performance of wood coatings - Western Wood Preservers Institute

18-MONTH REPORT
Performance of
Selected Wood-Protection-Coated
Lumber Products in Hilo, Hawaii Submitted to
Dallin Brooks, Executive Director
Western Wood Preservers Institute
Vancouver, Wash.
by
Jeffrey J. Morrell
Department of Wood Science & Engineering
Oregon State University
Corvallis, Ore.
August 2015
Introduction
While protecting wood with biocides is a widely used and generally accepted method for
extending the useful life of a wood product, some users have sought non-toxic systems
for wood protection. A variety of methods have emerged that claim to protect wood
without biocides or that use less toxic preservatives such as boron. While these
products are sold commercially, there is surprisingly little publically available data on
their performance.
Among the products that have emerged recently are BluWood, TimberSil and Eco Red
Shield. All of these products have, over time, claimed wood protection performance in
above ground exposures subjected to periodic wetting, or Use Category 3B according to
the American Wood Protection Association Use Category Standards. Wood applications
in this category include decking, railings, millwork, fence pickets and deck joists.
Developing data on the performance of these materials in relation to both non-treated
wood and wood pressure-treated with a conventional preservative for the same
application would help consumers make informed choices about materials for above
ground, exterior exposures.
The goal of this project was to evaluate the performance of wood products coated with
various materials and exposed at sites in Corvallis, Ore., and Hilo, Hawaii. This report
summarizes the inspection of the samples in Hawaii after 18 months of exposure.
Materials and Methods
All materials in this test were commercially treated and provided to OSU as nominal
2x4 lumber that was then cut to lengths appropriate for each test method. Samples
were also retained for later examination. The materials and species tested are listed in
Table 1.
There are two sets of samples placed at the test sites. In June 2015, additional samples
were placed consisting of new, non-treated Douglas-fir lumber, the new Eco Red Shield
(II), and HiBor borate treated wood in decay and termite ground proximity tests as well
as the above ground sandwich trials (Figure 2). The materials, species and number of
samples in this second set are detailed in Table 1.
The lumber was cut to the appropriate size for each exposure and then all of the cut
ends were dipped for 30 seconds in a solution of 4.8% pentachlorophenol in diesel oil
for the first set or 2% copper naphthenate in diesel oil for the second set to protect the
potentially untreated ends exposed by cutting. This was essential since most of the
tested treatments function as barriers and the penta and copper naphthenate create a
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 2 secondary barrier on the end cuts that should protect the wood from fungal and termite
invasion through these areas.
Samples were exposed in test sites at Hilo, Hawaii or Corvallis, Ore. The Hilo site
receives over 200 inches of rainfall per year and has average daytime temperatures
between 80 degrees and 85 degrees F, while the Corvallis site receives approximately
45 inches of rainfall per year and has daytime temperatures that range from 40 degrees
to 80 degrees F, depending on the time of year. The risk of decay at the Hilo site is
described as extreme while that at Corvallis is considered moderate.
Table 1. Treatments evaluated for decay and termite resistance in above ground
exposures at sites located in Corvallis, Ore. or Hilo, Hawaii.
Treatment
Wood
Number of Samples Exposed/Site
Species
E18 Termite
E26 Decay GP Sandwich test
GP
None
Douglas-fir
15
35
10
TimberSil
Southern
15
35
10
pine
Eco Red Shield I
Douglas-fir
15
35
10
BluWood
Douglas-fir
15
35
10
Copper Azole
Douglas-fir
15
35
10
Eco Red Shield II* Hem-Fir
10
10
10
HiBor*
Douglas-fir
10
10
10
* Added to test sites, June 2015
The materials were tested in three configurations. Resistance to attack by Formosan
termites was evaluated using a modification of AWPA Standard E26. Briefly, hollow
concrete blocks were placed on the soil. Pine sapwood stakes were driven into the
ground within the hollow blocks to attract termites, then the test blocks were placed on
the blocks (nominal 2x4 by 4 inches long) in between non-treated wood that serves as a
feeder material for the workers to explore (Figure 1).
The blocks were then covered with a water shedding cap that produced a dry, non-soil
contact exposure equivalent to a Use Category 1 or 2 exposure. It is important to note
that this test does not expose the wood to any rainfall and, as a result, there is no
potential for leaching of any active ingredients from the blocks.
Formosan termites are extremely aggressive and untreated wood at the Hilo test site is
typically destroyed within six months of installation. The control and test samples were
evaluated at six-month intervals for degree of termite attack on a scale from 10 (no
attack) to 0 (failure). Fifteen blocks were tested for each treatment and the test was
evaluated after 7, 12 or 18 months of exposure. The 10 samples in the second set will
be evaluated on the same intervals.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 3 Resistance to decay in a UC 3B-type exposure was evaluated in two above ground
tests. In the first, 5-inch long blocks were cut and placed on concrete blocks following
the procedures described in AWPA Standard E18.
Thirty-five blocks were installed for each treatment. Block condition was visually
assessed at six-month intervals on a scale from 10 (sound, no decay) to 0 (completely
decayed). Selected samples will be removed at the same intervals to determine residual
chemical content (where appropriate) as well as the presence of internal fungal decay.
Samples of each treatment also will be evaluated in a sandwich test. Briefly, a total of
30 samples 11 inches long were cut from the boards in each treatment. Three pieces
from a given treatment were combined and tied together using plastic zip-ties.
The assemblies were then exposed on aluminum racks approximately 12 inches off the
ground. These assemblies are designed to trap water and encourage fungal
colonization between the board faces.
These assemblies were visually assessed for degree of decay by removing the zip-ties
and assessing the surface condition of each piece on a scale from 10 (no decay) to 0
(complete failure). The sandwiches were reassembled and placed back on the racks for
additional exposure. A total of 10 sandwiches were exposed per treatment.
Boron Analysis
Samples of Eco Red Shield I and II as well as BluWood were analyzed for their boron
content. Since these are surface treatments that would not be expected to move deeply
into the wood, we modified the wood collection from the normal 15 mm deep assay
zone used for conventional wood preservative delivered using pressure processes.
Squares of wood were taken from the wide surfaces of three samples of each material
to a depth of 3 mm. This depth is similar to that used when evaluating concentrations of
fungicide applied for control of fungal stain and mold. These materials were air-dried,
ground to pass 20 mesh screen and hot water extracted. The extracts were analyzed for
boron content using the Azomethine H method (AWPA, 2012).
Boron contents were expressed on a boron oxide basis (B2O3). Eco Red Shield I
samples contained 0.01 kg/m3 of boron oxide, while the Eco Red Shield II samples
contained 0.03 kg/m3 of this compound. The manufacturer of this product had claimed
they increased treatment levels and these data support that statement. The BluWood
samples contained 0.017 kg/m3 of boron oxide.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 4 Boron Levels in Surface Treated Lumber
0.035
Boron Content (kg/m3)
0.03
0.025
0.02
0.015
0.01
0.005
0
Eco Red Shield I
Eco Red Shield II
BluWood
Figure 1. Boron content of three surface treated materials on a kg of boron oxide per
cubic meter of wood basis in a 3 mm deep assay zone.
Boron levels in both Eco Red Shield and BluWood samples are much lower than the
AWPA-specified 1.7 kg/m3 boron oxide level for wood used in UC1 or 2 for termite
protection in areas free of Formosan termites, although the assay zones are very
different. The low levels reflect the limited ability to deliver substantial amounts of boron
to the wood using spray or brief flood treatments. These shallow barriers are more
easily compromised in service and leave little boron reservoir for subsequent diffusion
inward from the surface.
Results and Discussion
Ground Proximity Termite Test
Termites had completely destroyed all of the feeder material placed around the test
specimens after 7, 12 and 18 months of exposure. This indicated that conditions were
suitable for aggressive termite attack over the entire test period. In addition, the covers
had kept the specimens dry, meaning the exposure approximated a UC 2 or UC 3a
exposure.
Untreated Douglas-fir samples experienced heavy attack at the seven-month exposure,
with an average termite rating of 5.53 (Table 2). Two samples were completely
destroyed and another four were near that point. Termite attack continued in the second
round of exposure and only two samples remained from the initial 15. Samples had
average ratings of 1.3 after one year of exposure. Untreated replacement samples
installed at the 12-month point had average ratings of 3.1 six months later, indicating
that termites were still aggressively attacking wood.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 5 All of the attack was from the sides, with no termite attack initiated at the ends at any
time point. This is important because all samples in the first set were end-coated with a
4.8% solution of pentachlorophenol that was intended to limit termite ingress through
exposed cut end-grain. This barrier appears to have worked on otherwise untreated
wood, with all of the attack occurring through the side or wide faces of the blocks.
The observed attack pattern largely eliminates the argument that cutting of the treated
samples negated the protective barrier since the supplemental barrier that was applied
was at least as effective as any of the initial treatments.
Table 2. Condition of blocks treated with various preservative systems and exposed
to Formosan termite attack for 7, 12 or 18 months in Hilo, Hawaii using an AWPA E26
Ground Proximity termite test.a
7 Months
12 Months
18 Months
Treatment
Untreated
Eco Red
Shield I
BluWood
Timbersil
Copper
Azole
Average
Rating
5.53 (2.80)
0.27 (1.03)
Samples
Remaining
13
1
Average
Rating
1.3 (3.3)
0
Samples
Remaining
2
0
Average
Rating
3.1 (3.3)b
0
Samples
Remaining
8
0
4.00 (3.20)
8.40 (2.02)
9.77 (0.37)
10
15
15
0.6 (2.3)
8.0 (3.3)
9.9 (0.3)
1
15
15
1.8 (2.4)c
9.0 (1.1)
9.7 (0.8)
6
15
15
aValues represent means of 15 specimens per treatment. Figures in parentheses represent one standard
deviation.
bNew untreated control samples were installed at 12 months to confirm that termite attack was continuing.
cAdditional BluWood samples that were damaged were installed at 12 months.
Termite attack was heaviest on the Eco Red Shield I blocks at the 7-month point, with
an average rating of 0.27, suggesting this material had little or no resistance to termite
attack. The heavy attack also suggests these samples were preferentially attacked and
all samples were destroyed at the 12-month inspection.
BluWood treated blocks also experienced heavy attack, with average termite ratings of
4.00 and 0.6 after 7 and 12 months, respectively. This result was similar to the rating for
the non-treated Douglas-fir lumber and suggests this treatment had little effect on
termite attack. Only one BluWood sample remained in test after one year, although
several other heavily damaged samples were installed at the 12-month point.
As shown in Table 2, ratings for the BluWood samples actually increased slightly (0.6 at
12 months vs 1.8 at 18 months). Ratings can change since this is a visual assessment
and damage can appear worse than it actually is. The results still indicate that BluWood
had little or no resistance to Formosan termite attack.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 6 Figure 2. Samples treated with Eco Red Shiled II, HiBor or left untreated in the E26
Ground Proximity termite test after installation in June 2015.
Timbersil treated wood has exhibited some resistance to termite attack, with an average
rating of 8.40 after 7 months of exposure. Again, attack did not occur through the cut
surfaces that were end-coated with 4.8% penta. Two specimens had ratings of 4.0, and
another two had ratings of 7; however, four specimens were still untouched by termites.
Sample condition had declined slightly to an average rating of 8.0 at the 12-month mark
with 12 of the 15 samples experiencing some degree of termite attack.
As with the BluWood, Timbersil ratings increased slightly in the 18-month evaluation,
from 8 to 9. As noted earlier, termites have explored the majority of samples; however,
their attack has not progressed further. These results indicate that properly treated
Timbersil does have some resistance to termite attack.
Copper Azole (CA-C) treated blocks provided the best protection against termite attack
with average ratings of 9.77 after seven months. However, some of these blocks
experienced slight attack, with two blocks rating 9.0. Interestingly, the attack was
initiated at incision points, which likely provided shelter for foraging workers although
the incisions also are likely to contain higher loadings of preservative.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 7 Ratings at 12 months were slightly higher than those from the 7-month inspection (9.9
at 12 months vs 9.77 at 7 months). Inspections were carried out without knowledge of
the prior ratings. Thus, it is possible to have slight variations in ratings over time. The
condition of the Copper Azole-treated samples had not changed after 18 months of
exposure.
Ground Proximity Decay Tests
Samples exposed in the Ground Proximity test look like they have been heavily
colonized, but have not yet begun to show substantial fungal attack (Figure 3).
Untreated Douglas-fir heartwood controls had average ratings of 9.9 with only spots of
decay on the edges of the samples (Table 3). All of the treated blocks had ratings near
those of the control.
One interesting observation was the extreme weight of the Timbersil treated samples.
These blocks were extremely hygroscopic. It is unclear how this water retention will
affect performance.
Table 3. Condition of various wood samples exposed to fungal attack in an AWPA
E18 Ground Proximity test for 18 months in Hilo, Hawaii.
Treatment
Average Conditiona
Control
9.90 (0.20)
Eco Red Shield I
9.86 (0.20)
BluWood
9.90 (0.20)
Timbersil
9.90 (0.20)
Copper Azole
9.98 (0.08)
aSamples
were visually assessed on a scale from 10 (no damage) to 0 (complete failure). Values represent means
of 35 samples, while figures in parentheses represent one standard deviation.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 8 Figure 3. Example of an E18 Ground proximity decay test prior to the 18-month
assessment.
Above Ground Sandwich Test
As with the Ground Proximity decay tests, the sandwich samples were UV degraded on
the upper surfaces, but there was no evidence of fungal attack on any of the samples
after 7 or 12 months (Figures 4 and 5).
The sandwiches were disassembled after 18 months of exposure (Table 4). Untreated
Douglas-fir samples had average ratings of 9.9 as did the BluWood and Timbersil
treated samples. As with the Ground Proximity decay tests, the Timbersil samples were
water-logged and there was evidence that fibers were flaking off the upper, ultraviolet
light exposed surfaces (Figure 6). The Copper Azole-treated samples had no evidence
of decay and had an average rating of 10 (Figure 7).
The Eco Red Shield I treated samples had a slightly lower rating than either the controls
or the other treated samples; however, virtually every middle sample in the sandwiches
treated with this system had evidence of fungal attack. While this attack had not yet
progressed to an advanced stage, the samples had pockets of bleaching and fungal
mycelium on the surfaces between the sandwich pieces (Figures 8-10). These results
suggest the Eco Red Shield I material has begun to experience active fungal attack.
One BluWood sample also exhibited evidence of decay on the middle board of the
sandwich (Figure 11).
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 9 Table 4. Condition of various wood samples exposed for 18 months as sandwiches in
an above ground test in Hilo, HI
Treatment
Average Condition
Control
9.90 (0.23)
Eco Red Shield I
9.47 (0.27)
BluWood
9.90 (0.18)
Timbersil
9.90 (0.18)
Copper Azole
10.00 (0.00)
aSamples
were visually assessed on a scale from 10 (no damage) to 0 (complete failure). Values represent means
of 10 samples, while figures in parentheses represent one standard deviation.
Figure 4. Example of an above ground sandwich test after 18 months of exposure in
Hilo, HI.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 10 Figure 5. Samples of Eco Red Shield II, HiBor and untreated Douglas-fir at time of
exposure in June 2015.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 11 Figure 6. Middle sample of a Timbersil treated wood sandwich showing extensive water
logging and loss of fibers near the upper, UV exposed surface after 18 months of
exposure.
Figure 7. Middle piece of a Copper Azole-treated wood sandwich showing wetting but
no evidence of fungal attack after 18 months of exposure.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 12 Figure 8. Example of the middle sample of an Eco Red Shield I sandwich showing
fungal bleaching on the wood surface after 18 months of exposure.
Figure 9. Samples of Eco Red Shield I from the Sandwich test showing evidence of
bleaching on the wood surface as well as extensive fungal mycelium after 18 months of
exposure.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 13 Figure 10. Middle sample of an Eco Red Shield I sandwich assembly showing evidence
of fungal attack and softening on the wood surface after 18 months of exposure.
Conclusions
Copper Azole provided the best termite resistance in the short-term exposure, while
Timbersil was slightly less effective. Eco Red Shield I and BluWood both failed to
provide any Formosan termite protection. There was only slight evidence of decay in the
Ground Proximity test, but decay had become evident in samples exposed as
sandwiches. The decay was most apparent on the Eco Red Shield I samples. These
tests will continue to be monitored.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 14 Figure 11. Middle piece of a BluWood Sandwich showing evidence of fungal mycelium
and some surface bleaching after 18 months of exposure.
References
American Wood Protection Association. 2012. Standard A65-11. Standard method to
determine the amount of boron in treated wood using Azomethine-H or carminic acid.
In: AWPA Book of Standards, AWPA, Birmingham, Alabama. Pages 334-336.
American Wood Protection Association. 2012. Standard E18-12. Standard field test for
evaluation of wood preservatives intended for Use Category 3B application exposed out
of ground, uncoated ground proximity decay method. In: AWPA Book of Standards,
AWPA, Birmingham, Alabama. Pages 480-484.
American Wood Protection Association. 2012. Standard E26-10. Standard field test for
evaluation of wood preservatives intended for interior applications (UC1 and UC2):
Termite ground proximity method. In: AWPA Book of Standards, AWPA, Birmingham,
Alabama. Pages 514-520.
Performance of Selected Wood‐Protection‐Coated Lumber Products in Hilo, Hawaii 18‐Month Report, August 2015 Page 15