What is Epoxy Consolidation and Does it Work?
Epoxy Consolidation of Rotted Wood: Does it Work?
The concept of impregnating rotten and decayed wood with epoxy was first introduced by Morgan Phillips, a Columbia University graduate, back in the mid-1970’s during his work at SPNEA ( Society for the Preservation of New England Antiquities ). The consolidation method made it into The National Park Services’ Preservation Briefs written in the early 1980s. This concept of consolidation was quickly adopted into the commercial market by several manufacturers of epoxy compounds. Sold under the names such as: epoxy primers, penetrators, stabilizers, wood hardeners, and of course, rot consolidants.
So what is the process of consolidation and does it work to repair and preserve rotten wood?
Epoxy Consolidant mixed and ready to apply
The practice of consolidation is simply applying a heavy coating (sometimes pouring) of a low viscosity epoxy resin and hardener on rotten wood. After curing, usually between 8 to 10 hours, the treated area is usually filled with an epoxy paste to even out the surface and create original profiles before painting. The original idea was that the rotted wood is now consolidated into one mass and therefore preserves the historic fabric of an old building.
Here is the problem with this method:
Poor surface prep:
Without removing all the decayed and damaged wood to sound, bright wood the adhesion of any low viscosity epoxy is greatly compromised by the presence of decayed fibers, fungi spores, dirt, oils and moisture.
The dentist analogy:
Leaving any decay behind is like a dentist capping off a tooth without first removing the decay. The decay will return as soon as moisture is present.
Gravity and basic physics:
The consolidation method relies on gravity and pooling of the consolidant giving it sufficient time to wet the substrate. Vertical surfaces pose a unique challenge because of the basic laws of physics. Any liquid material brushed will be quickly carried down by gravity and not forced horizontally into the wood. Drilling holes to channel the epoxy into the vertical surface is rarely successful in achieving more than a 20% bond.
Working Blind:
The consolidant method assumes that the low viscosity penetrating epoxy makes its way through the matrix of decayed matter and then anchors into sound wood beneath. 95% of the time this doesn't happen. Core samples taken from rotten wood treated with the consolidation method show a large failure rate of the consolidant making its way through the decay and into solid wood. The method assumes good penetration yet is a 100% blind practice with no viable way to validate a quality bond in situ.
Moisture and temperature variations:
Most epoxies will not bond if a high wood moisture content is present. All moisture meters are calibrated to measure the moisture content of sound wood, so it's nearly impossible to ascertain whether the decay wood is at an acceptable degree of moisture without isolating the area to be repaired.
All epoxies are exothermic curing materials. The warmer the substrate, the faster the material cures. The colder the substrate, the slower the cure. Typical insitu repairs rarely take this variable into account. A horizontal windowsill on a southern exposure can be well over 125 degrees on a summer day causing the epoxy consolidant to gel quickly without giving sufficient time to wet the decayed wood mass.
So back to the original question: “Does epoxy consolidation work”? In short, no it doesn't.
Give it a try yourself. Take a 1 ½” or larger hole saw and drill a core sample from a consolidated windowsill. Test for penetration. I'd love to hear about your discovery.
So, what is the solution? Ask your local dentist.
Remove all the paint from the affected wood. Remove all the decay and gray wood by using a die-grinder, multi-tool, chisel, or gouge. In the case of gray and checked wood, sand the surface to expose bright wood and open up the checks to a depth of 3/8” and a width of 3/16” using a carbide scraper, grout removal tool, or a die-grinder with 3/16”fluted mortising bit. Remove all loose wood fibers from the surface by sanding. Vacuum the area clean.
Decay removed to bright wood using a die-grinder
Once the decayed wood is removed the moisture content will quickly return to an acceptable level to begin.
With the Dura-Fix System, an epoxy primer is not required.
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Link to YouTube video part 1 and 2 with overview of a commonly used epoxy consolidant:
You can get more information on the Dura-Fix Flexible Wood Repair System here.