Buffing Nitrocellulose Lacquer

[Rmouton]

Thanks Charles. I'll add some 800 to the mix. The LMI web site does not specify, but I can assure you that it's 3M. I've been using it for a while. Lee Valley sells it too. It's not cheap by any means.

https://www.leevalley.com/en-us/shop...-dry-sandpaper

[mirwa]

In australia the nitro comes froma company called Mirotone, that is who i use.

I typically flat sand wet a surface with 600 grit then 1000 then 1500, buff on a machine with medium compound, w58 i think it is and then fine compound p195, i could be wrong on numbers, sitting at home typing reply.

The trick for me with sanding and buffing is just go one direction, then when you go up a grit you change 45 degrees to the old direction, any scratches going the old way are still to deep and keep sanding

Once all buffed on the machines I let it sit an hr where i then hand buff or use a drill buff any super fine scratches that may be still prevelant.

As most people know, its a slow process and you cannot rush it

Steve

[Rmouton]

Thanks Steve. I am definitely going to change my sanding direction for each grit like you recommend. Thanks everyone for the advice. I am convinced my grit progression was my issue. I was going from P320 to 600 ANSI previously. Then from 600 ANSI to 1200 ANSI. I have closed those gaps.

My new routine is set to be:
P220 - sand bare wood up to this grit
4 coats lacquer 1 to 1 to get started
4 coats lacquer 3 to 1
P320 - first lacquer level Dry Stearate paper
4 coats lacquer 3 to 1
P400 - second lacquer level Dry Stearate paper
4 coats lacquer 3 to 1
P600 - third lacquer level Dry Stearate paper
4 coats lacquer 2 to 1
Then final leveling and polishing
600 ANSI - Wet
1000 ANSI - Wet
1500 ANSI - Wet
Buffing wheels with Menzerna Brown, Pink then White.
Meguiars swirl remover then Meguiars show car glaze with a 3" random orbit and foam pads.

All to be done very patiently without using too much pressure and doing everything I can to avoid cross contamination.

[mirwa]

Way to complicated. I dont sand any of my nitro coats during the paint work.

Flat sand 220 grit.

Shellac seal the wood, scuff sand with marroon scratch pad

Color coats 3 (5:1 nitro to thinner ratio) and allow to dry over night, no sanding unless you got runs, 2 coats clear next day same ratio and the next and the next, so around 6 good thick clear coats, let it sit a couple of weeks, flat sand with 600, if it looks good leave it for another two weeks, if it doesnt put another build coat on

Then finish sand and buff

Steve,

[Rmouton]

Noted. I like less complicated. Thanks for the advice so far everyone.

[Rmouton]

Well, I cobbled together all of the advice you each gave and obtained a hugely successful outcome. I have a near perfect finish on my most recent guitar. I understand my issues completely now. I had a few, but the biggest issue was not getting out the previous grit scratches. I'm terrible about that. NO patience. Here's what I did to correct my process. I only level sanded once during the spraying sessions due to defects/runs etc. I started with 1000 grit ANSI because not getting out the 600 grit scratches was my biggest issue. No problem, I just simply didn't put any 600 grit scratches to have to later remove. I also changed direction for each grit when wet sanding and I spent more time on the buffing wheel with each compound. Now here's my question. It took me 7 hours total to wet sand and buff. I'm just wondering if that's slow, fast or about normal. Here's what took 7 hours.

1000 grit wet sanding 3 hours
1200 grit wet sanding 1.5 hours
2000 grit wet sanding 1.5 hours
Heavy, Medium and Fine buffing compounds on the buffing wheel 1 hour

Thanks for the great advice everyone. I was able to simplify the process and make it better.

[charles Tauber]

Originally Posted by Rmouton

It took me 7 hours total to wet sand and buff. I'm just wondering if that's slow, fast or about normal.

Slow.

In the early days, it took me that long as well. There are things I've learned along the way that radically reduce that.

A lot of how much time it takes to do the final sanding and buffing depends upon what you have after the last coat of finish is applied/sprayed. If the texture left behind by the spray gun is small and without defects (runs, drips, orange peel, etc.) the amount of level sanding can be very little. You are then literally only levelling the fine texture off the gun. If the gun leaves a lot of texture, you'll need a lot of sanding/levelling. And, that's the trade-off. As you already know, if you reduce sanding time by starting with a coarser abrasive, it is more difficult to remove the scratches it leaves. If you use finer abrasives, you avoid the big scratches, but it takes a long time.

Thus, a lot of the time savings is in surface preparation before applying any finish and, in open-pored woods, ensuring that the pores are fully filled and/or levelled prior to applying the top coats. You don't want to be trying to level pores using fine sandpaper - it takes too long. At the end of the pore-filling steps, the surface should be "perfect". If you then apply "near-perfect" coats of finish, there isn't much final sanding to do.

You might find that you don't need the "heavy" polishing compound, that the scratches left by the 2000 can be removed with the "medium" compound.

I recently purchased Jeff Hewitt's on-line course (from Robbie O'Brien) on "Levelling, Wet Sanding and Buffing". It is a new course offered in January and I was curious to see what Mr. Hewitt does. There were a few interesting things that were new/different to me. One is that he recommends specific automotive sandpapers that MUST be of the European "P" grading system. The reason for the "P" graded papers is for consistency as you progress from one abrasive to the next. He has chosen, in recent years, to sand to finer grits prior to buffing, which he states improves the result and reduces buffing time. If memory serves me, he starts at p1000 and goes to p5000. The sanding takes him an hour or so, the buffing less than that.

I have not tried the specific sandpapers that he recommends - some of them were new to me and some of them are "industrial" abrasives sold only in larger quantities at a price of about $200 to $300 per grit.

What I do know, however, is that not all "sandpaper" is created equal. Some is more uniform in its scratch pattern, a must for fine finishing. Using "good" sandpaper can reduce the sanding required to remove the scratches left by the previous grit. Mr. Hewitt makes the very good point that there is no economy is using dull sandpaper: switch to new, sharp paper frequently. That might be part of why it is taking you so long to sand.

[Rmouton]

Wow, that Jeff Hewitt guy is fast! Thanks Charles. I now have a new goal.
Increase my efficiency/speed. After reading all that you have offered, I would say my next thing to work on is texture off the gun. My pore filling and leveling is solid. I believe my sandpaper is good as well. I might also start with a little more aggressive paper than 1000 next time. I also considered that video. I have not purchased it yet, but I just might.

[Victory Pete]

It is great once you have a reliable system isn't it? My method took 20 years to evolve. I don't do wet sanding or use a buffing wheel. It takes me probably 4 hours to get a gloss level surface. I make sure my wood surfaces are as level as possible, which is difficult sometimes because you don't always know where the hills and valleys are until you get the surface to shine. I don't do any initial pore filling. Once I start getting some Nitro or Shellac spayed on I sand with 120 3M Stikit Gold on a somewhat hard block and look for the shiny low spots. I then use an Airbrush to fill the valleys. I put on more finish and then repeat the process. Once I am satisfied with the build and level of the finish I start sanding with 220 on a firm foam block, then repeat with all grits up until 800. 1800 MicroMesh on a foam block and then I used liquid medium buffing compound on a cloth rag and start buffing, you can get quite a shine up until this point. I don't usually use fine compound as I like a mirror finish but I like it to have a warm glow to it. To end up with perfectly consistent reflected contours in the guitar really makes it look great. Here is my most recent spray job, it is Nitro. https://www.acousticguitarforum.com/...d.php?t=607083

[John Arnold]

Old school here. Lamb's wool 8" Superbuff turned by a plug- in Makita variable speed drill or drill press. Compounds (coarse to fine) are Mother's Mag and Aluminum Polish, 3M Finesse-It II, and 3M Machine Glaze. 3M Hand Glaze by hand for swirl marks. Sanding is always linear, parallel with the grain. Buff across the sanding scratches until they are no longer visible when viewed using a long light (fluorescent or LED) aligned parallel with the scratches. Lessons learned include the fact that scratches need to be completely removed before proceeding to a finer stage. Use separate buffers for each stage to avoid contamination. In my experience, lamb's wool is more aggressive than foam. Always buff from the surface toward the edges.

[Rmouton]

Would an random orbit air sander be something to consider? I did all that sanding by hand. I've been considering taking the plunge and giving it a shot.

[Simon Fay]

If you haven't already invested in sandpaper -- then use the Kovax abrasives. It is a dry system and is absolutely game-changing. I've heard good things about 3M trizact but the general impression in the automotive and detailing industry is that nothing yet rivals the Kovax products. They are expensive but worth it, IMO. the American distributor is Eagle Abrasives.

I discuss them in greater detail in post on the OLF.

http://luthiersforum.com/forum/viewt...=10101&t=53979

[Victory Pete]

Originally Posted by Simon Fay

If you haven't already invested in sandpaper -- then use the Kovax abrasives. It is a dry system and is absolutely game-changing. I've heard good things about 3M trizact but the general impression in the automotive and detailing industry is that nothing yet rivals the Kovax products. They are expensive but worth it, IMO. the American distributor is Eagle Abrasives.

I discuss them in greater detail in post on the OLF.

http://luthiersforum.com/forum/viewt...=10101&t=53979

Yes, the Kovax blocks and papers are fantastic.
https://www.stewmac.com/luthier-tool...ir-system.html

[Victory Pete]

Here is what I get with my method. I use the reflections of the lights to show contours.

[mirwa]

Originally Posted by Victory Pete

Here is what I get with my method. I use the reflections of the lights to show contours.

The reflective light looks very dispersed. I would call that almost a satin finish.

There is a difference between polished and high gloss reflective surface.

Steve