One of my previous co-workers was in San Diego, on travel for work.. He saw an early model Porshe for sale out there and fell in love with the car, so much that he flew back a couple weeks later, bought it and drove it back east. I never looked at it that closely when he first got it, and it always looked like a clean little car. But about 6 months later the metallic silver sitting in the sun started to show defects (they may have been there the whole time, sunlight does wonders to show defects in metallic). You could pick out every stone chip across the front of the hood, and every sanding scratch that had been "filled". This is typical of the results seen from using a non-catalyzed spot putty (the lacquer based type in the tube) as it will shrink over time, especially given exposure to solvents from subsequent paint coats. Wasn't long and the door bottoms were showing rust bubbles, and it was obvious he had been taken for a ride on a car that had some poor repairs. The clearcoat still felt smooth to the touch, but visually the silver metallic mica showed every chip and scratch in the car.
This is why is is so important to use catalyzed glazing putties, like the Evercoat 416, or using paint products with high fill and no shrink properties. For the metallic to show those defects indicates the shrinking occurred after the silver went on. Cheap materials, cheap results, wasted effort. To add to that, minimize the sanding scratches by using a reasonable grit paper. IMO there is no need to use anything coarser than a 60 grit.
Missed one of your questions, how does primer shrink? Some of the primers that are not catalyzed are in a state where they can "soften up" given exposure to solvents. Some topcoats may contain solvents that react with various primers (try some spray bomb primers, see how well the wrinkles show up).
Last edited by MPandC; 08/14/2014 10:29 PM.
