When doing at-home repairs on dented cars, most people use body filler and then move on to spraying primer. Body filler has no flexibility and can easily crack when you drive the car after making repairs. Glazing putty is a type of filler with more flexibility that can be used on top of body filler to fill in smaller cracks. Putty is also softer and is much easier to sand than body filler which means you can use a higher grade of sandpaper without leaving deep scratches in the filler.
Sand the area to be repaired using 80-grit sandpaper on a dual-action sander. Remove all paint and primer so that only the bare metal is showing on the area that you intend to cover in body filler. Filler won't adhere properly to anything but bare metal.
Pour body filler onto a section of cardboard (something that you can throw away) and add a small amount of activator, according to the directions on the label. Use a squeegee to mix the filler and activator until the color is even.
Spread the filler over the damaged area until you have filled any low areas of the surface. Let the filler dry for one hour.
Use a dual-action sander and 120-grit sandpaper to sand the body filler smooth. Sand until the filler is smooth and is slightly lower than the surface area of the car. There should be much less filler now than when you first applied it to the car.
Mix the glazing putty and activator on a new section of cardboard until it is one color. Use a clean squeegee to apply the putty directly on top of the body filler, completely covering the filler. Let the putty dry for 30 to 60 minutes.
Sand the putty using 220-grit sandpaper on a sanding block. Hold the sanding block flat against the surface of the car and sand using the long edge as the leading edge. Sand until the surface of the putty is level and even with the surface of the car. You may be able to see some body filler through the putty, but most of the area should be only putty.
Wipe the area down with wax and grease remover or use an air hose to blow the sanding dust away. You are now ready to spray the area with primer.
