How to Repair Fiberglass Boat Floors
Equipment and Protective Measures
You will need a full set of fiberglass working tools, health accessories, and extra working materials. You will also need to have fiberglass and a supply of resin. Here’s a list of important tools and materials:
Orbit Sander
Tape Measure
Scissors
Saw
Screwdriver
Acetone
Wax paste
Smooth plastic laminate / thin layer of clear acrylic
Polyvinyl alcohol mold release
Squeegee
Polish
Fiberglass mat and cloth
Polyester resin
Resin catalyst such as methyl ethyl ketone peroxide
Protect your eyes with protective goggles. Your mouth and nose should be covered with a mask – lest you inhale fibers of glass while doing the repairs. It is advisable to wear a long sleeved shirt and long denim pants. Gloves are also necessary.
Assessing the Damage
Locate and correctly mark the areas of the fiberglass boat which have been damaged. Keep the required materials ready so that you can start working on the repairs.
The damage often results in delamination, so tap the area with the back of a screwdriver to see the extent of the damage to the laminate. Solid sounds crisp and sharp, while the delaminated part sounds dull. You can always compare by tapping one side that is good, and then the damaged area to notice any differences.
Repairing the Damage
Step One
First off, when you locate the damage you will need to use a small saw to cut away the damage and the surrounding delaminated area (circles work best). You should have a circle or oval to work from.
Step Two
Next, you will need to de-wax the area before you grind it. If you fail to remove the wax, the grinding will get mixed with it and this will cause a weak bond.
Step Three
Use a disk sander with a 36-grit disk to grind a bevel around the hole. The bevel length should be at least 10 times the thickness of the hull.
You should wipe down the area with a rag that has been soaked with acetone. Slather on some wax paste around the area where resin could drip down.
Step Four
You will need to place some sort of “backing” in the hole for supporting the layers of fiberglass as you fix them. A piece of smooth plastic or waxed Formica will serve well for the backing. Place the backing in the inside of the hull so that you can work on the outside.
Step Five
Next, prepare the fiberglass to fit the hole. You will need to apply two layers of cloth, and then alternate layers of mat and cloth. The number of layers will be determined by the thickness of the hull, a good rule is a layer for every 1/32 inch. Cut the first layer of mat one inch larger than the hole, overlapping the bevel by 1/2 inch all around. Each piece after that should be a half-inch larger around the circumference.
Step Six
The catalyst for resin that can be used is methyl ethyl ketone peroxide. Polyester resin usually requires one to two percent of hardener by its cumulative amount (or volume). Four drops of hardener is good enough to catalyze an ounce of resin. Stir it well, or else it could be under-cured and weaken the entire patch.
Step Seven
Next, it is time to begin the lay-up of the fiberglass layers (which you prepared in step five) and the polyester resin between them. Never do more than four at a time, and make sure you compress them while also getting out all the bubbles; consider using a squeegee. Continue layering up until the repair is flush, and then finish it by cutting some mat and cloth. Apply them over the patch and smooth them with a roller. Seal this layer with PVA mould release.
Step Eight
Finally, remove the backer from the surface, fill the imperfections, and add gel-coat paste as needed. You can polish off the final surface.