Conversion varnish vs. lacquer

      The pros and cons of each, including comparison of durability and repair. October 30, 2002

Question
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.

Forum Responses
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.



From contributor D:
There are other considerations before jumping on the conversion varnish bandwagon. While it is true that they are more durable than lacquers, this is a relative way of looking at film coating. The truth is they really aren't so tough. With a conversion varnish, you are just buying a little more time. In the end, they get just as scratched and dull as a conventional lacquer. If you read some of the testing done by industry, you will find that this is not as much time as you might think in light of all the ballyhoo.

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?



A conversion varnish finish may not last forever, but no finish will, and it will far outlast a lacquer finish. One of our customers took denatured alcohol to remove magic marker from one of our tabletops finished with cv with no ill effect. Try that with regular lacquer and you'll have problems. Our goal is to give our customers the best finish possible with the most resistance to chemicals, water and scratching.


I think it is that chemical resistance that the client presumes is there. They don't think about what they are cleaning with, they just clean.


For what it's worth, this is an apples and oranges comparison.

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



From contributor D:
Thank you, Russ. This was precisely my point. CVs are not indestructible, bulletproof or made of kryptonite. There are many household products and accidents that can damage them. I think what we really owe our customers is a little advice about the pros and cons of different finishes and what they can do to prevent an accident. Perhaps this situation is somewhat analogous to that of repairing an antique piece with an irreversible modern glue instead of animal hide glue without telling the customer what you have done.


In regard to CV's only being buildable to 3 mils, I would say you are safe at 5 dry mils.

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).



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