Liken the
procedure to that of a dentist filling a tooth. Only the
patient does not complain. For this house the rotted area was
about 20 inches long atop an 8” wide valley beam. Once all of
the rotted wood was dug out the resulting pocket was about 24
inches long, 6 inches deep, the full width of the beam at the
top and about 4 inches wide at the bottom of the pocket. That
is how big it was by the time the carpenter found good wood all
around the pocket. The carpenters used hand and power tools to
remove the rotted wood. The removal process requires the worker
to get back to undamaged wood. If the surfaces are left in a
roughened condition, all the better.
Like the
epoxy injection work the good wood must be dry to 19% or less
moisture content and kept that way throughout the repair time.
When the work cannot be completed and cured in one day as was
the case on this project, some weather protection has to be
erected to keep out rain. Do not do epoxy repair work in
temperatures below 50 degrees F. Best results are when
temperatures are between 60 & 90 degrees. Use tents and heat
when it is necessary.
The repair
process will require two different types of the same brand of
epoxy plus dry silica sand. The first type will be a low
viscosity, 2-part epoxy and the 2nd will be a
moderate to high viscosity, 2-part epoxy, both of which must be
compatible with wood and reach final tensile strengths around
10,000 psi.
The
process consists of the following:
·
Whether the damage is a pocket like above or a cut, gouge, hole,
etc., cut out the damaged wood back to good sound dry wood. If
there is a sag in the framing where the damage is get it shored
back to where it should be before repairing the damage.
·
If
the sides of the beam were cut away to remove the damaged wood then
prepare some side forms to cover the gaps. Plywood or OSB are good
products for this. Size them to fully cover the gap leaving space
for nailing or screwing to the sides of the beam. Before attaching
them stretch 4-mil poly over the inside face of the forms, stapling
the plastic on the OUTSIDE. Release oils, wax paper, plain wood
does not work. The epoxy destroys wax paper and bonds to wood
tenaciously, despite release oils. Some oils affect the epoxy
adversely. The poly peels off epoxy like a banana skin. Avoid
folds in the poly that will create patterns on the epoxy surface.
·
Before installing the forms mix and apply the low viscosity epoxy
using a throw away brush or brush-like, foam applicator. Apply it
liberally to get it into the wood crevices and so that it can sink
into the wood. This epoxy should set for an hour or so while
readying for the next steps.
·
Immediately install the side forms tightly to the beam with the poly
facing the repair side.
·
The
messy part – Using throw away tools and containers mix the 2-part,
high-viscosity epoxy components together and immediately add the DRY
silica sand, at a 1 to 1 ratio by volume.
·
Once thoroughly mixed start packing the blend into the cavity
pushing it tightly into and against the wood in layers about 1.5 to
2 inches thick. Repeat the layers until the cavity is filled. Mix
only what you can place within an hour because the pot life is only
½ to 1 hour depending on the brand of epoxy. The mix will be fairly
stiff. If the cavity does not require more than 2 – gallons of
epoxy then fill the whole void. Otherwise wait 1 hour between layer
layups to minimize heat build-up of the epoxy mix.
·
The
sand does two things. 1. It is a cheap filler to save on epoxy. 2.
It helps moderate the heat of reaction from the two epoxy
components. The sand must be DRY to prevent the epoxy from bonding
with any moisture rather than with the sand. Epoxies have an
affinity for water and will set up tertiary bonds with water before
bonding with the sand.
·
While keeping rain off and temperatures in the aforementioned range,
cure the finished repair as per the manufacturer’s printed
instructions, usually about 3 weeks. The first week is the most
critical. In one day the strength gets to about 2,000 psi and to
about 6,000 psi in a week, all dependant on the curing conditions.
Like concrete the epoxies take about a month to reach full
strength. You may strip the forms after a week. Keep any installed
shoring in place for at least 3 weeks.
·
Nailing to this epoxy repair is going to be virtually impossible.
Pre-drill holes and use special screws like those used for fastening
to concrete.
·
Close up the repair and install flashing that will not leak.
Remember the wood outside of the repair can still rot even if the
epoxy cannot. New rot will destroy the bond just created, making
the repair useless.
This repair can
be used to repair beams of open decks but extra-special precautions,
protections and paints have to be used to prevent water from getting
between the repair and the adjacent wood. Each project has to be
examined on its own merits and fixed accordingly. Use the same
epoxies mentioned in the previous article as well as their related
higher viscosity types. Use only the same manufacturer for the
whole job.
I hope that this
series has been helpful and educational. If you have any questions
you can contact me through GPR’s company website,
www.gpr-inc.com, or call me at
(978) 772-1590.
