The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

116 Core Boatbuilding Techniques
Figure 12-13 Cutting scarf bevels on stacked panels.
Clamping plywood scarf joints
<strong>The</strong> potential problem with the plywood scarf joint is
achieving proper clamping pressure. A large, flat work
surface of the size used to fit the joint is required for
clamping, but with one additional provision. <strong>The</strong> work
surface must be of a material which will receive staples
or small nails. If needed, you can position several sheets
of 3 /4" (18mm) thick sheathing grade plywood over
your floor or the workbench to receive fasteners readily.
Cover that part of the work surface that will be beneath
the scarf joint with wax paper or polyethylene sheet.
Apply the bonding adhesive, position the panels on the
flat surface, and join the bevel surfaces together so that
the surmarks line up. <strong>The</strong>n position a locating staple in
each edge of the joint to prevent any movement of the
two panels while you are clamping. Cover the top of
the joint with wax paper and place a strip of plywood
over the paper at the scarf joint. This plywood strip
should be about the same thickness as the material
being spliced together and should be wide enough to
cover at least the entire area of the splice. Drive a sufficient
number of staples or nails through the strip and
the scarf joint into the receiving material below,
drawing the two beveled surfaces firmly together.
You can create adequate pressure with staples when
clamping plywood up to 1 /4" (6mm) thick. With thicker
panels, nailing is recommended. When using nails, we
usually use a much thicker clamping strip, of perhaps
3 /4" (18mm) stock, so that fewer nails are necessary for
even pressure over the entire surface area. A piece of
curved stock, held in place with clamps as shown in
Figure 12-14, will help distribute clamping pressure
evenly across your joint.
Because you may be bonding wide panels, it is
extremely important to fair up these joints while the
adhesive is still in its partial cure stage. Use the same
tools and procedures to clean up and fair plywood scarf
joints as you would use with lumber scarf joints. It
works best to do the cleanup and fairing operations
while the plywood is still lying on a flat surface; this is
especially important with thinner plywood.
Scarfing in Place
Very often in a boatbuilding job, you may need a scarfed
panel of very large dimensions (for example, a complete
deck surface) which is impractical to install in one piece.
To solve this problem, we have developed a technique to
scarf together plywood panels right in place on the hull
as they are being installed. This scarfing-in-place procedure
adds two difficulties in the basic plywood bonding
operations: (l) the measuring, marking, and fitting of the
Curved clamping piece
Plastic
Sheet
For thin plywood or veneers,
use staples through pads on
the feather edge.
With thicker plywood,
fewer nails are needed
Backing blocks, table
or floor under scarf
In all cases, use several staples to
secure the scarf and prevent slipping
during the clamping or nailing operations.
Figure 12-14 Three methods for clamping scarf joints during
bonding.