Catalyzed (or conversion) varnish is well known for its durability and household chemical resistance, which is why it is used on so many kitchen cabinets, office desks and institutional furnishings. Catalyzed varnishes are popular because of the advantages they have over some other types of wood finishes. They are more durable, chemical resistant, less expensive on a solids basis, and build with fewer coats than pre- or post-catalyzed lacquers. They also approach the durability of many two component polyurethanes at a lower price per gallon and on a solids basis.
Wm. Hermann & Son, located in Indianapolis, Ind., uses catalyzed varnish to produce the look they want and the durability they need. Wm. Hermann & Son manufactures medium to high-end wood furniture for schools and churches. Bob and Rick Hermann, third generation, have noticed how the catalyzed varnish holds up better especially on school science cabinets and church pew caps and hand rails. They are also able to get a “high-build” look with just two clear coats. With only two finish coats, customized for their operation, and a halogen oven they have greatly improved the finish room's efficiency.
Their typical finish system is:
- Wiping stain / flash 5 minutes /oven @ 130F for 5 minutes / cool 5 minutes.
- Catalyzed varnish sealer @ 5 wet mils / flash 5-10 minutes / oven @ 122F for 5 minutes / cool 5 minutes / sand.
- Catalyzed varnish topcoat @ 5 wet mils / flash 20-30 minutes / oven @ 117F for 7 minutes / cool to handle.
The catalyzed sealer is a reduced version of the catalyzed topcoat. Reducing the catalyzed varnish sealer a few percent promotes better flow and leveling.
Catalyzed varnish is not to be confused with brushing varnish. Brushing varnish is a single component finish usually polyurethane and cures by oxidation. Catalyzed varnish is normally a blend of an alkyd and urea resin that will cure (or react) to form a film in the presence of a catalyst. The catalyst is usually an acid added to the varnish prior to use. Heat can also act as the catalyst, but the temperatures required to cure the film are typically above what wood furniture should be subjected to. The acid catalyst should be measured carefully to prevent over catalyzing, which can cause brittleness among other problems, or under catalyzing which can result in a soft film and wrinkling (or lifting) problems among others. Add the catalyst while mixing thoroughly. Some catalyzed varnishes need to set for about 10 minutes after the catalyst is mixed in, before using. Check with your supplier to see if this is necessary.
Most catalyzed varnishes have a pot-life (or how long the finish is useable after being catalyzed) of six to 24 hours; check with your supplier. Also, a few catalyzed varnishes “gel” (or turn semi-solid) soon after their pot-life expires. It is important to thoroughly clean your spray equipment after finishing or you may lose your equipment. Many finishers “de-catalyze” their left-over and previously catalyzed varnish by mixing in at least an equal amount of un-catalyzed varnish. This reduces the catalyst level prolonging the pot-life to the next day. To use the “de-catalyzed” varnish just add enough acid to catalyze the un-catalyzed varnish since the rest of the varnish was already catalyzed. Check with your supplier to see if this will work for you.
Catalyzed varnish is a little more difficult to work with than traditional lacquers and pre- or post-catalyzed lacquers. The lacquers rewet (or melt into) previous coats reducing scratch marks and other finish defects, the catalyzed varnishes do not rewet as lacquers. This means more care must be taken on each step to prevent finish defects and it may be necessary to use a higher grit sandpaper to prevent sanding marks from telegraphing through the topcoat. Lifting (or wrinkling) can be more frequent than with pre- or post-catalyzed lacquers since the entire film of a catalyzed varnish is cross linked. It is the cross linking part of the film that can lead to lifting. Lifting is most likely to occur with the second coat of catalyzed varnish over an un-catalyzed finish. A heavy glaze, toner or wiping stain not wiped well can act as the un-catalyzed finish and cause lifting problems. Some catalyzed varnishes have recoat windows (or specific time frames when they should be recoated to prevent lifting) and some don’t. Check with your manufacturer to see if there is a recoat window with the catalyzed varnish you are using.
The line between catalyzed varnish and catalyzed lacquer can sometimes be blurred. Catalyzed lacquer is a hybrid of a traditional lacquer and a catalyzed varnish. It can be more like the traditional lacquer or more like the catalyzed varnish. Sometimes catalyzed varnishes are modified with a very small amount of nitrocellulose or CAB resin to improve the flow and leveling (like an additive might). This slight modification with nitrocellulose or CAB resin, which are lacquer resins, may also lead some to refer to them as catalyzed lacquers.
Many sealers, catalyzed and un-catalyzed, have been used under catalyzed varnish. I prefer using the catalyzed varnish self-sealing (or using the topcoat as the sealer also). This makes it possible to apply multiple clear finish coats without lifting problems. Not only do many catalyzed varnishes have great topcoat properties, but they also sand very well. Sometimes it is necessary to reduce the catalyzed varnish a few percent with the appropriate reducer to promote better flow and leveling when used as the seal coat.
Increasing regulations on formaldehyde are making catalyzed varnish producers work to reduce the amount of free formaldehyde that might be emitted from the finish. Catalyzed varnishes should see continued use into the future as research is ongoing to reduce and eliminate the formaldehyde.