Hi Larry.
Yes, enamel dries or cures very slow so the longer it dries the harder it
will become. If you add hardener it will cure faster and harder and take a
better shine after color sanding. You've heard of "baked on enamel"? Only
reason it was baked is so it would dry enough to get the car out of the
booth so the next job could get in!
As far as drying from the outside in, what happens is after every coat is
applied the solvent needs to evaporate before the next coat is applied. If
you don't wait long enough then you get what is called solvent trapping. The
solvent pops through the coats above it and leaves little craters, not a
good thing.
So yes the solvents will continue to come out over a period of time which is
why you can smell fresh paint for several days.
Even urethanes which will not cure without hardeners can suffer the same
fate. Lacquer can be applied too quick or thick and will stay soft for a
long time until the solvents work their way out. Then you get lots of
shrinking. That's why waxing is not recommended for 30 days or so, wax will
seal the surface so the solvents cannot get out.
You can color sand pretty much anything, but your results will not be as
good on enamel as with lacquer or a urethane. I've done a lot of color
sanding on laquer, enamel with hardener, and urethane. Laquer is easy to
work with but chips and cracks over time, hardned enamel is ok, but doesn't
shine as well after being sanded. Urethane is by far the best, very durable,
holds a shine, easy to work with...if the chemicals don't kill you.
My 2 cents,
J
----- Original Message -----
From "Larry Miller" <millerls at ado13.com>
To: "John D'Agostino" <john.dagostino@comcast.net>
Sent: Thursday, April 29, 2004 1:54 PM
Subject: Re: Color Sanding
> John
>
> I was thinking in general terms, no specific paint job in mind. I've
always
> heard that enamel dries from the outside in so that it could be hard on
the
> surface but still soft underneath, even months down the road. Is this
true?
> If it is then it would make sense that color sanding would be difficult on
> all but older paint.
>
> Larry
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