Symptoms
- Thick caked-on grass under the deck, especially after wet mowing
- Reduced mulching or discharge performance
- Rust spots or flaking metal visible on the deck underside
- Mower feels heavier or the discharge chute is blocked
Likely causes
- CommonAccumulated wet grass clippingsGrass sticks and hardens under the deck if not cleaned regularly, especially after mowing wet lawns.
- CommonMoisture trapped against bare metalCaked grass holds moisture against the deck, accelerating rust over time.
- CommonInfrequent deck cleaningSkipping regular cleaning lets buildup compound season after season.
- PossibleDeck paint/coating worn throughOnce the protective coating wears off, bare metal rusts faster under trapped moisture.
What to do
- Disconnect the spark plug wire before tipping the mower or reaching under the deck.
- Tip the mower with the air filter/carburetor side up per the manual, and scrape out caked grass with a putty knife or scraper.
- Rinse the underside with a hose once loose debris is cleared, avoiding spraying water directly into the air filter or engine.
- Dry the deck thoroughly and check for any active rust spots or thin metal.
- Treat light surface rust with a wire brush and apply a rust-inhibiting spray paint made for outdoor equipment.
- Clean the deck after every few mows going forward, especially when cutting wet grass, to prevent buildup from returning.
Tools and parts
- Putty knife or scraper
- Garden hose
- Wire brush
Rust inhibiting spray paintSearch: “outdoor equipment rust paint”
When to call a pro
If rust has eaten through the deck metal in spots, a mower shop can advise whether a patch or full deck replacement makes sense.
Safety
Use caution
Always disconnect the spark plug wire before reaching under the deck.