block sanding regular 2K urethane

P

portland

I've shot my first round of 2K urethane on a hood and door. Parts sat for a few days and then I tried blocking with 180 dry. I found I had to be very careful to not gouge the primer. I had best the best luck with a flexible foam block.
Question: do most of you block wet or dry and do you have any tricks/suggestions to lessen the gouging?
 
Somethings not right, your primer shouldn't be that soft after a few days of cure. What was the complete proceedure you used to get it to this stage? flash times? shop temps? Rushed epoxy primer? mix ratio of the primer?
 
The parts were stripped to bare metal with 80 grit. Filler work done and then primed with SPI epoxy two coats with 30 min between coats. Epoxy is a 1:1 mix. The temp that day was 70F. Parts sat 24 hrs in epoxy and then coated with urethane primer SPI regular 2k (a 4:1 mix). Again two coats with 20-30 min between coats and about 75F that day.
 
That sounds correct, but oviously somethings wrong.
Could you have maybe not mixed the right amount of activator
like you think you did? We've all screwed up at one time or another.
That's what it sounds like, not enough or bad activator.
check your activator and make sure there are no solids in it.
If so, that's your problem.
If not, then it has to be the mix ratio.
I have used reducer instead of activator before.
If there's a way to mess it up, I've done it.
 
Why do we think the mixture is off? It seemed to flash and dry as normal. What I am trying to describe by gouging is that when I was blocking the primer it seemed like the edge of the paper would cut or dig into the primer. Maybe I was applying too much pressure. I'll see with the next round of sanding.
 
Were you hitting an adjacent edge, like where a wheel flare would be? I've done that and cut into the primer.
 
It just sounded like it's soft to me.
But maybe it's not?
Does it gum up the paper?
If not, then it's probably ok.
(I hope so for your sake)
 
The key to block sanding is not to apply much pressure but let the paper do the work. If your paper stops cutting don't press harder just change out the paper. Sometimes its hard to do cause you feel like your wasting that high dollar sandpaper.
 
It doesn't gum up the paper. I'm probably using too much pressure and need to back off. Paper never stopped cutting but i was using an air gun to blow it clean often.
 
I clean my paper and dust off parts with a bench top brush. I hate the dust cloud.

Check your block to make sure the paper is nice and flat on it.
 
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