Re: Primer

Posted by Marco on Sep. 23, 1998 at 13:43:09

In Reply to: Primer
posted by Dale Beckman on Sep. 23, 1998 at 11:22:34

Dale,
First, I just realized I hadn't answered your e-mail, my apologies.
There are several options available.Whatever you consider using, get the product information sheets.I always do and have a binder full.Your supplier will likely know only what he was told by the paint rep.The info sheets have extensive information on use and compatibility.
I work with clean blasted metal only as ken mentioned.If the blasting is done thoroughly enough you will have some time to work before any signs of rust.Any dark spots that start growing in a day or two weren't clean.Do as much metal work as possible before blasting and the surface will be ideal for fillers or primer.
I've not worked with self etching primer since I always work with an "etched" surface.I use PPG DP series epoxy primer as a base coat which MUST be top coated in less than a week.The stuff bonds like you wouldn't believe!I use PPG K-36 acrylic urethane primer surfacer over the DP.It has no time limit on re-coat.Like most primer SURFACERS it relies on the properly sanded surface and the porosity of the primer for adhesion.It will also require a sealer prior to most top coats.I use the DP thinned as a sealer.Sealers are a good habit over any primer surfacer.
A couple other things to keep in mind.As Ken said, blocking the primer surfacer is the key to success.Get proficient with the "long board".As you begin blocking you will find areas that are lower than you thought.They can often be tapped up from the back side at this time so you don't need fillers or an excessive amount of primer.Even the catalyzed primer surfacers will show some limited shrinkage for a week to ten days, so don't rush!Keep the primer surfacer as thin as possible (you will sand most of it off).
Primer surfacer is always the weakest link in a properly prepared paint job.If you get a chip in the finished paint, you'll find primer surfacer on the back of the chip and on the surface from where it came.
When using any catalyzed products, it's a good habit to limit use to temperatures above 64-65 degrees (especially on or near bare metal).The chemical interaction produces heat which in turn creates condensation under the paint destroying the bond (many paint reps haven't figured this out yet).A good example is mixing a little to much hardener in plastic filler and it can be very warm to the touch!The DP epoxy primer is a slow reactor and doesn't produce much heat.
Last, when ready for sealer and color, take the time to clean all countersunk holes to bare metal (or close).Also sand all door edges, hood edges, and other corners where possible almost to bare metal.Let the sealer provide the bond and you will have extremely chip resistant edges.
Remember, get those product information sheets!