By Brian Knight
Rot is one of the major disadvantages of a wooden fence. Wherever
there is a fastener—nail, staple or screw—there is a potential site for rot to
begin. Water gets around each fastener and soaks into the wood. When the temperature and
the moisture content are right, rot invades these areas. To make a fence that would not
rot quickly, I used a rot resistant wood and eliminated fasteners, gluing pieces together
instead of nailing. Not only was the process fast—I could assemble 42' of fence a
day—but warps and twists in the fence material were easily dealt with.
Our local lumberyard stocks construction grade cedar 2x4 and 2x6. I
bought a stack of each and began by machining the spindles—240 of them—at my
shop. I ripped them so they had a cross section of 1-1/2" square. Next I cut them to
length, cut a chamfer on one end, and sawed a shallow dado as an accent feature.
Starting with a jig
To build the fence, I needed a method of quickly aligning the spindles so
they were parallel, had consistent spacing, and had good alignment along the top. To
accomplish this, I built a jig to assemble the fence sections. The jig consisted of two
sheets of Oriented Strand Board (OSB) with a series of spacers screwed to each sheet. I
made the spacers with scrap stock left over from making the spindles and spaced them
1-1/2" apart—the same dimension as the spindles. The two sheets of OSB were
placed end to end so I could build 16' sections of fence.
Once I had all the spacers installed, it was easy to lay the spindles
between the spacers and at the same time align the bottom edge of each spindle flush with
the edge of the OSB. This automatically aligned the height of each spindle. The good side
of the spindles was placed face down on the jig.
Using the 2x4’s for stringers, I laid them across the spindles and marked
their location on each spindle. I moved the 2x4’s out of the way, mixed some WEST
SYSTEM® 105/206 with 403 Microfiber to a mayonnaise consistency, and put a glob of the
thickened epoxy where the 2x4’s crossed each spindle. When I had the globs of epoxy
in place, I set the 2x4’s in place and weighted them down until the epoxy cured. No
screws were necessary to anchor the 2x4’s to the spindles.
I used the "cake decorator" technique to apply the thickened
epoxy to the spindles. I mixed the resin, hardener and filler to the appropriate
consistency and dumped it into a Ziploc™ plastic bag. I sealed the top of the bag,
snipped a corner off the bottom and squeezed the material onto the spindles. The amount
deposited is controlled by the size of the cut corner.
When the epoxy had set, I lifted the fence section from the jig and
carried it over to the 4x4 posts that were already in place. I mortised the posts to
accept the 2x4 stringers and glued the posts and 16' section together. Then back to the
fixture to build another section. Because the temperature was very warm and the epoxy
cured quickly, I was able to build several sections a day.
Epoxy for gate construction
Epoxy can also be used to avoid stesses often associated with gate
construction. If nailed, screwed or bolted together, the gate pictured would only last a
year or two. The stress on the fasteners would begin to crush the adjacent wood fiber and
elongate the hole.
Eventually, the fasteners would begin to wobble in their holes and
make the problem even worse. To avoid the problem, this gate was glued together. The large
surface area in each joint distributes the loads and alleviates the point loads that are
the downfall of metal fasteners in relatively soft wood.
The boards that form the starburst pattern provide the strength to keep
the gate from sagging. The long boards in the starburst are being pulled lengthwise,
wood's strongest direction. The shorter boards are being compressed, but, because they are
short, they are not as easily bent as longer boards would be. The large gusset in the
upper hinge corner of the gate distributes all the stresses over a large area.
Once it was properly engineered, building the gate was easy. It is a
sandwich consisting of two rectangular layers, one on each side of the starburst pattern.
One layer of the outer rectangle was cut and laid out on the floor. The starburst truss
parts were laid on top of the rectangle and bonded to it. WEST SYSTEM epoxy was applied to
both surfaces using the two step bonding procedure and the process repeated to bond the
top rectangle. A little light clamping pressure was applied to the joints until the epoxy
cured.
To complete the assembly, hinges and a latch mechanism were installed.
Because the weight and leverage of the entire gate were concentrated at the hinge
fasteners, these were good candidates for hardware bonding. As we pointed out in the last
Epoxyworks, wetting the fastener pilot hole with epoxy doubles the pullout strength of the
wood. Drilling an oversize hole and casting epoxy around the fastener will, at a minimum,
triple the pullout strength.
Side loaded fasteners also benefit from being installed in an oversize,
epoxy-filled hole. Epoxy around the hinge bolts better distributes the loads placed on
them into the wood, and, as a bonus, the epoxy annulus keeps water out of the fastener
holes.