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(Return to the List of Articles)
"Finishability of CCA
Pressure-Treated Wood"
Joint Coatings/Forest Products Committee
Chairman: Alan Ross, Kop-Coat, Inc., Pittsburgh, PA
(1-412-826-3387) George Daisey, Rohm & Haas Company,
Springhouse, PA Charles Jourdain, California Redwood Association,
Novato, CA Sam Williams, USDA Forest Products Laboratory,
Madison, WI
Introduction..........(Return to
Table of Contents)
Preservative pressure-treated wood has been in commercial use in
the United States for over a hundred years. Today it is widely
used in such applications as utility poles, railroad cross-ties
and marine pilings. However, the greatest growth of
pressure-treated wood in the past fifteen years has come in the
residential and commercial decking market (1,2).
Most of the pressure-treated wood used in decking and other home
construction projects is factory treated with chromated copper
arsenate, more commonly known as CCA. Lumber which has been
treated with CCA bears the familiar green to light brown
appearance and is imparted with a resistance to decay and insects
which provides an almost indefinite service life. Originally,
manufacturers of CCA-treated wood promoted their lumber as a
"maintenance free" product. However, it was soon
recognized that preservative treatment alone did little to
address the important performance proper ties of surface
appearance and dimensional stability. Consumers realized that the
aesthetic appearance of their decks was just as important to them
as the long-term structural integrity.
Thus, a need arose for the development of surface finishes for
CCA-treated wood which could address the special requirements of
this substrate and provide protection against the ravages of
water, sunlight, mildew and other aspects of weathering and wear.
Initially, this need was not addressed; most wood preserving
companies had little expertise in surface finishes and most
coatings manufacturers saw the CCA-treated lumber market as too
narrow to justify major product development efforts. As a
consequence, "all-purpose" type products were sometimes
shoe-horned into the CCA deck category with less than optimum
performance results.
In the past few years, however, the dialogue between the wood
preserving and coatings industries has improved significantly and
there are now several quality finishes on the market designed
specifically for use on CCA-treated lumber. The challenge today
is to communicate to consumers, contractors and architects the
special requirements of coatings for CCA-treated lumber and the
proper techniques for their application.
CCA Treatment of Wood..........(Return to
Table of Contents)
What Pressure Treatment Does to Wood
Today most CCA is composed of a mixture of the oxides of
chromium, copper and arsenic. Each component has a specific
function-copper as a fungicide, arsenic as an insecticide, and
chromium as the bonding agent which "fixes" everything
to the wood. The CCA treating mixture is supplied to the treating
plant as a liquid concentrate. It is diluted with water to the
appropriate level and then injected into the wood under high
pressure in large, steel treating cylinders. After the wood has
taken up all of the treating solution it can absorb, the pressure
is removed and a short vacuum is applied to pull off any excess
liquid. The wood is then air dried or kiln dried before shipment
to the lumber yard.
Once inside the cellular structure of the wood, the CCA treating
solution undergoes a complex series of chemical reactions with
the major wood components-cellulose, hemicellulose and lignin
(3). These reactions result in a bonding of the CCA ingredients
to the wood fibers, rendering these chemicals insoluble and
resistant to water-leaching. Although the original treating
solution is a hazardous substance, the level of fixation of CCA
to the wood is so strong that the resulting treated wood is safe
to handle and use around the home. It is not classified as a
hazardous substance.
Since CCA treatment involves both the physical process of
pressure impregnation and the chemical process of fixation, it is
not surprising that the wood itself is both physically and
chemically affected.
In order to accept the preservative solution, green lumber is
usually dried to a moisture content of 25 percent or less. This
is accomplished by either kiln drying or air seasoning. During
treatment the wood fiber becomes completely saturated with the
preservative solution, which is mostly water. After the treating
process is complete the wood is still virtually 100 percent
saturated with water.
The highest grades of treated wood are kiln dried after treatment
to bring the moisture content down to 19 percent or less.
However, it is more typical to allow the wood to air dry to reach
equilibrium moisture content. In some cases treated wood will
reach the lumber yard while still very wet. Although the
preservative itself is fixed to the wood, excess residual
moisture can have a negative effect on finishability of
subsequently applied coatings.
The treating cycle of drying, saturating and redrying has a
marked physical effect on the wood. Internal stresses from
localized areas subjected to alternating shrinking and swelling
can result in cracking, checking, splintering and grain raising.
Chemical interactions of CCA with the wood also result in
changes. In general, the wood becomes weaker and more brittle,
again giving rise to splintering and cracking.
Thus, while CCA treatment renders wood resistant to decay and
insect attack, it also causes changes in the wood structure which
affect its physical properties and its finishability.
Grades and Species of Treated Wood
Many types of softwood can be pressure treated with CCA
preservative; however, the species most commonly treated is
southern yellow pine. In the West, hemlock, hem, fir, ponderosa
pine, jack pine and red pine are also subject to CCA treatment.
Some species, such as Douglas-fir, have difficulty accepting
waterborne treatments; these are said to be refractory. In order
to promote penetration of the preservatives, these woods are
sometimes mechanically incised before treatment. Treated lumber
will then have the characteristic rows of incising marks.
Redwood, cedar and most hardwoods are not normally pressure
treated with wood preservatives.
The standards setting organization for pressure-treated wood in
the United States is the American Wood Preservers' Association
(AWPA), and the primary specification governing treated lumber is
AWPA Standard C-2 (4). This standard sets the requirements for
preservative level in the wood, depth of penetration, species
which may be treated, and other important treating parameters.
Adherence to standard is checked via third party inspection at
the treating plant. Those treaters who consistently meet the AWPA
standard are allowed to display the AWPA mark on their lumber,
along with that of the third party inspection agency.
Treated lumber will also often bear a grade stamp and a mark
designating the level of CCA treatment. Grade stamps are similar
to those for untreated lumber. CCA level is listed as a retention
number which represents the pounds per cubic foot (pcf) of
preservative in the wood. For aboveground applications the
specified retention of CCA is 0.25 pcf, for ground contact uses
it is 0.40 pcf, and for treated plywood it is 0.60 pcf.
Preservative-treated Plywood
Plywood used in most construction applications requires no
preservative treatment. However, in certain uses and climates it
may require the protection from fungi and insects provided by
preservative pressure treatment. The most prominent use of
preservative-treated plywood is in permanent wood foundations.
In addition to CCA, two other waterborne inorganic preservatives
can be used to treat plywood for permanent wood foundations.
These are Ammoniacal Copper Arsenate (ACA) and Ammoniacal Copper
Zinc Arsenate (ACAZA). Required preservative retention for all of
these treatments is 0.60 pounds per cubic foot, which is 50
percent higher than the code requirements for normal ground
contact applications.
The finishing requirements and performance characteristics for
ACA and ACZA are generally similar to those for CCA. All of these
preservatives are readily paintable when dried after treatment.
The American Plywood Association has several publications
available (5-7) concerning the finishing of plywood treated for
use in permanent wood foundations.
Advantages of Coating
CCA-Treated Wood..........(Return to Table of Contents)
Coating CCA-treated Wood
Wood which has been pressure treated with CCA can be used in a
variety of applications in residential and commercial
construction. Most commonly it is used for decking and railing,
but it also finds application in lattice work, permanent wood
foundations, docks, gazebos, playground equipment and similar
wooden structures. In all of these uses the appearance of the
wood can be enhanced and protected by the application of a
surface coating of paint, stain or water repellent. Unlike most
other wood preservatives, CCA readily accepts coatings and can
actually help to increase the service life of some finishes.
Enhancement of Appearance
CCA treating solution is light yellow in color and when the wood
comes out of the treating cylinder it also has a light yellow
color. However, within a few hours of treatment the wood's
appearance changes to its well known flat greenish hue. While
this is pleasing to some users, many prefer to have a more
natural cedar, redwood or driftwood appearance to their wood.
Coating with protective stains or wood "toners" is the
best way to accomplish this. Toners are generally more
transparent than stains and they highlight the wood grain.
Finishing with any of these coatings will provide a more even
appearance to the treated wood, since board-to-board color
variations are not uncommon with CCA treatment.
Protection
As noted previously, pressure treatment with CCA provides wood
with long term resistance to decay and insects but it does little
to protect wood from the effects of the elements-rain, snow,
sunlight and mildew. The best way to protect against these
enemies of wood is with properly designed and applied wood
coating systems. The ideal finish will have water repellent
properties to protect against rain and snow, contain pigments or
UV absorbers to resist sunlight, and be fortified with
mildewcides to resist surface molds and stain.
Problems in Coating
CCA-Treated Wood..........(Return to Table of Contents)
Unlike most other wood preservatives, CCA does not adversely
affect wood finishes. It not only readily accepts most coatings,
but it has been shown to enhance the service life of paints,
stains and water repellents (8). In spite of CCA-treated wood's
general compatibility with most coatings, there are some
potential problems which users need to be aware of.
Lack of Penetration
Many types of nonfilm-forming wood finishes such as stains and
water repellents must be able to penetrate the wood's surface in
order to work effectively. The presence of 0.25, 0.40, or even
0.60 pounds of CCA per cubic foot of wood is not sufficient to
hinder penetration. However, excessive moisture, which can be
present if treated wood is not sufficiently dried, can impede
penetration of these finishes. Lumber that is saturated with
water should be allowed to air dry before coating is attempted.
In most cases 2-3 weeks of seasoning in dry weather should bring
the moisture or content down to an acceptable level.
Substrate Limitations
Southern yellow pine, as previously mentioned, is the most common
species subject to treatment with CCA. It is a relatively
permeable wood with wide latewood bands and flat-grained
characteristics (9). While these properties enhance the
treatability of southern yellow pine, they work against it as a
coatings substrate.
In general, this type of wood has poorer finish-holding
capabilities than species such as cedar and redwood. However,
these deleterious effects are somewhat offset by the
performance-enhancement properties of the CCA.
Color Bleed-through
CCA-treated wood will take on a color of anywhere from a light
brown to a bluish-green. The color is a consequence of the
reaction of the treating chemicals with the wood components.
Since wood is tremendously variable, the color of CCA-treated
wood can vary significantly from board to board and sometimes
even within the same board. As might be expected, application of
a clear or lightly pigmented finish will do little to mask the
color or even-out the appearance. In light colored coatings the
CCA green will appear to "bleed-through" the finish.
This is not a physical bleeding of the treatment but, rather, an
optical show-through effect. The use of darker colors, more
opaque finishes and/or a second coat can reduce or eliminate the
green show-through and even-out the substrate appearance.
Products Used to Coat
CCA-Treated Wood..........(Return to Table of Contents)
For Decks
The majority of CCA-treated wood in home construction goes into
decks. Most paints, varnishes, and solid color stains are not
recommended for exposed horizontal deck surfaces,
pressure-treated or untreated. Because they are film-forming
coatings they have a tendency to peel, blister and mar when
coated on horizontal substrates subject to weathering and
traffic.
Clear or pigmented water repellents, wood toners and
semi-transparent stains are the finishes most often used on
either treated or untreated decks. In order to work properly they
must be able to penetrate the surface. Due to the permeability of
pine this is usually not a problem.
For Other Surfaces
CCA-treated wood is compatible with most coatings products. Solid
color stains and paints can be used successfully on vertical
surfaces such as siding, trim, plywood foundations and lattice
work. Both solvent-borne and waterborne coatings can be used to
finish CCA-treated lumber. With the increased emphasis on
VOC-compliant coatings, several waterborne stains and water
repellents have recently been introduced for use on
pressure-treated wood.
Test Methods for Evaluating
Performances of Finishes..........(Return to Table of Contents)
Finishes for CCA-treated wood can be evaluated by the same
standards and test methods used for other types of coatings.
Water Repellency
This is an important property due to the need to protect
CCA-treated wood from the absorption of water which can cause
splitting, checking and warping. A widely used industry standard
for water-repellent effectiveness is Federal Specification
TT-W-572B (10). The water-repellent effectiveness of a coating is
evaluated on a device called a swellometer which measures the
amount of water taken up by a coated end grain wafer of Ponderosa
pine. It is expressed as the percentage of water repelled in the
coated sample compared to that of an uncoated control. To meet
the specification, a coating must have a water-repellent
effectiveness of at least 60 percent.
Mildew Resistance
Although CCA treatment protects lumber from decay, it provides
little resistance to surface molds and mildew. These fungal
organisms can deface both the surface of the wood and the
coatings themselves. Thus, it is important that finishes for
CCA-treated wood contain additives which control the growth of
mildew. Mildew resistance of coatings can be evaluated both in
the laboratory and in field exposures.
In a typical laboratory mildew test such as ASTM D3930 (11), a
sheet of filter paper coated with the finish under evaluation is
placed in a petri dish in a nutrient medium consisting of
potato-dextrose agar. The paper is then inoculated with a
concentrated sample of mildew spores and allowed to incubate for
a week at 85°F and 90% relative humidity, ideal conditions for
mildew growth. If the finish is mildew resistant, the fungi will
grow on the surrounding nutrient but not on the coated paper
itself. If it is not resistant, the coated paper will exhibit
mildew growth. Variations of this method using wood wafers as the
substrate are also utilized.
Outdoor field exposures are another way of evaluating the mildew
resistance of coatings for CCA-treated wood. Though they take
longer than laboratory tests, they are usually more meaningful
since they take into account the effects of sunlight and
weathering which can degrade many mildewcides. Wood panels or
boards are coated with the products under test and placed on
exposure outdoors. To speed up results they are often placed on
racks facing south at a 45 degree angle for maximum sun exposure.
In addition, mildew exposure tests can be run in tropical or
subtropical environments, such as Florida or Puerto Rico, to
further accelerate mildew growth.
Weathering Resistance
This is an important property for any exterior finish. In the
laboratory, artificial weathering machines are used to evaluate
the performance of finishes over CCA-treated wood (12-15).
Generally, these are cabinets containing a source of artificial
sunlight such as a carbon arc, a Xenon arc or fluorescent UV
lamps, along with spray heads to simulate rainfall and humidity
cycles. Coated CCA-treated panels are placed in these machines
and exposed over periods ranging from 200 to 2000 hours. Coating
performance is periodically evaluated for fading, erosion,
peeling and discoloration and is compared to that of panels
coated with known controls. This technique is most useful as a
comparative method for evaluating performance of coatings.
Generally, it is not successful as a means of predicting
long-term coating durability in service. For that purpose
exterior weathering is preferred. Exterior weathering performance
is evaluated on outdoor test panels in a manner similar to that
for the outdoor mildew tests described above. Since sunlight
plays a major roll in coatings failure, accelerated testing is
often conducted by having exposures in high sunlight level
climates such as Arizona and Florida. It can take 1-2 years
before long-term coating performance can be adequately evaluated
for water repellents, clear finishes and semi-transparent stains.
For paints and solid color stains, test periods of five years and
longer are sometimes needed to separate excellent from average
finishes.
Field Testing
The ultimate performance evaluation of any finish is on actual
exposure in the end use for which it is intended. Since most
finishes for CCA-treated wood are used on decks, it is critical
that new products be thoroughly evaluated on deck exposure. This
is a harsh environment for most finishes; many products which
perform adequately on siding will fail much sooner on decks. In
addition to the horizontal surface, which maximizes exposure to
sunlight, rain, snow and standing water, deck coatings are
subject to abrasion from foot traffic, which can also lead to
premature failure.
Costs..........(Return to
Table Contents)
The cost of a CCA-treated wood deck is a significant investment
for most builders and homeowners. Although several brands of
treated wood are now available with long-term warranties against
decay and insect attack, this material is still subject to water
damage and defacement from sunlight and mildew. Thus, many
consumers find it prudent to protect and beautify their deck
investment through the use of a protective surface finish. As
with most painting projects, the majority of the cost in
finishing CCA-treated lumber is in the labor of application
rather than in the materials. Labor costs will vary depending
upon the condition and design of the deck, its location, and
local market conditions. Typically, the cost (1990) for surface
preparation and coatings application is on the order of $1.00 to
$1.50 per square foot of deck surface. Thus, the labor to prepare
and finish a 300 square foot deck would range from $300 to $450.
Obviously, this overshadows the cost (1990) of materials, which
for the approximately two gallons of coating needed for this
deck, could run anywhere from $20 to $50 ($10 to $25 per gallon).
From the example above, it should be clear that the use of
premium performance finishes is the most economic course of
action. An additional $30 investment in premium quality materials
will likely result in increased service life and thus longer time
until recoat, thereby providing reduced maintenance costs. For
this reason, the use of quality products specifically designed
for pressure-treated decks, though possibly more expensive than
all-purpose coatings, is more cost effective in the long run.
Do-it-yourselfers, who make up a large portion of deck-care
finish users, do not have direct labor costs. However, they
should consider the costs involved in their own time and effort
to apply coating products. Again, the up-front investment in a
higher quality finish will have an ultimate payback of longer
time until recoat and less need for maintenance.
Painting contractors also need to consider the consequences of
using less expensive, lower quality deck coatings. Ultimately,
these can lead to complaints, re-do expenses and the hidden cost
of lost sales.
Performance Expectations..........(Return to
Table of Contents)
As noted previously, CCA-treated wood is mainly used in home deck
construction, and wood decks are one of the more difficult
substrates to adequately protect. The major performance
expectations for these coatings are aesthetic appearance and
durability-protection of the wood from the effects of water,
sunlight and mildew.
Depending upon exposure, application technique and deck use
conditions, water repellents and clear finishes can perform for
up to two years before the need to recoat. Since these are
transparent finishes, application is usually easy, requiring no
more than 1-2 hours for the typical deck.
Pigmented stains are more heavy-duty products designed to last up
to four years on exterior deck surfaces. They are a little more
difficult to apply than clears and thus will require slightly
longer application times.
A successful coating will provide the CCA-treated wood deck with
water repellency, mildew resistance, and resistance to graying
from sunlight. In addition, pigmented finishes will provide color
retention and will help resist peeling or marring.
All finishes for decks should have good recoatability. This means
that when it's time to reapply, surface preparation will be
minimal and the new coating will have good compatibility with and
adhesion to the finish on the deck. In the past, some coatings
manufacturers and painting contractors have expressed concern
about the ability of CCA-treated wood to accept most finishes.
However, a recent investigation at the U.S. Forest Products
Laboratories (8) has demonstrated that CCA treatment not only
does not interfere with coating performance but, in fact, it
enhances the service life of most surface finishes. The study
showed that clear water repellents, semi-transparent stains, wood
toners and even paints all performed much better on CCA-treated
wood than they did on untreated lumber of the same species. Thus,
owners of CCA-treated wood decks can expect excellent performance
and service life from high quality deck finishes.
Field Hints..........(Return to
Table of Contents)
For the most part, finishes for CCA-treated wood can be applied
in the same manner as coatings for any exterior wood substrates.
However, there are a few field hints which are especially
important for CCA-treated wood and the products applied over it.
Surface Preparation
Proper surface preparation is an important factor in the ultimate
performance of coatings for pressure-treated wood or any wood
surface. Surfaces should be clean, dry, and free of mildew before
coatings are applied. Recommendations for preparing the wood are
usually found in the label directions on the coating containers.
While bleach, cleansers and trisodium phosphate are sometimes
suggested for preparing weathered wood, many manufacturers are
now recommending the use of one of several deck brightener and
wood restorer products which have recently become available. Most
of these products are specifically designed to renew the surfaces
of weathered decks and prepare them for subsequent coatings
application. The better deck preparation products will remove
dirt, mildew, grayed wood, loose fibers and coating particles in
one step. As always, label instructions regarding safety and
environmental concerns should be closely followed.
Weathering or Seasoning
Contrary to the belief of many consumers and paint companies, it
is not necessary to allow newly installed pressure-treated wood
to weather or season for long periods of time before applying a
coating. Most newly built CCA-treated wood decks can and should
be protected with a water repellent, toner or semi-transparent
stain as soon as possible after construction. Recent research
(16,17) has shown that exposing unprotected wood to weathering
for even short periods of time can cause surface damage. This
damaged surface reduces the ability of the wood to hold onto
subsequently applied coatings-a situation that can ultimately
lead to premature coatings failure. Thus, unless the new treated
wood is still very wet, it should be coated as soon as possible
after deck construction. If the wood is obviously wet, no more
than 2-3 weeks of air-drying should be allowed before a coating
is applied.
Over-application
A major source of problems and complaints for all wood finishes
is over-application of the coating. Many do-it-yourselfers and
some painting contractors believe that when it comes to coating,
more is better. This is simply not the case and is particularly a
problem for decks. Most deck finishes are designed to penetrate
the surface of the wood. Putting too much of these coatings on
the wood leads to a buildup of material, forming a film which can
ultimately peel or crack. For water repellent products,
over-application can result in a surface that is overly waxy,
sticky, or slick. Over-applied stains will often result in sticky
surfaces, since the coating buildup interferes with their ability
to dry properly.
In all cases it is important to follow the manufacturer's label
suggestions regarding coverage. Rough sawn surfaces are able to
absorb more coating than smooth sawn substrates. However, since
most CCA-treated wood will have a smooth surface, particular care
should be taken against putting too much material on it. One coat
is usually sufficient for most deck finishes. If two coats are
desired, it is important to be sure that the first coat properly
penetrates the surface before the top coat is applied.
Application Methods
Coatings for CCA-treated wood can be applied by a variety of
methods including brush, spray, roller and pad. Brushing is
considered to be the best technique for detail work such as
spindles and railings. However, for large horizontal deck
surfaces spray application is quickest and easiest. Either
airless power sprayers or pump hand-held sprayers can be used. It
is important when spray applying pigmented finishes to back-brush
the wet coating with a brush or push-broom. This evens-out the
finish and eliminates drips and lap marks. Pads are also well
suited to coat CCA-treated decks. Individual boards should be
coated along their entire length to prevent lap marking. Paint
rollers are more suitable for applying siding finishes than for
deck coatings. However, they can be used successfully to apply
clear finishes and water repellents to CCA-treated decks.
As for most exterior coatings, it is vital that deck finishes be
applied under proper weather conditions. Solvent-borne coatings
are a bit more forgiving than water-based formulations and can
usually be applied when outside temperatures are in the range of
40-90°F. Water-based products should not usually be applied if
outside temperatures will fall below 50°F in the 24 hours after
application. Deck coatings ideally should not be applied if
precipitation is forecast for the 12-24 hour period after
coating. This will prevent the possibility of water spotting or
wash-off. Once they dry, of course, these finishes will be
resistant to precipitation.
Label Instructions
Since each commercial formulation is a little different, the
manufacturer's label instructions should be consulted and
understood before the product is used. This is important not only
from an application and performance standpoint but also with
regard to user safety and environmental considerations.
Unfortunately, many consumers fail to read the product label
until after they experience a problem, at which point it may be
too late for easy corrective action.
Research Needs
The paint industry and the forest products industry have
independently conducted quite a bit of research over the years in
the respective areas of coatings and wood treatment. However,
relatively little work has been done in the area of coatings for
treated wood itself. The U.S. Forest Products Laboratory in
Madison, Wisconsin has carried out a large portion of the work in
this field (18). In the previously mentioned study evaluating the
performance of a variety of finishes on untreated wood versus
CCA-treated wood, the CCA treatment was shown to enhance the
service life of subsequently applied coatings. In almost every
case, coating performance over CCA-treated pine and hemlock
exceeded that of the same coating on untreated pine and hemlock.
A second phase of this project is just beginning. It will
evaluate some of the newer VOC-compliant coatings over
CCA-treated versus untreated wood.
One significant research need is the development of coatings
which would provide even greater dimensional stability to
CCA-treated wood than can be obtained with current water
repellents or stains. CCA-treated pine readily absorbs water
which can lead to cracking, warping, grain raising, etc. Most
surface coatings today will provide some measure of protection,
but the internal stresses on the wood are so great that cracking
and checking will ultimately occur. Thus, there is a need for
coatings products which can penetrate further into the wood and
interact with it to provide enhanced dimensional stability.
Manufacturers of treated wood have begun to address some of the
performance issues of their products by incorporating water
repellent and mildew resistant additives into the wood during the
pressure treatment process. These ingredients provide initial
protection that may last from a few months to a few years.
Ultimately, treatment with surface coatings is required to
provide ongoing protection. There is a need to evaluate the
performance of surface finishes over these newer treated wood
products.
Conclusion..........(Return to
Table of Contents)
Preservative pressure-treated wood is a valuable and widely used,
especially in the growing area of home deck construction. While
the CCA treatment provides long term protection to the wood
against decay and insect infestation, it is not very effective in
resisting damage and defacement from the effects of water,
sunlight, temperature variation and mildew. Surface finishes go a
long way toward providing this protection and they can also
improve the aesthetic appearance of CCA-treated lumber.
Most exterior wood coatings products are compatible with
CCA-treated lumber. The treatment does not interfere with
coatings compatibility unless the wood is coated before it is
adequately dried from the moisture introduced during the treating
process.
In that case an air drying period of 2-3 weeks during dry weather
is usually sufficient to allow for successful finish application.
There is now evidence that CCA treatment actually enhances the
performance of subsequently applied finishes.
Critical factors for successful finishing of CCA-treated wood are
proper surface preparation, correct application procedures and
correct coverage rate. As with many finishes, more is usually not
better and over application can lead to early coatings failures.
Timely application of protective finishes to new CCA-treated wood
is an important consideration. Allowing new wood to weather or
season for more than 2-3 weeks without a protective finish can
damage the surface to the point where it impairs the performance
of subsequently applied coatings. Thus, most new wood should be
protected with a finish as soon as possible after it is in place.
Finally, since most CCA-treated wood is used in deck
construction, the choice of protective and decorative finishes
which are especially designed for use on decks will provide the
best performance results. These products usually have advantages
over "all purpose" type stains and water repellents in
that they contain ingredients which are specifically suited for
use on decking lumber. Because the major cost of most coatings
projects is in the labor to apply, the use of high quality
premium performance finishes is ultimately more cost effective to
the contractor as well as the do-it-yourselfer.
References..........(Return to
Table of Contents)
1. Ross, A.S., "Preservative Treatments for Wood and
Successful Coating Techniques," presented at Federation of
Societies for Coating Technology Seminar on Coatings for Wood
Substrates, Seattle, WA (1987).
2. Anderson, J.T. and Ross, A.S., "Coatings for Treated Wood
Products," Wood Protection Techniques and the Use of Treated
Wood in Construction, Forest Products Research Society, Madison,
WI (1988).
3. Hartford, W.H., "The Practical Chemistry of CCA in
Service" (and references therein), Proceedings of the
American Wood Preservers' Association, Vol. 82, 28 (1986).
4. American Wood Preservers' Association, "Annual Book of
AWPA Standards," Stevensville, MD (1990).
5. American Plywood Association, "Finishability of Plywood
Treated to the All-Weather Wood Foundation Specifications,"
Report No. PT 82-6, Tacoma, WA (1982)
6. ibid., "Finishing Plywood Treated for the Permanent Wood
Foundation," APA Technical Note L340, Tacoma, WA (1986).
7. Wood Products Promotion Council, "Permanent Wood
Foundation, Guide to Design and Construction," Form No.
A400Q American Plywood Association, Tacoma, WA (1990).
8. Feist, W.C., "Performance of Surface Finishes Over
CCA-Treated Wood," presented at the 43rd Annual Forest
Products Research Society Meeting, Reno, NV (1989).
9. Cassens, D.L. and Feist, W.C., "Finishing Wood Exteriors
- Selection, Application and Maintenance," Agriculture
Handbook No. 647, USA Forest Service, Washington, DC (1986).
10. Federal Specification Wood Preservative: Water-Repellent, No.
TT-W-572B, U.S. Government Printing Office, Washington, DC
(1972).
11. American Society for Testing and Materials, "Test Method
for Mildew Resistance," ASTM D 3930, Annual ASTM Book of
Standards, Philadelphia, PA (1989).
12. ibid., "Standard Practice for Operating Light-Exposure
Apparatus (Carbon-Arc Type) With and Without Water for Exposure
of Nonmetallic Materials," ASTM-G23-81, Annual Book of ASTM
Standards, Philadelphia, PA (1989).
13. ibid., "Standard Practice for Operating Light-Exposure
Apparatus (Xenon-Arc Type) With and Without Water for Exposure of
Nonmetallic Materials," ASTM G26-84, Annual Book of ASTM
Standards, Philadelphia, PA (1989).
14. ibid., "Standard Practice for Operating Light-Exposure
Apparatus (Fluorescent UV-Condensation Type) for Exposure of
Nonmetallic Materials," ASTM G53-84, Annual Book of ASTM
Standards, Philadelphia, PA (1989).
15. ibid., "Standard Practice for Operating Light- and
Water-Exposure Apparatus (Carbon-Arc Type) for Testing Paint and
Related Coatings and Materials," ASTM D822-86, Annual Book
of ASTM Standards, Philadelphia, PA (1989).
16. Kleive, K., "Weathered Wooden Surfaces -- Their
Influence on the Durability of Coating Systems," Journal of
Coatings Technology Vol. 58, No. 740, 39 (1986).
17. Williams, R.S., Plantinga, P.L. and Feist, W.C.,
"Photodegradation of Wood Affects Paint Adhesion,"
Forest Products Journal, Vol. 40, No. 1, 45 (1990).
18. Feist, W.C., "Coatings Research at the Forest Products
Laboratory," Proceedings of the Seminar on Coatings for Wood
Substrates, Federation of Societies for Coatings Technology,
Seattle, WA (1987). Additional Sources of Information The
following organizations can provide further information and
publications on the topics discussed in this paper.
American Plywood Association
P.O. Box 11700
Tacoma, WA 98411
American Wood Preservers' Association
P.O. Box 849
Stevensville, MD 21666
Federation of Societies for Coatings Technology
492 Norristown Road
Blue Bell, PA 19422-2350
Forest Products Research Society
2801 Marshall Court
Madison, WI 53705
National Forest Products Association
1250 Connecticut Avenue, N.W.
Washington, DC 20036
National Paint and Coatings Association
1500 Rhode Island Avenue, N.W.
Washington, DC 20005
USDA Forest Products Laboratory
One Gifford Pinchot Drive
Madison, WI 53705
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