Official Luthiers Forum!

I would like to survey the forum for sprayable finishes that melt. Melt now, melt later. I.E, repairable, resistant to witness lines. As of now, I only can think of a few

Nitro
EM-Tech 6000
Shellac? (Crystal-lac??)

Recent experience (I had no choice, repair work) with Enduro-var ii confirmed that it is no longer a useful finish for guitar work. I minimized issues with rapid fire coats. But still... And regardless, it is not repairable in the melt/re-melt sense.

It seems the conventional thinking in the finishing trade these days is to have finishes that are tough and high build, and if damaged are either stripped and recoated completely, or the damage is filled in with lacquer sticks or CA. Most finishers want an "off the gun, as is" finish and aren't inclined to do a lot of rubbing and buffing.
With a high build finish and good technique you may be able to buff out the last coat without cutting through it and creating witness lines. Not having the best technique, I still prefer Nitro and shellac. The old Enduro-var worked O.K. when applied with minimum recoat times.

I would say Nitro fits the repair-ability slot the best. I have never had an issue repairing nitro and have been able to spot finish with no tell tale signs. I have even repaired tops and backs without spraying the whole surface. Spotting in with Lacquer is probably the easiest of any of the finishes. I have never had to repair a french polished finish but have experimented a lot with trying to spot finish just using scraps and I am confident I could repair FP if I needed to. FP seemed quite a bit more fussy doing spot repairs but I was able to do a decent job of the practice pieces I tried.

Have not tried to do an invisible repair on urethane or Polyester because I don't think it can actually be done without witness lines, those I usually just stain to color and drop fill with CA or Lacquer and then level and buff.

Maybe someone else has had better luck (or technique) than I have but Nitro is the easiest to repair.

Cheers,
Bob

Ya'll talking about burn-in?

Witness lines are when you sand or buff through a layer and apply another coat of finish and you can see right where you went through the previous coat(s) of finish.

It also means when you spot finish something and rub it out, you see where you stopped spraying.

Cheers,
Bob

I believe so Barry.

_________________
Steve Smith
"Music is what feelings sound like"

Shellac is the easiest of all finishes to repair imho with Nitro a close second. I even use shellac to repair other finishes too for very minor touchups.

Nitro for us. Still very hard to beat when serviceability is a priority AND the thing will be subjected to a typical guitar's life meaning not always taken care of, dings, cracks, etc.

It's also one of the few finishes that is durable AND matching an original brand is not necessary.

Mike when I was about to pull the trigger on why production run of a couple a month I made a matrix of all available finishes and the specifics. Nitro won hands down for my situation where I did not want to invest in a big spray booth or spaceman suit.

There is also some history on the forum of finishes that were not only unsuitable but a big mistake for Lutherie. Remember the hard shellac that wasn't...

I felt better choosing something with a hundred year track record that was well understood.

Would you care to post your matrix? Yes, I meant "burn in". Surely there are other finishes that burn in?

I most certainly would post it Mike but I don't have it anymore I made in 2009 so it's been a while. Sorry.

Nitro hands down and we are not talking deft at Home depot
Mowhawk
Seagraves
Sherwin Williams
azko nobel
I use these azko is my go to Martin uses that and Sherwin Williams
I have used both shellac ( mix my own ) and vinyl sealer
I prefer shellac
I have a series of finish videos on you tube
If you choose nitro
Get a Good gun and have a proper spray area that removes the VOC's and a mask that is rated for VOC

_________________
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

Hesh wrote:
"There is also some history on the forum of finishes that were not only unsuitable but a big mistake for Lutherie."

There are some who would consider nitro to be in that category... It may well be that it has advantages that accrue to the maker/repairman, but it has a lot of disadvantages down the road that can affect the subsequent owners of the instrument.

The miracle of the marketplace has all but erased the downsides of nitro, and yellowing, checking and so on is now viewed as desirable by a large enough segment of the guitar-buying public that there are high-end builders throwing newly sprayed $10k guitars into the freezer to get a kick-start on some of that desirable damage.

Even if you like your guitars pristine and shiny, you may still be better off with a nitro guitar which can be returned to that state relatively cheaply, without the full strip and refin required by some of the more modern finishes.

I like to say, I love Nitro but Nitro doesn't love me

I want to say this has been informative. But nobody has added to my list of melting/repairable finishes. Is this it?

I don't see how the marketplace can get around the problems of nitro breaking down with age; that's a simple function of the basic chemistry of what is, after all, the little brother to a high explosive. Since UV light is one of the things that can speed it up UV blockers might help, but they won't alter the nature of the material. Most of the 'improvements' have come through the introduction of other materials, such as polyester or acrylic resins, but although they are sprayed finishes that can look similar, those are not 'nitro'.

Does EM600 actually melt once it is hardened though? I've tone Nitro repairs from guitars from the 1930's and shellac repairs from guitars from the 1840's and both those STILL melt in. I always thought those were pretty much the only melt in finishes there were, at least used commonly on guitars though.

The marketplace hasn’t solved the issues technically, of course, it has merely acculturated a proportion of guitarists to think of the nitro degradation process as desirable. From a particular philosophical standpoint this could be construed as the same thing:

If the guitar’s owner desires yellowing, crazing and other volatile behaviour, then nitro has no problems. In fact, it’s all the “better” coatings that are problematic for this person.

The entire concept of “the guitar”, how we expect it to look and sound, is a social and cultural construct, entirely subjective and subject to change. After all, there’s people who really like Ovations.

I am not an expert, but I believe that EM6000 coats will burn in to prior coats as long as you re-coat within 100 hours. I think that's what the TDS says. However, that may change if you add the cross-linker; in other words, the cross-linker may make the finish less capable of burning into prior coats. Either way, it is not an unlimited burn-in period. Within a few days, you will be applying new coats that do not burn in. I agree with you that shellac and nitro are the only unlimited burn-in finishes I have heard of.

I believe that Em6000 will burn into cured Em6000 if given time. You get witness lines if you sand a patch within a few days of the patch, but, if you wait a couple if weeks, it usually sands without witness lines. It helps to rub the area of the patch with alcohol before touching it up. I’ve been using it for years and have often appreciated this feature. It’s not that it melts, but rather the acrylic plastic molecules bond with each other. It’s not a strong bond. Alcohol can break it. One of my customers has sweat that can destroy a beautiful finish even with crosslinker.

How do you guys manage a temp/humidity controlled well ventilated space for a nitro finished guitar to off gas without filling your house or shop with fumes? Tough in a MN winter.

Jim Olson said that’s what led him to UV cured finishes.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

That's why I quit using nitro - made my shop stink for several weeks. Fortunately my shop is not attached to the house. I have a drying cabinet and I was going to vent it with a small fan but ended up going with Royal Lac. If I was building to sell to the market I might have to figure out a way but I build what I want and if they sell fine, if not, that's fine too.

_________________
Steve Smith
"Music is what feelings sound like"

I have an attached garage and leave the door open with a plastic drape over the doorway to slow down air transfer. My make up air is pulled from the house. An explosion proof fan removes vapors during spraying. Then a bathroom vent fan is turned on for several days to slowly pull vapors out. The vent fan doesn't move a lot of air but it is sufficient to prevent vapors from entering the house. After 3-4 days there is no longer any smell in the shop.

The bathroom vent fan has the advantage of not overcoming my A/C and dehumidifier in the shop, and it's not very loud. As long as you maintain a slight negative air pressure in your shop, the air should be drawn into it instead of it leaking out. This is the concept we used when doing mold remediation in houses back in the day.

I've heard that the least toxic thing in lacquer thinner is toluene, which is toxic at a concentration 1/10 of what you can smell.

My older brother liked to make model airplanes. The finish ('dope') he used was nitrocellulose lacquer with banana oil as a plasticizer. He'd come down to supper dizzy when he was painting a plane. When he went in for his draft physical he was declared '4F' due to kidney damage. It gave him a lot of trouble over his life. Just saying...

This may be more than what was asked but here is my process.

I do not have an issue of stinking up my house with lacquer fumes.

I also have an attached shop with a single door going into it from my downstairs. I have a store room that converts into my spray booth where I have an explosion proof fan connected to a variable speed controller. When I spray lacquer I just crack the door going into my shop so I am pulling air from my house. My furnace is a ceiling mount 50,000 btu shop heater with a fresh air intake for the combustion. THIS IS VERY IMPORTANT! I do not draw air from my shop into the gas burner, it comes from outside.

IF YOU ARE PULLING AIR FROM YOUR SHOP INTO YOUR HEAT SOURCE DO NOT SPRAY ANYTHING THAT WILL COMBUST!!!

When I am ready to spray I turn my exhaust fan on full. That changes the air in my booth a couple times a minute so I have plenty of exhaust so I just barely smell lacquer fumes in my shop. I am able to shut the fan off from inside and outside the booth so I can open the door without pulling in dust. I leave the fan on through out the finishing process(other than going in and out). I spray double coats of finish and flash it off for about 20 minutes between coats. After I have all the finish on I will turn down my exhaust fan to about 1/4 speed and let it dry for an hour or two. All this time I am pulling air from my house INTO my shop so none of the fumes go in my house.

Here is the part I know some of you will disagree with...

When it is dry to touch I set it up in my shop on a guitar stand. About 8 feet away from the guitar I set a little 750 watt quarts heater. Some of you may know this, but a quarts heater will only heat objects, not the air. I monitor the heat on the front of the guitar using an infrared thermometer. I don't let the temp go over 90 on the surface. I adjust the heater to maintain about 90 degrees by moving the heater farther or closer. I will let it cure for about an hour a side. by turning the guitar stand a bit every 10 or 20 minutes.

I know.... you all are saying... NO NO NO.... don't use heat because you will loosen up all the glue and destroy the guitar.

But. I have done this for years and years. I body shops they always have quarts heaters just for that reason. I could spray a fender in the morning, put the heaters on it for a few hours and level sand and buff it in the afternoon. I prided myself for not getting come backs and I have never had someone bring a car back because the finish dulled out. (that is what happens when you buff lacquer too soon.

On guitars, I do not let the finish get over 100 degrees and try to keep it around 90. This will evaporate the thinners and cure the lacquer so in just a couple of hours you will have flashed most of the thinners out of the finish and it will no longer smell.



Not much different than placing a freshly lacquer finish out in the sun. On guitars I am not really trying to dry the finish as much as I am getting rid of all the thinner in the finish. Remember lacquer gets thinned quite a bit depending on temp, humidity, once you drive the thinners out of the finish it will no longer smell up your shop.

The Smell test... You can pretty much tell when your finish is cured because it will no longer have that lacquer thinner smell.

If I am rushing to get something done I will put the guitar under the lights for an hour. Then let it sit and cool for a couple of hours (it is still off-gasing) Put the lights back on for another hour, repeat that about 3 times. I check it by finding a spot on the finish that isn't noticeable and I very lightly press the edge of my fingernail into the finish. When you can do it and not leave an impression you are ready to do the first level sand.

I level sand the finish using 800 grit paper wet, Then I will let it sit for a day or 2. By level sanding you are opening up the finish so it will cure even faster. After 2 days I will wet sand with 1000 grit, then 1500 grit and polish.

You will probably notice I don't go crazy with ultra fine grits and I also start with 800 and finish with 1200. You can do this only if you are able to lay down a perfectly smooth and glossy final coat of finish. I have been doing this for the better part of my life so I am able to lay down a near perfect finish with no orange peel or dry spots.

I also rub out all of my finishes by hand. I start with 3M Orange (course) then White followed by swirl polish. I can usually buff out a guitar in a couple of hours. I should note that between compounds I clean the finish really well so there is no "old" compound on it when starting the next.

So, I know I will get some flack about using heat but I am confident in my process and it works well for me. I would not suggest anyone do this if you are not confident with your finish abilities.

So... Flame On......

Cheers,
Bob

P.S.
I mentioned I do double wet coats when I finish. This is not what some of you may think. I am not laying down heavy coats. I know how to thin lacquer and I know how to handle a spray gun. My wet finish is wet, but I am not flooding the surface by any means.

So this is pretty much how I spray out a lacquer finish. I do all sorts of furniture projects so this doesn't just apply to guitars. On most furniture I usually do not level sand and buff. The finish I get from the gun is more than sufficient for most furniture projects except if someone wants a mirror like finish.