why cant enamel paint over enamel?

[SCOTT EVIL]

I have two cars both with great condition factory acrylic enamel paint. Both have had body work on the LR quarter repainted, Both had the paint turn flat after 5 years.
Very close inspection the paint has a crazed fine cracked look, just like old laquar does.
I just happened to read that enamel is not allowed to recover with enamel but requires laquar paint type.
Really? I have no paint experience and wanted to know why:
my paint failed ( work done by body shops not me )
and why cant enamel cover enamel?
Thanks, Glen

 

[66 Dartman]

9 times out of 10 this usually happens on the panel the blend is done on.Back in the acrylic enamel days there was a blender used to "melt" the old to the new. In my experience this was the area that had faded or checked!! I have sprayed enamel over enamel many times and never had it check or fade but the surface that you are spraying on must be fully cured.
Just my 2 cents!!!

 

[junior]

I'm a painter and have never been a big fan of blending, in time the blended area will break down for two reasons... first being older paint has been exposed to UV longer and will break down faster than the new hence the checking second the solvent used as the blending agent does not really give you a deep melt in and doesn't provide good adhesion. I always recemend repaint entire panel as I hate come backs that people expect done free. Can't even buy enamal any more where I'm from up here in the great white north.