Official Luthiers Forum!

I think to help the newer people we should have a finish topic per finish material.

I will start and hope we only include Nitro in this topic and we should have topics of other finish products.

Advantages of nitro is the repair ability. You can fix it years down the road.

Any finish is about prep and application. I have been doing this about 20 yrs. I live in pa and I mention this as one of the variable of finish is the RH of the area and how that affects the finish.

so my prep is to sand to 220 grit. I want to have some tooth for the finish to hold to,

after sanding I wipe with Naphtha , mineral spirits and allow to dry.

My finish booth allows me to use heat lamps to warm the body and neck , also my finish is heated to about 95 degrees F. I use a few different guns. 1.3 and 1l4 needles.
I have a fugi semi pro with 1.0

my first coats are vinyl sealer 2 light coats and scuff sanded after about 1 hr.

Filler if choice is aqua coat 2 applications on most woods nothing on spruce
allow 1 hr dry and level sand with 400 grit
another 2 coats let dry overnight level sand

Lacquer is Mowhawk instrument lacquer 2 oz thinner per 1/2 gal

HVLP guns are gravity guns and air set to about 18lb

I use a rotisserie to turn the body. heat lamps keep the body and guns warm. I do 1 coat about 45 min to 1 hr apart
spray booth is vented and heated. RH control to 45% to 50% 75 to 80 degrees.

I use tape under the fingerboard extension to pull and measure coat thickness.

Allow about 2 to 3 weeks cure before level sand and buffing.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I think your idea on one finish topic per finish material is a good one. Nice start--thanks

Dave

After curing time I level sand
This is a technique that must be mastered. Often most beginners don't go down far enough and leave a lot of dips and sinks. I will also say that not all sand paper is the same, I use
Klingspore and Mirka and micro mesh

I dry sand with Mirka 400 to start. I may also add my sander is a Random Orbital Festool a good sander is required

I sand to about 1/2 of the shine marks are gone move to 600
sand till most are gone but not all

now I start wet sanding with klingspore 800 1000 2000

now hand set sanding with micro mesh to 24000

then I buff using Mazzerna compounds medium fine finish and P175

after this I may use Maquires swirl remover

this process can take anywhere from 2 hrs to 4 depending on how well your prep was.

Learning to read the surface is a skill that takes time.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I wish I was a beginner who didn't sand enough because on practically every guitar I have done in Nitro I sanded through the finish. That has always been my biggest problem. I cannot imagine ever using a ROS on a finish, I would burn through it in no time.

Gah!!! I HATE finishing.

John, I agree that the Festool ROS is a step above. I also have an older Mirka ROS which works very well. But a comment for newer folks is that when using any ROS sander, it requires a light touch if you don't want to leave swirl marks.

_________________
Steve Smith
"Music is what feelings sound like"

I can't imagine not using a ROS now that I have one. I used it on my last nitro guitar without an issue.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

Having ladled the stuff on to my first few builds I have been trying to keep the thickness down so I too have had sanding through problems. And it takes ages to fix when you do.

Interesting that you go to such a small grit on the micromesh John, before buffing. Some people seem to go to the wheel at much smaller numbers.

Not having a bufffing setup I accept a lower sheen from the micromesh.

Oh and this is a good idea. Cheers Dave

I'm sure technique plays a huge part in this. If I was training an apprentice for example and I said, "Only lightly sand it..." What would he think that means? It's the kind of thing you have to figure out yourself.

I love my Festool ROS and use it to prep every gutiar now. But I can't imagine using it on a finish especially in areas like around the curves of the upper bout, the waist and so on.

John thanks for the details. Could you please clarify are the sandpaper grits mentioned in your finishing schedule CAMI or P grade? Just wanted to draw a distinction for posterity as especially in the finer grades there is a big difference between the two grading systems.

For those using a ROS, are you using it on the sides as well as the back and soundboard? Do you still hand-sand the waist?

P grade paper I have CAMI on the 2500 3000 and 3500
as mentioned swirl marks can be a problem and with the Festool I have a speed control. I like to run in the middle and I do say just let the weight of the sander do the work .
Once I get to the 3500 the swirl marks are there but light and micro mesh at this point is 15000 up to the 24000 and this I do in a straight line. My first buffs are across the grain and this helps remove the sand marks that I do with the grain.

I have a number of ROS and the only one I would use on a finish is the festool , I have a millwalkee and its good but the festool as way better than any I have ever used.
I use it on the waist there is a technique to it but it works . If your ROS spins when you pick it up it isn't a finishing sander

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I will have to try your method John. I've been using Benedetto's finishing schedule for many years as his book was used in building my first guitar, an archtop. I use Mohawk instrument lacquer but no vinyl sealer but I've often wondered if that would help make it easier for me. I've had a lot of very good finishes, but would like to get to the next level in ease of getting to something with less flaws. Could be more of the experience and "feel" that you mention though.

one thing is the the lacquer has changed in the last few years from what it was even in the 90's it is almost as much about chemical compatibility as it is about technique.

I hope others that shoot nitro can add to the discussion. I know at one point I was using more thinner and retarder than I do now.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I appreciate this thread. I know a fair bit about guitar setup, repair, building, etc... but I'm a complete beginner when it comes to finishing. I got the Stewmac book and have been drinking it in... but I want another source or two. With the Stewmac book, you kind of have to piece it all together and there are a lot of gaps. And I'd love for more source to buy the material than Stewmac. I got their aerosol kit and that's fine for a first guitar, but it's like training wheels... I need to eventually learn the real way.

Any suggestions?

John, thanks for the great details.

Hey Ryan, looks like you're just down the road. In my opinion, finishing is one of the hardest things to do in guitar building. In the last 20 years of guitar building I've read a bunch of books, screwed up more than a few guitars, and refinished them. I can get decent results now. I finally just picked one type of finish and then kept at it till I learned to do it right. Would be nice if there was someone around that was teaching instrument finishing. I've taken some furniture finishing classes and they were useful but, of course, furniture and guitars are not the same. Pretty much learned by trial and error along with lots of help from the folks here at the OLF.

_________________
Steve Smith
"Music is what feelings sound like"

I have been finishing with nitro for 45 years....

I thin my lacquer with 10% thinner and 5% retarder. I find the retarder helps the lacquer flow better-I use a little more when it is humid.

I spray about 6 coats per session in a dy-2 at a time with an hour between double coats-I do this twice and let it set for a day or two and usually give it another double coat.

I sand with 400 paper in between coats.

I then let it dry for a minimum of 2 weeks.

I with wet sand with 600 grit by hand on a padded block,let it rest a day then buff with the orange then white Menzerna.

The sanding takes usually 2 hours,then an hour on each wheel.

I think I get great results and get many compliments on my finishes.

I am starting to do some satin nitro finishes- 4 coats of gloss then 2 coats of satin (20 Sheen)-straight off the gun...it comes out nice- 1/8 of the work.

If you go to Robbie O’Brien’s website, O’Brien Guitars, you will see several excellent video courses led by Jeff Jewitt. Jeff and Robbie will also be leading an in-person instrument finishing class in Indiana next year.

A good resource for sure. Too bad Robbie’s stuff wasn’t around when I was trying to figure out how to finish guitars.


Sent from my iPhone using Tapatalk Pro

_________________
Steve Smith
"Music is what feelings sound like"

I'm not sure how lacquer has an "advantage of repairability years down the road." Advantage over what other finish. Urethanes are incredibly repairable. In fact more so than lacquer. With urethane, it's a CA repair. Hardening happens quickly. Easier to level and stay level to rest of finish. Doesn't shrink after a few months, like a lacquer repair will (compared to the existing, far more cured finish). I might say, having down thousands of both repairs (we do a lot of them), nitro is actually a more difficult finish to get to an excellent end product. New lacquer shrinks versus old lacquer. No way around that. It's softer ... and easier to buff a crevice. Which doesn't matter as it will further shrink, anyway. We often see lacquer touch-ups come back for more work months down the road, and in fact advise the need for this with discerning repairs (i.e. high-end instruments and highly detail-oriented owners).

But maybe that statement was made in reference to some other finishes - certain varnishes, perhaps?

Urathanes don't cross link like nitro . A nitro and shellac finish can be repaired without witness lines.
Urathanes are other finishes are used on electrics and I don't see much on acoutstics

this discussion is on lacquer and its application and the process of finishing. Most buyers of acoustics do prefer nitro. There are some very good products out there for finishes being used and will be discussed on another thread. May I suggest if your are an expert on Urathane finishes post about that. Catalized varnish is another good guitar finish

As a repair person i see many more nitro finishes than anything else as they have been used for over 100 years.

agree with you that repairs take a bit of expertise but can be done and done will

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I was only responding to your original post, which posited nitro having repair advantages over other finishes in the long haul. That's just false in my experience, and has nothing to do with process, so not sure why it was stated at the beginning of what is said to be a process thread.

If one deals mostly with Martins and the like, absolutely repair experience is going to be mostly nitro. We do a lot of Martin (and other brand) nitro finishes, and I mean a lot of them. It's really not an issue of skill (any good repair person that spends time on finish repairs is going to get good at lacquer repairs - they are simply not that hard to perform). But new lacquer shrinks, and while things like convection boxes can help, lacquer is still going to shrink.

There are enough urethane finishes floating around (Taylor and many others) - we're no longer in the world of just slathered, cheap and quick urethane finishes of the 80's and 90's.

On the subject of witness lines, it's a good idea to consider what products one uses to perform urethane repairs. We don't have witness line issues - if we did then I could not have made the counterpoint to nitro being claimed as superior for repair. In fact if we had witness lines, then repairability would be poor and I'd completely agree with the original claim. Simply for the end customer - which is what matters most - urethane is every bit as repairable in the long haul as lacquer, regardless of which guitars a luthier sees more or less of. One just needs suitable experience performing those repairs, much like with lacquer.

Back to process discussions.

Would you consider sharing (in a separate, urethane-themed thread ) some of your techniques and processes for urethane repair? I’m very interested and I suspect others would be too.

Nitro is much more repairable than most finishes and that is a fact. Many finises when drop filled will leave witness marks , Urethane is one of them. This thread isn't about those finishes it is about nitro and basically the initial finish sequence.
I have dealt with many finishes through the years You are entitled to your opinion

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

A couple months ago I had a guitar in that was built in 1920's which is about the time Nitro was adopted to use in guitars. The Nitro repair melted right in beautifully with the original Nitro almost 100 years old now. I think that's probably what John was talking about. I find Nitro a joy to work with. I don't finish guitars with it anymore though. Glue Boost imho is by far the best CA for modern finish repairs. I love the stuff.

Our friend Rick Turner has been bringing up in the last few years from time to time the idea that nitro wonderful as it is we think will deteriorate when it's getting close to 100 or so. We seen this happening now on a few and so has Rick.

Our experience is like your's JF and John Halls too, it's great stuff with limitations but for it's day and even beyond it's a pretty good choice for many applications. I buy a lot of guitars these days in so much as I am actively collecting now (and playing a lot too) and my finish of choice for what I do and like is nitro.

Especially when building nitro is a great choice because it gives you essentially unlimited do-overs with out much rework during the finishing process if something happens to go wrong. This can be the difference between making a profit and loss on an instrument, if the alternative is stripping and starting from scratch. Agree also that it adds value for the customer in that they also get access to this lifetime of seamless, invisible repairs during their time with the axe should accidents occur.

100 years is a pretty reasonable lifespan for a coating and well outside the warranty coverage I offer

Genuinely curious RE claims about invisible urethane repairs as I haven’t seen a truly invisible one and the existence of such a thing would be kinda revolutionary.