101 Uses for Bedliner – Undercoating Your Car with Herculiner

Liquid bed liner has been around for a few decades, becoming quite the cottage industry in the world of trucks. DIY kits hit the shelves almost 20 years ago and gearheads being an ingenious bunch, figured out all kinds of alternate uses. Here at NAPA Know-How, we have shown you how to restore the factory texture on 70s-era muscle car door panels, now we are going to show you a different use – undercoating your chassis.

Rubberized undercoating works OK for a while, but eventually it hardens and becomes a magnet for mud and road grime, soaking up water and eventually looking horrible and can even lead to the thing it was supposed to prevent- rust. The nice thing about bedliner is that moisture, dirt, grease and other contaminants simply don’t stick to it, making it perfect for undercarriage protection.

We had a project in the shop that needed a good looking and durable topcoat. We could have painted it, but paint will chip and peel. Herculiner is a little different from the other DIY bedliner kits, as it is formulated with tiny bits of ground rubber mixed right in, so you get durable protection that softens the blow of any road debris impact (which means it is perfect for off-roaders). This is perfect for the underside our project, which is a 1962 Mercury Comet road racer.

Herculiner can be applied by brush, roller, or spray. The kits come with a foam roller and a chip brush. Spraying the Herculiner product requires a special large orifice sprayer, we have used a drywall texture gun for these types of project, but any paint gun with a 2.5 or larger tip can accommodate the bed liner. For our project, we wanted to keep the mess down to a minimum, so we opted to use the roller and chip brush.

The prep is important, while the Herculiner will stick to just about anything, the cleaner the parts are, the longer the coating will last. We used a wire wheel to clean all of the old undercoating and grime from the sheet metal. There had been some rust repairs on the floor pans, all of the seams were wiped with seam sealer and allowed to cure for at least 24 hours.

In the moments before the application of the coating, all of the surfaces were scrubbed down with the supplied Scotch-Brite™ pad, and then wiped the entire surface with Prep-All, a wax and grease remover. You can use non-chlorinated brake cleaner as well.

You can see the rubber chunks on the mixing stick here. You need to thoroughly mix the material before application.

You can use a painter’s tray, but we just poured the liner into a plastic tub.

A painter’s tray would have worked a little better than our flat-bottom tub. The roller soaks up the liner, ready for application.

Then we just rolled the coating right onto the metal. The entire underside was coated this way. In the tight corners, we used the small chip brush. 

The kit says it will cover a 6-foot bed with one gallon; an 8-foot bed requires and additional half gallon. We applied one solid coat, which used about a half-gallon of the Herculiner coating. We spent about four hours coating the floor pans. This is a fairly messy process, particularly when working under a car, so wear clothes you don’t mind throwing away. Cleaning up after applying Herculiner requires Xylene, and then soap and water.

Check out all the paint & body products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on undercoating your chassis, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.