# Help me to understand laquer



## Maylar (Sep 3, 2013)

I'm looking to understand lacquer finishes as they apply to wood finishing and I'm confused about some of what I see written.

I started painting motorcycles and cars some 35 years ago. Back then, acrylic lacquer was the paint of choice. DuPont and R-M were the big suppliers. The paint dried fast, took an incredible polish, but was brittle and needed additives to make it flexible. Acrylic enamels, the other choice, were more durable and flexible but didn't have the depth of lacquer.

Then there's nitrocellulose lacquer, which is what you get in a rattle can. Dries slower than the acrylics and not quite as hard which means it doesn't come to the same level of gloss.

All lacquer dries by solvent evaporation. By definition, lacquer will dissolve if exposed to the original solvent. There is no "curing", only literally "drying" by evaporation.

So... (yes, there's a question here finally) - when you guys talk about catalyzed lacquers - pre cat and post cat - what is that? There were never any catalysts in the lacquers that I've used.


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## Steve Neul (Sep 2, 2011)

I don't have all the answers but any finish has resins which harden into a plastic and they just have solvents keeping them liquid. The precat lacquers and fully catalyzed lacquers are more similar to your automotive lacquer. They just have hardeners in them which make the resins harden more. The precat lacquers have a much milder hardener which once mixed has a shelf life roughly six months. The fully catalyzed lacquers you add hardener to each batch as you use it and normally has a shelf life of only six to eight hours. This puts you in a situation of being careful not to have much left over as you would have to throw it away. Both the precat and fully catalyzed lacquers have acrylic resins and because they are acrylic will remain clear. The resin in nitrocellulose lacquers is made from dissolving cotton in nitric acid. Because it is made from cotton it is prone to yellow from sunlight like a cotton tee shirt would. It's also a softer lacquer so it's more prone to scratch and is less water resistant. 

Fun fact: A lacquer finish originally comes from Asia. It was derived from the sap from a lacquer tree which would give you the itchy like you got into poison ivey harvesting the sap.


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## ChiknNutz (Apr 22, 2011)

What about lacquer that the mfg says is "water white" but doesn't indicate it is precat lacquer? Example, I have some PPG Speedline lacquer that says is water white but I'll be damned if I can see anywhere that says it is precat, though I asked for precat lacquer when I bought it.

http://www.ppgpaints.com/products/speedline-lacquer-water-white-clear-sing-sealer


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## Steve Neul (Sep 2, 2011)

Water white lacquer is the same stuff, only filtered more. It will still yellow with age. It still has the cotton used for the cellulose.


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## RandyReed (Jul 30, 2014)

Maylar said:


> All lacquer dries by solvent evaporation. By definition, lacquer will dissolve if exposed to the original solvent. There is no "curing", only literally "drying" by evaporation.
> 
> So... (yes, there's a question here finally) - when you guys talk about catalyzed lacquers - pre cat and post cat - what is that? There were never any catalysts in the lacquers that I've used.


I will answer your question first:
A pre cat lacquer is already catalyzed by the manufacturer and usualy has a shelf life of 1 year up to 2 years.
Post cat lacquer is a lacquer that you have to catalyze in your shop with a catalyst supplied by the same manufacturer. Some last 24 hours, some last only 3 hours depending on what it is and the manufacturer. 

Dry and cure are 2 different things. Dry means dry to the touch and not "tacky". Cure means that the finish, again, depending on the type, is hardened and can withstand what it meant to stand up against. Lacquer cures by solvent evaporation, and sometimes depending on the type, it may take 24 hours up to 2 weeks to fully cure.

Catalyzed lacquers consist of both pre and post catalyzed versions. Instead of curing by the evaporation of a solvent only, they cure chemically.


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## RandyReed (Jul 30, 2014)

ChiknNutz said:


> What about lacquer that the mfg says is "water white" but doesn't indicate it is precat lacquer? Example, I have some PPG Speedline lacquer that says is water white but I'll be damned if I can see anywhere that says it is precat, though I asked for precat lacquer when I bought it.
> 
> http://www.ppgpaints.com/products/speedline-lacquer-water-white-clear-sing-sealer


Water white simply means that it will not yellow over time when sprayed over colors like white. They are made from different types of clear resins.

Im not sure if that product is a pre cat, but it may be. Does it have shelf life information? Water white lacquers are made from clear (water white) resins.


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## RandyReed (Jul 30, 2014)

Steve Neul said:


> Water white lacquer is the same stuff, only filtered more. It will still yellow with age. It still has the cotton used for the cellulose.


Yep. Cotton is nitrocellulose. There is a dry cotton and a liquid cotton. Highly explosive. Dry cotton must be kept moist and air tight or it can/will combust on its own at any minute.


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## Maylar (Sep 3, 2013)

RandyReed said:


> I will answer your question first:
> A pre cat lacquer is already catalyzed by the manufacturer and usualy has a shelf life of 1 year up to 2 years.
> Post cat lacquer is a lacquer that you have to catalyze in your shop with a catalyst supplied by the same manufacturer. Some last 24 hours, some last only 3 hours depending on what it is and the manufacturer.


OK. Then the automotive lacquers that I used long ago were pre cat. The only thing I added to it was thinner. I'm familiar with catalysts (hardeners) as I use them in urethane paints and polyester primers.



> Dry and cure are 2 different things. Dry means dry to the touch and not "tacky". Cure means that the finish, again, depending on the type, is hardened and can withstand what it meant to stand up against. Lacquer cures by solvent evaporation, and sometimes depending on the type, it may take 24 hours up to 2 weeks to fully cure.
> 
> Catalyzed lacquers consist of both pre and post catalyzed versions. Instead of curing by the evaporation of a solvent only, they cure chemically.


 One of the tests auto painters do for determining if an old finish is lacquer is to put a drop of lacquer thinner on an inconspicuous spot. If the paint melts, it's lacquer. It never really "cures". Enamel on the other hand cures in 2 stages - first by solvent evaporation, then by chemical bonding with oxygen. Once cured, it's very solvent resistant. In my mind, that's the difference between drying and curing.

Catalyzed urethanes cure by addition of the hardener. Once mixed they have a short pot life. I wasn't aware that there are lacquers that require a hardener.


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## RandyReed (Jul 30, 2014)

Maylar said:


> OK. Then the automotive lacquers that I used long ago were pre cat. The only thing I added to it was thinner. I'm familiar with catalysts (hardeners) as I use them in urethane paints and polyester primers.
> 
> One of the tests auto painters do for determining if an old finish is lacquer is to put a drop of lacquer thinner on an inconspicuous spot. If the paint melts, it's lacquer. It never really "cures". Enamel on the other hand cures in 2 stages - first by solvent evaporation, then by chemical bonding with oxygen. Once cured, it's very solvent resistant. In my mind, that's the difference between drying and curing.
> 
> Catalyzed urethanes cure by addition of the hardener. Once mixed they have a short pot life. I wasn't aware that there are lacquers that require a hardener.


Not necessarily pre-cats, but more than likely, you used single stage lacquer, urethane, or enamel, etc. These do not require any hardeners, and as you would think, are not as hard a finish as 2 step paint systems.

Automotive paint started off as a varnish in the early days. Then it went to stoving enamels, to acrylics, to acrylic stoving enamels. Sometime around 1970, Catalysts were introduced to produce a harder finish. In the late 70's, the government started being concerned about VOC's and so on which brought us to basecoat clear coats and now water bourne paint systems.

Lacquers dry and then cure. Lacquer is just a soft finish.Drying occurs when the solvents evaporate from the surface of the film and it becomes tack free. Curing is when the residual solvents leave the film and it begins crosslinking with oxygen in the air to develop its strength, toughness, abrasion resistance, and chemical resistance. Although most finishes reach 90% cure in seven days, full cure takes up to thirty days.

Example. A conversion Varnish is a catalyzed topcoat finish and is harder than any other finish other than UV finishes. Its dry to touch in 30 minutes or less, but it actually take anywhere from 12-24 hours to fully cure out. You can take MEK and apply to the CV and it will melt the finish, but it is cured, while some other solvents will not melt the finish of conversion varnish. We actually have a test kit that we can apply to any finish and tell what it is.

Lacquer is the same way, even on a car. All automobile painters will tell you not to wash or wax a car painted with single stage paints for at least a couple of days to allow the paint to fully cure out. Its dry when it comes out of the booth the next day, but it hasnt reached that fully cured stage yet.


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## Maylar (Sep 3, 2013)

OK. So, back to wood finishing. I've never sprayed clear finish on any wood project, though I'm comfortable in doing that and am fully equipped with an array of sprayers, buffers, polishes etc. I'm considering spraying some turnings this fall and I'd like to get something that behaves like what I used in the old days - a quart of clear and a couple different speeds of thinners should do me for a long time. I'd rather mix my own and spray small parts with an airbrush than use a rattle can.

What should I look for?

I'm also going to try some urethane clear coat, which I have a stock of (yes, I'm aware of the iso's)

Thanks


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## Steve Neul (Sep 2, 2011)

Wood is a little different to finish than metal. Any finish will raise the grain and make the surface fuzzy. You need to sand between coats and this step is made easier if you use a sealer first and sand it smooth. On nitrocellulose lacquer you could use a lacquer sanding sealer. On pre-cat lacquer you use a vinyl sealer. For a urethane you could use a dewaxed shellac such as Zinsser Sealcoat.


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## RandyReed (Jul 30, 2014)

Steve Neul said:


> Wood is a little different to finish than metal. Any finish will raise the grain and make the surface fuzzy. You need to sand between coats and this step is made easier if you use a sealer first and sand it smooth. On nitrocellulose lacquer you could use a lacquer sanding sealer. On pre-cat lacquer you use a vinyl sealer. For a urethane you could use a dewaxed shellac such as Zinsser Sealcoat.


You can also use a vinyl sealer under a urethane as well. I use a vinyl sealer under all my topcoats. When i use a catalyzed system, I also catalyze my vinyl sealer, otherwise your putting a tougher coating on a weaker coating and eventually it will wrinkle.


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