I've been reading many articles on block sanding and working your way to the final sealer before starting the BC/CC. In Chevy High Performance a PPG rep said you could actually sand the primer TOO SMOOTH that the BC won't adhere properly. The last grit they used prior to sealer was 400g.

SO, my questions are these:

1) I've got my car blocked down to 320g dry and it's so freakin smooth (my arms are like Popeye) that I'm tempted to stop there, seal and paint the BC/CC....

2) I plan to reduce the SEM High Build Primer as the sealer (per SEM instructions); does it need to be sanded?

3) Does the last sand need to be wet? Dry sure is smooth :)

Thanks,
Duff

Yes it can be too smooth. Generally primer is sanded with 280 or 320 between coats and 400 before top coating. Wet sanding just keeps the paper from plugging up and makes it go farther. It doesn't change the texture of the primer.

Sealers are not sanded before the top coat. SEM makes a non-aerosol primer?

Tom

I'm at 320 now and don't think there would be much improvement going to 400g; Yes/No?

It seams like I could apply sealer, then BC/CC? Is that acceptable?

Yes, I've been using SEM ML01 Metalock High Build Primer; Great sanding qualities!!! They sell a Gallon Kit (primer and hardner) for about $100. To seal, you just add their reducer (temp dependent of course) and it's ready to go....

SEM is a local company here in the Charlotte NC / Rock Hill SC area and I've been playing with their products since being in night school. They have a very informative web site.

Thanks, Duff

The difference in 320 to 400 is none, don't waste your time.

Personally, I dry sand my stuff with 320-400, depends on what the store has on hand.

I hate wet sanding!!

Once done with 320-400 Ill apply the sealer, wait the flash time normally about 45 mins then go STRAIGHT to paint. No sanding the sealer coat at all.

So yes, sealing the primer then going to base coat is ok, its done in thousands of body shops daily.

Sealer prevents sand scratches from showing back up, aids in adhesion and provides a constant uniform color for the paint.

If you DO NOT go the sealer route which just ok as well, I would sand up too 600 grit. 320-400 grit is way too coarse to apply paint directly over, the finer grit will prevent sand scratches.

Sevt - thanks for the input; makes sense and is consistent with what I've read. I'm going to use sealer, then start my BC/CC.

I'm just hoping the sealer applies nicely; it should flow nicely since it's reduced but then again, this is my first "real" car shoot.... I'll follow the SEM instructions religiously....

Thanks All, I'll post some pictures after I finish the 320 on all panels...

My restoration is posted on www.fquick.com/ragtop396

Uhhh.....If you haven't sanded with 320 yet, I suggest going to 400 instead, a little insurance. I personally would use 600 though.

First you must know the type of paper you are using there is P grit metric sandpaper which is much more aggressive then standard A type paper which 320, 400, 600 is a true grit. We use in my shop A type paper but also have a chart which breaks down the grit difference of P paper. Any type of metallics we spray we finish with A type 800 because it leaves a small scratch and the metallic lay down real nice, if you sand with a more aggressive paper lets say 400 grit the metallics stand up and the paint looks very coarse and rough. After winning 2 years in a row at Pebble Beach 100 points and as well as other national shows Amelia Island and many others final sand before paint is the most important step !!!!!!!!!! Good luck.

Do you recomend the sealer after the final sand

Do you recomend the sealer after the final sand

This forum, page 4. "Sealer"

First you must know the type of paper you are using there is P grit metric sandpaper which is much more aggressive then standard A type paper which 320, 400, 600 is a true grit. We use in my shop A type paper but also have a chart which breaks down the grit difference of P paper. Any type of metallics we spray we finish with A type 800 because it leaves a small scratch and the metallic lay down real nice, if you sand with a more aggressive paper lets say 400 grit the metallics stand up and the paint looks very coarse and rough. After winning 2 years in a row at Pebble Beach 100 points and as well as other national shows Amelia Island and many others final sand before paint is the most important step !!!!!!!!!! Good luck.


The online spec sheets for House Of Kolor give both a P-grit recomendation and a standard grit recomendation. For my paint it was either 400 grit or 500-600P-grit.

The difference was really evident in color sanding. I went up to P2000 and had to buff my butt off. After getting some regular 2000 grit, the buffing was much easier.

P800=400grit,p1000=500grit,p1200=600grit etc.If I am sealing 400 wet is ok,I usually finish in 500 wet and go straight to paint.

I had NO idea of the type A vs P. WOW.... I will check what I've been using and adjust from there.

BERGERZ28 - Did you use "sealer" after your final sand?

Thanks - Duff