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Is it possible for nitro lacquer to fail to cure?


I've seen one or two posts on some archived threads that advise caution in adding too much retarder to basic nitro lacquer as well as the caution on the can not to use as a thinner. Reasons being slower curing, and go as far as stating the nitro never properly cured because of adding too much retarder to the mix.

I tend to use a generous amount of retarder to get my coats to flow out and eliminate dry spray, orange peel, striping, roughness, uneven sheen. The only thinners that are available locally are high flash tool grade thinners and MEK which virtually make the spray dry before it hits the work piece. Xylene is also available locally, though I've never tried it; would that be worth a shot?

Anyway, the main question is, is it possible for nitro lacquer to fail to cure indefinitely due to using too much retarder. If so, can someone explain why; after all, retarder is just a mix of slower flashing solvents, right? What solvent in particular would be the culprit? What would they have meant stating that it would never cure; just permanently soft, cracking, flaking, etc? So far, I've never experienced issues and never had call back, knock on wood.

Thanks to anyone who can provide a factual answer/explanation.

9/8/16       #2: Is it possible for nitro lacquer to ...
Paul Snyder  Member


Nitrocellulose lacquer cures by evaporation - there is no chemical reaction taking place like a catalyzed finish. The lack of cross-linking is why it's less durable than other finishes.

Adding retarder (a slow evaporating solvent) will NOT stop the cure cycle of a finish. It will simply cause the finish to dry more slowly which has the side effect of allowing more dust to settle on the wet surface causing more nibs.

If you need a decent thinner, go to any auto paint supplier and get some medium reducer. It's compatible with solvent based finishes, including NC lacquer, and has a moderate evaporation rate which works well almost all the time.

If you're able to purchase lacquer, I don't understand why you can't purchase lacquer thinner. It's the best choice - it’s a blend of solvents from the following solvent “families”;

  • Ketones - acetone, Methyl Ethyl Ketone (MEK), Methyl n-Propyl Ketone, Methyl Isobutyl Ketone (MIBK), Methyl Isoamyl Ketone (MIAK), Methyl n-Amyl Ketone (MAK), Diisobutyl Ketone, etc.

  • Esters - Ethyl Acetate, Isopropyl Acetate, Propyl Acetate, Isobutyl Acetate, Butyl Acetate, Methyl Amyl Acetate, Propylene Glycol Methyl Ether Acetate (Eastman PM Acetate), Amyl Acetate, Ethyl 3-ethoxypropionate (EEP), etc.

  • Glycol Ethers - Propylene glycol monomethyl ether, Propylene Glycol Butyl Ether, Ethylene Glycol Butyl Ether (Butyl Cellosolve, Eastman EB), etc.

  • Alcohols - Methanol, Ethanol, Propanol, Butanol, Diacetone Alcohol, etc.

  • Petroleum Distillates - Toluene, xylene, “high-flash” naphtha (fast evaporating), naptha, etc.

The solvents in each family above are listed according to how fast they evaporate, fastest to slowest. In these blends, the Ketones, Esters, and Glycol ethers have the strength to actually dissolve the lacquer and are called “active” solvents.

Alcohols don’t have the strength to dissolve lacquer, but work in combination with the solvents that do, so they’re called “latent” solvents.

Petroleum distillates don’t have enough strength to dissolve lacquer but are useful to adjust viscosity (how thick/syrupy or thin/runny the finish is) and they’re called “diluents.”

If the lacquer thinner contains too much diluents (which is sometimes the case with inexpensive brands), the lacquer will not stay dissolved and will come out of solution causing it to turn white or have white chunks in the final finish.

Good brands of lacquer thinner that are made for coatings are interchangeable. The main differences between brands will be minor variations in the evaporation rate and the HAPs and VOCs.

Slow evaporating active solvents are called retarders. You can add these in small quantities to eliminate blushing. Also, if your lacquer has orange peel or dry spray, thin it with more lacquer thinner and adjust it slightly with medium to slow evaporating solvents to improve its flow-out.

9/8/16       #3: Is it possible for nitro lacquer to ...

Thanks for replying Paul; I appreciate your informative response.

I do have lacquer thinner available locally, I just meant to say it seems to be good for clean up only in my experience. It makes the lacquer dry faster than just using it straight out of the can. I'll take your suggestion and check the local auto parts stores for a slower thinner.

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