RESTORATION OF ROTTED WOODWITH A FLEXIBLE PENETRATING RESIN
Establishment of a Restoration Standard forMeasuring the Performance Characteristics ofProducts Used to Effect Restoration of Deterioratedor Rotted Wood
Study of Smith & Co. Professional Version™ ClearPenetrating Epoxy Sealer™ (CPES™) Impregnatedinto Wood with Varying Degrees of Fungal andBacterial Rot Formation
Structural Characteristics of Natural andImpregnated Wood
byEugene Wedell, Architect, Restoration SpecialistSteve Smith, Research Chemist, PhysicistBob Fraatz, Staff Scientist
ABSTRACT
Restoration of rotted wood has beenstandardized by the development of a surrogatestandard for rotted wood. This has becomenecessary because restoration is now a recognizedprocess (since at least 25 years) and a permittedprocess (latest rule issue, California State PestControl Board, see Appendix, section 8.6). Thereare no standards for measuring performance of thevarious products offered commercially by manycompanies and promoted for this purpose and,indeed, no such thing as a standard piece of rottedwood to use in repeatable tests.
The concept of a test series was conceivedfrom a study of rotted wood with the aid of a newproduct developed by Smith & Co. of Richmond,California for restoration of deteriorated wood.From penetration and impregnation studies intowood with varying degrees of fungal and bacterialrot, a testing procedure was developed. Themechanical properties of specimens of treated anduntreated wood were tested at varying stress levelsup to failure.
SummaryThis paper documents a technique to
identify two important qualities of restored rottedwood: (1) Microscopic fungal and bacterial rotchannels can be thoroughly impregnated, and (2)The mechanical qualities of impregnated wood aresimilar to that of undamaged wood.
Restoration using epoxy-based products has beenused for 30 years. It falls within the scope ofprocesses permitted by the California State PestControl Board. However, standards to measure theperformance of various commercial products havenot been available. This is due to the fact that a"standard" piece of rotted wood does not exist andnever will exist, since every piece of rotted wood isdifferent.
A testing procedure was developed with theaid of a new impregnating compound developed bySmith & Co. of Richmond, California. Woodexposed to different levels of fungal and bacterialrot was successfully and rapidly impregnated toleave a complete deposition of resin in thedamaged, microscopic channels.
A parallel test to define the mechanicalproperties of treated and untreated wood wasdeveloped using a surrogate which closelyresembles the mechanical properties of moderatelydamaged wood. This was based upon the fact thatthe Smith & Co. product will penetrate undamagedwood a significant distance (approximately 1/4"through end grain, 1/32" through side grain).Though distances and volumes vary according tospecie, it was observed that cedar shingles willabsorb the Smith & Co. product in approximatelythe same volume as lightly rotted wood This is theresearch path which led to the topic of this paper.It was therefore decided to use cedar shingles as aconvenient medium to observe mechanicalproperties of treated wood compared to untreatedwood.
A major result of the cedar shingle testsdemonstrated that for this particular product, theresin-cellulose bonds have a similar flexibility tothat of natural wood. The treated surfaces may beslightly stiffer which adds resistance to bending butthey also carry a greater load which results in a netgain in overall bending capability. This wasespecially true of wood samples that tended to failunder lesser loads. The mechanical properties ofthe treated material were consistently moreuniform than untreated wood. A test fixture andmethodology was designed specifically for thisapplication since no ASTM test is suitable, andsince it was desired that anyone be able to easilybuild their own fixture and conduct their own testson any other product. The test fixture design isincluded in an appendix to this paper.
1.0 INTRODUCTION
1.1 History of Smith & Co. products
Smith & Co. developed its initial line ofepoxy products in 1972 for use in the recreationalmarine marketplace to remediate rot damage inwooden boats. The starting market was the SanFrancisco Bay region, but increasingly Smith & Co.epoxy products have been used over a wide areaincluding specialized outlets as far away as westernEurope. The standard consumer grade is marketedunder the trademark name Clear Penetrating EpoxySealer, also referred to as CPES.
In the early 1980's, founder Steve Smithnoticed that local building inspectors werepurchasing his product to restore deteriorated woodin their own homes. It was also clear that theproduct improved the long-term adhesion ofvarnish, enamel and latex paints to wood. This ledto the development of several new productsspecifically formulated for architectural applicationswhile retaining the formulation principles whichmade his product uniquely successful in the moresevere marine environment. Seasonalmodifications to the various formulas were added tomaintain consistent performance in weatherextremes. As the architectural market began togrow, fillers and compatible coatings were added tothe product line. The Professional Version, used inthese tests, was developed in 1995. A moredetailed discussion of the product is to be found inthe Appendix, section 8.6.
1.2 Summary of tests
This paper describes two test series, one todocument penetration of the impregnating resin intoseveral representative classes of rotted wood, andthe other to demonstrate the structural properties oftreated and untreated wood.
1.3 Test methodology
1.3.1 Epoxy penetration of rotted wood.
Samples of wood that had been exposed tomoist conditions over several years were cut intoblocks approximately six inches long. The sampleswere from apparently sound and from severelydecayed (in a region) Fir 2 x 6 material, andseverely decayed (in a region) Redwood 2 x 6
material. The resulting test blocks were 1-1/2 to 1-5/8 inches high by 5-1/2 inches wide by one inchlengths (1-1/2" x 5-1/2" x 1") exposing end grain inthe one inch direction. These blocks were placedin a shallow aluminum pan, end grain up. A darkblue dye was added to the impregnating resin tomake the penetration more visible. A quantity ofimpregnant was poured into the pans, and theblocks were placed in the liquid to 1/4" immersiondepth. The blue dyed liquid wicked upward intothe samples. The result was documented forsixteen minutes by timed photography. The resultswere assembled into the photographic sequences onthe following pages. As you look at these, noticehow the aged but apparently sound fir specimen inthe first sequence showed prompt penetration of theimpregnant through a small deteriorated regionalong the top edge, and through a few small cracks.Notice there is no porosity (within the limitations ofthis test) within most of the area of this evidentlysound specimen. Compare with this, the behaviorof Fir or Redwood with more severe deterioration,as shown on the following pages.
