He Tested 3 Products For Keeping Grass Off His Lawn Mower Deck – The Winner Might Surprise You

We may receive a commission on purchases made from links.

After spending a hot afternoon mowing, the last thing any of us want to do is spend another hour cleaning off a cruddy lawn mower deck. Unfortunately, without performing this lawn mower maintenance task, problems can start to grow faster than the most persistent weeds. Caked with damp earth and grass clippings, a dirty lawn mower deck can eventually start to rust. Leaving it for too long can also put more strain on your engine, potentially leaving you sobbing over scraggly cuts. Even experienced DIYers are always looking for ways to keep grass from sticking to a lawn mower, so one of them tested three products to find out which one would make the biggest difference. After undercoating his wide mower deck with three different options, popular YouTuber @RepairGeek declared Cosmoline the clear winner.

Before starting the test, he thoroughly pressure-washed and dried his riding lawn mower decks to create a blank slate of sorts. He then liberally sprayed each blade chamber with a different undercoating: B'Laster Surface Shield, Fluid Film, and CRC HD Corrosion Inhibitor (which he refers to as Cosmoline). Next, he mowed his yard and a neighboring property, totaling around two acres, then compared the buildup under the three chambers.

Because all three products are used as rust inhibitors, you can find them at auto parts stores, home improvement warehouses, or online through retailers like Amazon. Fluid Film and B'Laster Surface Shield are typically priced around $10 for one can. CRC HD Corrosion Inhibitor costs a little more, but according to @RepairGeek, the extra expense is more than worth it.

"The Cosmoline did by far the best out of the three," RepairGeek pointed out, "On the bottom of a mower deck, it works great... It is by far the cleanest of the three." While the blade chambers treated with Fluid Film and Surface Shield had regained that familiar opaque green sludge, the Cosmoline coating had all but eliminated the issue in the third chamber.

These results likely come down to what the three products are made from, and how this impacts their adhesion and permanence. Both Fluid Film and Surface Shield are lanolin-based products. Since the sticky, sheep-derived substance naturally repels water, it makes sense that it would find its way into rust-inhibiting products used to protect lawn mower decks. CRC Heavy Duty Corrosion Inhibitor, meanwhile, forms a dry, flexible, waxy coating that provides similar protection and, at least in RepairGeek's test, did a much better job of keeping grass off the mower deck. 

This difference matters because the bottom of a lawn mower deck is an abrasive environment that's constantly exposed to debris and clippings. Because they never fully harden, Fluid Film and Surface Shield attract and hold onto the dirt, grass, and leaves hitting the bottom of a lawn mower deck. Cosmoline's dry wax finish is less likely to hold onto debris while also creating a protective barrier against moisture and corrosion. That makes it a good choice during the grass-cutting season and when your mower is sitting unused for months at a time when the weather gets cooler. For the best results, apply it in thin coats only to clean, dry surfaces. Because the aerosol is extremely flammable, keep it away from heat, sparks, and open flames, and follow the manufacturer's storage-temperature limits. It's also wise to wear appropriate protective gear and work in a well-ventilated area to avoid skin, eye, or respiratory irritation.