How to Repair a Rotten Boat Floor

A soft, spongy deck is more than an eyesore – it’s a safety hazard that can shorten your boat’s life and slash its resale value.

This guide walks you through spotting early warning signs, choosing the right replacement materials, and installing a rock-solid boat floor that will last for seasons to come.

Follow along and you’ll finish with a deck that’s lighter, tougher, and sealed tight against future rot.

Why a Solid Deck Matters

Maintenance issues, especially hidden rot, can quickly translate into real-world risks. A weakened floor can split or collapse, and stress the hull. Left unchecked, it invites mold, corrosion, and electrical shorts that pile on repair costs.

On the flip side, a fresh, watertight deck stiffens the hull, keeps gear and passengers secure, and instantly boosts the resale value. And if you’re taking on the job yourself, you’ll not only save thousands in yard fees, but you’ll also gain the confidence to tackle future projects on your own schedule.

Hidden Costs of Skipping Repairs

Rot spreads fast. The longer you wait, the deeper moisture creeps into stringers, bulkheads, and wiring. By the time a deck panel feels “a little soft,” structural lumber beneath may already be mush.

Replacing deck plywood early is far cheaper than ripping out stringers later.

Spot the Rot Early

Look, Listen, Feel

Look out for these clues to catch rot early before it spreads too far. Spotting these signs during spring commissioning gives you time to plan a controlled repair instead of scrambling mid-season.

1. Discoloration or black streaks around deck hardware signals trapped moisture.
2. A dull “thud” instead of a crisp tap when you knock on the deck hints at delamination.
3. Soft spots or flexing under bare feet means the core below has already broken down.

Secondary Clues

• Mildew smells under hatches
• Rusty or weeping fastener heads
• Persistently wet carpet backing

Match the Material to Your Style

Choosing the right panel is half the battle. You’ll want one that matches both your boat’s mission and personal style. A trailer-kept skiff might prioritize weight savings, while a cabin cruiser could benefit from the proven durability of plywood with glass skins. Each core has trade-offs in weight, cost, and longevity:

Proper Gear

A smooth job starts with a complete kit equipped with all of the essentials. You’ll want to have the following laid out on the dock:

• Safety gear: gloves, eye protection, respirator
• Cutting tools: circular saw for long rips, jigsaw for curves
• Sanding gear: 80 and 120-grit discs, random-orbit sander
• Fasteners: #8–#10 marine-grade stainless screws, fender washers for thin skins
• Adhesives: thickened epoxy or structural polyurethane for bonding
• Sealants: polysulfide or hybrid silicone for perimeter seams
• Fiberglass cloth & CSM: 1708 biaxial for strength, mat for print-through control
• Finishes: non-skid paint or EVA foam pads for traction

Lay plastic sheeting under the work zone to catch dust, and keep acetone, rags, and a sacrificial brush on hand for quick cleanup.

How to Repair a Boat Floor

Step 1: Clear the Deck

Start by removing seats, consoles, and wiring looms, then pry up any carpet or vinyl. Mark the outline of each panel with a grease pencil. Set your circular saw about ⅛ inch shallower than the panel thickness to avoid cutting into the stringers. Use a pry bar to lift panels, working from the center out to protect hull sides.

Step 2: Prep the Substructure

Vacuum any debris, then scrub thoroughly with a stiff brush and a 1:1 mix of warm water and degreaser. Let the area dry overnight.

Use an awl to probe the stringers – if wood fibers crumble, scarf-in new treated lumber bonded with thickened epoxy.

Before moving on, wipe down every surface with acetone to ensure adhesives bond cleanly to wood or fiberglass.

Step 3: Measure & Dry-Fit

Before transferring deck templates to new panels, number the underside of each piece to make reassembly foolproof. Next, cut each panel slightly oversized, drop it into place, then scribe for a tight fit. Leave ⅛ inch around the edges to allow room for epoxy fillers and thermal expansion. Number the underside of each panel so reassembly is foolproof.

Step 4: Lock It Down

Back-butter the panel with thickened epoxy or marine adhesive, bed it onto the stringers, and toe-kick bulkheads. Drive screws until epoxy squeezes out, be sure to stop turning as soon as the screw head kisses the surface to avoid starving the bond. Wipe away any squeeze-out for a flush lay-up.

Step 5: Glass & Seal

Feather the panel seams with 40-grit so cloth lies flat. Wet-out 6-inch glass tape centered over every joint, then follow with a full layer of biaxial cloth across the deck. Roll gently to chase out any bubbles that form. When the epoxy kicks, scuff-sand and repeat until you’ve built back to original thickness. Finish with two coats of UV-stable non-skid paint or install EVA foam pads for instant grip and cushioning.

Step 6: Finish & Protect

Re-bed hardware with new butyl tape or polysulfide, torque screws snug, and cap exposed plywood edges with fresh epoxy. Add anti-slip strips on traffic lanes and reinstall furniture. Wait the full cure time (usually 48–72 hours) before replacing heavy loads.

Pro Tips for a First-Class Deck

• Measure twice, cut once. A $100 panel mistake hurts more than a few extra minutes with a tape measure.
• Work in pairs. One person mixes epoxy while the other lays glass, keeping pot life under control.
• Pre-coat plywood. Rolling neat epoxy on both sides before installation locks out future moisture.

Keep It Solid – Maintenance Plan

Inspect deck seams and hardware every oil-change cycle. Reseal screw heads that lose their gasket, and hose down the deck after each salty run. A five-minute fresh-water rinse prevents salt crystals from chiseling away at the sealant.

At the end of every season, pull deck plates to check for standing water and air-dry bilges thoroughly. Catching drips early can save you from having to hack out rotten panels later.

Sea Tow Team

Sea Tow has been the premier leader in on-water boating assistance since 1983. We want to share news, press, tips and all things boating.