A couple of questions on blocking 2k

B

Benny

Mt 2k primer arrived on Friday, so I had my first shot with it over the long weekend....now I've got a couple of questions:

-What is the best grit of paper for blocking 2k? I only had 150 and 320 on-hand....`150 seemed far too aggressive, and 320 clogged way too quickly. I'm guessing 220 would be more appropriate for a first pass, correct?

-I hit a highspot that went to bare metal before I knew it. The spot is about 1 sq. in., so how do I handle this? Blow a little epoxyover it before shooting another couple of coats of 2k?

Thanks
 
The high spot may need to be bumped down with a hammer and dolley. You may be able to tell if it will need bumped by using a straight edge or by feeling it. Rub throughs should be spotted with epoxy before 2k.

Grit selection depends on how wavy the panel is. For the first round of blocking 150 is usually a good choice if the panel is not perfect. 320 is too fine for your first cut but it still should not clog. Maybe your parts need to cure a bit. Some time out in the sun works wonders.
 
Yes, ideally I would bring the high down, but it's right in the middle of a fairly springy roof panel with a headliner installed. I'm afraid of what else it might do if I try to bring the spot down. It really isn't that severe, you can't really detect it with a straight edge, it's just in an awkward location where the block drags on it.

The car sat in the sun for several hours, and then sat in a hot garage for 24 hours. Maybe 'clogging' wasn't the right term for what I'm seeing with the 320. It blows right off the paper, but it definitely builds up on it.

Thanks for the tips.
 
You'd be happier with some 220, a good way to sand an application that will be reprimed is to start with 150 to remove all texture and straighten, then guide coat and sand again with 220.
 
Benny;23728 said:
Yes, ideally I would bring the high down, but it's right in the middle of a fairly springy roof panel It really isn't that severe, you can't really detect it with a straight edge,
Click to expand...
It could be that you are applying too much pressure on the sanding block.
 
chevman;23734 said:
It could be that you are applying too much pressure on the sanding block.
Click to expand...

I've heard people use the phrase "blocking wave into it" over the years. Is that the case when you apply too much pressure to a flexible panel?
 
Absolutely. When you "straighten" the panel by blocking, the shape of the panel needs to be the same as how you are going to see it after paint. On large flexible panels you want to use coarser grits to cut, less pressure, and always new paper. I save the half worn out paper and use it on a more rigid area (because Im a cheap skate). A trick I learned from Shine to help me with the hood on my 34 chevy is to use foam or old rags to lightly support the panel from the back when possible to reduce flex. This is where you want to d what crash suggested. Cut with 150 then take out the 150 scratches with 220.
 
There was a discussion on here somewhere about this. It mentioned sanding flexable panels and when the block comes across a reinforcement brace it could show up as a high spot if the block is flexing the panel. And it will also leave the waves in the panel or make new ones.

If it truly is a high spot, I have had good luck with a pick hammer or punch. Just blunt the point slightly of either so it doesn't leave marks, then hold the pick like a punch and place it on the high spot then gently use a rubber mallot on the hammer face. Its surprising how little force is needed and just move the point all around the high spot. With practice it won't require any filler and just a coat of primer.
 
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