Urethane base paint...

[Omahaug]

A lot of touch-up paint suppliers sell touch-up paint in spray cans that are urethane base (not enamel or lacquer).

How does urethane base cure? Does it catalyze like 2k clearcoats? I'm mainly looking to be able to remove the touch-up if I don't like the look of it or apply it incorrectly. What removes urethane base? Lacquer paint can be removed easily with acetone or lacquer thinner, will lacquer thinner remove urethane touch-up paint?

The other big question is will removing the urethane touch-up remove any underlying paint? Lacquer paint is easy to work with because even a year after application you could remove it with lacquer thinner and it will only remove the lacquer paint, not the underlying factory paint or whatever was used in a body shop. Does urethane work that way?

 

[nthach]

AFAIK, the SprayMax/U-Pol fill-in cans that are "blank" except for reducer and propellant don't have a hardener. All the paint shop does is mix up .5-1oz of basecoat per the formula and "loads" it into the can with a special machine. Only the factory-fill 2K SprayMax cans and the few places that can fill 2K single-stage fill-in cans have the catalyst in it. You activate those with a pin on the bottom of the can and use it after shaking and waiting for 5 minutes and have up to 48 hours to use it.

All basecoats are acrylic. They can be considered urethanes as well as they form one part of the chemical reaction for one.

Urethanes can cure from the moisture in the air or crosslinking with a isocyanate which greatly speeds up the process. The hardener for any primer/base/clear is the isocyanate component that reacts with the acrylic resins to form a urethane film.

I think you can "wash" off uncatalyzed basecoat with reducer or lacquer thinner but once a catalyst/activator or a reactive reducer is added to the basecoat you can't. PPG Deltron DBU wasn't a urethane per se, but mixing it with the required reactive reducer catalyzed it. Same with DuPont ChromaBase. Most modern solventborne basecoats do allow for adding a small amount of clearcoat hardener to make it more durable and it's a warranty requirement to "activate" waterborne basecoats with an activator.