R E - D R I E D
T R E AT E D
L U M B E R
LIGHTER, CLEANER,
ENVIRONMENTALLY
SOUND
Foreword
The purpose of this booklet is to assist you in
getting more value, performance, and satisfaction from pressure-treated lumber.
Since the earliest days of our country, Americans
have built their homes of wood. Even after the
passage of centuries, lumber is still our most
popular building material.
Now, pressure-treated lumber provides architects, designers, and builders with bold new
options when formulating construction plans.
New pressure-treating technology has greatly
extended the range of safe, dependable usage
for lumber. No longer inhibited by hazards such
as decay and termites, architects, engineers,
designers and builders are giving free rein to
their imagination in wood design and construction. The advantages of wood’s inherent properties – strength, versatility, ease of fabrication,
resiliency, resistance to wear, warmth and economy – can be utilized in most structures under
conditions of severe weather exposure.
Wood is our only renewable natural resource
and by pressure-treatment, one tree will last
for a period that would require the use of ten
untreated trees. This is true conservation. We
enjoy the prolonged use of the wood while
conserving our forests as well.
Architects, contractors, lumber dealers, building
officials and especially home builders will find
the information contained in this booklet useful.
D RY P r e s s u r e - Tr e a t e d L u m b e r H a s G r e a t e r S t r e n g t h
Souther n Pine . . .
The Raw Mater ial
The United States is blessed with a remarkable
building material, Southern Yellow Pine. United
States Department of Agriculture tables show
that properly DRY Southern Pine is among the
strongest of all woods and is the wood with the
greatest nail and bolt holding power. Pound for
pound, clear, DRY Southern Pine is stronger
than steel. In fact, it is known as the “Supreme
Structural Wood of the World.”
As a bonus, the sapwood of DRY Southern Pine
treats very readily with a modern EPA registered
preservative, making it decay and termite resistant for decades.
When treated Southern Pine comes from the
treating cylinder, the wood fibers are saturated
with excess water. Thus it does not emerge as a
finished product; another essential step is
required to make it ready for consumer use.
That process is the re-drying of the lumber after
treatment and before it is used.
Re-dr y ing After Treatment
. . . Vitally Impor tant
One of the authorities on building standards in
the United States is the Federal Government’s
Forest Products Laboratory. The Laboratory
scientists say it is “vitally important” to use only
lumber that is properly “seasoned” (that is, redried after treatment to an average moisture
content of 19% or less).
The benefits are numerous for pressure-treated
wood that is re-dried after treatment:
◆
Dry Pressure-Treated Lumber minimizes
shrinkage problems.
◆ Dry Pressure-Treated Lumber has greater
strength and stiffness.
◆ Dry Pressure-Treated Lumber is more
uniform in size.
◆ Dry Pressure-Treated Lumber has better
nail and bolt holding power.
◆ Dry Pressure-Treated Lumber is safer.
◆ Dry Pressure-Treated Lumber is cleaner
and lighter.
◆ Dry Pressure-Treated Lumber can be easily
painted, stained, water repellant coated, or
left to weather to a natural driftwood gray.
◆ Dry Pressure-Treated Lumber meets
building codes, FHA, and grade stamp
requirements.
Q u a l i t y - C o n s c i o u s B u i l d e r s Us e O n l y D RY P r e s s u r e - Tr e a t e d L u m b e r
Simple Rules to Follow
When Buy ing PressureTreated Lumber
Take the guesswork out of buying pressuretreated lumber by adding proper moisture content provisions to your purchase specifications.
When the moisture content of pressure-treated
lumber is not specified, the buyer has no assurance that the lumber purchased will be satisfactory for its intended purpose.
The following specifications can be used as a
guide:
*“Each piece of Southern Pine lumber shall
comply with the American Softwood Lumber
Standard PS 20-70, and the Southern Pine
Inspection Bureau grading rules. Each piece of
lumber shall bear the grade mark of a recognized agency or independent inspection service
certified by the Board of Review, American
Lumber Standards Committee.
In addition, all treated Southern Pine shall conform to the approved standards of the American
Wood-Preservers’ Association. Each piece shall
be treated in accordance with AWPA standards
and certified by an approved inspection agency.
All lumber, 2˝ or less in thickness, treated with
waterborne preservatives should be re-dried
after treatment to an average moisture content
of 19% or less. For the lumber grademark to be
valid after treatment the lumber must adhere to
the grade requirements and the moisture content of the grade represented by that mark.”
Proper re-drying after treatment is a protection
that rightfully belongs to every builder or home
owner. You should insist on it always.
*“Pressure-Treated Southern Pine” by Southern Forest
Products Association, 3/87
DRY Pressure-Treated
Lumber Minimizes Most
Shr inkage Problems
Wood technologists tell us that the fiber saturation level of wood is reached when it holds a
moisture content of about 28%. They also point
out that wood shrinks approximately 1% for
every 4 percentage points below the 28% level.
To insure maximum satisfaction then, the lumber should be dried or “pre-shrunk” before
installation. Changing conditions such as rain,
temperature, sun, shade, and relative humidity
will all affect the moisture content of wood.
Thus, some changes in its size can be expected.
Experience has shown that lumber dried to 19%
moisture content, installed outdoors, will undergo limited dimensional changes. Warpage,
another result of lumber shrinkage, is also minimized when the wood has been properly dried
prior to installation.
All lumber shrinks as it dries. The place for this
shrinkage to occur is under controlled conditions at the treating plant, not after it is erected
in a home or other structure.
DRY Pressure-Treated
Lumber Is Safe, Light
& Clean
D RY P r e s s u r e - Tr e a t e d L u m b e r i s E a s i e r t o H a n d l e
Today with the heightened concerns about the
potential hazards of chemicals, there are two
things that should be considered when specifying or purchasing pressure-treated wood: 1) that
it is safe, and 2) that it works.
The re-drying of pressure-treated lumber is the
only way to insure immediate and complete fixation of the preservatives within the wood cells,
providing a safe, clean, and durable building
material.
The excess moisture resulting from the treating
process adds appreciably to the weight of the
lumber. This added weight increases handling
costs for the supplier and the builder throughout the construction process. Properly re-dried
pressure-treated lumber is the type of wood that
carpenters and other workers prefer to handle,
cut, and install on any project.
To satisfactorily accept paint, stain, or a coat
of water repellant sealer, pressure-treated lumber must be re-dried properly to assure the
necessary penetration and adhesion. Moisture
trapped inside improperly re-dried wood is the
most common cause of paint blistering and
peeling. Always follow the paint manufacturer’s
recommendations.
FHA & Building Codes
Require or Specify DRY
Pressure-Treated Lumber
The Federal Housing Administration, the North
Carolina State Building Code, the Standard
Building Code and the Uniform Building Code
all require that pressure-treated lumber two
inches or less in thickness contain not more than
19% moisture content at the time of installation.
Most architects specify that pressure-treated
lumber be re-dried to assure satisfactory performance in their projects. The Southern Pine
Inspection Bureau grading rules for untreated
Southern Pine include moisture content limits
for all grades of lumber.
Dryness or “seasoning” of Southern Pine is a
standard grade requirement. (This is expressed
as maximum moisture content under paragraphs 160-168 of the Southern Pine Inspection
Bureau Grade Rules.) The grade mark is an
identification of the grade, seasoning and producer. Once graded and grade marked, Southern
Pine that is then treated with waterborne preservatives has its grade mark invalidated. In this
wet state, pressure-treated lumber would no
longer meet the seasoning requirements established for untreated lumber.
It is obvious that these authorities regard the
proper re-drying of pressure-treated lumber as
important.
D RY P r e s s u r e - Tr e a t e d L u m b e r I n s u r e s T h e I n t e g r i t y o f Yo u r P r o j e c t
DRY Pressure-Treated
Lumber Has Better Nail
Holding Power
Nails are critical to the structural integrity of a
building as they hold together the principal parts
of its framework. Driven into DRY pressuretreated lumber, nails hold tight and stay tight.
With lumber that has not been re-dried after
treatment, the drying that occurs after it is
installed causes it to shrink, thus loosening and
weakening joints. A substantial part of the nails’
holding power is lost. The United States Bureau
of Standards and the U.S. Forest Products
Laboratory report that this loss can be as much
as 75%.
Corrosion
If a piece of wood with a nail in it is placed outside, temperature changes, water, oxygen and
other elements in the environment will promote
the corrosion of metal fasteners.
For this reason hot-dipped galvanized or stainless hardware is recommended. Many fastener
and hardware companies who have tested with
the new alternative preservatives suggest that
minimum standards for hot-dipped fasteners
should meet ASTM A 153, and for connectors
ASTM A 653, class G-185.
Dealer Name
Dealer Address
Dealer City, State Zip
Dealer Phone Number
Dealer Fax Number
Industries, Inc.
P.O. Box 1124 Orangeburg, SC 29116
(800) 476-4401
www.coxwood.com
2008
DUR-02