As long as the areas are small-no more than one or two square feet-repairs are quite simple and can usually be accomplished by injecting epoxy resin underneath the skin into the affected area. Areas larger than this may require extensive replacement of the outer deck skin, which is a major project.
To make a small repair, first define the soft area by judicious pressing with the hands and feet, or by rapping with a plastic mallet. Delaminated areas will ring dull and lifeless, and the outer laminations will usually deflect slightly before the added resistance of the stiffer core material is felt.
Mark the perimeter of the soft areas with a pencil. Then drill 1/4” holes on about 6” centers through the outer skin, being sure to position holes at both the high and low points of the delaminated area.
There’s a good chance that moisture will be trapped inside the core of any section of the deck that has delaminated. If you try to reglue the fiberglass skin to a damp core, you’re doomed to failure.
The most reliable way to dry damp areas of core is a hand-held hair dryer. After drilling the venting/filling holes, heat the deck in the area that has delaminated. If any steam comes out, keep heating until it stops. Then, using a hobbyist’s glue syringe, inject acetone into the highest holes. The acetone will help dry condensation between the laminate and the core.
Mix a small amount of epoxy resin and hardener, and pour the mixture into the syringe. Inject the resin mix into the hole or holes at the high point of the repair. Gravity and capillary action will draw the resin slowly down to the lower holes.
Because only a little resin can be injected at a time, you’ll have to keep at it, adding small dollops of resin until it finally begins to ooze out of the lower holes. At this time, cover the lower holes with masking tape to keep all the resin from running out. Make sure that the high holes are topped up. When you’re satisfied that the delaminated area is filled with resin, clean up spills with denatured alcohol, an excellent, fairly mild solvent which works with most epoxy resins.
In some cases, gravity alone may be inadequate for moving the resin under the deck laminate. You can greatly increase the flow of resin by loading it into a clean grease gun rather than a syringe. Regular grease fittings can be screwed into the holes you’ve drilled in the deck, but be sure that the deck has really delaminated in the area into which you’re injecting the resin. If the deck hasn’t delaminated, you can cause it to do so under the pressure of the resin powered by the grease gun, which creates enormous force.
This grease gun fix is most suited for fairly large areas of delamination, and must be used with caution to avoid actually increasing the amount of damage. After use, the grease gun can be cleaned by filling it with hot soapy water or alcohol, pumping it out and refilling several times. Don’t count on getting it clean enough to reuse, so use the smallest, cheapest gun you can find.
A weight such as a concrete block set on a piece of plywood or Masonite over the repair will help improve contact while the resin cures, but be sure to put a sheet of plastic between the deck and whatever weight you use to keep it from sticking to the deck.
Always wear rubber gloves when working with epoxies. Epoxy sensitization is cumulative, so small amounts over time can hurt you. The job is apt to be a messy one, so have your solvent and plenty of rags or paper towels ready to clean up the inevitable drips and runs. Tape either newspaper or polyethylene (garbage bags work fine) around your work area to avoid random spills or footprints.
When the epoxy has cured, there are several ways to finish off the repair. You can apply dots of deck color paint or gelcoat to the holes, or you can repaint the entire area. Don’t leave the bare epoxy exposed to sunlight, because it will start to break down in a few months if unprotected from ultraviolet rays.
If there are only a couple of holes in the repair, you can drive short, pan head stainless steel self-tapping screws into the holes. This is a good dodge, because the screws look like they’re doing something, even if they’re only cosmetic.
I have used gorilla glue in same fashion. You don’t have to dry the rot as moisture helps it set. Use a couple times on my whaler. I used holes 3 inches apart and strengthened a bit ahead of time as gorilla glue expands. Used pa head screws as author recommended . Came out great.