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Finishing Lessons Learned


John Abbett
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All,

I've been posting and asking questions on finishing for a while. I've done a few guitars and have learned a lot about finishing through suggestions from the board and trial and error. Here are some of the things I've learned. Hopefully it will help someone.

Things I've learned.

1. I don't bother fine sanding the guitar as I build. My shop is dirty, I can't possibly keep a guitar clean as I built it. I shape the guitar until it's time for finish, then I finish sand all at one time and immediately start the finish process. No more fixing little scratches as I go and wasting time.

2. I don't sand the guitar to crazy grits when I'm going to apply a stain. I sand to 320 then it's good. Sanding wood to 1000 grit and applying a water based stain is a waste of time for me..

3. I sand to 320 grit, getting everthing even and level. I pre-wet the wood with a sponge, raising the grain and then lightly sand it smooth again with 320 or 400.

4. I apply two coats of dye, putting it on heavy. If I put it on too lightly it doesn't look as even as a heavy coat that I put on with a clean rag. I put the second coat on fairly soon after the first coat. I don't wait for it to dry. I do this just to even out the color and darken it. I don't sand after, I apply two coats of blue with an old t-shirt and let it dry. That's all there is too it. It's not complex. From all the discussions it would seem it's rocket science. Two heavy coats with a rag over a 5 minute period. Done.

5. I wait for the stain to dry completely. I don't want moisture under the clear coat.

6. I wait for a time when the garage is warm and make sure the guitar is the same temp as the garage. I had trouble when I brought a warm guitar from the house into a colder shop, the guitar cooled and gave off little bubbles that showed up in the finish. I work with different temperatures, but heat has been a problem. I've sprayed in a cold shop without any issues. I heat the garage, making sure the concrete is warmed up. I open the garage door and spray. Once the overspray is out, I close the garage door and let the garge warm back up. I think this works because the spray and the guitar are warm, and I warm the garage back up before the spray starts to harden. It only takes a couple of minutes to spray and the room heats back up quick. Not ideal, but it has worked and I don't have to leave a guitar waiting to spray until summer. Heat has caused me problems. Clouding and bubbles. I don't spray over 80 degree's anymore. It's too risky for me. I have a lot to learn about that.

7. I spray Behlans Instrument Lacquer at 1-1, one lacquer thinner to one lacquer. I use dixie cups to measure. One of each with get me a nice thick coat. I don't use sanding sealer anymore. It doesn't make as good a bond between the lacquer and the wood as lacquer without sanding sealer. I have places where I bumped the guitar before it was fully cured (Like two weeks later) and I get little ghosted opaque places where the sanding sealer and the lacuquer meet. I just use lacquer.

8. I spray the top of the guitar horizontal. If you spray with it hanging on a hook you have a slightly higher risk of runs and sags. I put it on a stool or workmate, spray the top until it's wet looking and let it sit for a few moments. It only takes a couple of minutes to firm up. Then I hang the guitar and do the back and sides.

9. The little fuzz that you see right in the middle of the guitar - DON'T TOUCH IT. I found that no matter how careful you are, you get your finger in it and then you've moved the finish and have a mess. If you wait until the coat is dry you can take the fuzz out with 600 grit sandpaper and it will come right out without leaving a mess.

10. 2 coats a day, 2 hours apart for 2-3 days gives me a nice coat. I use about 1/3 - 1/2 of a quart of lacquer.

11. I hang it on a hook through the tuner holes for about a week. It's firm to the touch in a day, but if you put it on a stand or a anything, it will take impressions of what it's sitting on. I put it on a table after 3 days and there was a rubber placemat, when I picked it up 5 minutes later the placemat was impressed on the guitar.

12. After about a week, I level sand with 600 gritt until it's evenly scuffed.

13. Buff with cotton wheels with plasticote fine and ulra fine bar compund. The first guitars I did I did with increasing grits of sandpaper and scrach remover at the end. Took several HOURS. Buffing took 5 minutes tops after 600 gritt. Best investment I've made in tools is the buffer (Home built). I wish people had told me that yes you can do it by hand, but it's a major pain in the ass. Get a buffer or buy the wheels and put them on a drill or something, doing by hand with sandpaper is a long process.

This is my current process, which will change each time I build, but this past guitar it worked great. I have a Blue Curly Maple top that has a deep 3d effect, like looking at the grand canyon from a plane, the finish moves when you move the guitar like one of thos code rings. The lines shift and move all over. The blue is even and dark. The finish is thin and even and clear.

It took one evening to completely finish sand the guitar, tape up the binding and apply two coats of blue. It took three more eveings to spary the Nitro. Let it sit a week, it took one long evening to sand with 600 and buff. An evening for me is a couple of hours after my Daughter goes to bed.

Anyway, hope this helps.

-john

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Good post. I've learned some of those same lessons. Number 1 especially. There's no reason to sand the same guitar out 4 times. I also don't sand to high grits. For oil or dye jobs, 320-400 is fine. For lacquer jobs on woods that don't show scratches too easily, I just go to 220.

I started out spraying Behlen stringed instrument lacquer mixed 1:1 with thinner. Never had any real problems, but I've since switched to McFadden. The Behlen stuff is intended for acoustic instuments and had plasticizers added to make the finish more flexible. The McFadden lacquer seems to cure a little harder. I can get the McFadden lacquer to flow out better than I was able to with the Behlen lacquer, but that may be more due to improved technique than anything else. I spray a couple coats mixed 1:1 over raw wood as a sealer, then about 10-15 coats mixed 75/25 with 5% retarder to build the thickness. I only sand between coats if I need to take care of inclusions, runs, or sags. I level sand the guitar once after about 6 coats using 600 grit and again after the last coat of 75/25 lacquer using 800 or 1000 grit. After that I spray 2 coats of 50/50 lacquer and hang the guitar up to cure for a month. I don't use vinyl sealer either. I haven't had many problems with runs or curtaining, but if I get one, I don't worry about it. I just finish spraying, wait a few hours, then sand it level with 600 grit. I do the same thing when some little piece of fuzz gets into the finish. Trying to pull it out while the lacquer is still wet just causes more problems. This has worked quite well for my last three guitars.

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+1 painting flat. This has really improved my coats and lowered my sanding work.

+1 no sanding sealer. The last guitar turned into a nightmare trying to get the lacquer to stick after a bad sanding sealer ordeal. For some reason they just did not get along and forced a complete sand back and restain..

+1 320 Grit sanding - no 600 grit until a couple of coats are on.

I now stay away from Steel Wool. It is hard to find it without oil.

Watch the water sanding. It is easy to get too much water on the guitar and it get under the finish through an unfinished hole.

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+1 on steel wool.. It caused me a nightmare. You can't see all the little particles and blowing with the air compressor doesn't get rid of them.

I've banned the stuff from my shop. It's a shame, because it does a good job and cleaning up fretboards and frets and polishing inlays. It's just not worth the problems it causes.

-j

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great post here....I agree 100% with John's findings and if I can add that I use min spirits to wet sand vs. water to avoid ruining a finish with water creeping underneath, ask me how I know! I made up a crude rotating fixture that allows me to spray one side and the sides then turn it over so it can flash with minimal crap landing when it's wet. flip, and do the reverse. my first 'real' quality finish was a shoreline gold strat body that recieved 10 thin to medium coats of clear then blocked with 1000G and polished using 3M product with my PorterCable orbital set at 1500 rpm.

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I've been researching brushing methods and think I've found what I'm going with. I'm gonna' use a Target coatings product. Not sure which one yet, Either their Oxford USL or Emtech em6000. They're waterbased, and their website has some good info. You can mix them 15-20% with their SA5 Retarder and pad it on using T-shirt material. I asked about using pigments for an opaque color too, and they said to add pigment to the laquer witgout the retarder, as the pigment will thin the laquer enough to pad it on. I think that's the method I'm gonna try on my next project.

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It doesn't have to be expensive to spray nitro. Nitro is so forgiving you can spray it with about anything. \

I keep a few of the Preval Sprayers(sp) around, they are about 10 bucks with the replacement cartridge about 4 bucks, they are disposable sprayers. It has a little glass jar that you put the Nitro in, and a pressurized cartridge. I used them outside and they worked great. I went through three of them to spray my first guitar.

If you were doing one guitar it would be cheaper then investing in a sprayer.

The sprayer I use is a cheap-o from Harborfreight tools. It's a gravity feed sprayer and I hook it up to my porter cable pancake compressor. I got the compressor with a nail gun for under 100 bucks. The sprayer goes on sale for 20. The sprayer does a good job. I don't run it non-stop. I spray, then release the trigger then spray and release the trigger, when the compressor comes on so that I keep the right pressure up. I spray at 40 lbs. My compressor can keep up fine if I don't hold the trigger down the whole time.

I found that if I hold the tigger down and the pressure drops I get larger droplets that are harder to level.

I'll keep the magnet idea in mind, it would have been the obvious way to remove them from the surface of the guitar. Wrap a magnet with a rag and run it over the guitar.

Oh another lesson learned. Make sure the holes you drill for the studs for your bridge are deep enough. If they are too shallow and you take a hammer and pound them in and they are sitting pround of the body, it's a pain to pull them out without marring the finish. Ask me how I know that one!

I was able to remove them by inserting a bolt into the stud, and cutting a block of wood that fit in the pickup cavity that was slightly higher then the bolt. I used big pliers to lever the studs out. No damage to the finish. I did use some words that would impress a sailor when I realized what I did..

So then you are really Pissed and take the body to the drill press to deepen the holes. You forget that the bridge ground wire is in the hole. The drill grabs the wire and pulls it right around the bit and then you can't get the bit out. It was a bad night. More creative language utilized.

-John

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My finish process goes something like this:

day 1. 2 wash coats 50/50 lacquer to thinner. I like Mcfaddens the best. 1-2 top coats that are 90/10. pour fill if needed, let gas off for 2 days.

day 2. 5 top coats. scuff sand the next morning with 220, let gas off for the day.

day 3. color day, plus 5 full coats. drop fill where needed. scuff sand the next morning, try to get it as flat as possible, let gas off for a day.

day 4. 5 full coats, drop fill if needed. flat sand the next morning, let gas off for a day.

day 5. 2 light coats.

let cure for 2 weeks, wet sand with 600 then 1000 grit then buff.

There is no sense in doing any finish sanding while you are still technically building it. Once the building stage is complete, CLEAN your entire work space. Finish sand to 220, any higher and the lacquer doesn't stick too well. Clean your work space again. Once its done curing you want an immaculate clean area to work on it.

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