Building a new floor in the boat with polyester

Want to repair the bottom of your polyester boat? At Polyestershoppen, you can find everything for optimal boat maintenance. From polyester to handy supplies, we provide everything you need to help you repair the bottom of your boat.

Many boats, especially motorboats, have a flat wooden inner floor. It is common for this floor to spring. Closer inspection reveals that the wooden panel under the polyester is rotting or starting to decay or mold. What can you do about this? A repair by a professional will cost a lot, often more than the boat is worth. Discard? That's a shame, especially if the rest of the boat is still in order. Repair it yourself? Isn't that difficult? It is a job that may take 2-3 weekends, but it is not that difficult and the satisfaction is great!

Supplies needed for a floor repair

Tools

• Reciprocating saw
• Pendulum saw
• Screw gun
• Angle grinder with fiber disc
• Polyester auxiliary material kit medium
• Corner roller

Commodities

• Underlayment
• Polyester resin (2-3 kg per square metre)
• Fibreglass chopped strand mat 450 gr/m² (2-3 m² per square metre)
• Cotton fibre (0.4 kg for every 4 square metres)
• Polyester topcoat in colour (400 grams per square metre)
• G4 adhesion primer (300 grams per square metre)

Protection 

• Polyester protection kit (vapour mask, gloves and an overall)

How can I repair or replace a rotten boat floor?

Step 1. Demolition of the bottom, trusses and keel box

Before demolition, carefully measure the position of the bottom of the boat. Measure the dimensions and take a few photos if necessary. If there is a carpet in the boat, it may serve as a template for the new bottom. Support the boat as possible and start cutting next to the centre. Use the pendulum saw to do this. Demolish with care. Make a small hole and check to see if there is anything in the way that could make demolition difficult. Usually the bottom is completely empty and can be simply sawn away. Remove the entire bottom and, if affected, also the trusses and, before removing the trusses, make cardboard templates of the trusses. Also check the keel beam, it is often in poor condition and should be replaced immediately.

When all rotten parts have been removed, grind the polyester clean of glue and wood residues. The fastest way to do this is to use a grinder with a fibre disc. Also grind the polyester of the hull up to 10 cm above the bottom down to the laminate.

Step 2. Making new trusses

Now make the replacement trusses from new wood. The cardboard templates you have made come in handy for this. Place each truss in the boat and measure carefully measure whether the top will lie nice and flat. After all, this is where the bottom will be placed later on. Saw water drainage holes in the rafters so that any leakage water can flow to the deepest part of the boat and can be removed there.

Do not cut holes in the keel beam, for safety reasons it is better to keep two compartments. If you start sawing in the keel box, water can flow from one compartment into the other and the risk of  sinking is greater.

Step 3. Gluing in the new trusses

Treat the new trusses all around with a brush with G4 primer and then glue them into the boat with polyester resin mixed with cotton fiber. When the trusses are attached, fill the corner between the hull and truss with the same glue paste and round off (a so-called fillet joint). For extra reinforcement, another glass mat with polyester resin can be applied over this.

Once the trusses heven been placed, it can be checked whether the top is completely flat. Correct if necessary.

Step 4. Making and gluing the new wooden bottom into the boat

Now cut a new bottom and make sure it fits properly on the trusses. Using a flat brush, coat the underside of the new bottom with G4 primer and an adhesive consisting of polyester resin and cotton fiber to the underside of the trusses. Let this harden for at least 24 hours.

Step 5. Providing the new bottom with fibreglass and polyester laminate

Now that the new bottom is in place, it is important to laminate it with a layer of glass mat 450 g/m2. First fill the seam between hull and bottom with polyester and cotton fibre. Complete the transition between floor and hull with another mixture of polyester resin and cotton fibre. Primer the bottom with G4 primer and apply a layer of glass mat and polyester resin. Allow the layer to extend approx. 7-8 cm up against the hull. If necessary, laminate an extra layer of glass mat 10 cm wide over the transition for extra strength. Now allow to cure.

Step 6. Finishing the new bottom in the boat

Basically, the boat is now healthy again and can be walked on. For a better finish, the inside of the hull can be sanded with 60-grit sandpaper and rolled in topcoat provided with a colour. Do this with a nylon roller. Optionally, anti-slip grit can be applied to the topcoat. If desired, the new bottom can also be finished in other ways, such as with carpet, with decorative wood or after smooth sanding and filling with a varnish. After completing the work, items such as chairs, steering, tables, engine box, etc. can be replaced.

Want to know more?

Do you have questions about repairing the bottom of your boat? Our specialists will be happy to help you further with your project. You can contact us on work days until 5 pm Dutch time by phone, email, WhatsApp and livechat . We are happy to help you on your way!

Also take a look at our information centre. Here we have published several step-by-step plans on renovating your boat! See, for example, the article "Boat repair and restoration" and see which manuals are of interest to you.