Does Nitrocellulose lacquer go bad in the can?

[Brian Evans]

So Barry Daniels' comment in my other thread that "If you could handle nitrocellulose lacquer, that is where I would steer you. It is old school and toxic as hell, but it sprays like a dream." made me think. And go out to the shop to make sure that I still have a brand new 15 year old never opened quart can of Mohawk Classic Instrument Lacquer, Gloss, and a can of Mohawk reducer. Is there a chance this stuff would still be good? It cost $25.99 in around 2002...

How toxic is this stuff anyway? Can I spray with a 3M vapor mask or do I need a air-supply mask and a full body suit? The instructions on the can are to use HVLP equipment, spray base coats full strength and top coats reduced 1:1.

If I can get past this "I hate finishing guitars" phase, I might build another guitar. At this point I am thinking I will build guitars and sell them as a 90% finished kit, you get to apply the finish of your choice.

[Barry Daniels]

I wouldn't listen to that guy. He has no idea what he is talking about.

Lacquer does not go bad. As long as it has not lost a lot of the volatile content (indicated by the lacquer being thick like syrup) it will be fine. Your vapor mask should be fine. If you can smell lacquer while using the mask then it is not working and should be replaced or change the cartridges. No skin protection is necessary.

The key with lacquer is thinning it down to the point that you get a full wet coat with your spray setup. Practice on a large piece of plywood setup vertically until you get your gun adjusted, lacquer thinned and spaying technique worked out to get the wet coat that also does not produce runs. Have a light pointing at the work surface from behind your back so you can see its reflection on the sprayed surface.

What you need to be careful with is preventing the fumes from getting inside your house. Have some type of ventilation to get the fumes out of the shop or open doors and windows to allow the fumes to dissipate. The lacquer will continue to off-gas during the next 2 to 3 weeks so the need for ventilation does not stop after the lacquer dries.

If you can't get the spray finish working right you could always brush on varnish or rub on Tru-Oil, etc. There are lots of ways to get a decent finish. But don't give up. This is the most challenging and time consuming aspect of building a guitar. You are not alone in this. Everyone has struggled with finishes. Also, as a last resort, there are a few people who specialize in finishing guitars built by others. They are not cheap but I have seem amazing work by several of these folks.

[Alan Carruth]

A friend of mine says that if there are a lot of different ways to do something, it's a sign either that all of them work or that none of them do. Guitar finishes are an example of the latter.

As far as I know, lacquer doesn't really start to break down until light gets at it, so it should be safe in the can. It's nasty stuff in a lot of ways, but it is 'the devil we know'. I can't use it any more, in large part, I think, because I used to spray it with just a dust mask, and became very sensitive. Try to be smarter than I was. The thinners are toxic, the finish itself is a fire hazard, and of course the spray and fumes are explosive. Treat it accordingly.

[Gordon Bellerose]

I have to say that for me, spray finishing had the sharpest learning curve.
I tried 2 or 3 different spray setups before settling on one that works for me.

Water base lacquer is not unlike Nitro, except the amount of toxic fumes is almost zero, and there is no explosion danger, and filters for a decent face mask are common.
Once you get the right mixture of lacquer, pressure and feed rate, it sprays beautifully. If you are getting plugged up, perhaps the lacquer is not designed for spraying, as Barry said. Or the opening in your gun is too small for the medium being sprayed. My gun has a 1.4 opening.

I struggled with a couple of false starts in all of the above areas before getting it right.

We live in Canada. Winter is cold here. Temperature in the shop and air supply piping is important too. I use "heat tape" designed for keeping water supply lines from freezing, to heat my air supply line. I also use a "heated" spray gun. It warms the finish as it goes through the gun.
When I spray, I have to go to the shop and turn the heat up for at least an hour before spraying. I also plug in the heat tape. This warms the air supply, the finish, and the guitar.
Lighting as Barry said, is important too. Too little light and you tend to overspray, because you can't see.
I use a lot of light in my shop. I have old eyes that need it. Lights that will reflect your surface back to you is the best.

[Brian Evans]

I'm going to work with the Brite-tone, because my current project has raw wood at this point, after sanding off the failed attempts. But I have two projects to re-do that have a ton of shellac and acrylic lacquer that is failing and flaking off. I found a source of high quality nitro-cellulose in Canada, apparently the same stuff that Manzer and all the other Toronto based guys use, but it would cost $100 to ship a $45 can to me because it's a hazardous material. I have a buddy going to Toronto next month so I will probably get him to bring me some back, but I really think the brite-tone is the way forward.

My shop is better heated than my house, and is a separate building, so I can bring it up to 70 degrees the night before I want to spray finish. I am going to completely rebuild my air system, if only because I am going to have to wait for my new stuff for a few days. I may get a new air hose, if only to make me feel better.

[Dan Smith]

I'm suprised the Mohawk instructions say thin 1:1.
I only thin enough to minimize orange peel, per instructions I received from one of their associates.
I suggest using Mohawk reducer to thin, not hardware lacquer thinner.
I had bubbles appearing in the finish, Mohawk suggested the thinner I was using had water in it.
Using their reducer solved my problem.

[Brian Evans]

I found out that Mohawk and Behlen are the same product, so I will read up on what they say about Behlen as well. I did call them, they said "they thought" that it had a shelf life of three years. We will see, when I finally open the can (I'm kinda afraid of opening it).

[Barry Daniels]

I have opened 20 year old cans of lacquer and there is zero degradation. It is kind of like twinkies.

[Mark Swanson]

I have had similar experience. a few years back, I bought a few gallons of lacquer from a wholesale business supplier, they said they had to sell it for 5.00 a gallon because it was a couple of months "expired". It's still good.

[Todd Stock]

Shelf life has more to do with the storage container than the lacquer - steel cans rust and leak when stored on concrete, and that's where most paint and varnish ends up...on a concrete slab in someone's basement or a paint locker in a factory. Same here with McFadden's and other standard instrument lacquers...some 12 year old stock I use for touchups and still perfect. In cold/damp weather, consider shooting with a turbine - the current generation of guns are as good as my SATA and Iwata industrial stuff, and the warm, dry airflow heats the finish at the tip and reduces blush above 70% RH. I thin Mohawk 4:1 lacquer/thinner by volume with standard Kleen Strip lacquer thinner (I buy 5 gallon cans from a local refinishing place at about $50)...I break down the gallon cans of lacquer as I use them...glass 1 qt Mason jars and fill to a marked line with lacquer, then using a gun stand with filter ring, add filtered thinner...the premix keeps well and avoids trying to mix up a batch while the half-sprayed guitar is waiting. I'll use retarder when I absolutely need to, but that's generally only on repair work where the manufacturer used precut or other lacquer which requires a slow drying tie coat to burn into the old finish. Kleen Strip seems to be as clean as the much more expensive reducer sold by Mohawk, but I would avoid Crown and store-branded solvents for paint and varnish mixing unless decanted and filtered. If in doubt, pour the contents of a gallon can into Mason jars, let it settle, and inspect for junk...Kleen Strip seems to be the only commonly available thinner that does not show contaminants...YMMV.

[Greg Martin]

Lac wont go bad. Ive had a cider jar of it outside near the shed for over 12 years,its gone to a great maple surup color and i only now use it for touchups. I dont see any degrading of the lacqure although re adding thinners and good straining is necessary.when im done i cover the cap with plasitc electric tape and a plastic bag with more tape to keep it well sealed. Ive had to replace the cider bottle cap twice during all that time.
When i spray i use my accuspray hvlp system with the 3m PPS cup liner and lid system. And a half mask with the pink 3m filters.

[Barry Daniels]

Greg, I think the pink filters are for particulates only and not for organic vapors. Make sure you have ones rated for organic vapors or you will not have any protection. Thanks.