| A useful item from boats.com deals more directly with deck caulking,
but some of these principles may apply to bottom caulking as well. Is
you boat bottom lapstrake or carvel planked? If carvel, it would be
logical that it's more like doing a deck because your seams are flush. Follows: Recaulking Basics
Removing and replacing caulking can bring new life to your boat 2000
by David Brown
boats.com
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. |
