What are the pros and cons of spraying conversion varnish as opposed to lacquer? I work with lacquer regularly and there is a lot of talk about conversion varnish on this forum.
Pros: Far more durable. Especially in a kitchen or bath environment. Higher in solids, so fewer coats to reach same film thickness.
Cons: Need to add catalyst and dispose of left-over catalyzed material. Requires a minimum temperature of 60F to begin cross-linking process. Should not be used at lower temperatures. Maximum thickness is normally 3 mils. Higher than that and it cracks.
Originally, when conversion varnishes came out, they were not recommended for wear surfaces since they are very difficult to restore. In fact, I don't think you can truly get a conversion varnish top back to natural once you have beaten it to death with strippers, scrapers, sanders, bleaches, etc. On the other hand, lacquers are easier to repair. I've seen some lacquer refinishing artists do onsite restoring that was pretty commendable (when they can find a lacquered surface these days). I'm not sure, if our customers knew about these things, that they would be hot for so-called durable, scratch resistant finishes. Maybe conversion varnish is more of a benefit to industry than to the consumer?
Conversion coatings by *definition* form films by undergoing a chemical conversion process that is not intended to be very reversible. Most types of liquid coatings in use are of this type. Two-pack (2k) coatings, acid catalyzed, or auto-oxidative (e.g. oil-based) coatings are all examples.
Non-conversion coatings by *definition* are reversible, since they form a film entirely by solvent evaporation alone. Single component lacquers and shellacs (or any other spirit varnishes) are the two common examples.
There are some hybrids that seem to straddle these definitions, but these definitions apply to the dominant resin comprising the film and not whether one solvent or another can or cannot dissolve it. The simple test is whether a solvent applied to a dry film damages the properties of that coating to re-form a film (even if it's not pretty) that has the exact same properties it had before the solvent was applied. Conversion coatings can always be dissolved by something, but they are irreversibly damaged in the process. Non-conversion coating films are not normally damaged when re-dissolved, and this is the essence of why standard lacquers are easy to repair.
As suggested, the chemical resistance of conversion varnish is typically implied in a household situation, and possibly in a commercial situation, but quite a number of folks doing conference tables, for example, rightly use lacquer because the surfaces they deal with are perpetually damaged. You have to think about all of your ideal requirements, including ease of application, and try to find the best match you can. Availability of product is another consideration.
Russ Ramirez, forum technical advisor
Check out a high-solid catalyzed lacquer. They are available at 44% solids, 19 sec visc (Zahn #2 before catalyst) and very, very rubbable.
Durable and repairable with nitro. Rubbable, spray visc with no reduction, 44% solid, lacquer feel, UV blocks to protect the film and also the wood, etc. A lot of pros in a system like that (self seal or with a sanding sealer).
Cons: needs a catalyst, so you have to do some measuring (not a big deal, really). Also, at the end of the day, you need to discard old material (with proper planning, this is also not a huge deal).