Replacing Plywood Boat Floors: A Step-By-Step Guide

Replacing the plywood floor of a boat is a complex task that requires time, money, and a certain level of expertise. It is important to understand the reasons behind a damaged boat floor and the steps involved in replacing it. Boat floors are usually made of plywood screwed down to the top of stringers and frames, often with a layer of carpet or vinyl flooring. Over time, moisture can enter the plywood through screw holes and cause delamination and rot, making it unsafe and uncomfortable to walk on. To repair this, one must remove the damaged floor, treat the affected areas, and install a new floor, ensuring proper sealing to prevent future damage.

Removing the damaged floor

Firstly, remove any equipment or hardware screwed down to the floor. This includes items like seat bases, cooler brackets, and step or ladder brackets. Carefully detach these items, preserving the screws and brackets for future use if they are in good condition.

Next, pull up any carpeting or floor covering. This will expose the fasteners or tabs used to secure the plywood to the frame and stringer system. If there are cutouts in the floor for storage compartments, carefully remove any trim around these areas as you may want to reuse them later.

Before cutting or removing any fasteners, ensure the hull is adequately supported. In some boats, the removal of the floor can cause the hull sides to move or become floppy. It is crucial to stabilise the hull to maintain its shape during the repair process.

Now, you can begin removing the damaged plywood. If only a portion of the floor is damaged, you may choose to cut out a section and replace it. Use a sharp knife or a jigsaw to cut through the plywood, ensuring you don't damage the underlying structure. If there is no structural member below to create a clean joint, consider using cleats bonded under the edge of the remaining deck to support the new plywood.

If the entire floor needs to be replaced, carefully remove the pieces of plywood, ensuring you don't damage the surrounding areas. The floor may be bonded to the stringers and cleats, so use a chisel and grinder to carefully remove any bonded material from the tops of the stringers. Take your time with this step to avoid causing further damage.

Once the damaged floor has been removed, inspect the stringers and cleats supporting it for any signs of moisture damage. It is essential to repair any structural damage before installing the new floor.

These steps will ensure a safe and thorough removal of the damaged floor, setting the foundation for a successful boat restoration project.

Inspecting the structure below the floor

Begin by carefully examining the hull of the boat. Look out for any signs of damage such as blistering paint, corrosion, large cracks, dimples, warps, or mismatched paint. These issues could indicate that the hull has been previously repaired.

Next, move on to inspecting the interior of the boat. Keep an eye out for signs of mildew, rust, or pests. These issues could be indicative of negligence or improper care from previous owners. Pay close attention to the deck and tap or press on the wood to check for any soft spots, which could indicate rot.

Now, it's time to inspect the areas below the floor. Start by checking the engine oil. Ensure that it is clear, fresh, and free of any metal shavings or debris. Additionally, check the fuel tank by smelling its contents to make sure the gas hasn't gone rancid.

Another important area to inspect is the transom, which provides support for the engine. Use the handle of a screwdriver or a small plastic hammer to tap on the transom and listen for any signs of softness. A healthy transom will produce a solid ring, while a dull thud could indicate a soft spot. Stains around fittings, such as transducers or tie-downs, may also suggest water leakage, which warrants further investigation.

Finally, don't forget to inspect the deck and floor for any signs of water intrusion. Leaking fittings, such as railings and cleats, can cause the deck core to absorb water and delaminate. A delaminated deck will feel soft underfoot. Additionally, check for rot around seat bases, as water may have leaked past the fittings, causing the plywood to deteriorate and resulting in mushy or wobbly seats.

By thoroughly inspecting the structure below the floor, you can identify any issues that need to be addressed during the replacement process, ensuring a safe and reliable boat for your future adventures.

Installing the new floor

Before installing the new floor, it is important to inspect and repair any damage to the structure below the floor. If the structure is in good shape, you can proceed with the following steps:

• Cut out new pieces of plywood using careful measurements or the patterns from the old floor. Ensure that the new plywood is at least the same thickness as the original material.
• Dry fit the sections and drill any fastener holes, then remove the section.
• Coat the back side with two or three coats of epoxy to prevent moisture from penetrating the bottom of the new floor. It is crucial to completely seal the edges of the plywood and the fastener holes.
• For pontoon decks, install the new floor by screwing the plywood down to the stringers. Coat the fastener holes with epoxy before inserting the screws to prevent moisture from entering the plywood.
• For runabouts, bond the new plywood floor to the hull, stringers, and cleats. Use a mixture of epoxy and a high-strength filler to create a putty to bed the plywood into.
• If you are replacing only a portion of the floor or using multiple sheets of plywood, create a joint between pieces by dishing out the joint with a grinder and joining the pieces with fiberglass tape.
• Prepare the hull surface for bonding by sanding a 4"-6" wide strip on the hull above the floor with 80-grit paper.
• Mix epoxy and add a filler to create a peanut butter-like consistency. Apply a fillet of thickened epoxy along the hull-to-floor joint to form a radius.
• Apply 4"-wide fiberglass tape over the fillet and wet it out with epoxy. You may need multiple layers to match the thickness of the original tabbing. Stagger the edges of the tape when using multiple layers to avoid ending in the same place.
• Reinstall the carpeting or floor covering after the epoxy has cured. If painting the floor, ensure you wet sand the surface to remove any gloss. When reinstalling seats and deck hardware, seal the fastener holes with epoxy to prevent future damage.

Tabbing the floor to the hull

Before you begin tabbing the new floor to the hull, it is important to prepare the surface properly. Ensure that the hull is clean and free of any debris or residue. Use a grinder to remove any old paint or primer from the area where the new floor will be tabbed. It is recommended to grind up to 6 inches or so to bare glass for the best adhesion. Creating a smooth and even surface will ensure a strong bond between the floor and the hull.

Once the surface is prepared, you can start the tabbing process. Cut the new plywood floor to size, making sure it fits snugly in the space. You can use glue and screws or epoxy thickened with a filler to attach the new floor to the hull. This will provide a strong base for the tabbing. If your boat is larger than 20 feet, consider using additional layers of tabbing for added strength.

After the floor is securely attached, you can begin glassing. For a strong tabbing, use 1708 biaxial fibreglass fabric. This will provide the necessary reinforcement to the joint between the floor and the hull. Cut the 1708 fabric to size, allowing for a few inches of overlap onto the hull and the new floor. Mix your resin and hardener according to the manufacturer's instructions, and apply a coat to the tabbing area before laying the 1708 fabric. Smooth out any air bubbles and ensure the fabric is fully saturated with resin.

Once the first layer of 1708 is in place, you can add additional layers if needed. Two layers of 1708 should be sufficient for most boats. After the final layer, apply a coat of resin over the fabric to seal it. You can also add a non-slip texture to the floor at this point if desired.

Allow the resin to cure completely before using the boat. This process may take several hours or even a few days, depending on the resin used and the temperature. Once the resin is fully cured, your new boat floor will be strong and durable, providing a safe and enjoyable boating experience.

Reinstalling the carpeting or floor covering

Once you have cut out the new pieces of plywood, dry-fitted them, and drilled the fastener holes, it's time to coat the back side with two or three coats of epoxy to prevent moisture from penetrating the bottom of the new floor. It is also very important to completely seal the edges of the plywood and the fastener holes. Sealing the edges of the plywood is especially important at the edges of a deck on a pontoon boat. If using Douglas fir plywood, you should use a light layer of woven fiberglass fabric on both sides to prevent the checking—6 oz. glass is usually sufficient.

For partial replacement of the plywood or multiple sheets of plywood, dish out the joint between pieces with a grinder and join the pieces together with fiberglass tape to make a single panel.

If you are installing a pontoon deck, you will need to screw the plywood down to the stringers. Coat the fastener holes with epoxy before inserting the screws. This will prevent moisture from getting into the plywood endgrain at the fastener holes. We usually coat or fiberglass the top side after the floor is installed.

If you are tabbing the floor to the hull, prepare the hull surface for bonding by sanding a 4″—6″ wide strip on the hull above the floor with 80-grit paper. Mix WEST SYSTEM epoxy and add either 406 Colloidal Silica or 407 Low Density filler to create a mixture with a peanut butter consistency.

Apply a fillet of thickened epoxy all along the hull-to-floor joint. This will make a radius which will allow the fiberglass tabbing to lay easily across the joint without seriously distorting. Apply 4-inch wide 727 Biaxial fiberglass tape over the fillet. Wet out the tape with either a 105 Resin/205 Hardener or 105 Resin/206 Slow Hardener epoxy mixture. If necessary, apply multiple layers of tape to build up to the same thickness as the original tabbing. Stagger the edges of the tabbing when using multiple layers so they do not end in the same place on the hull side or floor. A good trick is to apply the first layer up the side 3″ or so, the second layer 3″ out on the floor, and the third layer centered over the corner. This creates an aggregate build-up three layers thick on the corner without causing a hard spot at the edges of the tabbing.

Finally, reinstall the carpeting or floor covering after the epoxy is cured. If painting the floor, make sure to wet sand the surface to remove all gloss before priming and painting. When reinstalling seats and deck hardware, be sure to seal the fastener holes with epoxy. This will prevent the same type of damage from recurring.

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