I finally gave up on Bondo for quarter panel patches

Spent 15 years using Bondo on everything but after a 2018 F-150 job in Modesto I switched to a fiberglass reinforced filler for quarter panels. The difference in cracking over time is night and day, that old stuff just doesn't hold up on bigger repairs. Anyone else make the switch or still sticking with the old school way?

2 comments

2 Comments

evan1513d ago

Wait, you actually used Bondo for 15 years on quarter panel patches? That stuff is basically just glorified spackle for metal. I remember my first big job using plain Bondo on a Chevy Silverado bedside back in '05, it looked perfect for like 3 months then spiderwebbed all over when the temp changed. That fiberglass reinforced filler is seriously the way to go on anything bigger than a quarter sized dent. I switched to it about 8 years ago and I won't even touch the old stuff for panel work now.

wrenwilson3d ago

Yeah, I read somewhere that the fiberglass reinforced stuff actually bonds differently at a chemical level. It's not just thicker, the strands create a mechanical lock instead of relying only on adhesion. That spiderwebbing you got on the Silverado is exactly what I've heard happens when you put regular filler over a large area without enough metal backing. It just can't handle the expansion and contraction. Fifteen years on Bondo alone sounds like someone got lucky with their climate or never drove the thing in winter. I switched after seeing a YouTube breakdown where a guy tested both side by side with heat cycles. The regular stuff cracked every time, the fiberglass version held up. Makes you wonder how many "rust repairs" folks are doing are really just time bombs under paint.