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.
Protect your eyes with protective goggles, and your mouth and nose should be covered with a mask that covers your air inlets completely–lest you inhale fibers of glass doing the repairs. It is advisable to wear a long sleeved shirt and long denim pants. Do not forget the gloves too.
Assessing the Damage
When your boat has a damaged area, you may feel the urge to get angry and slam it with a hammer, especially if it is the boat's floor. However, it is important to remain calm. There are actually several ways to repair a fiberglass boat floor. First though, you will need some essential safety supplies, such as masks rated to handle the fibers (because if you breathe them in it can hurt/kill you). You will also need to have glass fabric and a supply of resin. Your applying a repair is not like slapping on a fancy band-aid that will slip off eventually; in fact doing it yourself is likely to be just as good as having your repair done at a boat shop that has the fiberglass materials. You are also likely to save more money this way too.
Repairing the Damage
First off, when you locate the damage you will need to use a small saw to cut away the damage, and the surrounding area (circles work best). What you will have is a perfect circle or oval to work from. Usually the damage 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 and sometimes odd. You can always compare by bumping one side that is well and good, and then the damaged area to notice any differences.
If the damage is small, and it is above the waterline, make the repairs on the inside if possible–however if unable to do so, you will need to make the repair from the outside (which results in more resin and refinish damage since you will be making a bevel cut around the hole). 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. Using the disk sander with a 36-grit disk to grind a 12 to 1 bevel around the hole will get the job done nicely.
Once you have sanded the hole and around it, it should have a dull look. You should wipe it down with a rag that has been moistened with acetone; and then slather on some wax paste around the area where resin could drip down. Cut some of the smooth plastic laminate or a thin layer of clear acrylic, making sure it is a foot larger than the hole you made earlier. Wax it, and then lightly mist it with polyvinyl alcohol mold release, then tape the backer on to the outer surface. Next, cut the fiberglass to fit the hole, beginning with two layers of one and a half ounce mat, then the alternate mat and six-ounce cloth. The number of layers will be determined by the thickness of the hull, a good rule is a layer forever 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.
The catalyst for both resins 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). It is generally known that four drops of hardener will catalyze an ounce of resin at a percent. Stir it well, or else part could be under-cured and weaken the entire patch. Next, it is time to apply the gel-coat, and then begin the lay-up. 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, and applying them over the patch, smoothing them with a roller. Seal this layer with plastic to allow a cure to happen. Then remove the backer from the surface, fill the imperfections, and add gel-coat paste as needed. Lastly, polish it off the surface.
