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Experts
in polyester report that most defects on the gel coat surface
of a mold - such as blemishes, glass transfer, dull spots
or haziness - are the result of a failure in the laminate.
If the resin has been under-catalyzed, post-curing will take
place as the surface of the mold is heated during production.
Post
cure will create a hazy, blemished surface as the laminate
attempts to cure under heated conditions. Orange Peel can
become a factor if the laminate shrinks during the curing
process and moves the gel coat.
Guidelines
for laminating a good, solid mold:
1.
Know the recommended catalyst levels of the resin as issued
by the resin manufacturer.
2.
Measure precisely the mixing of resin and catalyst.
3.
Keep the glass to resin ratio as close as possible to 70%
resin and 30% glass. When applying a hand laminate, use
a "felt roller" to wet the glass out in order
to keep the laminate within the proper ratios.
4.
Do not allow the resin to puddle. Because these areas will
release heat at different rates, all puddles will eventually
transfer to the surface of the mold, regardless of where
the concentration of resin is in the laminate schedule.
5.
Allow each layer of laminate to dry and cool prior to applying
the next layer of laminate.
6.
Take barcol readings after each layer and look for at least
a 15-20 after cool down.
7.
Document any corrective measures taken on the "mold
birth certificate".
8.
Use the same catalyst levels throughout the laminate schedule,
including the glass covering the bracing.
9.
Never use a diluted version of catalyst with the lamination
resin.
10.
When using core materials, make certain the temperature
of the laminate is cold to the touch to avoid any transfer
of the core material.
11.
Lightly sand between each layer of laminate. This will enhance
the mechanical adhesion of the laminate.
Remember
that the laminate should be compatible with the gel coat.
Both should move or flex at the same rate. If the gel coat
is harder than the laminate or the laminate is harder than
the gel coat, a failure will occur and will normally appear
on the gel coated surface of the mold. When the lamination
process is completed, the backside of the mold should not
have a shiny appearance, indicating too much resin. This should
be true for the glass covering the bracing.
Make
the laminate as neat as possible.
BRIDGING
OR BRACING THE MOLD
Brace
a mold with wood, steel, paper tubes or fiberglass. Regardless
of the type of bracing, the purpose of the bracing is to support
the mold during production as the tool becomes heated and
pliable.
Suggestions
concerning the installation of bracing.
1.
Never allow the bracing to touch the back side of the laminate.
Generally, if the bracing touches it will transfer to the
gel coated surface.
2.
Place the bracing in a way that maximizes the strength of
the material. If 2x4 or 2x6 is being used, turn the lumber
on edge for strength.
3.
Areas that have radii should not require bracing. A radius
exhibits strength by design.
4.
When laminating the bracing to the mold, use the same catalyst
levels used throughout the laminate schedule.
5.
When steel or metal bracing is required, remove any oils
or contaminates from the surface.
6.
Laminate the bracing as neatly as the mold.
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