Research
on Treating Wood window Joinery with Impel Rods.
This is a condensed version
of a rather lengthy technical paper. Out of respect for the authors, we are only
publishing parts of this paper. For a full copy, contact the Forest Products Research
Society at (608) 231-1361
Fused borate and bifluoride remedial treatments for controlling
decay in window millwork.
By
Mark G. Dietz and Elmer L. Schmidt
Abstract
Conventional
ponderosa pine window millwork was subjected to basidiomycete
decay by inoculation with a brown-rot fungus and sampled for viable fungus
before and 8 months after remedial preservative treatment. Treatments applied
were fused disodium octaborate rods (Impel) at boric acid retention levels
of 1.5 and 4.0kg/m3 . The elimination of decay fungus after remedial treatment
was nearly 100 percent effective in all treated material regardless of remedial
treatment used or chemical loading. By contrast, isolation frequency of
decay fungi in the control samples increased from 27 to 69 percent. Color
reagent dye testes for diffusion indicated excellent distribution of chemical
in wood material where moisture contents exceeded 25 percent. Substantial
savings to the consumer in labor and material costs could be realized when
compared to current repair or replacement methods. Research should continue
on the use of these treatments in forest products where wood moisture contents
may occasionally favor attack by wood decay fungi.
Increasing
awareness of premature failure in window millwork due to the biodeterioration
effects of wood decay fungi (11,16,20,23) has led to the search for reliable fungistatic
remedial treatments to be utilized in situ to arrest or inhibit decay activity
(8,9,16,19,22). Various reasons have been cited for these failures, the primary
reasons are related to the failure to keep wood dry in service, or more importantly,
the lack of proper preservative treatment prior to installation (3,16,22,23,25,28).
While pretreatment of most millwork
components with a water-repellent wood preservative at the point of manufacture
is quite common today (12,18), certification of compliance with industry
standards by official test methods was not actively promoted in the United
States until the early 1950’s (15). Industry representatives estimate that
prior to this time, 20 to 50 percent of all window millwork components may
have been produced without preservative treatment. Moreover, while current
standards set minimum requirements for the preservative solution in terms
of its formulation, penetrability, and water repellence, they do not address
specifically the amount of preservative retention. Also, due to recently
enacted environmentally related Hazard restrictions of the use of pentachloropherol
(penta) in the United States, a number of new preservatives have been put
into use for millwork treatment for which no long-term performance records
are available. Should these begin to fail, as has been cited with one widely
used penta alternative (7), the necessity for a proven remedial treatment
would be enormous.
Replacement
of defective millwork is quite labor intensive and costs are often
prohibitive (24). The common practice of excavating decay and filling the void
with putty is more a cosmetic solution rather than a corrective solution of reasonable
duration. Remedial preservative treatments of window millwork components may therefore
prove useful as an alternative solution to replacement or temporary repair methods
by decreasing the labor and material costs of maintenance and repair. Implementation
and subsequent inspection of these treatments could easily be made part of a routine
periodic maintenance program (e.g. painting).
Past
experiences with fluoride
and boron compounds has documented their ability as wood preservative
chemicals (4,6). Field and laboratory studies in other countries have examined
two recently developed remedial treatment products based on these chemicals:
1) a fused crystalline borate rod (Impel ) available in the United States
from CSI, Charlotte, NC; and 2) a liquid bifluoride injection (IMPROSOLâ
). The borate rods have shown potential as a remedial treatment for window
joinery components of Scots pine (pinus sylvestris L) in Sweden (9) and
door joinery of western hemlock (Tsuga Heterophylla [ Raf.] Sarg.) In England
(8). A Canadian study demonstrated the effectiveness of a boron diffusion
treatment to control decay in western hemlock and amabilis fir (Abies amabilis
[ Doug] . Forbes) lumber (21)
|
A study in the United States of the effectiveness
of boron rods in protecting Douglas-fir (Pseudotsuga menziesii [ Mirb.] Franco)
pile cutoffs has shown positive results (14). Similar studies to assess the potential
for the use of bifluorides as remedial treatments have demonstrated success on
spruce (Picea spp.) window joinery in the Netherlands (19), and as a liquid brush-on
application for hardwoods and softwoods in the United States (13,14).
Studies in the United Kingdom (8,26) have
shown that the diffusion of boron is greatest in wood most at risk to decay (i.e.,
joint areas with exposed end grains and with the highest moisture contents). This
relationship between moisture content (MC), wood volume, and remedial treatment
must be understood in order to use these treatments effectively.
To date, comparative studies and verification
of the efficacy of such treatments on window millwork are lacking in the United
States. While diffusion rates of boron in the various species of pine are considered
similar (27), individual component sizes for millwork are of smaller dimension
in the United States than abroad. This may create differences in the distribution
of active ingredients of remedial treatments, and therefore, differences in efficacy.
Also, the predominant mode of construction in the United States is wood-based
frames and exteriors, whereas in Europe, masonry is more common in building construction.
This practice of building with masonry creates considerable changes in the relative
MC of in-use millwork components (11,28) by causing moisture exchanges between
interior and exterior spaces that take place primarily through the window joinery
(11). On the average, this joinery exhibits a higher MC than is found in similarly
exposed joinery in a building with a wood-based frame, thus increasing the diffusion
potential for remedial preservatives in wood that is associated with masonry-based
construction.
To test the efficacy of these remedial treatments
to inhibit decay in windows, a study was conducted in a controlled greenhouse
environment, on a predominantly utilized and locally available wood species.
Results
and Discussion Diffusion
Study
Initial
MCs at the time
of chemical deposition averaged 36 percent (ovendry basis) in the heartwood and
41 percent in the sapwood, indicating that the free water necessary for chemical
diffusion was present in the wood material. Previous studies (9,19) indicated
that at least an inhibition concentration should be attained within 9 months in
the sapwood portion of the millwork. Edlund’s (9) tests also showed that this
concentration was reached in Scots pine at 11 to 12 cm from the side of deposition
at 9 months. Given the initial loadings of preservative used, the dye tests (2,5)
were capable of portraying inhibition concentrations in the ponderosa pine millwork.
Borate diffusion results at 6.5 months show
average diffusion distances longitudinally of 82 mm in painted sapwood material
and 95mm in unpainted sapwood, with an average 0.5g of residual chemical. Diffusion
was significantly less in heartwood samples (46mm for painted; 68mm for unpainted).
Across grain diffusion averaged 29 mm, regardless of wood type or surface coating.
Based on the remaining chemical, it is assumed that coverage in ponderosa pine
would be equal to that of Scots pine after 9 months.
Within the IMPROSOL treated samples, the statistical
results were nonsignificant for apparent coverage differences, either longitudinally
or across the grain regardless of surface coating or sapwood/heartwood composition.
As noted in earlier reports (4,19) diffusion appears to be fairly rapid and lasting
within a zone of application, although this test was of too short a duration to
assess the permanence of the treatment.
Conclusions
Both
the IMPEL rods and IMPROSOL
injection treatments (at treatment loadings of 1.5 to 4.0 kg boric acid/m3 IMPROSOL,
respectively) were very effective in eliminating established decay in wood windows,
indicating their potential usefulness as remedial treatments. Diffusion of boron
longitudinally from IMPEL rods was more extensive, over a given time of incubation,
in sapwood than heartwood, but distributions were not significantly affected by
painting. The potential shortcomings of crystal blooming and glass etching (reported
for some fluorides (19) but not evidenced in this study) are not really problematic
in service. The usefulness of IMPEL rods and IMPROSOL injection as remedial preservative
treatments appears promising. Further applications in wood not exposed in a constant
high moisture hazard (leaching) situation should be investigated. Busan 1009 seems
to be as effective as penta in preventing decay in the greenhouse accelerated
decay hazard environment.
|
|
