Rebuilding Pocket-Damaged Timber Framing with Epoxy:
In Part 1, “Epoxy Injection Repair of Split Framing”, I wrote about the use of epoxy injection to repair splits in timber beams and framing members. In Part 2 I will address the use of epoxy to repair pocket-type damages to timber framing. The damage spoken about here is that of localized pockets of rot, insect damage, mortise pockets, deep gouges, cuts or drill holes. Here a chop, there a chop and the member is reduced in strength, perhaps right where you need it most. It happens to newly constructed framing and to old existing framing.
This procedure is not an appropriate repair for extensive framing damage such as long lengths of rotted sills or insect damage. It is far too expensive. In these instances the members should be replaced or, if possible, treated with epoxy as described on the Rot Doctor web site. So far I have not found a web site that presents the repairs described herein. Like the epoxy injection repair, I have evolved this repair since 1987.
There are many occasions when it will be less expensive to sister a member, that is to say, fasten a new member alongside and against the damaged one to restore the strength needed. There are times when that cannot be done such as when a timber valley beam has a pocket of rot caused by leaking flashing. I’ll use that as the example here because it actually happened to a 60-year old, post-and-beam house that needed help. I found that there was no room under the beam in which to work. Replacing it would have required dismantling the multiple roof members and connections to the valley beam. The process I used here would be similar for most other localized-damage cases.
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 carpenter used hand and power tools to remove the rotted wood. As required, he had to get back to sound, undamaged wood. He left the surfaces in a roughened condition to assure the best anchorage for the repair.
Like the epoxy injection method 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 or if the wood is wet. Do it when temperatures are between 60 & 90 F. 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 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 had to be 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 screwing to the sides of the beam. Before attaching them stretch 4-mil poly tightly 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. Use the polyethylene sheets. They peel off epoxy like a banana skin. Avoid folds and wrinkles in the poly because they will create patterns on the epoxy-repaired 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 after 6 to 8 inches worth of layups to minimize heat-of-reaction build-up of the epoxy mix. There is expansion and then contraction during the heating then cooling phases of the blended, two-part epoxies.
· 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. Amine-type epoxies have an affinity for water and will set up tertiary bonds with water molecules before bonding with the sand or wet wood, for that matter.
· 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 dependent 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 because epoxy repairs will creep and distort until fully cured.
· Nailing to this epoxy repair is going to be virtually impossible. Use special screws, like those used for fastening to concrete, and pre-drill the holes.
Close up the repair and install flashing that will not leak. Remember, the wood adjacent to 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 Part 1 along with their related higher viscosity types. Use only the same manufacturer for the whole job. I hope that this two-part article has been helpful. Consider it when you encounter similar timber damages.
EPOXY INJECTION REPAIR OF SPLIT FRAMING:
What do you do when a perfectly fine timber beam splits?
Repair it with epoxy of course. That is what this article is all about - using epoxy to restore the structural integrity of wood framing that has split wide open. I developed and evolved this method since 1987. It is not about patching exposed trim, matching mouldings of fancy trim or restoring rotted wood. There are products and methods on the market for those purposes, such as those made by Abatron, Inc. For pocket-type damage to timber framing see Part 2 below, "Rebuilding Pocket-Damaged Timber Framing with Epoxy"
Why would you consider restoration instead of replacing or adding another wood member alongside the damaged one? A few reasons are: 1. The member may be part of a larger frame, like a truss, that cannot be partially dismantled or that the wood type (Elm, Chestnut or specialty wood) cannot be found anymore. 2. The beam may be large and long like 11”x17” southern yellow pine beams in the old mills of New England. 3. The member may be a hip or valley rafter or ridge beam or an exposed beam of a post-and-beam framed home or commercial building. Splitting, cracking or fracturing of the wood members in any of these situations lends itself to epoxy injection repair methods. Epoxy materials can take higher tensile and compression forces than wood yet are compatible with and behave similarly to wood. Both materials are carbon/hydrogen compounds, an ideal match.
Some attempts at repair have made use of steel angles, channels or plates to re-attach split wood. They were not successful over the long term because the two materials behaved so differently when subjected to temperature and seasonal moisture changes. Those repairs came apart or the metal trapped moisture against the wood and caused rot to ensue.
The first time I encountered the need to repair a beam was in 1987 when an 11”x17” x 20’-0” long timber beam of a Lowell, MA mill-complex split longitudinally. The beam had been over-loaded from stored goods. It sagged over 12”. Southern yellow pine beams of this size and length were not available. Removing it and replacing it with a steel beam would be costly. Engineered lumber had not come onto the market at that time. Having used epoxy injection since 1969 for concrete repairs I decided to use it here. Adhesive Engineering (no longer around) in Haverhill, MA had the equipment and materials and did the work. I did the assessment and engineering. I use the same technique today.
The process consisted of the following:
· Remove the loading. Jack and shore the beam to level until all of the wood fibers come back close together, leaving 1/16” to 1/8” cracks.
· Apply an epoxy putty across all of the cracks while inserting plastic, injection-tube 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.
This particular repair was a total success leaving the beam stronger than it was before the mishap. Unfortunately three years later a fire destroyed this entire building and three others. I have used the injection repair procedure on five or six buildings since then. Each situation requires a thorough investigation and analysis of the failure to be sure the method will work and be cost effective. If it will work then provide clear drawings/and specifications for the repair. I require the general contractor to retain an experienced epoxy-injector company to do the work.
The fundamental conditions that make this restoration useful is when other options are less viable. This is especially so when the member has a clean break or split and the wood is dry to standard 19 +/-% moisture content. DRY WOOD is critical to success. 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 type of 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 very 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 to assure strong mechanical bonding while the epoxy, itself, reacts without air to become a solid material that will never rot. When completed 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.
By Lynwood Valentine Prest, P.E., S.E., President Groton Engineering, LLC.