How To Repair Core Damage in Fiberglass Boats
The traditional method of repairing core damage in fiberglass boats is to cut out and replace entire sections of the hull or deck. The drawback to this approach is obviously a huge mess, large monetary expenditure, and the possibility of changing the final shape of the hull or deck. A revolutionary new approach now enables the restoration of the existing core material without the drawbacks previously mentioned.
This new and advanced method is possible by using Clear Penetrating Epoxy Sealer (CPES) made by Smith & Co. of Richmond California. CPES is the only product that will penetrate the decayed wood and evaporate the excess moisture in the wood fibers. Complete saturation of the core is the most important part of this procedure.
The typical fiberglass deck or hull consists of a wood core (typically plywood or end grain Balsa wood) within a polyester resin fiberglass cloth encapsulation of both surfaces. When new, this type of boat construction is stable for a while. Over time water will penetrate into the lamination and settle into the wood core. Water soaks through cracks in the fiberglass, incorrectly bedded hardware, or from the improper construction procedure of the fiberglass surface itself. Once water has entered the core of the boat the damage can begin. Bacteria present in the water settles and finds a food source in the wood. At first the wood is eaten just below the fiberglass skin. Warming and cooling of the deck or hull (day, night, winter, summer, and direct sunlight) creates a bigger bubble of moisture under the fiberglass skin. As this bubble expands so does the extent of bacterial and fungal decay. Eventually the entire deck or hull will be damaged. A surveyor will detect this damage during an inspection when hearing a hollow sound as the deck is tapped with a hammer. The hollow sound is the void where the glass has separated from the core.
Identify areas of delamination by lightly tapping with a mallet. Circle the hollow sounding areas with a pen. In the center of the hollow area drill a 1/2 inch hole (use a Forstner type drill bit) through the top layer of glass and wood core stopping at the bottom layer of glass. Do not drill through the bottom layer of glass and create a hole in the deck. Inspect the removed material. Decayed wood will be dark and usually moist when squeezed between your fingers. If the wood seems new, look in the hole for evidence of separation of the fiberglass from the wood. Continue drilling holes away from the original hole in roughly a circular pattern. Space these holes 3 to 4 inches apart. Vacuum drill waste as you drill to reduce mess and airborne fiberglass particles. Inspect the material as it comes out of the hole to determine the extent of the core damage. Start at the highest part of the deck and work downhill. Don't be surprised to find standing water at the lowest grouping of holes. Once the deck is open water will migrate to the lowest point since water seeks its own level. Use a wet dry shop vacuum to remove the water. Remove all hardware with fastenings through the core and plug the bottom of the hole with Fill-It epoxy to act as a fluid dam to prevent fluid draining into the boat.
At this point the most important part of the procedure begins, drying the core. Erect a lean-to or roof over the boat. Sailboats should be dismasted to ensure a continuous cover. Tarps and tents may work but require much effort to maintain. Do not allow rain, dew or spray from entering the deck! Keep the cover a minimum of two feet over the deck surface to allow airflow over the deck. Constant airflow is the best drying technique. Use fans as natural airflow is almost always insufficient. Heating the hull or deck from underneath may accelerate the drying in colder weather. Do not use solvents to dry the core! Allow approximately 1 week drying. Check dryness by drilling a few test holes in the wetter sections.
Once drying is complete it is time for restoration of the core. The best tools can be found at the supermarket. Purchase a few 4" funnels and turkey basters. The funnels should fit snugly into the 1/2 inch holes without touching the bottom. Shorten the neck as necessary. Insert funnels into the holes. Pour the mixed CPES into the funnels. Have a few rags and Epoxy Clean Up Solvent (ECS) handy. As you pour watch the surrounding holes. You will notice the CPES running through the core from hole to hole. If the CPES turns milky stop immediately; the core is not sufficiently dry. Some holes will seem bottomless while others do not take much. Allow the CPES to sit in the funnel for about 5 minutes. Any CPES left in the funnel may be sucked out using the turkey baster. Move to the next set of holes making sure all of the holes have CPES introduced to them. Start uphill and keep an eye on the downhill holes. If CPES is starting to flow out of the downhill holes stop applying. There is no sense in wasting the CPES. Keep it clean keep it safe. Use proper safety gear (gloves, organic respirator, eye protection) at all times. Remove footwear when leaving and leave the footwear at the job site.
CPES is engineered to soak deep into the wood core. The solvent blend will absorb and evaporate the moisture left in the wood as the solvent evaporates out of the holes. This is the essential reason why this core restoration method works. No other epoxy will evaporate the moisture and all others will fail if used in this manner. Unlike an adhesive epoxy, CPES is made to replace the lignum lost to bacterial consumption. Once the core is fully saturated it must be left to dry again. The solvent blend in the CPES must be allowed to evaporate. Remember to keep rain, dew or spray from entering the deck!
After a day or two you will notice the CPES odor has subsided. Drill a few more test holes to determine the extent of the CPES penetration. The material from the test hole should have that telltale CPES odor. If the test hole material is wet with CPES allow more drying. The length of dry time will depend upon the amount of ventilation available, ambient temperature and nature and depth of decay. The next step is the same as the first. Repeat the CPES pouring procedure over again. This time you will notice it will take less material than the first pour. The idea of the second pour is to fill any remaining porosity and evaporate any moisture left in the core. Allow a few days drying to allow full cure of the CPES. Remember to keep rain, dew or spray from entering the deck!
Count the number of holes and note the thickness of the core. Cut 1/2 inch plugs out of the same material as the core to the same thickness as the core. Solid wood is OK of for plywood core. Using a 1/2 inch acid brush coat the bottom and walls of the hole with All Wood Glue (AWG) and insert the 1/2 inch plug. The top of the plug should be the same height as the top of the core and not above. Repeat for all of the holes. AWG is specified for this application because it is thick and will not allow the plug to float freely if the hole is not snug.
As discussed earlier the decay of the core created an air bubble under the top layer of fiberglass. The next step is gluing the fiberglass layer back down to the core to eliminate the air pocket. Starting at the high-end pour Layup and Laminating Epoxy (LLE) into the holes over the plugs. Use a small screwdriver to lift the glass up to allow the epoxy to flow under the fiberglass. LLE is a thin adhesive epoxy and can be further thinned with a small amount of ECS if necessary. Apply LLE along the same path as the CPES. As you move downhill remove the screwdrivers uphill and place weight on the deck. Be sure to enclose the weight in plastic bags, cover the deck with plastic sheeting, or cover the weight with box tape to prevent gluing the weight to the deck. For large areas lay plastic sheeting, place plywood over the plastic then add weight. The plywood evens out the weight over the surface and prevents unfairness of the surface.
Once the LLE has cured the remaining holes should be filled with Fill-It. Fill-it is a pre-thickened epoxy made by Smith & Co. Fill-It is easily sanded, spreads smoothly, non-blushing, flexible, lightweight and is easy to use. Again plastic sheeting may be used to spread out the Fill-It to reduce fairing time.
When the Fill-It has cured remove the plastic and sand fair. At this point the surface is now waterproof and the core restored. For further protection against water absorption and to seal the old glass laminate, paint with High Build Epoxy Paint. Finish with a topcoat of paint and nonskid if on a deck. Re-attach all hardware previously removed and bed it with a flexible sealant such as 3M 4200.
The use of Smith & Co. products ensures compatibility and the correct product for the various tasks involved. All of the products used feature an easy 50:50 mix, can reliably cure down to 28 degrees F, and will not produce an amine blush. The lack of amine blush allows rapid sequence of steps without the need for washing or sanding between applications. Be sure to follow the manufacturers instructions when using these products.