My "new" 1954 CTC2B 21CT55 21" roundie

[Kevin Kuehn]

Is that SW Pre-cat lacquer still dissoluble by lacquer thinner once it's fully cured, so you can blend in repairs like traditional nitrocellulose? I'm thinking not, but I've never used the stuff. However we may not have many choices in the near future, other than to use some non dissoluble finish.

[ohohyodafarted]

Originally Posted by Kevin Kuehn

Is that SW Pre-cat lacquer still dissoluble by lacquer thinner once it's fully cured, so you can blend in repairs like traditional nitrocellulose? I'm thinking not, but I've never used the stuff. However we may not have many choices in the near future, other than to use some non dissoluble finish.

Kevin,
I can tell you the pre-cat Sherwin Williams lacquer I use is Nitro-Cellulose based. They also make a pre-cat Acrylic lacquer for applications where you can not tollerate the fact that NC turns yellowish over the years. The acrylic pre-cat is useful for light blonde finishes that must not yellow over time.

The claim is that pre-cat is more durable than a conventional NC lacquer. I have read that if you re-coat during the time frame when the pre-cat is still not completely cured, the re-coat "melts" into the existing finish. I did read a thread where the poster spoke to SW tech support people and they assured the poster that regardless of how long the pre-cat had cured, re-coats would adhere into the existing finish.

I read another post by a furniture re-finisher who said he uses pre-cat lacquer all the time and it is easily "repaired" unlike polyurethane varnish.

Other sources say that pre-cat must be sanded prior to a repair job to make the new repair adhere mechanically. This infers that the cured pre-cat can not be dissolved by the new lacquer.

That said I can say that the Nitro Cellulose component of the pre-cat product should always be lacquer thinner soluble regardless of how old the pre-cat finish is. I just can't quantify for you how easily it will dissolve. I would suspect it would dissolve very much like 50 year old conventional NC lacquer that was applied to our tv sets back in the 60's

From what I understand, conventional NC lacquer dries when the thinner evaporates. Pre-cat has additional components that "cross-link" making the product more durable. Still the bulk of the product is nitro cellulose and should be soluble in lacquer thinner.

Varnish does not "dry" it "cures" through cross linking. That is why old varnish is notoriously difficult to soften and re-coat. Usually you have to sand varnish to re-coat to get mechanical adhesion. Or else you strip old varnish and refinish.

Post-catalyzed lacquers are a bit of a different story. You add the catalyst right before spraying. The cross-linking takes place very quickly. The terminology is post-cat finishes are very "HOT". The pot life can be as short as 15 minutes to 90 minutes. After that the product starts to gel and harden. The re-coat time on post-cat product is very short. If you miss the window, you have to wait until a full cure is obtained, sand and then re-coat.

Back in the 1970's I repainted a car. Back then base coat, clear coat was a new cutting edge process. I painted the car with a lacquer base coat (lime green), and then I use a post-cat urethane clear coat over the top of the lacquer. The pot life was about 90 minutes and after that, the left over clear coat product turned into a rubbery substance that could not be dissolved.

If you are concerned that a pre-cat lacquer is like IE: "2 part epoxy" or cured polyester resin after you added the methyl ethyl keytone peroxide, (which basically nothing on earth will dissolve after it sets up), I can assure you that pre-cat lacquer is nothing like that.

Unfortunately I can not give you a definitive answer on whether or not very old pre-cat will be repaired as easily as conventional NC or Acrylic lacquers.

But for me at least, the quality of the finish and ease of use is most important. I will let somebody else worry about how to fix the pre-cat finish on my antique TV sets after I am dead and the sets go to a new caretaker.