Do I need to wire brush surface rust before applying Fluid Film?
You do not need to meticulously scrape or remove all surface rust before applying a lanolin-based coating like Fluid Film, as long as loose scale is brushed off. Lanolin-based sprays work by penetrating existing rust and cutting off oxygen to halt further corrosion, making extensive manual removal unnecessary unless preferred.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Spraying the undercarriage directly without overthinking it.
- 2Using a wire brush, hammer, or screwdriver to knock off loose rust scale before spraying.
- 3Leaving the rust alone
- 4Spraying the metal with lanolin aerosol cans or cosmoline black
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I (New England area) have a 2019 used Mazda with existing rust. At this point, is it still worth treating the rust, or just leave it be?”source ↗
“I was planning on getting fluid film applied to the underside of my car this weekend, but wanted to know if I should take a wire brush to the underside of my car first and get the surface rust the best that I can?”source ↗
“I don't have a lift or anything, so I'd have to figure my best way underneath.”source ↗
Where this came up
People with this problem also raised
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- 4How to fix dull spots left on metal legs after removing rust