Boating USA — February 2018

BOAT DOCTOR ///WHAT TO LOOK FOR

QUICK TIP

Leaks aboard are a headache, fi guratively, of course. But

selecting between myriad sealants and caulks at the marine

hardware store might cause a literal headache. Before reach-

ing for the OTC analgesic, consider what you’re trying to bond

or seal, and select the right product based on its properties.

—Capt. Vincent Daniello

POLYURETHANE Poly-
urethanes, like 3M 5200, are
best for hardware above and
below the waterline, like cleats
and prop struts, with little need
for removal in the future. Fast
Cure 4200 from 3M, roughly
half as tenacious as 5200,
provides more than enough
adhesion for most applications
above or below the water but
is more easily removed with a
stiff putty knife. (Read about
four solvents you can use to

remove 5200 at boatingmag

.com/marine-solvents-for-

removing-5200.)

POLYETHER AND SMP

Polyurethane yellows in the

sun. Silane-modifi ed polymers

(SMP), like 3M 4000UV, and

polyethers, like Star brite Boat

Caulk or West Marine Multi-

Caulk, off er good adhesion

while still being removable,

but UV rays won’t discolor

them. Skin-over and cure

times are similar to fast-cure

polyurethane.

POLYSULFIDEBoatLife’s

Life-Calk is the sole polysul-

fi de on the market. Its fl exi-

bility, resistance to chemicals,

gas and diesel, plus sunlight

stability make polysulfi de a

good choice for bedding fuel

fi lls and teak decks.

SILICONE AND BLENDS

Silicone is primarily a sealant

— a fl exible, sunlight-resistant

gasket, not a glue. For water-

proofi ng hardware that you

know must come apart again

someday, like navigation

light fi xtures, marine silicone

products from 3M, Star brite,

West Marine and BoatLife are

hard to beat. BoatLife’s Life

Seal is a blend of silicone for

UV resistance and polyure-

thane for better adhesion. The

3M 3000UV is an SMP formu-

lated for less adhesion, specifi -

cally for sealing.

PLASTIC AND PAINT

COMPATIBILITY Silicone

can’t be painted; most other

sealants can. But silicone is

compatible with many plas-

tics; other caulks may not be.

Always read instructions and

always test a sample fi rst.

CAULKS AND

SEALANTS

Push caulking tubes through the bead — don’t drag the bead behind — and then “tool”

the caulk to remove air pockets and smooth it out. A gloved finger wet with just a bit of

mineral spirits or acetone works well on polyurethane, polyether and polysulfide. Water

with just a drop of dish soap does the same for silicone. Or try BoatLife’s new Super

Slick Sealant Smoother, which isn’t solvent-based but works on all sealants.

TOOLING

THE

BEAD

PHOTOS: (COUNTERCLOCKWISE FROM TOP LEFT) COURTESY 3M, COURTESY STAR BRITE (2), COURTESY BOATLIFE, COURTESY 3M

SEAL THE DEAL

Marine sealants and

caulks come in a variety

of types for a variety of

onboard applications.

With the exception of silicones, you can cause many caulks and

sealants to skin over more quickly by using a spray bottle to

apply a light mist of water to the bead. Always read directions.