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Continued from
October Newsletter - page 1
 The
process consisted of the following:
-
Remove the
loading. Jack and shore the beam to level. (All of the wood
fibers came back together, leaving 1/16” to 1/8” cracks.)
-
Apply an
epoxy putty across all of the cracks while inserting plastic
tube injection ports about 18” on center on both sides of the
beam. This creates the seal to keep the injected epoxy within
the beam.
-
Using pumping
equipment suitable for blending a low-viscosity, 2-part ,
Concresive Liquid LPL epoxy or other suitable 2-part epoxy, pump
the epoxy into the cracks starting from the ports nearest the
ends of the beam and work towards the center and from the bottom
up at the break. As the epoxy oozes out of the next port pinch
off the ones being used and move to the next ones in succession
until all of the cracks are filled.
-
After 24
hours of curing remove the surface putty and injection ports and
let the beam cure for seven days before removing the shoring and
four weeks before putting loads onto the beam.
I have used
the injection repair procedure on four or five buildings since
then. It requires an investigation, analysis and specification
write-up of the failure to be sure the method will work and be cost
effective. Each time the general contractor for the project has
retained an epoxy injector company to do the work.
The
fundamental conditions that make this restoration usable is when
other options are less viable, the member has a clean break or split
and the wood is dry to standard 19 +/-% moisture content. The
2-part epoxies must
be of the same manufacturer, designed for bonding to wood and have
fully cured strengths of 5 to 6 times that of the allowable
strengths of the wood. Do not use epoxies if the wood will be
subjected to submergence in or constant exposure to water because
the wood will only rot and fall away from the repair. It is okay to
use epoxy repairs if the member is exposed to the weather AND the
wood can be thoroughly protected against rain and snow. The wood
must be clean or cleaned to remove dirt, paint or other foreign
substances that would interfere with the penetration/bonding of the
epoxy to the wood.
There are now
numerous manufacturers of the correct epoxy. The Concresive Liquid
LPL by Adhesive Engineering is now made by Master Builders, Inc.
Sika makes Sikadur 35, Hi-Mod LV that is suitable for wood
injection. All of the epoxies are expensive so the case for using
them has to be considered carefully. The joints of the splits or
breaks have to be less than ¼” wide. When the surface putty is
pealed off the repair is barely visible and the behavior of the
epoxy is virtually the same as the wood. The low viscosity of the
epoxy allows it to soak into the wood as well as react without air
to become a solid material that will never rot. Therefore the
repair has a penetrating physical bond to the wood and the epoxy has
a linking, chemical bond to itself.
To see what a
typical injection port might look like before it is installed visit
ChemCo Systems at
http://www.chemcosystems.com/. They manufacture a type of port
that can be used on wood even though they specialize in repair of
concrete. The ports are centered over the cracks while the initial
putty, that holds them, is being placed Another type of port,
usually made of brass, is installed in a drilled hole off to one
side of the split. The drilled hole leads into the split.
In the
November newsletter, Part 2, will cover repairing wood that has
extensive but localized deterioration. That repair requires some
cutting and drilling to remove the deterioration, somewhat like
drilling out tooth decay.
EPOXY REPAIR of TIMBER FRAMING
By Lynwood
Valentine Prest, P.E., President
Goldsmith,
Prest & Ringwall, Inc., Ayer, MA
October, 2006 |
