The joke is that "finishing" should really be called "starting".
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| buffing/wet sanding through, egad! http://luthiersforum.com/forum/viewtopic.php?f=10102&t=15162 |
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| Author: | Stefan [ Fri Dec 28, 2007 5:24 pm ] |
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Hi all, I'm pretty novice at finishing, so I'm learning. I sprayed 12 coats nitro 50/50 lacquer/thinner and wet sanded to 400. Didn't go through on the top, but on the back I did while buffing. I want to spray some more on now but will that menzerna wax that I buffed with interfere with the lacquer? Seems like it would. How to deal with this? Also, when wet sanding how do I know when I've sanded enough? I can see sparkly pricks of reflected light which I assume to be little tiny divits in the lacquer that haven't been sanded out yet. The sanded stuff is a dull, the minute depressions still reflective. So I theorize. Is this how it is with wet sanding? You guys are great, thanks for all the advice I've got from folks in the past with my guitar problems. Stefan |
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| Author: | Rod True [ Fri Dec 28, 2007 6:57 pm ] |
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Stefan, first off I think you've thinned your lacquer to much. I only thin my lacquer about 10%. You may have sprayed 12 coats but you don't really have 12 coats of lacquer, you really only have about 6 coats with the rest flashing off due to how thin the finish material is. On to the sanding. I tend not to wet sand myself although I've done it. I start my leveling at 400 and go to 800 dry using 3M gold fre-cut sandpaper (thanks Mario). I get them from Lordco autobody painting supply store. Than I wet sand with mineral spirits not water, but that's just me. You can use mineral spirits to remove the wax from buffing. You got it right with the leveling. The tiny glossy divots are the low areas, when there are no more tiny glossy divots the finish is leveled and you can move on as long as you haven't sanded through anywhere. The nice thing with lacquer is that it is an evaporative finish which means it will melt into previous levels of finish and you can build up the thickness again without worrying about witness lines. Anyway, use some mineral spirits or naphtha to remove the menzerna wax than respray the back, (don't thin the lacquer so much) and than work at leveling again. |
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| Author: | Brad Way [ Sat Dec 29, 2007 2:07 am ] |
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Just a few things to add. You have the right idea how to tell if you have sanded far enough. What I have found in the past is that never sand on corners (you will go through) and really focus on getting everything nice and even. Take it slow and work your way around the guitar. If this is done correctly then the buffing is easy and brings everything together. |
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| Author: | Mattia Valente [ Sat Dec 29, 2007 2:20 am ] |
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A few things: 1) probably very thinned out coats. I almost always shoot straight if it's stuff formulated for musical isntruments. Up to 5-10% thinner, tops, and about 12 coats 2) 400 grit is very coarse. I scuff sand between every three coats (= beginning of each day of shooting), usually 600 or 800 grit, very lightly. Before the final coat, I level sand with whatever's feasible; 800 or 1200 grit if it's essentially flat anyway, as low as 400 to 600 if it's a little too bumpy or there are runs, etc. 3) I then shoot two very light mist coats, and don't level with anything less than 1200, preferably 1500, and then go to buffing (or abralon, or micromesh). 4) I also tend to lay down a little more around edges and corners (extra pass per coat), because of the risk of sand-through. |
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| Author: | Jon L. Nixon [ Sat Dec 29, 2007 2:32 am ] |
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The joke is that "finishing" should really be called "starting".
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| Author: | Dave Anderson [ Sat Dec 29, 2007 2:37 am ] |
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I like to wet sand with 1000 grit ,then 1200 with a drop or two of Murphys oil soap for lubrication.I'll dry sand with 800 first then go to the wet sanding.Very lightly if at all on the edges! |
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| Author: | Dave Anderson [ Sat Dec 29, 2007 2:39 am ] |
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EDIT: Also,Its good to soak your paper overnight before using. |
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| Author: | erikbojerik [ Sat Dec 29, 2007 3:16 am ] |
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I've only done 1 nitro job ever, but this worked very well for me: 1) ~5 coats thinned 10%, level with 400 grit wet (soapy H2O only), repeat. Drop-fill persistant low spots between, don't worry about tiny divots just yet. 2) 5 coats thinned 20%, level with 600 grit wet getting rid of all shiny dots. At this stage you can add more coats if you feel you don't have quite enough build. 3) 2 coats thinned 20%, level with 1000 grit abralon. 4) 1 last coat thinned ~50%, then let the finish firm up for a month. 5) finish off with 2000 & 4000 abralon, then buff out. The idea here is that successive coats fill in and melt down any scratches left from prior levelling efforts, and IMHO gives a finish that is superior to one that attempts to take a highly built coat and go all the way from 400-leveling to buff-out all in one go (i.e no coats in between). Some keys here: (a) make sure the wood sanding prep is well done; (b) take care of all drop-fills, runs and sags as they occur, I use a razor blade as a mini-scraper for knocking these down to the level of the surrounding coat; (c) do all wet sanding by hand with a firm rubber block (forget the random orbital here); (d) don't buff out before the finish is firm enough, when you gain buff-out experience you'll be able to see the difference in a buff-out attempt that was begun while the finish was still too soft. For all wet sanding I use soapy water only, enough Ivory liquid hand soap to get a decent foam going, and I rinse the sandpaper liberally and wipe the instrument off frequently to remove abraded coat. |
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| Author: | Bill Greene [ Sat Dec 29, 2007 3:25 am ] |
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[QUOTE=Rod True] Stefan, first off I think you've thinned your lacquer to much. I only thin my lacquer about 10%. You may have sprayed 12 coats but you don't really have 12 coats of lacquer, you really only have about 6 coats with the rest flashing off due to how thin the finish material is. On to the sanding. I tend not to wet sand myself although I've done it. I start my leveling at 400 and go to 800 dry using 3M gold fre-cut sandpaper (thanks Mario). I get them from Lordco autobody painting supply store. Than I wet sand with mineral spirits not water, but that's just me. You can use mineral spirits to remove the wax from buffing. You got it right with the leveling. The tiny glossy divots are the low areas, when there are no more tiny glossy divots the finish is leveled and you can move on as long as you haven't sanded through anywhere. The nice thing with lacquer is that it is an evaporative finish which means it will melt into previous levels of finish and you can build up the thickness again without worrying about witness lines. Anyway, use some mineral spirits or naphtha to remove the menzerna wax than respray the back, (don't thin the lacquer so much) and than work at leveling again.[/QUOTE] Rod rocks! I'll only add this: if you're sanding "down" in order to get rid of a few low spots, and the bottom of the low spot is very close to the wood, well, you'll run the risk of sanding through, right? So if everything looks level (an even scratch pattern) except for a few low spots, drop fill'em, let'em shrink over a couple of days, drop fill again, etc. Then, when the spot is filled, use a razor blade to take the bump down to the finish level, and gently resand. Worked perfectly for me. Just another way. Bill |
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| Author: | Stefan [ Sat Dec 29, 2007 4:46 am ] |
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Thanks for all the great advice, guys! Stefan |
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| Author: | Dave Rickard [ Sat Dec 29, 2007 7:20 am ] |
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[QUOTE=JNixon]The joke is that "finishing" should really be called "starting". With me it's "Surrender" |
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