THE BOTTOM LINE
There’s much to like about butyl tape for
bedding deck hardware. It takes a bit longer
to apply, but it’s easy, relatively mess-free,
and the job is finished as soon as the nuts
are tightened — no waiting for the sealant
to cure. It’s the best choice for framed portlights, but should be avoided where it may
come into contact with chemicals. It does not
cure, so butyl tape properly installed should
remain watertight for decades, yet it’s also the
easiest to dismantle.
If you can’t find butyl tape or have more
faith in a curing sealant, Boatlife Life-Calk
polysulfide, applied as described in the article, “Re-Bedding Deck Fittings”, (see page
88) will be your best choice for bedding metal
and wood (but not ABS or Lexan) because of
its excellent chemical resistance and emphasis
on sealing rather than bonding. The polyethers accommodate movement better than
the polysulfides and have better UV resistance, and 3M 4000 UV is even compatible
with plastic. But the stronger bond will be
problematic if disassembly is required.
Sikaflex 295 UV polyurethane is another
alternative to polysulfide. A combination of
superior UV resistance, liberal elongation,
and compatibility with plastic (in concert
with a primer) makes this a versatile sealant.
Its advantage over 3M 4000 UV and over
all of the other polyurethane products is its
lower strength, which makes future disassem-
bly/removal easier. You can, of course, use any
of the other polyurethanes, but unless your
intent is to bond rather than seal, these are
choices you may come to regret.
Don Casey contributes to BoatU.S. Ask The Experts.
AN OLD SEALANT
MAKES A COMEBACK
BUTYL TAPE has been used success- fully for years, and has numerous advantages. With adhesive strength
similar to duct tape and about a tenth of
the tensile strength of even the weakest
curing sealant, butyl tape doesn’t harden,
but remains sticky and pliant. While that
makes future disassembly a snap, butyl tape
is still less likely to break its seal because it
stretches. If a gap does open up, the still-sticky tape self-heals.
Cutting, fitting, and molding butyl tape
can be more labor intensive than squeezing
on a squiggle of Life-Calk, but tape is far
less messy, eliminating the need to mask.
Compatibility with plastic, combined with a
gasket-like and uniform application, make
butyl tape the most reliable sealant for
framed portlights. Butyl tape doesn’t cure,
so you can take all the time you need fitting hardware. Success is less dependent on
technique than with the curing sealants. It’s
easier to control, seems unaffected by UV
exposure, is relatively low in cost, and has
a shelf life measured in years rather
All is not completely rosy, however. The
malleability of butyl tape changes with temperature, making it difficult to use in cold
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