Pre-Cat vs. Conversion Varnish

Ask an Expert From: Products Finishing, , from C-Care

Posted on: 3/26/2014

How difficult are conversion varnishes to use?

Q. We manufacture kitchen cabinets and have been using a pre-catalyzed material. Lately, we have had customers ask for a more-durable finish, and we have looked into various conversion varnishes. How difficult are these materials to use? What do I need to know about this type of material? —C.H.

A. No doubt pre-catalyzed material (“pre-cat” in industry slang) is easier to use in lieu of the catalyst and other issues associated with conversion coatings, and today’s pre-cats do offer a decent finish, but they still may not hold up to the rigorous requirements of ASTM standards from the Kitchen Cabinet Manufacturers Association (KCMA) for things like scrub-ability, chemical resistance, etc.

As you have noted, many customers now seem to understand the value of a more-durable cabinet finish, and many shops are transitioning from pre-cats to conversion-type coatings (“post-cat”). Although there are concerns about improper catalyzing and post-cat coatings being harder to spray and having shorter pot lives, once you learn how to work with these types of finishes, you will never want to go back to a pre-cat. 

Yes, adding catalyst is a very important step in the mixing process, and it is very important to follow the percentages recommended by the manufacturer. If you do not add the proper amount of catalyst to the coating, it may not correctly cross-link or cure. When you forget it all together, it will not cure at all. (However, if this happens, you do not need to strip the cabinet down. Simply correctly catalyze another batch and spray over the tacky, uncured finish, and, in most cases, the subsequent coat will cure.) If you add too much catalyst it can actually cause a finish to become brittle or “cold check” which potentially can be a major problem. 

In terms of spray-ability, it is important to understand the difference between viscosity and the solids content of a material. Volume solids are the actual amount of resin material left after all the solvents and co-solvents have evaporated. Conversion varnish finishes generally run in the 30–38 percent volume solids range or sometimes even higher. But do not confuse volume solids with proper spray viscosities. Conversion varnish is more viscous and generally cannot be sprayed straight out of the pail. It typically needs to be reduced before spraying.

Check with your supplier for recommended spray viscosities. Many finishers use a #2 or #3 Zahn or #4 Ford cup to check viscosity, which should done with a stopwatch at the recommended spray temperature (usually 70°F). The colder the material, the more viscous it will be. When material is cold, some will add solvents to it to arrive at the proper viscosity only to find that it runs or sags during spraying after it has warmed up. This is why it is always important to check viscosity at the manufacturer’s recommended temperature.

On another note related to spray-ability, if you have not already, you may want to look into purchasing an air-assisted airless spray gun system with a 15-1 ratio pump and a spray gun fitted with a 9- to13-thousandths tip size. This type of system will lay down conversion varnish like nothing you may have ever seen. The 15-1 ratio indicates that for every pound of air pressure that goes to the air-motor/pump, you will get 15 lbs of fluid pressure back out at the tip. Generally, you would operate the pump anywhere from 400 to 600 lbs of fluid pressure (depending on tip size and viscosity).

Lastly, today’s conversion varnishes can have a pot life anywhere from 8 hrs to 3 weeks. Pot life is measured from the time you add the catalyst to the material until the product is no longer usable for spraying. If a conversion varnish goes beyond the specified pot life, it becomes gel-like and can no longer be sprayed. Some users will try to cheat by adding solvents, but this will not undo the curing process. So what do you do if you are shutting down operations for the weekend and have a gallon of excess material?  Simply add “virgin,” uncatalyzed material at a ratio of one part catalyzed to 2 parts uncatalyzed. This will keep the product from curing over the weekend. Then Monday morning add the amount of catalyst needed for the 2 parts, mix well, reduce viscosity if needed, and start spraying.

While pre-cat material is generally less-expensive initially, conversion-type coatings offer the higher solids and increased durability that will satisfy the demands of your customer.


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