The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 20 – Building a Mold or Plug 225
Figure 20-5 <strong>The</strong> ribbands for this 26' (7.9m) mold were run
parallel to the sheer and butted along the centerline of the
keel.
Figure 20-6 A ribband mold for an IOR 1 ⁄2 ton racer. Note
the use of shorter ribbands to fill gaps between full-length
ribbands. <strong>The</strong> skeg shown was laminated out of veneers
beforehand, then secured to the mold. <strong>The</strong> veneer used to
plank the hull was bonded to the skeg. This was done to
save the extra expense and time of molding such an
extreme shape during general laminating.
too much space between ribbands reduces potential
stapling area and may compromise the rigidity of the
mold.
It’s easy to reinforce a mold when it seems to be too
flexible. Short stringers can be inserted between longer
ones, as shown in Figure 20-6, if the gaps between
ribbands are too large. To provide additional support
to ribbands midway between station frames, bond and
staple 2" (50mm) wide strips of thin plywood to the
inside of the mold. If you use extraordinarily thin
ribbands and therefore need additional reinforcement,
two or even three of these strips can be evenly spaced
between frames. A final and effective way to build
rigidity into a weak stringer mold is to cover it with a
layer or two of veneer and turn it into a solid mold.
Fastening Ribbands to Mold Frames
We generally fasten ribbands to mold frames with a
staple gun and narrow crown wire staples up to 11 ⁄4"
(30mm) long. Staple guns are fast and easy to use, and
air-powered models will jar the set-up much less than
hammering nails will. <strong>The</strong> staple gun automatically
recesses staples about 1 ⁄8" (3mm) below the surface,
so they do not get in the way of fairing. This system
successfully fastens planking up to 3 ⁄4" (18mm) thick.
Nails are the second best fasteners for attaching
planking. If you use them, drill your planks first to
prevent splitting and to minimize the hammering
needed to drive them home. Use finishing nails,
recessing them to facilitate fairing. An air nailer with
18-gauge brad nails up to 2" (50mm) long also
works well.
You may also use screws to attach ribbands to mold
frames, especially over sharp curves where additional
holding power is needed. Always drill a lead hole with
the proper size bit and countersink the screw. Selftapping
screws are the best choice if you are working
with chipboard mold frames. We sometimes bond or
nail pieces of scrap wood to both sides of chipboard
frames, close to their edges, and staple or nail ribbands
to these rather than to the chipboard. This technique
may be quicker than drilling and inserting screws.
If a mold is to be at all permanent or if it will be
moved, we bond the ribbands to the frames with a
mixture of high-density filler and WEST SYSTEM ® epoxy.
Occasionally, we do this after installing the ribbands,
running fillets on both sides of the joint between the
ribband and the mold frame. When we lay veneers
over mold frames to make a solid mold, we edge-glue
them and make the entire mold a rigid, monocoque
structure.
If you are building a mold for use with the vacuum bag
method of applying pressure, your prime requirement
is that the mold be airtight. You must maintain this
airtightness even though you have driven staples into
the mold and removed them numerous times. You need
a few staples to hold the veneers in general position