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When
the plug is finished and approved, it must be prepared so
that the mold will release from the surface of the plug. Many
release agents, compounds and procedures in today's market
work well in the fiberglass industry. Therefore, this document
will suggest a method of selecting the system itself. Due
to the complexity of specialized release agents used with
a wide variety of techniques when addressing plugs that are
comprised of sophisticated materials, we will focus on plugs
that have been surfaced with polyester-type materials or with
materials that are compatible with polyesters.
The
four basics of preparation are:
- Sanding
- Compounding
- Sealer
Glaze
- Waxing
/ Release Agent
1.
Sand the surface with the finest grit of sandpaper possible.
The larger the number on the sandpaper the finer the grit.
Example:
(a) 1200 Super fine grit
(b) 600 Finer grit
(c) 400 Fine grit (d) 320 Medium grit
(e) 220 Medium grit(f) 180 Course grit
(g) 80 Rough grit
These
number ratings are generally printed on the backside of the
sandpaper.
The
two types of sandpaper are wet and dry and dry open grit.
When sanding is required on a wood plug, use dry, open grit
sandpaper in order to eliminate the possibility of swelling
any exposed wood areas with water. If the plug is totally
encapsulated, wet sanding is possible. In fact, it is better,
since it will cut faster and limit the amount of work required.
Always
block sand with a flat sanding block, unless the design of
the plug does not allow you to do so.
Sand
with 400 grit, follow that with 600 grit then finish with
1200 grit. Next, sand the 400 in one direction, then the 600
in the opposite direction, followed with the 1200 in the same
direction as the 400. This would sand the coating down in
a uniform manner and end with all scratches left by the 1200
grit going in one direction. The straight scratches would
then be removed by the circular motion of the buffing pad
that would cross over the scratches left by the 1200 sandpaper.
2.
Compounding with materials made by the same manufacturer seems
to be one of the most overlooked procedures when selecting
a compound. There are thousands of buffing compounds on the
market today. Some are formulated exclusively for paints,
metals, plastics or polyesters. Using products made by the
same manufacturer guarantees that when heavy-duty compounds
and lighter grit compounds are used they will be compatible
in chemistry and will not have an adverse reaction with each
other.
Most
buffing pads are 7-inch, curved-edge 100% wool material. Synthetic
materials can leave a residue that can cause a breakdown of
the waxes to be applied later. Buffing pads should not be
laundered with industrial soaps. These can contaminate the
surface, leaving a residue that is released on the unit when
the pad becomes warm during the buffing process. In buffing,
the pad is placed on the curved edge of the pad and pressure
is applied to the compound via the pad. Polishing
the streaks left by the buffing action is accomplished by
laying the pad flat and applying very little pressure. During
this process, keep the buffing pad clean and free of grit
while moving the buffer briskly over the surface.
After
the buffing process has been completed with heavy duty compounds,
regular compounds and fine-finish compounds, the entire area
that was compounded should be wiped clean with warm clear
water and dried. This will remove any existing compounds and
will prepare the surface for the sealer glaze.
3.
Sealer Glaze seals the microscopic pores (not porosity) in
the surface of the gel coat, (which were opened by sanding)
and leaves a glaze on the surface in preparation for the wax.
Sealer Glaze should be applied with a machine buffe, using
the polishing technique of laying the pad flat and applying
little pressure. Always
use a clean pad that has not previously been used for buffing
compounds. This will prevent the possibility of applying compound
back to the surface that you had previously washed with clean,
warm water. Again,
for chemical compatibility, the sealer glaze material should
be from the same manufacturer as the buffing compounds.
4.
Waxing the plug accurately and with an adequate amount of
wax will assure the releasing of the plug from the mold. Failure
in this procedure can result in the entire loss of both the
plug and mold.
The
following procedures for waxing are considered basic guidelines:
a.
Start the waxing in one specific area and stop at the same
area. This should guarantee coverage of every inch of the
plug's surface. When you start and stop in different places,
you can forget where you have been with the wax.
b.
Make small circular motions when applying wax. Let them
overlap each other, being cautious not to apply heavy concentrations.
Heavy concentrations of wax will not release the solvent
and will smear when you try to remove the wax.
c. Allow the wax to become hazy, but not completely dry
before wiping the wax from the mold. If you apply wax, remove
it and apply a layer immediately on top of this green, non-cured
layer, you accomplish nothing. After you remove a layer
of wax, allow time for the solvents in the wax to be released.
Usually 30 to 60 minutes is adequate.
d. For wiping materials, use a lint-free, undyed, uncontaminated,
clean material.
If
you use this A-B-C-D-system of wiping off waxes, you should
end up with a clean piece of wiping material when you have
finished.
Depending
on the size of the plug, start with the number one rag in
one hand and the number two in the other. With the same circular
motions used when applying the wax, wipe the wax off.
Use
the number three and number four rags in the same manner.
After the wax has dried for several minutes, wipe the entire
unit one more time with a clean rag.
Allow
each layer to cure for 30-60 minutes prior to the next layer.
4.
Every builder has his own theory concerning how much wax is
enough. If it's not broke, don't fix it! If you have problems,
usually 7 coats spread over a 2-day period seems to work well.
Thus
far, we have built a sound foundation, formed our shape to
dimensions, made radii and design lines using drags, sealed
the under side, applied a primer, sanded, applied a mirror
finish, sanded lightly, buffed, seal-glazed and waxed the
plug. We
are now ready to build a mold, or the reverse image of the
plug. Remember: Any flaw in the plug, regardless of how minor
it may seem, will transfer to the mold surface. Prior
to making a mold the plug must be perfect!!
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