Fuel fills. Water fills. Stanchion bases. Cleats. Rail landings. Most likely, if you own your boat for a good while, one or many of these babies will eventually have to be removed and rebedded with new caulking material. I mean, let’s get real here—no matter what stuff you use to seal a chunk of metal to a fiberglass surface, it’s going to either drearily deteriorate some day or disappear altogether, thereby allowing both salt and freshwater to destructively penetrate coring materials and/or substrates.
There are two basic methods of caulking, however. The first entails merely slathering caulking material either onto the underside of the piece of hardware involved or onto the fiberglass underlying the hardware or both, and then, after reseating the chunk, tightening the related screws or bolts with enough force to squish virtually all of the caulking material out of the joint. A good workout? Maybe, but also a very poor way to rebed a cleat, a stanchion base, or anything else for that matter.
The second, better way? Start by cleaning the old, worn-out caulking material from the fiberglass and metal surfaces you’re dealing with using a tool like a chisel, screwdriver, or pocket knife and then an applicable solvent. Next, reseat the metal component temporarily, carefully mask off the fiberglass area around and adjoining it with varnishing tape, and, after removing the component (again, temporarily), just as carefully cover the outer edges of the thing with varnishing tape as well. Now finally, with the tape guaranteeing a crisp, careful-looking job, apply the caulking material liberally to the fiberglass surface and then simply sit back and wait for a while. Twiddle your thumbs if you have to.
This last point, as you may have guessed, is key. It’s critical here is to allow enough caulking material to remain in the metal-fiberglass joint so that, upon curing, it forms a gasket of sorts, with adhesive properties on both sides. To facilitate this, after you’ve wiped away any excess caulking with a rag or paper towel, you need to let it cure for a while before permanently seating the component. How long depends upon what caulking material you’re using, the ambient temperatures involved, and the physical characteristics of the metal chunk you are dealing with.
A certain firmness is what’s called for. Once the caulking material has cured to a point where it nicely resists the weight of the component, then go ahead and seat and secure it with the appropriate retaining screw or bolts. And hey, do not overtighten these fasteners, thereby quashing the approach described thus far. You are trying to strike a balance, after all, between maintaining the rigidity of the component’s attachment to the underlying fiberglass and guaranteeing enough gasket-like resiliency in the caulking material underneath to keep water and other nastiness out for a good long time.