resin can be made to cure in periods ranging from 30
Damaged ferrocement can be cut away with a ma-
minutes to over 24 hours.
sonry blade in a portable circular saw. The edges of the
hole can then be scarfed with a heavy duty sander, but
not to the degree of taper possible with fiberglass.
REPAIRING PLASTIC BOATS
Additional reinforcement can be added to the rear of the
Although the use of plastics in naval construction
patch. Epoxies bond very well to ferrocement.
and repair is relatively new, plastic materials and boats
Larger damage may require some structural rein-
have become important for naval use.
forcement. Structural steel members may be repaired by
The factors in favor of the plastic boat are many; it
welding, and steel backing to repaired areas can be
has a monolithic structure (can be cast in one piece), it
welded to structural members. Welding heat will de-
can be mass produced, and it can readily be maintained
compose some of the surrounding cement, which
and repaired. Ships are supplied with metallic pipe and
should be chipped away and replaced with epoxy.
general-purpose repair kits. These pipes and kits are
To bolt repair patches to ferrocement, use plain
used for emergency repairs of battle damage to piping
black iron carriage and stove bolts. Galvanized hard-
for water, oil, gasoline, and refrigeration lines. Materi-
ware does not stand up well in ferrocement.
als and instruction are provided not only for repairing
pipes, but also for repairing damaged glass-reinforced
plastic structures such as boats, floats, deck cabins, and
PLASTIC BOATS
hull and deck coverings.
Some types of damage to plastic boats require slight
deviations from the standard repair procedures, but
Repair Kits
personnel who can effectively repair a hole in the hull
should have little or no trouble with other plastic repairs.
The metallic pipe and general-purpose repair kit are
repair locker equipage. The repair kits are not to be
removed from the repair lockers except in the case of
USES AND IDENTIFICATION OF
an emergency and with the authorization from the lead-
PLASTICS
ing HT or the damage control assistant (DCA), or when
the shelf life date has expired and a new kit has been
Plastics in naval construction have become increas-
placed in the locker. The shelf life of a kit is 2 years.
ingly important. Plastic patching has become standard
When a kit is removed from the locker because it is past
practice aboard most ships in the Navy.
its shelf life, the HT shop may keep the kit for boat
Plastics can be identified by their chemical and
repairs and training purposes. The repair kit contains
physical properties. For repair purposes, the most im-
epoxy resin, hardener, and glass reinforcement in the
portant plastic categories are the cellulose products, the
form of mats or woven cloth. Auxiliary materials in-
protein plastics, and the synthetic resins. Physically,
clude separating film, kraft paper, protective gloves,
plastics may be divided into two basic groups: THER-
wooden spatulas, resin spreading tools, brushes, and
MOSETTING materials and THERMOPLASTIC ma-
repair instructions. Sufficient quantities of these mate-
terials. A thermosetting plastic has no melting point.
Although a thermosetting material can flow and be
rials are provided in a standard kit to replace about 400
square inches of damaged 1/4-inch laminate, and tubes
molded, it will neither soften when heated nor return to
of paste resin are provided for repairing minor surface
its original liquid state. A thermoplastic material, how-
imperfections.
ever, will soften when heated. To illustrate, let us com-
The kit supplier has preweighed and packaged the
pare these two kinds of plastics with steel and concrete.
resin and hardener in the proper proportions. The resin
Steel can be heated and formed, and when reheated, will
soften; a thermoplastic material is like that. On the other
cans are only slack filled to allow the hardener to be
added to the can of resin when the two are mixed.
hand, once concrete has set, it cannot be reformed; this
Proper storage of plastic repair kits is important.
is characteristic of a thermosetting plastic.
Polyester thermosetting resins, known as polyes-
They should be stored in a cool, dry place. Temperatures
should be kept below 70F and the relative humidity
ters, are extensively used by the Navy. By adding vari-
should be less than 50 percent. Kits should never be
ous activators (catalysts and accelerators) in small
stored in temperatures below 32F. Storage life of the
quantities to the liquid polyesters, chemical reactions
resin will vary; however, under these specified storage
occur that cause the material to become rigid. This
conditions, the resin should remain stable and usable for
process of changing from one state to another is called
an indefinite period of time.
curing. By varying the percentage of catalyst added, the
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