by Eric Borden
We build along the Jersey shore, and whether a house fronts
the ocean, the bay, or the river, our clients want to enjoy the
view. To give them a good view from inside the house, we might
have to go up three stories. But for the view from outside, we
add a deck or two.
The project discussed in this article is typical of most of
our jobs, because the decks serve double duty — as both
outside living space, and as a weatherproof cover for rooms
below. At the rear of the house, we added a deck off the
second-floor kitchen that overlooks the pool and creates a
covered patio underneath. At the front of the house, we removed
an existing first-floor exterior porch to make room for an
enlarged great room. We extended this deck to one side to cover
the entrance to the garage and to provide an additional
12x20-foot covered carport with access from the dining room
through a new slider. We also extended this deck 8 feet to the
other side to create a covered entrance to the house.
Both of these decks had to protect the spaces below from
water. We could have used EPDM single-ply rubber, which is easy
to install, but has to be replaced eventually. And because EPDM
can’t be walked on directly, we would have had to install
deck boards on top of it.
The option we prefer is fiberglass, which does not need any
additional decking to protect it and, if re-coated every 7 to
10 years, will last forever. A fiberglass deck covering is also
relatively inexpensive and, in most cases, can be completed in
two days. Costs in our area range from $6.50 to $8.00 per
square foot, including the second layer of plywood and all
resin fiberglass has a solid track record — it’s
been in use since the 1950s in the boating industry — but
it’s messy and somewhat finicky to install. To avoid
problems later, we spare no expense preparing a sound deck
First, we step up one size on our joist sizing, because we
rip a pitch (1/8 inch per foot, minimum) into the deck framing.
You can also create a pitch by adding sleepers to the top of
the joists, but I feel that this increases the odds that the
finished deck will squeak.
Next, we sheathe the deck with 3/4-inch tongue-and-groove
Douglas fir plywood, glued with construction adhesive and
fastened with 8-penny ring-shank nails placed 8 inches
on-center. If you use square-edge plywood, be sure to block all
seams; any movement in the plywood substrate will stress the
fiberglass. When the sheathing is complete, we through-bolt any
railing posts to the framing at the intersection of the joists
and the inside of the rim board. We add blocking so that the
post is secured on three sides, because any movement could
cause the fiberglass to crack and leak.
Applying the Resin
the application of the fiberglass coating to the professionals.
Former boat builders Dan and Rick Winkle take great pride in
their finished product and are knowledgeable about the quirks
Polyester resin fiberglass is a two-part product. The
general-purpose resin is mixed on site with a hardener (see
1. Fiberglass resin is mixed on site with a
hardener (methyl ethyl ketone peroxide) in a ratio that
can be varied to extend or shorten set time. The base
coat is applied over plywood with reinforcing mesh at
joints and penetrations, then finished with a gel
The mix ratio determines how long the resin remains
workable, and may need to be adjusted for weather conditions
and other variables. Humid weather will delay drying, so we
increase the amount of hardener added; conversely, dry weather
will cause the resin to set up too fast, so we use less
hardener. Open time can also be affected by the surface area of
the container used to make the mix; a larger container
disperses the heat of the chemical reaction, delaying the
chemical reaction and extending open time.
The resin is applied over a fiberglass mat, which acts as a
binder and adds strength to the coating. Essentially, the mat
serves the same function as wire mesh does in a concrete slab.
Various other components, such as ground silica and
microballoons (small glass beads) can be added to the resin for
filleting or patching.
Double plywood layer.
When Dan and Rick show up on site, they bring with them the
second layer of plywood for the deck. They use 1/2-inch AC fir
plywood, which provides a smooth surface for the resin to
adhere to (Figure 2).
2. On the day the fiberglass will be applied, a clean,
dry layer of 1/2-inch AC plywood is laid over the base layer of
3/4-inch T&G plywood. Joints are staggered and the sheets
are fastened with 8d ring-shank nails.
They prefer to provide the plywood because they can be sure
of the moisture content of the wood. Moisture is probably the
biggest problem at this stage of the game. The resin does not
soak into the wood very well, so any moisture in the pores of
the wood prevents the resin from penetrating and destroys the
bond. The key is to never install more plywood than can be
covered with fiberglass in a day’s work: Two experienced
workers can cover about 600 square feet in a day.
Joints in the second layer are staggered over those of the
first. The two layers of plywood are not glued together;
they’re only nailed with 8-penny ring-shanks, 6 inches
on-center at the joists and 4 inches on-center at the edges.
This makes it easy to remove the top layer of plywood if there
is a problem down the road.