April 2002 Telltale page 3 - by Tom Winlow and Marcel Laroche.
Springtime, while the boat is still ashore, is a good time to do some re-bedding.
Re-bedding all the fittings at once, is quite a large task. Because of this, it is often put back to later on and never gets done. The inevitable result of this neglect, is a wet deck core. Why not do some selective re-bedding, starting with the most abused and highly stressed hardware on the deck, like the stanchion bases, genoa tracks and mooring cleats. The idea here is to re-bed the fittings that are most likely to let moisture into the deck core. Ideally, a moisture meter should be used, as it will quickly identify the areas where water is seeping into the core.
Begin by removing all traces of old bedding compound. You will probably notice that it has hardened and turned to powder in some areas. Re-bore each bolt hole using a drill bit 1/8 inch larger than the bolt hole. This is to remove old bedding compound and expose fresh core material around the perimeter of the hole. Seal the bottom of each bolt hole with two layers of masking tape, pour in the resin until the hole is filled, top up as necessary, as the resin soaks into the core. Once the resin has hardened, drill the hole 1/16 in larger than the bolt. This is to provide an escape path for the water, in case the fitting leaks again. This method seals the core, but does not appreciably increase the compressive strength of the core around the bolt hole. The following method is similar to the above and greatly increases the compressive strength of the core around the bolt hole. Typically, this method would be used to secure stanchion bases, genoa tracks and mooring cleats where large mostly vertical loads are applied.
Using a 3/4 inch hole saw, remove the bottom skin and core material by drilling from below, being careful not to damage the top glass laminate. NOTE- THE BENT NAIL METHOD MAKES A MESS. Remove all remnants of core material, using a flat blade screwdriver. Seal the bottom of each bolt hole with masking tape, pour in the resin and top up as necessary. Once the resin has hardened, drill each hole 1/16 inch larger than the bolts. This will facilitate the installation of the bolts and provide a drainage path, allowing water to drain into the cabin instead of being trapped in the core.
Some deck fittings are fastened with screws through the deck top skin only! This is a horrible way of fastening anything to the deck of a boat, not only because the holding power of a screw is poor, but worst of all, the hole is usually only through the top skin of the laminate. In case of a leak, the water will automatically be trapped in the core. If at all possible, replace screws with bolts.
If screws must be used, remove all debris from the screw hole all the way down to the bottom skin. Do not drill through the bottom skin at this time. Fill the screw hole with resin and after the resin has hardened, drill a hole all the way through the bottom skin, using a smaller diameter drill than originally used. This procedure will seal the core, provide drainage and give slightly better holding power to the screw. Why is it that the word screw has a bad connotation?
All the magic stuff that comes in a tube and is not supposed to shrink or harden, will do exactly what it is not supposed to do. Why is it that after a year or two, the unused portion of the tube can be used as a doorstop? For the last 4 years, I have used butyl tape, which is a sealant used by commercial glass installers. It comes in a 50 ft. roll, is either 1/16 or 1/8 inch thick by 3/8 inch wide. A roll costs $7-$10 and is sufficient to seal all the hardware on two 30 ft. boats. It is the same material that oozes from the hull/deck joint on some sailboats. This stuff is still flexible and sticky on my 28-year-old boat. The remnants of a two year old roll of butyl tape, is still as flexible and sticky as the first day it was used, even though it has been exposed to the air all that time.
If you decide to use butyl as a sealant, roll the material into a shoe lace form and apply around the circumference of the hole, so as to form a donut shape. The inside edge of the donut should be about 1/8 inch larger than the hole. Lightly place the fitting on top of the donut shape. Do not press down on the fitting at this time, because doing so would cause the butyl to obstruct the bolt hole. Now, apply some butyl under the head of each bolt and gently insert the bolts in the holes. (Drilling the bolt holes 1/16 inch larger than the bolts, facilitates the insertion of the bolts as well as ensuring a drain path.) Avoid getting some butyl on the lower threads of the bolts, because when the washer and nut are tightened, the butyl will seal the deck from below. That is a NO-NO. If this happens, don't take a chance, remove the bolt, clean the lower threads and try again. Once the bolts have been inserted properly, press down on the fitting, and bolt heads. Don't tighten the bolt by turning the head, because this has a tendency to break the seal, especially on existing bolts. Always tighten by turning the nut from below.
Many wet decks can be attributed to improper fastening of the hardware at the factory. From small screws in large holes, to small or no washers under the nuts and no sealant under the bolt heads, many builders can be blamed for lots of our wet deck problems.
When re-bedding a fitting, use as large washer as can be accommodated. Shops specializing in fasteners can provide you with oversize washers (FENDER WASHERS) in any material. If large washers seem too flimsy for the load, double them up or large backing plates out of 3/16 inch aluminum and install them under the stanchion bases. The area around stanchion bases is probably the most likely area to have deck damage, so reinforce the deck with the proper backing.
Re-bedding deck fittings could be a summer long project, with a little bit done on those windless days. Re-bedding does not cost much and pays great dividends.