Sealing and Touching Up the Factory (OEM) Undercoat on the Undercarriage

Asked by kimcane Nov 01, 2023 at 10:07 AM about the 2021 Mazda MX-5 Miata RF Grand Touring RWD

Question type: Maintenance & Repair

On the ND2 MX5, Mazda installs from the factory a rubberized coating that
starts after the frame rail and pinch weld and stops just before the front and
rear crossmember and transmission tunnel. I noticed that 2 very small
sections of the (OEM) factory-installed rubberized coating has peeled. I am
also aware that Zeibart rubberized coatings and rattle-can rubberized
coatings will trap moisture and cause accelerated rusting. However, I do not
want to leave these 2 small areas of the metal exposed. The 2 tears in the
undercoating are about the size of a nickel. There are no dents. Would
applying a little bit of automotive primer followed by applying Rust-Oleum
Flat Black Paint be effective? Or, should I apply the primer, add a little bit of
Bondo to match the depth of the OEM coating and then apply Rust-Oleum
automotive flat black paint? I am also open to other strategies. Please
advise. 

2 Answers
311,505

Gene answered about a year ago

The truck with undercoating is to throughly warm the vehicle like in a paint booth, this takes care of trapped moisture and helps with adhesion of the undercoat. On spot repairs I have used hot air guns and even high intensity lights to warm and dry the area. Good luck.

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40,365

beatupchevy answered about a year ago

Clean the lose rust , hit it with rust reformer , Work it into the metal while wet with a wire brush , Prime and paint or just paint it . Wipe clean with thinner and light buff with a brass brush between coats . That's about the best I've come up with .

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