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567chevys
07-15-2011, 02:40 PM
Here are some basic sanding techniques that can help you obtain a premium finish.

The objective in sanding is to remove all deeper scratches and leave fine scratches from the fine sanding operation. The fine scratches allow the paint to adhere better to the surface.

Using a coarse grade of sandpaper, go over areas where marks from shaping the body filler may remain. After you have removed all deep marks, switch to medium-grade sand paper and remove all marks from coarse sanding. End with a fine grit paper.

It is important to remove all of the marks from sanding with the previous grade paper before moving on to the next grade. Fine-grade sandpaper will not remove all of the marks, so begin with a coarse grade on the initial go-around when working with body filler.

If you are sanding stable paint work that needs a better shine, it is OK to start with a medium grade sandpaper. If you are sanding between coats of paint or lacquer, use a fine grade of sandpaper.

Use the "flats" of your fingers, as opposed to your finger tips, when sanding concave or small areas. This way pressure will be distributed evenly over the area. Keep your fingers at right angles to the direction of rubbing and your wrist close to the panel. This prevents the "grooving" that using individual fingers will cause. Always sand in straight lines: sanding in circles will show lines, whereas sanding in straight lines will not.

To remove road tar or grime from the surface, use mineral spirits before you begin sanding. Attempting to remove grime or road tar with sandpaper will only drive it deeper into the surface. Remove all such contamination completely before you begin sanding.

It is OK to use a sanding block on slightly convex and larger level surfaces.

You are going to use a technique called "feather edging" to blend painted areas. Use this method after you have applied new paint after a repair, after you have completed repairing rust damage, or where the paint in an area is simply too thin. This means you are going to sand so that there is no noticeable ridge where the new paint begins. Sand over a wide area, feathering the edges gently to prevent them from crumbling.

Primer, sanded paint, and body filler all have a bad habit of hiding faults. These faults, however, will show through after you apply your coats of paint. You can more quickly and easily spot these faults by using a "guide coat" of cellulose lacquer, either from a spray can or heavily thinned from your spray gun. This provides a nearly transparent glossy coat that shows you the faults. Avoid using shades of yellow or red for the guide coat because these colors will most likely show through the layers of paint you apply subsequently.

chevynut
03-22-2012, 08:43 AM
I just got through doing a lot of priming and sanding on my Nomad, and here's how I did it. I had coated the bare metal with PPG DPLF epoxy primer after I prepped it long ago. So I scuffed the epoxy and shot another coat for good adhesion as recommended by PPG. Next, I shot a coat of Evercoat Slicksand, a high build polyester primer. In areas where I had more irregularities, I shot two coats. Evercoat says you can sand in 2 hours, but I found that not to be true. Curing overnight produces a very nice easily sandable surface.

When doing your initial sanding on areas where you know you're going to need to take off significant material, you should avoid using too fine sandpaper or it will not get flat. I used 120 grit for the blocking of the Slicksand, which seemed to work very well. The nice thing about Slicksand is you don't really need a guide coat. It's easy to see the high and low spots. Use a long board at least 16" long on large flat areas like top, fenders, hood, doors, and quarters. Also, MAKE SURE your longboard is FLAT. I was using one that kept giving me a high spot on my hood, and after applying more coats of Slicksand to try to even things out I found out that it was concave on the bottom, so it was only cutting on the ends leaving the middle high. I ended up using a sanding board I made out of a flat 1/4" aluminum plate with a handle, and no rubber pad to finish it out.

Use long strokes on the longboard, aligning it with the flat direction of the panel, but sand at an angle to the axis of the board. Don't use a lot of pressure on the board, or you will distort the surface. Let the sandpaper cut with fairly light strokes. Cross-hatching by changing the direction of the angled motion makes the sanding much faster and the panel flatter. Slightly curved areas can be sanded with a short rubber block, and fingers or other sanding blocks can be used as necessary.

Sand until you start seeing the epoxy primer below, but try not to go further or you will hit metal again. I try to remove as much of the Slicksand as I can to avoid too much buildup, but your high and low spots will dictate that. If you don't have any low spots left, you are ready to apply your final primer-surfacer.

If you have more low spots, you will need to add more Slicksand or other high-build primer. The tendency is to spray the high spots first, since they expose the epoxy, but you don't want to do that. What I do is spray a coat on the low spots first, then follow that with a coat over the entire surface. You do want to spray the high spots because they're your sanding guide and let you know when to stop.

Once all your low spots are gone, and you have sanded everything, spray your final primer. As you spray, you should see a nice, flat, smooth shiny surface if you blocked the Slicksand correctly. I used PPG K36 as my final primer and it covers any sanding scratches left in the Slicksand by the 120 grit. You could move to 180 before final primer if you wanted a smoother surface.

This is where I'm currently at, and I am very pleased with the flatness of the body using this technique. When I resume sanding before paint, I plan to start with 180, then go to 320, 400, and finally 600 grit. I will use mostly the same sanding techniques as above, but will need to use a guide coat since the K36 doesn't change color when sanded like the Slicksand does.

Arrowhead32
03-26-2012, 08:32 AM
I had to sand off a little nick up near the front bumper. The circumference of the scratch wasn't anything bigger than say a dime, but sure enough, it was the exposed metal part and not the plastic bumper. Regardless of the scratch, I had to sand it down and touch it up with similar paint because if you let it go too long, the metal will rust and corrode into a bigger headache. Just remember to not be too aggressive with the sanding pressure. I got carried away with the force of the sander and made a tiny hole near the rear wheel well. :(