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A metal mower deck is much sturdier than a plastic one and can withstand much more abuse, but it has one distinct weakness: rust. Even if you store your mower indoors between sessions, wear and tear will eventually take its toll. The ambient humidity and the moisture in the grass itself can eventually lead to corrosion.

There are a few different ways to deal with this. One hack that can extend the life of your mower is to regularly spray the blade and interior of the deck with WD-40. This helps keep grass from sticking and prevents moisture from penetrating the metal. You can also use it to spot-treat areas of rust that have already formed. It doesn’t last very long with regular use, though, and it isn’t ideal for the deck’s exterior, as it can break down sealant layers and protective waxes over the paint with prolonged exposure.

You can always sand down any damaged areas and apply new layers of rust-resistant paint to both the top and the underside of the mower deck. This adds a new protective layer that can help prevent further erosion of your mower. This is a long-term solution and can get your mower looking brand new, but it’s a lot of work. There’s one solution that you can add on top of the paint to take rust prevention even further, and applying it is dead simple. It’s called Fluid Film.

Fluid Film is an extra protective layer you can apply over your mower’s paint, specifically designed to serve as a high-end corrosion-preventative and lubricant. This means it can help prevent your mower deck from rusting without disrupting any of its attached mechanical components. It’s a lanolin-based substance that not only prevents rust from gathering, but stops existing corrosion from spreading on contact. It’s non-toxic, has no solvents that could damage paint (though you should avoid spraying it on any rubber parts), and lasts significantly longer than other substances. It doesn’t remove rust, but it does prevent new rust from accumulating and prevents existing rust from spreading.

The company specifically recommends this substance for mowers. “Fluid Film can be applied over a damp surface and will leave a non-drying film, cutting off all oxygen from the surface and creating a barrier of protection that prevents all corrosion from occurring,” it states. “Because of its non-drying characteristics, Fluid Film also works as a release agent, helping to keep grass and debris from sticking, making clean-up a breeze.”

It’s also regularly recommended for use on mowers by users. One claimed that Fluid Film reduced the amount of grass buildup on the underside of his mower by at least three times what he would typically get without treatment, resulting in less clogging and less moisture buildup on the metal. Others regularly state that it works similarly to WD-40, but seems to last significantly longer, with some claiming that they only need to apply it once or twice a year. Still more have stated that it’s a good all-around tool for outdoor equipment, working well with hedge trimmers and other tools.

Fluid Film is sold in multiple different form factors. There is the standard formula, which creates a somewhat clear, but slightly amber-colored, film designed to protect metal without fundamentally changing its appearance. You can get this version of the product in an 11oz. aerosol can for about $10. Alternatively, you can get it in its liquid form in a 1-gallon paint can for about $43 or a 5-gallon bucket for roughly $171. The other option is to get the Fluid Film Black formula (AKA Fluid Film Noir), which comes in all the same sizes and delivery systems. As the name suggests, this one goes on like black paint, so you shouldn’t use it on anything you want to keep its original color, but it can be good for hiding already discolored or eroded areas. Some users have noted it’s a bit thicker and goes on with a bit more tack, but the formula is otherwise pretty much the same. It’s about $17 for the aerosol can, $48 for the 1-gallon can, and $185 for the 5-gallon bucket.

For most people who are just looking to protect their mower deck, the 11oz. aerosol should work fine. Simply wash all the dirt and grime off the underside of your mower, and anywhere else you’d like to apply it. You can do this with a power washer, or a bit of dish soap, a scrub brush, and a hose. Once it’s clean, let it fully dry, then thoroughly shake the can and apply it, spraying from approximately 1 foot away from the surface you wish to coat. Then simply leave it on the metal and allow it to soak into the pores.