new bristle brush. Until then, how do I proceed? I didn't have this problem brushing KTM9 with the same foam brush. What gives? Thanks in advance.

Heath

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sweat the small stuff.

Sand back, and recoat - it's what I would do.

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"Act your age, not your shoe size" - Prince

Urgh. Don't wanna. I tend to post questions I already know the answer to.

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sweat the small stuff.

Interesting, I've been using KTM-9 for a while and had the exact opposite problem: a bristle brush caused air bubbles, but a foam was perfect. I find that the air bubbles often disappear while the finish is drying (at least IME) and if you go a moderate speed, not too fast nor too slow, you can avoid them entirely. If the air bubbles are still there after the coat has a few hours to harden, I would sand.

NOW I'm frustrated. Went and bought a bristle brush. Nothing special, $10 Purdy designed for clear finishes. SAME result. Tried two different cans of KTM-SV. If I didn't hate finishing before, I do now. Frustrating.

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sweat the small stuff.

You need a better brush. Ten bucks won't get it.

Heath, I noticed a 2009 thread with lots of good info ...
viewtopic.php?f=10101&t=22737&st=0&sk=t&sd=a&hilit=brushing+ktm%2A
Randy Muth (who seems to have as much experience as anyone with -SV) suggested he didn't think foam would be very good and had some recomendations for brushes, (as well as the homestead link where I'm sure you could get more info). (...or, PM Randy)

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Dave
Milton, ON

Thank you gentlemen for your input. Dave, interestingly enough, I asked Randy about brushing KTM-SV in that very thread! Three years later and I still don't have it figured out! Anyone want to recommend a specific brush for spar varnishes? I'm thinking about thinning it 50/50 with mineral spirits and wiping it on. What sort of pad would one use for wiping on a varnish?

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sweat the small stuff.

My first four guitars were finished with spar varnish using an expensive boar bristle brush. I am not sure if this type of brush is still available. I will look around and see if I can find a source for you.

Heath - make sure that you have the brush bristles dipped into the finish all the way to the ferrule. Natural bristle brushes will swell in water based finishes, so I would suggest that you use a top quality synthetic brush.

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

Heath, late in that thread, Randy suggested some things re brushes...
Typically natural hair brushes are used for oil based finishes and synthetic brushes are used for waterborne. Ironically, I found that a very fine china bristle brush is pretty good with KTM-SV and I didn't like the nylon brushes. The best bet however is a golden taklon brush. Homestead sells these, but good brushes are not cheap.
I don't have any experience with -SV, but my best brush is a "badger hair" brush, which seems pretty good at flowing & "tipping off" a variety of finishes.

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Dave
Milton, ON

These brushes are close to what I was talking about but note that they are for solvent finishes only. They also have synthetic brushes for water based finishes too.

http://www.toolsforworkingwood.com/store/item/GT-SHEBRU.XX/Gramercy_Tools_Finishing_Brushes_for_Shellac_and_Lacquer