Checking your lawn mower deck

Cutting grass is a messy business and when you think about it; a lawn mower is kind of a rolling contradiction. The purpose of the machine is to maintain the quality of the lawn and improve the appearance of the lawn. And it does this by cutting the grass in half and dispersing the clippings all over the place!

And what to do with all those clippings? That’s a pretty significant question for many homeowners. So much so that there is an entire line of blade and baggers and mulching attachments and plugs designed to address that question alone.

The Hidden Enemy

When you’re standing there, surveying the lawn trying to figure out what to do with all those clippings, I’ll bet that there is one mess you aren’t thinking about! It’s always there when you’re done cutting, it builds and builds, silently working to undermine your lawn mowing plan.

It’s the grass and moisture and dirt and rust building up under your deck. It’s there, believe me. Go out and take a look right now. I’ll wait right here…

See. Told ya.

So what to do?

Well, if it gets too bad, we could be looking at some elbow grease and an afternoon of scraping and sanding. If it’s something you address on a regular basis it may take nothing more than a garden hose and a rag. But most of us weren’t really aware that there was a bottom to that deck to begin with. I mean “Out of sight-out of mind” thank you very much.

But here’s something that will hopefully bring this thing home to you: The deck is a safety shield that keeps the rapidly spinning steel blade from causing injury or death. And it’s made of steel. And steel rusts…and breaks…and fails. And then the screaming, and the running and the explosions and the zombies. All because you didn’t bother to clean off the bottom of your deck.

Happy now?

Here’s the plan, Stan!

  • Turn the mower off. If it’s a riding mower, disconnect the battery. If it’s a walk behind mower, disconnect the cable from the spark plug.
  • You need access to the underside of your deck but we want to be safe about it. If you have a riding mower, a jack or lift would be best. Make sure you have an assistant standing by (trust me, you’ll be glad you do). Chock the wheels and lift the front of the mower until you can clearly see the deck.
  • If you have a walk behind mower, it should be significantly easier. Chock the wheels and tip the mower backwards. This is a good time to have that helper hold the handle down. A couple of cinder blocks or a small car jack will hold the front end up.
  • Now that we have access to the deck, get a flashlight and take a look around. Be prepared to cringe, it might be ugly under there. But don’t worry, every mess can be cleaned up. Look at the 70’s!
  • The next step is to get that blade off. If you’ve never done this before, don’t be too proud to seek guidance and a little assistance. Blade bolts can be stubborn, so take your time and when in doubt; enlist the assistance of your local shop. Many shops won’t even charge you to loosen a bolt, but ask first.
  • More than likely you’re going to need a putty knife or something to scrape the build up off. Gloves are going to pay off in dividends if you like your knuckles in one piece. For stubborn spots, giving the putty knife a tap or two with a hammer should be right as rain.
  • Once the main stuff has been removed, it’s time to break out the steel brush. There are also these lovely little steel brush attachments for power drills which work wonders and will save you time. Oh, remember those safety glasses sitting over there in your tool box. You might want to put those on…if we want to keep seeing…
  • Once again, take you time and get it clean. Improvise if my suggestions are not working for you. You’re cleaning grass and dirt off of a steel surface so don’t worry so much about being careful with the metal.
  • Take a close look at the underside of the deck. We’re looking for thin spots, heavy rusting, cracks, chips… any kind of compromise to the decks integrity. It may not be bad now, but it’s going to get worse as time goes on so let’s deal with it now so here’s my best advice. Cracks, fissures, breaks…these need to be welded and it needs to be done by someone who know what they’re doing. A poor welding job will just weaken the mower housing and that is what we in the business call “bad”.

Keeping it clean

Some manufacturers now install wash out ports in the mower decks. It’s simply a female threaded connection for your garden hose that has been inserted into the deck shell. They tend to work pretty well provided you actually use them.

Lot’s of folks have the luxury of a power washer. Another great way to turn your garden hose into “super garden hose”. A quick spray and the deck will be clean enough for your mother in law to eat off of it.

If you use pressurized water to clean off the deck, it’s a pretty good ideas to run the blades for a few minutes. This will dry off the deck as well as the bearings in the blade hub. Always a good idea!

The incredible new SUPER SPRAY, with 20% more “good“!

Now the internet is full of all kinds of claims and testimonials for all kinds of products scientifically designed to prevent build up from occurring on your deck. I’m not here today to endorse or dismiss any of them. Feel free to give any of them a shot and let me know how it worked for you. When making the decision as to which one to use, here are a couple of things to keep in mind:

Grass builds up because it’s being slammed into the bottom of your deck at an incredible speed. It goes on wet and dries out fast and that is how you get “stuck on yuck”. If you’re using your mower to cut grass, then the grass clippings are going to stick. It’s the circle of life.

So you went online and dropped $24.95 + shipping and handling for a can of the brand new “Astro-mow 5000 non stick polymer spray with the new mower scent”.

You followed the directions, cleaned the undercarriage and sprayed it on and it’s shining like a greasy new dime. Great! So you fired up the old girl and took her for a spin, but when you get back to the shed and lift that bad boy up, the undercarriage looks like Popeye’s spittoon.

“What in the heck?” You exclaim, staring at the fine print on the can and wondering what went wrong.

Most of these space-age products are great for displacing water (WD-40) and creating a low-friction surface (Lemon Fresh Pledge), and some of them can leave your mower smelling down right delicious (Butter flavored Pam), but when the dirt and sand and rocks get to swirling around under there, no spray in the world is going to make much difference. And once the magic in a can is gone…you got build up.

So…what are you saying?

What I’m saying is this. Pro-active and preemptive are fine, but persistent and periodic are better. We as Americans live in a “magic pill” society. We want a simple device that eliminates the bother with one easy application.

Let me introduce you to your garden hose. It’s already hooked up, charged and ready to go…and there’s no shipping and handling involved.

To keep your deck in good shape, free of debris and living large you need to stay up on it. Inspect it and clear it each time you mow.

I agree…it is a pain. But so is kneeling down in your driveway, peering under your mower deck with your butt sticking up in the air.

Stay up on it. It’ll pay off in the end.


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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.