How to Use Gel Coat for a Sail Boat

Gel-coated boat.

Modern sailboat manufacturers lay fiberglass cloth with polyester resin to create the hull, deck and framing members of the boat. Not very aesthetically pleasing, bare fiberglass does not accept paint very well, especially in high wear areas. Gel coat provides a tough, wear resistant coating that protects the fiberglass from water intrusion and may be pre-tinted almost any color to match or complement the vessel color scheme.

Things You'll Need

• Surfacing agent
• Gel coat (pre-tinted)
• Paint sticks
• Plastic container
• Acetone
• Methyl ethyl ketone (MEK) catalyst
• Brush or roller
• 600 grit wet/dry sandpaper

Instructions

1. Add 7 fl. oz. surfacing agent per gallon of pre-tinted gel coat. Mix the agent well into the gel coat using a clean paint stick.

2. Pour 1/2 gallon of the treated gel coat into a clean plastic container. Thin the gel coat with acetone until the desired consistency is achieved. Mix well with a clean paint stick.

3. Add the methyl ethyl ketone (MEK) catalyst to the treated gel coat. Refer to the manufacturer's instructions for detailed information on catalyst-to-gel coat ratio. Mix the gel coat well with a clean paint stick.

4. Roll or brush the gel coat onto the boat. Overlap the passes slightly to get good coverage of the gel coat. Add more acetone to thin the mix if too much roller stipple or brush streaking occurs.

5. Mix another batch of gel coat and repeat this process until the entire area to be painted is covered. Allow the gel coat to harden before attempting to touch it or add subsequent coats.

6. Sand the brush marks and roller stipple out of the gel coat with 600 grit wet/dry sandpaper and water. Use long fore-and-aft strokes (strokes that follow the length of the hull rather than across it) when sanding the bottom to provide a smooth surface that will reduce drag and improve laminar flow of the water over the hull. Repeat this process if a heavier coating is desired.

Tips & Warnings

• Gel coat hardens through an exothermic reaction with the MEK catalyst. Air temperature above 70 degrees Fahrenheit and direct sunlight can drastically increase the hardening rate and reduce working time. Mix smaller batches if you find that you cannot apply the entire 1/2 gallon batch before it becomes unworkable.

References

• Fiberglass Hawaii: Gel Coat Usage
• Capt.TJ Hinton; commercial fishing vessel captain; Gulf Coast, Miss.

Resources

• Boatkeeper Series, Alaska Sea Grant: Post-Season Lay-Up: Winterizing Saves Trouble (PDF)
• Boat Repair Videos: Fiberglass and Gelcoat Repair Application