I"m to the point where I'm ready to start block sanding the body to get it ready for paint. With so many curves on the Corvette body, what do you guys use to block sand and maintain the contour of the body? Also what grit paper do you use?

 

You have to be a little creative.

Long convex areas are first done with a long board. Most of the convex areas of the body can then be done with a regular rubber block. The concave areas (fender flares, front top of the quarter, etc) can be done with an unopened soda can wrapped in sand paper (works well, don't knock it 'til you try it).

As for the paper grit, it depends on what you're working on. Repair areas start at 40 grit, then 80. We shot primer on top of 80 grit. Once the primer is on you go 220, 320, 400.

You should also guide coat your primer when blocking.

Water is a real good tool when blocking. Wet the area and look at the reflections. You can tell right away if there's a problem.

 

I do not know what level of blocking you are referring to "before painting". Below is what I would use if the body was stripped of all paint. Some guys just sand the paint and re-paint over it where it is entirely different. This is why I mentioned "what level".

A section of a radiator hose, a 5 gallon wood paint mixing stick from one of the home improvement stores then cut it to the size you want to use, a section of 5/8" and 3/4" heater hose. I use the long board file and have perfected my technique over 20+ years to be able to shape the body correctly...which also goes "hand in hand" with being able to feel the body to know where to sand. Some "Dura-blocks" from time to time.

The sand paper grit is all depending on what you are planning on applying over the bare fiberglass or SMC. I usually stop at 180 grit...but I am applying some really stout primer that builds very well.

It also depends if you are sanding on the urethane bumpers which is another issue all together.

IN MY OPINION:...and for what it is worth.

When you are blocking...and if you use the 3M dry guide coat powder. I do not block the body flat by sanding the heck out of it to get it FLAT. I prefer to keep as much thickness of the original body thickness as possible....SO..... If there are warps, buckles and other issues that are severe enough that I know would be detrimental to the body structure integrity IF I kept sanding....that is when I STOP and either fill them in or know that the primer can fill them in well. Now..I can not tell you what is severe in your case because it has to do with me not being there...obviously. So it will be up to you to know WHEN to stop sanding...and either prep the area for filler...or it being close enough for the primer you plan on using can fill it in. And ...YES...I more times than not...have to re-prime and block the body AGAIN after I have already primed it once. I watch and see what the sandpaper is "telling me" when I am sanding it...and by watching how the sandpaper sands the panel and how flat or straight it is while sanding the panel lets me know when I am done and can move on with the block sanding.

DUB

 

Thanks Zwede and DUB, I have the entire car striped to bare SMC using chem striper and sanding with 180 grit. Not sure if I can primer it now or sand the body a little smoother. My gut agrees with DUB and not sand on the SMC to preserve the integrity of the fiberglass. Probably prime it and then block with 220, 320, etc. Can you tell I've never done this before?

 

Don't sand the panels. Only thing you do to the panels is to rough them up so that filler or primer will stick. You don't want to remove any material from the panels. If you have low spots, fill them filler, then block. I recommend you use a primer with some build to it, and then block it. We used PPG K36, but there are many other primers that build.

 

I plan on using a high fill 2k primer then block and prime again if needed and finally a seal coat before I paint. Thanks Again

 

If it is a high build 2K primer...you can stop at 180 grit on...lets say 1 headlight bezel...and even one side of it . Prime it and see what happens. If it fills in really well...then blocking it with 180 or 220 and re-priming would be fine. The I would water sand the final coat of primer with 500 grit wet/dry. The apply a sealer and paint.

DUB