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Posted by Kevin in Ohio [50.41.113.192] on Saturday, December 22, 2012 at 20:24:05 :
In Reply to: Primer paints posted by Bruce in BC [24.207.110.106] on Saturday, December 22, 2012 at 19:35:43 :
That is very interesting. I worked with the local PPG store on mine and this is what they explained to me.
They said Epoxy primers are like glue and the stick to just about anything. Most PPG epoxy have a 24 hour recoat window for other coats. If you let it sit longer than that you have to scuff it all up for next coats adhesion. They told me the strongest, most durable finish is epoxy primer straight to topcoat. That is what we used to do with fertilizer equipment at a former job.
When I did the leaf springs on my truck I remembered that and asked again and they confirmed. I didn't want a bunch of layers on mine for the crack aspect of it. For flexing they recommended the max thinner witch it says in the sheets as well. I ground/sanded them down, lightly sand blasted, epoxied, and the next day straight to top coat with no resand. It's glass smooth and has held up great so far. I did it on the axles and other suspension parts as well this way.
On the body I lightly sandblasted, body work, fillers, epoxy, sandable primer,epoxy sealer,color and then clear.
I did research the filler thing and it's about 50/50 each way. According to Len at autobodyforum.com, filler first. His explanation is Paint companies want primer first because it means another round of sales as they know you'll sand through it anyway. I feel water contamination and bad pre surface have a lot to do with the horror stories of failures. Again, I'm no expert, this is just what I've been told buy guys who do it for a living.
One thing you mentioned that has me puzzled. You say Epoxy needs a topcoat because some of them let water through. Compared to????? Sandable primer is way worse and fillers are like a sponge. Admittedly all primers need a topcoat but epoxy is about at the top of the list for durability correct?
One thing to add, that I was told, is sealer primer after your sandable primer is for topcoat color uniformity and adhesion. You spray it on and when it is still tacky you go to color coat.
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