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| Air bubbles in finish http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=37492 |
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| Author: | Heath Blair [ Mon Aug 20, 2012 6:20 pm ] |
| Post subject: | Air bubbles in finish |
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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| Author: | Chris Pile [ Mon Aug 20, 2012 6:44 pm ] |
| Post subject: | Re: Air bubbles in finish |
Sand back, and recoat - it's what I would do. |
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| Author: | Heath Blair [ Mon Aug 20, 2012 8:21 pm ] |
| Post subject: | Re: Air bubbles in finish |
Urgh. Don't wanna. I tend to post questions I already know the answer to. |
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| Author: | oval soundhole [ Mon Aug 20, 2012 11:05 pm ] |
| Post subject: | Re: Air bubbles in finish |
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. |
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| Author: | Heath Blair [ Mon Aug 20, 2012 11:13 pm ] |
| Post subject: | Re: Air bubbles in finish |
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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| Author: | Barry Daniels [ Tue Aug 21, 2012 9:22 am ] |
| Post subject: | Re: Air bubbles in finish |
You need a better brush. Ten bucks won't get it. |
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| Author: | Dave Stewart [ Tue Aug 21, 2012 11:23 am ] |
| Post subject: | Re: Air bubbles in finish |
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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| Author: | Heath Blair [ Wed Aug 22, 2012 10:23 am ] |
| Post subject: | Re: Air bubbles in finish |
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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| Author: | Barry Daniels [ Wed Aug 22, 2012 10:43 am ] |
| Post subject: | Re: Air bubbles in finish |
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. |
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| Author: | Alex Kleon [ Wed Aug 22, 2012 11:04 am ] |
| Post subject: | Re: Air bubbles in finish |
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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| Author: | Dave Stewart [ Wed Aug 22, 2012 11:25 am ] |
| Post subject: | Re: Air bubbles in finish |
Heath Blair wrote: .... 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! 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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| Author: | Barry Daniels [ Wed Aug 22, 2012 1:22 pm ] |
| Post subject: | Re: Air bubbles in finish |
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 |
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