I finally caught why my filler work kept failing after 10 years

I always sanded filler with the grit sequence I learned in school until a guy in Denver told me to stop using 80 grit on the final pass. He showed me how the scratches were too deep for primer to fill and I felt like an idiot. Anyone else have a basic habit they had to unlearn the hard way?

2 comments

2 Comments

holly_craig6d ago

Hold up though, 80 grit is perfectly fine for a final pass on filler if you know what you're doing. I've been using 80 grit as my last step for 15 years on auto body work and my primer never shows scratches because I lay it on thick and let it shrink back properly. The trick isn't the grit number, it's how hard you press and whether you're using a block or not. If you're making deep gouges with 80 grit, you're pushing too hard and probably using a DA with too much orbit. Denver guy might have had a point for his specific situation but that doesn't make it a universal rule.

richardrodriguez2d ago

You said you lay it on thick and let it shrink back, but that's actually part of the problem with 80 grit. Thick primer shrinks differently than thin coats and can still telegraph those scratches later, especially on a hot day or after a few months in the sun. I've seen guys swear by 80 grit for 20 years who still fight ghost scratches when the paint cures out. I'd rather spend the extra five minutes with 120 or 180 and not have to gamble on my primer filling deep marks.