# Can I get an education about nitro ve pre-cat vs post-cat?



## Quickstep (Apr 10, 2012)

I'm about to have my first foray into spraying lacquer. I have a basic understanding about nitrocellulose lacquer and I understand that catalyzed lacquers cure via a catalyst, but I'm interested to learn more about the practical differences for use on musical instruments. Below are a list of questions, but please don't hesitate to chime in on any aspect that may seem helpful. 

Does catalyzed lacquer "burn in" like nitro? 

Is there a re-coat window like there is with urethanes?

Does catalyzed lacquer look thicker than nitro? 

Is catalyzed easier or harder to spray than nitro?

Is catalyzed easier or harder than nitro to polish to gloss?

Are there other pros and cons?

What are the pros and cons of pre-cat vs post-cat?


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## Steve Neul (Sep 2, 2011)

Functionally nitro, precat and fully catalyzed lacquers work pretty much the same. They spray the same and gloss and polish the same. The biggest difference is nitro lacquers use cotton fibers for the cellulose which makes the finish. Since it is made from cotton fibers it's prone to brown over time like a cotton tee shirt darkens. If you use it on light colored woods or over a white wash finish it will show up sometimes initially but for sure over time. Also when using nitro lacquer you use a lacquer sanding sealer under it. On catalyzed lacquers you use a vinyl sealer under it so it will remain clear like the finish. Precat lacquers usually have a shelf life of about six months. Be sure to watch the expiration date when purchasing it. Fully catayzed lacquers are the same as precat lacquers with the exception you mix the hardener yourself by the batch as you use it. It uses a stronger catalyst which only has a shelf life of about 8 hours. It does make a slightly harder finish however if you mix too much finish for the project you are doing you just have to throw it away. For sure don't pour what is left over back in the can. It will make the whole can harden. You can often cheat the shelf life of precat lacquers by keeping them in a refrigerator when they are not in use. Hot weather is especially hard on the shelf life. 

There is not a recoat window with lacquers although there is somewhat of a problem with adhesion with fully catalyzed lacquer done days or weeks apart. You have to scuff the finish pretty good to have assured adhesion. Precat or fully catalyzed lacquers are also more water resistant than nitro lacquers. Used to kitchens were finish with nitro lacquer because it dries so fast. It doesn't take very long for water running down the front of sink cabinets to lift the finish. Nitro used on table tops such as an end tables where folks usually sit a glass in the same spot usually have the finish start flaking off on those spots. If you are finishing a piece of furniture like a chest of drawers where water isn't involved the finish can easily look great for 40 or more years. I have furniture built in 1973 done with nitro lacquer that still looks good as new. 

Nitro lacquers usually build faster and look thicker than catalyzed lacquers. 

The benefit of using fully catalyzed lacquer over precat lacquer is if you don't spray a lot of finish to where you can use it up before the expiration date. Without the hardener the shelf life of fully catalyzed should be the same as nitro lacquers. The hardener may go bad but the lacquer shouldn't.


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