The rust was undoubtedly caused by buildup of wet grass clippings against the back of the mower deck, the part that supports the motor and shields the spinning blades. The damage you see is probably just the start of a more widespread problem. Tip the mower and inspect the underside of the deck. If the rust is indeed widespread, it might not be worth trying to patch the area where the rust has completely eaten through, because the surrounding metal will probably succumb soon, too. Plus, there could be a safety issue if you try to mow with a machine that has little solid metal to support the motor and shield the blades.
“If you start to see holes, it’s generally rusting from the underside,” said a service technician at Virginia Outdoor Power Equipment in Fairfax (703-207-2000; vopec.com). “It’s time to retire the mower and move on to a new unit.”
A technician at Vienna Lawnmower Sales & Service (703-242-9300; viennalawnmower.com) was just as discouraging. “They call rust a cancer for a reason,” he said. “Once it starts and you get a hole, it’s pretty much the end of the line for it.”
Mower-repair companies can order a replacement deck, but by the time you pay for labor, the cost could be 75 percent or more of what a new mower would cost. The technician at Virginia Outdoor Power Equipment said a new deck for a Honda mower such as yours would probably cost around $250. Less-expensive mower decks are listed on various websites, but you’d need a way to install them.
These concerns aside, because the mower has been working fine, there are ways to patch the holes. Simplest and cheapest, though not the most elegant, is to cover the damaged area with duct tape. Clean and dry the surface first, and use a heavy-duty type, such as Gorilla Heavy-Duty Duct Tape ($4.97 for a 12-yard roll at Home Depot). Niki Popken, a consumer affairs specialist for Gorilla Glue in Cincinnati, suggested wire-brushing the damaged area first to get down to shiny metal where the paint is gone. Otherwise, she said, the tape will bond to the rust, which is prone to flaking. Apply a couple of layers of tape, with each new layer extending out a little farther than the one underneath. Multiple layers will be stronger in case the mower blades hit a pebble and fling it toward you or a bystander.
You also can patch the holes with metal flashing, cut big enough to extend past the rusted area. You can glue on small patches with a two-part epoxy, such as J-B Weld Twin Tube Cold Weld ($5.67 at Home Depot for a package with two one-ounce tubes). For a larger patch, where it might be hard to bend the flashing to match the contour of the mower deck and hold it in place while the epoxy cures, you could secure the patch with pop rivets — a way to fasten two sheets of metal together when you only can access the front surface. You will need a rivet gun, a hand-operated contraption that looks a bit like a wrench, and a few rivets; the Tekton Rivet Gun with 40 rivets is $13.51 at Home Depot. You will also need a drill with a bit matched to the shank diameter of the rivets.
Or, for the tidiest patch, apply multiple layers of fiberglass cloth with epoxy resin. Wearing rubber gloves, hold an oversize patch of cloth in place and brush on the resin. Press with the brush to form the mesh to the curve of the mower deck. Build up the patch with multiple layers. An eight-square-foot package of Bondo Fiberglass Cloth costs $6.97, and a quart of Bondo Fiberglass Resin is $14.97 at Home Depot.
Once dry, you can paint the patch red, if you want, so that the neighbors won’t notice your handiwork.
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