Learn how to use epoxy to fill in holes below the water line Rich Johnson Trailer Boats January 22, 2008

When Aaron Hill decided to upgrade the depthfinder on his 1994 Maxum 2300 SC, one of the challenges he faced was that the screw hole pattern of the old transducer did not match the pattern for the new unit. The old holes would need to be properly filled with a material suited for life under water.

Some fillers and sealants are water resistant but not waterproof and are, therefore, not appropriate for this job. In other cases, however, such materials may be OK if the repair area is treated with a waterproof coating after the filler has cured.





PREPARE THE SURFACE

Begin by preparing the holes and surrounding surface so that the filler material will bond properly. This usually means carefully sanding or drilling out the old cavities to get rid of any moisture that may have penetrated the hull. Hill started with a drill bit that was slightly larger then the holes, probed, found wet wood, increased bit size and probed again until he was satisfied that he was drilling into dry, core wood. Just make sure you don’t penetrate all the way through the transom.

Next, prepare the filler and apply it to fill the voids completely. This can be a messy job, so it’s a good idea to wear rubber or surgical gloves. You can minimize problems with excess goo by masking the area with tape, but just this once Hill thought he’d work without masking adjacent surfaces — next time, he’ll know better.



MIX IT GOOD

For this project, Hill used System Three Quick Cure 5 (systemthree.com), a five-minute, two-part epoxy adhesive that is water resistant but not waterproof. This product is not recommended for use below the water line unless it is overcoated with a waterproof resin, which Hill intended to do. An epoxy syringe is the best tool for filling small holes, though applying enough pressure when spreading material with a spatula can also fill voids (for step-by-step instructions, log onto TrailerBoats.com). If the holes had been larger, he would have used the epoxy adhesive to coat a plug made by cutting a short piece from a dowel of the appropriate diameter, but for these small holes it was sufficient to let the epoxy serve as filler.

The cured epoxy in the holes is slightly opaque, but it’s going to hide beneath the new transducer, so no one will notice. Once the repair was sanded smooth and flush, Hill’s final step was to apply an overcoat of waterproof fiberglass resin that is suitable for use below the water line. Mission accomplished.



EXPLORE YOUR OPTIONS > alternative fillers

There are loads of epoxy options, and it seems like every boater has a different preference. West System makes a wide variety of epoxy products, including the 101 Handy Repair Pack. There’s lots of advice on westsystem.com. Paint companies like Interlux also makes epoxy products. Learn more at yachtpaint.com. For emergency epoxy repairs, it’s hard to beat Splash Zone, from Pettit (pettitpaint.com), which can be applied under water.



BONUS WEB INFORMATION

STEP BY STEP: SEALING HOLES



STEP 1: The old transducer had been installed with two stainless steel screws that were close to each other. The new transducer mounting screws were more widely spaced — meaning that we wouldn’t be able to simply use the old holes. The holes needed to be prepped and filled. Before filling the old holes, it was necessary to drill them out to remove any soggy material inside the transom. In this case, the holes were enlarged until we found dry core wood. When drilling, take care not to penetrate all the way through the hull. Then it was time to mix the filler material. Boatowner Aaron Hill used a quick-curing, two-part epoxy adhesive that is water resistant but not waterproof. Consequently, he planned to protect the repair area by finishing the job with a coating of waterproof resin.



STEP 2: Almost anything, such as a pencil, small dowel or even a screwdriver, can be used to insert the epoxy all the way into each hole, but it’s best to use a syringe-style injector.



STEP 3: Before the epoxy is completely cured, use a putty knife, spatula or something with a straight edge to remove slop-over epoxy on the area around the holes. (An old credit card can be a great tool for this job.) No matter how hard you try to clean up the surrounding area, there will always be some hardened epoxy to sand later. Judicious use of masking tape can help eliminate a lot of mess and reduce time spent with sandpaper. Keeping recommended thinners or solvents and a rag for cleanup close at hand is also a good idea.



STEP 4: For this job, the final steps were to sand the repaired surface smooth, and then apply an overcoat of waterproof fiberglass resin that is suitable for use below the water line. At this point, the transom is ready for drilling and installing the new transducer.