Official Luthiers Forum!

Today, I used a bigger spray gun to apply the finish. I use balloons to plug the sound holes. After 8 heavy coats, I stopped for the day. I pulled out the balloon and some of the finish peeled off. So, I took a large(ish) sample and put it between the calipers. 2.5 thousandths. Kind of shocked me. Guess I will apply 8 more.

Mike

Why were you shocked?

I usually spray about 20 coats to get an un-leveled finish of around 7 thou (+/- 1 or so) . .008/20 = .3 thou / coat

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

And I got ragged on for spraying 8 to 12 coats before I try to level.

_________________
Steve Smith
"Music is what feelings sound like"

Why? Because I never measured it before. I admit it. I had no idea how thin the stuff dried out too.

After you level, do you reapply any more?

Mike

After leveling I apply another 8-12 coats, finish sand to 2000, then buff by hand. Got a buffer on the tool wanted list.

_________________
Steve Smith
"Music is what feelings sound like"

I don't apply any more coats after leveling. I shoot for a final film of around .004. Don't remember where exactly I got that from but I remember that it was a typical thickness.

I figured that a film of about .008 after leveling would come down to that thickness-ish. Last instrument I did, I had tape over the bridge and I left it on during level sanding and buffing. When I took it off I measured and it was right in the range of what I was looking for. Don't remember exactly what it was but I remember that it was right in there.

There's another thread here: viewtopic.php?f=10101&t=32479 where a number of experienced luthiers are recommending leveling after just a few coats. Not to disrespect their opinions but I haven't seen any evidence that it helps anything. I've tried it both ways and couldn't tell any difference.

Just thinking things through to me, it doesn't seem like interim leveling is absolutely required and I'm still not convinced that it helps anything at all. As mentioned in the other thread, good surface prep is most important to avoid burn through but, it's still more possible to burn through with a thin film than a thick one. As long as the final film is the thickness you want, what's the difference in when you level it? With 100% burn in which Target claims, how does the finish know when you've leveled it? On top of that, the finish gums up the sandpaper more when it's soft like that.

I can see some logic in waiting several days between sets of coats to allow more volatiles to outgas but I just can't see it with the leveling step. As I said, I've done it both ways and the final finishes are just as good, the one rub is that when I leveled half way through, I sanded through a bit on a very mild burst (right at a round over - most likely place). Something I haven't done since I switched to applying all coats first.

I'm not trying to get anyone to change their ways but, for those who haven't decided yet, it's worth trying. If you compare them, get back with us on your results.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

The ONLY reason I have ever sanded back was because I had pores showing. Of course, the pores were filled by the finish to some extent. Thought process was that by sanding back, I could "flatten" the pore edge caused by surface tension. On my last project, I discovered a technique for filling with epoxy that was so effective (one coat) that my em6000 shows no surface imperfections! So, I agree with Andy that it is difficult to come up with a reason to level sand and reapply. Seems like extra work, loss of material all for no good reason.

I'm learning... Albeit slowly, that the lynchpin of finishing is excellent surface prep.

Mike

I have also learned over the years that the surface prep is crucial. I have no reason for leveling and then re-applying. That was the way I learned.

Andy, I think I'll give your way a try - should save a fair amount of time and labor. How long do you wait after application before final leveling? I've been waiting at least a week but more coats may need a longer wait?

_________________
Steve Smith
"Music is what feelings sound like"

I've typically waited three to four weeks. Don't know if that's totally necessary though.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Makes sense to wait longer since you are doing final leveling for buffing. I suppose I will wait at least two weeks or so to make sure the finish won't shrink after I'm done.

_________________
Steve Smith
"Music is what feelings sound like"

One more thing I remembered - I will sometimes knock off any nubs or specks in the finish about halfway through if they're growing too much.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I tend to do the same. Just checked the file on a recent one, & I used 400 gold after 12 & 16 coats, and 600 gold prior to the last couple of "finish" coats. Deposition was about .006" before level/buff.

_________________
Dave
Milton, ON

Dave:

How much does the buffing impact the final thickness of the finish and in what direction? I would think heat may expand the finish, but the polish would reduce it, What actually happens?

Danny R. Little

Danny, about the only figure I capture is total deposition sprayed, because it comes from flakes removed from soundhole masking acetate. Leveling for sure removes some material ........ my guess is buffing removes a bit too. I'd be sceptical hearing film thickness was higher after buffing than before, but stranger things have happened (sometimes to me!)

_________________
Dave
Milton, ON

Well, been using a new, bigger gun. Turns out I have been laying down too much. No runs or anything like that. But too much texture build up. I just readjusted the gun to reduce volume of finish. But I decided to knock the texture back.

Mike

Ok, to those that I told (in another thread) that 20 coats was too much, I retract that. If you have trouble believing this, then do as I did. Use a balloon to plug the sound hole. The most I could get done in an evening is 8 coats. That is a poor measure, since we all will experience different coating layers given gun setup. Yet, done right without out runs, and excess wetting, it should average out. After 8 coats, I was able to peel some coat off of the balloons. Average thickness was 2.5 thou. 2.5/8 is about 0.3 thou per layer. I am finding that a quick 220 nub sanding followed by a quick 220 ROS sanding (I mean lightly!) and a rub down with mineral spirits is working the best. 3 nights of this results in about a 7-8 thou cumulative layer. The final layer should require min leveling. I will post before and after pics.

Mike