Grey vs Black Primer for Block Sanding

[Andre.servin]

When it comes to primer (Poly-High Build Filler/2k urethane) what is your color of choice for blocking and why?

Im currently blocking out my poly primer, my first and second round were grey, blocked that out. Now that it's getting closer I decided to change to black. I figured black would help me to get a better visual if there were any imperfections. Can't really say if it in fact enhanced my ability to see any imperfections that the grey didn't. I also can't say that it was easier for me to block out the black as I didn't use a guide coat, I saw a video that said black acts as it's own guide coat, as in it's color change from sanding. Which definantly seemed useful, just not 100% sure if it worked as a legitimate guide coat.

Im thinking of going to grey and using the powder guide coat over the rattle can guide coat. This should be my last sanding session. Hopefully.

Any advice?

thanks

[jlcustomz]

Color choice is not for sanding benefits. Benefit can be getting closer to your basecoat color which sometimes can require less basecoat.
As far as it's own guidecoat, some such as evercoat g-2 do that;;;;;; it sprays on rough & is smooth after sanding.
SPI black epoxy is shiny before sanding, which helps you see the surface.
Some people spray a light coat of a 2nd primer color over the first sometime during the sanding process & sand most of it off to see where they are at in the process..
A thin rattle can guidecoat before final sanding is a pretty traditional method.
Basically some of this comes down to personal preference.

Also there are poly spray primers, which are a sprayable body filler & better where thicker is needed. Can take the place of slathering the whole car by hand for all but the bad spots. Needs to be sealed with 2k or epoxy before paint. 2k primers aren't meant to be used as thickly as sprayable poly, can show shrinkage later if overused instead of filler.

[HotRod47]

As stated above, I choose primer color based on topcoat color. It will help later on with coverage. Painting silver over black would suck. Also, I like powder guide coat because it gets down in the scratch and tells you when it's gone. Spray can guide coat just sits in the surface. It bad for the initial block, but when going from one grit to the next I personally don't find it very helpful.