Is silicon carbide harder than windshield glass?

Yes. Silicon Carbide is about 9 on the Mohs hardness scale - just under sapphire; glass is about 5.

Use this to remove auto paint and put new paint on but should I sand down before I apply clear coat ?

If you don't sand before applying clear coat, the clear coat may not stick. It is always recommended to sand existing paint first with 600-800 dry, or 600-1000 grit wet sand before the clear coat. The gray sanding pads (like Scotchbrite) can also be used to scuff an existing surface. if you use a grit that's too coarse, you will end up with scratches in the final finish. Here's the process: If you need to use Bondo, sand with fairly coarse grit - 80-100 grit, to remove paint to bare metal. Apply Bondo needed and contour the surface. Final sand the Bondo with 220-400 grit. Apply a sandable primer and sand with 320-400 grit. Then use a primer coat which should fill small bubbles in the Bondo. Apply the color base coat, then sand with 400 or finer before applying the clear coat. Clean the surface with a grease remover between each layer to remove the oil from your fingers, which can reduce adhesion, and between each subsequent coat. If you are applying a base coat over old paint that is in good condition, other than fading, you can use a finer grit like 600-800 grit to scuff the surface. I have not had good results with an off-the-shelf DupliColor because of color matching, but you might. Very light colors are more difficult to match, because there isn't much pigment in these light colors, and color matching becomes more difficult. I would use a custom mixed color for light colors for sure, but with darker colors you might be OK with off-the-shelf base coat. YOU should clear coat over base coat, whihc can be polished by using something like 600-1000-1500-3000 wet sanding, followed with a polish. If you try to bring up the gloss with one coat - you will probably end up with runs. I watched a pro patch a car in my neighbor's drive. When he sprayed, he cut the spray way down to about a third of what comes out of a regular spray can, and applied several coats to build up the paint thickness. The base coat doesn't need to be glossy, and the clear coat, which is difficult to see when applied, can be sanded and rubbed out to a high gloss. Runs can be sanded out, but it's extra time and materials. SprayMax 368 0061 is a two part catalyzed (2k) urethane clear coat containing toxic isocyanates. It comes in a single spray can and is sold here on Amazon. SprayMax Clear results in a tough, hard finish similar to OEM clear coats. But beware - this chemical is very toxic if breathed, so heed the warnings and keep it off of your skin if you don't want to take a trip to the hospital. You might be OK with a Covid mask outdoors, on a small area, but to be sure you might want to wear a chemical respirator. DupliColor Clear or other single component (1k) clear coat that comes in a kit with an exact match base coat is pretty tough if you aren't OK with the SprayMax, which is sold with minimal instructions, as a professional-only product. Some might want to use the regular 1k clear coat. There are lots of "how-to's" on the Internet, which should help you to learn how to go about paining a vehicle yourself. And you will find differing opinions there. Hope this helps.

Manufacturer	3M
Part number	9084
Item Weight	50.9 g
Product Dimensions	30.48 x 24.13 x 1.27 cm; 51.03 g
Item model number	9084
Size	1 Pack
Colour	No Color
Material	Silicon Carbide
Item Package Quantity	1
Grit Number	600
Grit Description	Dry, Wet
Batteries included?	No
Batteries Required?	No

600 Wet-Or-Dry Sandpaper 5Pk

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