A 2018 F-150 I fixed in April is already showing rust in the same spot.

Used a cheaper undercoating spray from a parts store instead of my usual 3M stuff. Anyone else had a product fail that fast?

3 comments

3 Comments

the_fiona21d ago

Ugh, cheaper stuff always traps moisture and makes things worse.

the_piper1mo ago

A 2018 F-150 shouldnt be rusting that fast unless something went wrong with the prep work. Ive seen cheap spray on undercoating trap moisture against the metal instead of sealing it out. Those parts store cans are mostly just rubberized goo that cracks and lets water in after a few months. If you didnt sand the old rust down to bare metal first, the new coating just seals the rust in and it spreads underneath. The 3M stuff you usually use costs more but it actually lets the metal breathe while stopping rust. You probably need to grind that spot down to clean metal again and start fresh with a proper product.

bettywood1mo ago

My uncle had the same problem on his 2014 Silverado, used that cheap spray from the auto parts store and six months later the rust was worse than before... he ended up having to cut a hole in the floorboard and weld in a patch panel. @the_piper is right about sanding down to bare metal, that's the only way to stop it from spreading underneath. Took him three weekends to fix it right, and he still talks about how much of a pain it was getting all that goo off before he could start over.