To "cork off," is a nautical expression meaning to sleep on the job. Legend holds that it comes from the colorful jargon of sailors that turned words like "fore castle" into "foc's'l" and "leeward" into "loor'd." Following that pattern, the word "caulking" naturally became "corking." Old-timers are still heard to say that a boat needs "re-corking" when it needs new caulking.

In the days of the clipper ships, deck seams were "corked" with oakum and hot pitch. Hot, tropical sun tended to soften the pitch and create leaks that would show up weeks later in the cold waters of Cape Horn. While in the tropics it was common for sailors to sleep on deck instead of in the stuffy foc's'l where their bunks were located. Anyone who slept on the deck would wake up with tell-tale stripes of pitch caulking on his clothes ... proving he had been corking off.

Hot pitch has long been consigned to Davy Jones' locker. Modern deck seams are corked with polysulfide or polyurethane caulks. Properly done, these modern materials give true multi- season service with no tell-tale tracks down the backs of sunbathers. While the caulking materials have been improved over the years, one thing has remained the same: renewing deck seam caulking is still not a sailor's favorite job.

Reefing Out Old Caulking

Removing old caulking is called "reefing" the seam. A special hook-shaped tool is traditionally used for this job. It's pulled along the seam, lifting the old caulking as it goes. Modern synthetic caulks don't pull out of a seam as easily as old- fashioned oakum. Often as not, the reefing hook skates down one edge of a modern rubber seam, leaving a band of wrinkled caulking still in place.

Professional boatyards remove old caulking with a hot knife that makes the job easier. A hot knife is rather expensive for the do-it-yourselfer's toolbox. With luck, it may be possible to find a yard that will rent out its hot knife. Always observe electrical safety precautions when reefing seams and be sure to keep the hot knife out of the hands of small children.

A lower-tech method is to slice down each side of the seam with a knife. The blade must be sharp. Control the tip so that the blade slices caulking cleanly away from the wood without cutting into the plank. Practice on an out-of-the-way spot. Observe the grain structure of the planks. Grain run-out toward the knife will allow the blade to cut into the plank. If the knife wants to dig into the wood, try cutting the opposite direction.

An ordinary wood chisel works well to lift out the old caulking. The only problem is that the sharp chisel point wants to bite into the underlying wooden deck. Buy a 1/4-inch wide chisel and grind down the sides of the blade until it is the exact width of the groove. Hold the chisel so that the beveled edge rides along the bottom of the caulking groove. It takes only a few minutes to learn how to rock the blade on the bevel to control the depth of cut.

Preparing The Grooves

All traces of the old caulking must be removed. Even tiny scraps may cause adhesion problems with the new caulking material. Careful scraping of the sides of the grooves with a very sharp chisel should remove any residue left by the knife. A shop vacuum will clean out the inevitable chips and gunk in the bottom of the grooves. Use a stiff-bristle nylon brush to help the vacuum suck up the dirt.

Run strips of masking tape along each side of all the grooves. The edge of the tape should align with the groove edge. This tape prevents caulking from smearing all over the teak. It also insures that the new seams will stand proud of the wood by at least the thickness of the tape. Proud seams are easy to sand back to level with the planks, making a professional-looking job.

The Right Caulking

Until the fall of 1993, there were two choices in caulking for deck seams. Now, there are three. The traditional first choice is two-part polysulfide compound. This material is mixed on the job and stuffed into empty caulking gun cartridges before being pushed into the seams. Although widely used by professionals, two-part polysulfide caulking is difficult to find because it is not widely stocked by stores. Most large chandleries will special order it. (Empty caulking gun cartridges can be purchased at paint stores catering to professional painters.)

Two-part polysulfide caulk lasts longer in deck seams than its one-part cousin because it has more polymer in its formula. Good results can be obtained with one-part polysulfide materials which are less expensive and widely available. One-part polysulfide caulk is acceptable for a boat that is always kept in a boathouse or under a mooring canvas. Difficulty obtaining an acceptable two- part product may also force the use of one-part polysulfide.

The second traditional choice for deck seams is polyurethane adhesive/sealant. These materials stick like crazy to everything except oily wood such as teak. Good adhesion requires the use of a primer sold separately by the manufacturer of the caulk. Poly- urethane materials are not popular for deck seams despite their long lifespans due to incompatibility with popular teak cleaners and oils. This incompatibility is the reason some polyurethane manufacturers do not offer black material. Most deck seams are caulked with black. By not offering black, caulk manufacturers discourage the use of polyurethane materials.

Until 1993, polysulfide and polyurethane were the two choices. Silicone sealants were unthinkable for deck seams because they could not be sanded flush with the planks. Worse, ordinary silicone materials change size over time, resulting in ugly seam gaps. BoatLife has just introduced a new product, Silicone Seam Sealant (r) that apparently overcomes these objections.

According to BoatLife vice president Steven Tilders, this new product is, "a low modulus silicone rubber that is sandable." In layman's terms that means seams can be sanded flush and it won't change size. This product is too new for serious opinions, but Tilders says it has been used successfully on cruise ship decks in the Caribbean for several years.

Paying The Seams

"Paying" is the verb used to describe the actual squeezing of caulking into the plank grooves. This part of the job is best done by two people. One worker handles the caulking gun and actually pays the caulking into the seam. The second worker uses a putty knife to smooth the seam and remove any excess caulking. Both should wear very old clothes as this job is always a bit messy. Short pants are definitely not recommended.

The people at BoatLife suggest the use of a layer of paper or cotton string in the bottom of the caulking groove. This acts as a "breaker" to prevent the caulking from adhering to the bottom of the groove. The purpose is to allow the cured caulking to "move" with the planks as they swell and shrink during the season. Because it sticks only to the sides of the groove, the caulking can bend or twist with the natural movement of the wood. A special cotton string is made for this purpose, but other materials such as shredded computer forms might be used as well.

One-part caulking comes packed in tubes ready for the caulking gun. Two-part polysulfide caulking must be mixed according to the instructions. Trowel the mixture into empty caulking gun tubes for application. Use care to avoid mixing air bubbles into the caulk as they will appear as voids in the seams which will require painstaking repairs. Curing starts the instant the two parts come into contact, so mix only as much as can be used during the pot life of the caulk.

Cut cartridge tips so that the openings are slightly smaller than the grooves in the deck. (The openings can always be made bigger, but there is no way to reduce the size of holes that were cut too large.) Caulking should be pushed into the seam. Moving the tip forward down the seam pushes the bead of caulking ahead of it. Air bubbles will be forced out of the caulk by pressure from the gun and the groove will be filled from top to bottom. It's always better to put too much caulking into the seam rather than too little.

Pro Tip: Chill Out

The cure rate of two-part caulking depends on temperature. Tubes of mixed caulking can be refrigerated to prevent premature curing. Let cold tubes return to room temperature before applying.

Smooth the top of the seam with a putty knife. Have a scrap of cardboard handy as a pallet for wiping rid excess caulking off of the putty knife. Reasonable speed is needed to smooth the seam before the caulking starts to set up. An absolutely perfect job isn't necessary as high spots will be sanded out once the caulking is fully cured. Low spots, however, must not be allowed. Use uncured material from the cardboard pallet to level out any hollow areas.

Masking tape should be pulled off the deck as soon as the caulking has cured enough to have a tack-free skin over it. Do not leave the tape on the deck overnight. Walking on the deck must be avoided until the caulking has fully cured. Clean tools with the solvent recommended by the caulking manufacturer. If no solvent is suggested, try ordinary mineral spirits.

Final Steps

Sanding can be done as soon as the caulking is fully cured. Some material always finds its way onto the teak planks where 80 grit paper usually does a good job of removal. Experiment with grits when it comes to sanding high or uneven spots in the caulked seams. Finer grits give a better appearance, but this has to be weighed against the amount of effort needed to get the job done. Hand sanding is recommended over power sanding to avoid damaging the new caulking.

Portable belt sanders do a fantastic job of leveling out the caulking, but are equally fantastic at creating massive gouges in the wood. A dual-action circular sander also works well, but orbital palm sanders may tear the new caulking away from the sides of the grooves.

A fresh sanded deck should be protected with a teak oil compatible with the caulking. Read the instructions on the tube of caulking to find which teak oils or cleaners will cause damage.