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Marine Caulking products
Leaks can be just annoying, or cause structural damage and even
lead to
sinking .
Despite this leaks are very common and can be found on new boats and old boats
alike.
This page is dedicated to caulking products. Choosing the right sealant
or caulk to bed fittings is confusing and a walk down the isle at the
store leaves you wondering what do I need.
A sampling of caulking materials found at the
chandlers, include fast and slow cure, permanent or removable,
polyurethane adhesive/sealant, polysulfide bedding compound and
silicone, as well as glazing adhesive, teak deck caulk etc,
too many choices.
Properties of sealants
Good caulking products have several features; the
ability to adhere to two surfaces, excellent elasticity, easy to apply
and work with.
| Properties |
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Many caulks are moisture cured. |
1 part slow Curing times 2-14 days. |
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2 part fast cure |
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Elasticity |
Caulk can have between 100 and 800% elongation and more at
break. |
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Consistency |
Liquid, paste or tape |
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Bonding adhesion |
adhesion = peel strength, strength = tensile strength |
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Cleanup & Ease of use |
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Curing; may take days, depending on the material, air temperature
humidity-most urethane sealants actually cure in the presence of
moisture, which is why they're excellent for emergencies underwater
repairs
Adhesive by the numbers;
This chart gives you an idea of the difference between the
types of major caulks. These numbers are a rough guide as products vary.
Bear in mind 700psi could tear apart fiberglass when removing a fitting.
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Polysulphide |
Polyurethane |
Silicone |
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Elasticity |
>400% |
300-800% |
>350% |
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Tensile strength |
140psi |
300-700psi |
220psi |
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Stretch or Elongation; Elongation is a measure of
Stretch. The higher the stretch the better the caulk bond will hold up.
Types caulk and
Manufacturers
Below is a list of the most common sealants you will find in a
chandlery. Most of these sealants are high viscosity liquid sealants
(except Butyl a tape) which are applied by tube, or
caulk gun. They are applied like tooth paste. The liquid is able to easily spread onto a fitting and when
pressured it flows into all voids.
Types of Caulk include; Silicone, Polyurethane, Polysulphides and
hybrids.
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Silicones SR |
Silicones
are inert synthetic polymer compounds. Primary used as sealers,
with little bonding capabilities. can be used with almost any
material and is an excellent insulator between metals. |
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There are 2 types of
silicone; One is based on acetic acid (vinegar smell), while the
other is ammonia-based.
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Properties |
Silicone is a gasket material |
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Use above waterline only |
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A weak adhesive |
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High elasticity |
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UV stable |
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Safe for plastic fittings |
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Silicone sealers cannot be painted. |
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Forms chemical-resistant gasket. |
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Good insulator |
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| Disadvantages; |
Any trace of silicone will cause problems with
paint. Silicone runs the risk of contaminating surfaces to be painted or varnished. |
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Weak adhesive |
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Only for above waterline |
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Examples;
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3M marine grade silicone sealant,
Boatlife silicone rubber |
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Silicone/Polyurethane Hybrid |
Similar characteristics as silicone, |
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Properties |
Better adhesion than silicone |
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Excellent
for port lights. |
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Silicone sealers cannot be painted. |
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Less
aggressive than straight polyurethanes |
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| Applications |
Ports, glass, plastic, |
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| Disadvantages |
Low adhesion |
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| Examples |
BoatLife Life Seal, |
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Polyurethanes PU
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Polyurethane is the sealant when you are looking for a permanent bond.
Excellent for hull to deck and hull to keel joints. |
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| Properties |
Not for fittings that may need to be removed |
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Below waterline use |
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Can be painted. |
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Polyurethanes not UV stable unless
stated |
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Not for polycarbonate, acrylic, ABS, and PVC |
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Although PU attacks plastic, Marelon thru
hulls are OK |
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| Disadvantages; |
Stay away from 5200 unless you are
looking for a permanent bond |
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Solvents in Polyurethane attacks plastics, like polycarbonate, acrylic,
ABS, and PVC |
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Examples; |
3M; 5200 & 4200, Sikaflex 292,
Sikaflex 291,
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Polysulfides
PS |
A synthetic rubber with excellent
adhesive properties. A good caulking compound that has a
combination of adhesion and is flexible.
The best choice for most deck fittings except plastic.
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| Properties |
Both good adhesives and good sealants. |
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Bonds well to teak
and primed oily woods
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Polysulfides have good resistance to UV |
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Polysulfides also possess excellent resistance to petroleum products |
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Can be painted. |
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| Disadvantages |
Solvents in Polysulfide and Polyurethane will soften
some plastic,
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Do not use with Plexiglas or Lexan ports. |
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Examples;
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3M Marine Sealant 101
Life calk by Boatlife
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Bedding Deck Hardware With Butyl Tape
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Butyl Tape |
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Butyl tape is very easy to use |
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Temperature; sticky in warm, hard in cold |
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Butyl is a flexible gasket |
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Butyl tape is convenient to use |
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Butyl is NOT an adhesive |
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Do not use where bonding is required,
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No curing, waterproof immediately |
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| Disadvantages |
Disadvantages include the tape is not impervious
to gasoline, or diesel,
Sticky in high temps,
does not flow
in cold temps.
Best use is at 70 degrees |
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Other Caulking compounds
Polyethers PE; 3M 4000 is an example and are new and have very good UV
resistance. Their lack of solvents minimizes shrinkage.
Plexus; used by Tillotsen Pearson and J
Boats. Plexus is so good an adhesive J Boats use it for Hull to Deck
joints and do not use any mechanical fasteners.
Home improvment Caulk; These tend to be cheaper, what a
surprise, however many of them are acrylic based and do not have the
adhesive qualities. they also shrink and break down in the marine
environment. You get what you pay for at least sometimes.
Applications
Choosing the right caulk for your application will be simplified by
answering these questions;
Above or below waterline,
Do you need bonding or just a gasket,
Will you remove fitting later, are fittings plastic.
The table below breaks down typical maintenance projects into categories
above and below the waterline, with the
recommended products from major manufacturers.
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Applications |
3M |
BoatLife |
Sikaflex |
Dow |
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| Above waterline |
Metal Deck fittings |
4200 or 4000 UV |
Life-calk |
291 or 292 |
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Metal Port hatch |
4200 or 4000 UV |
Life-calk |
291 or 292 |
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Plastic ABS or Lexan Ports & Hatches |
Marine sealant 101 |
LifeSeal |
295 UV |
Dow 295 |
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Electrical fittings |
3m silicone |
Silicone rubber & Lifeseal |
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Windows glazing panels |
Marine sealant 101 |
LifeSeal
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295 UV
or 296 |
Dow 795, |
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| Below
waterline |
Hull keel joint or Hull
deck joint |
5200 or 4200 |
Life-calk |
292 |
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Thru hull |
5200, 4200 or 4000 |
Life-calk |
292 |
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Surface Preparation
Without proper surface prep any caulk will not live up to its potential.
Surface preparation;
Clean well to remove dust, wax oil and all contaminants. In some cases
you could sand with 180 or 220 paper.
Follow the manufacturer instructions for prepping the surface before
applying sealant; some manufacturers have primers, notably Sikaflex.
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