F: PRESSURE TREATED COMPOSITES
Jurisdiction: AWPA Technical Committee T-8
This section applies to pressure-treated plywood, glued
laminated timber, mechanically fastened timber, laminated
veneer lumber (LVL) and parallel strand lumber (PSL).
1. Seasoning or Conditioning: At the time of
manufacture, plywood and other composites are dry and this
condition should not be changed appreciably prior to
treatment. If laminations or other elements of a composite
product are treated before gluing, they should be dried
before assembly using an appropriate seasoning method.
2. Treatment:
a. Incising. For structural glued laminated timbers treated
after assembly, incising is not required for Southern pine and
red oak. Incising is required for all other listed species to
achieve best treatment results. If the incising requirement is
waived by the specifier, penetration and retention
requirements still apply. Unincised glued members of
species for which incising is required shall be individually
inspected. Each section of a lamination between end joints
may be considered as a separate piece of lumber for
sampling purposes. Each member shall be considered a
separate lot of material for evaluation of penetration and
retention according to the appropriate section of AWPA
Standard M2. Failure to incise can require retreatment
that may lead to bleeding and surface appearance
problems with some preservatives. For individual
laminates treated prior to gluing, incising is not required for
Southern pine. Incising is not required for plywood or
structural composite lumber products.
b. Maximum Pressures. The maximum pressure used for
treating assembled members shall not exceed 1050 kPa (150
psig). Limitations for individual laminates depend upon
species and can be found in Section 8, Commodity
Specification A.
c. Solution Temperatures. A maximum temperature of
90C (195F) is allowed for structural composite lumber
products.
3. Final Conditioning:
a. Final Steaming. Final steaming to clean the surface is
not allowed for plywood. Steaming is permitted with glued
laminated members and laminates not to exceed 3 hours at a
maximum temperature of 115C (240F). For structural
composite lumber, the limitation is two hours at 115C
(240F)
b. Expansion Baths. Expansion baths are not permitted
for plywood laminates. A two-hour final expansion bath not
to exceed 100C (212F) is allowed for structural composite
lumber products. For structural glued laminated timber, the
expansion bath temperature shall not exceed 105°C (220°F).
c. Kiln-drying after Treatment. When treated with a
waterborne preservative, plywood products shall be redried
to a moisture content of 18% or less and structural
composite lumber products shall be redried to a moisture
content of 19% or less unless waived by the purchaser. The
maximum permissible kiln temperature is 70C (160F).
4. Results of Treatment:
a. Plywood The analytical method used to determine the
retention by assay shall be in accordance with the applicable
AWPA analysis method. The penetration and retention shall
be determined by assaying a minimum of 20 samples taken
from the face of not less than five panels in each lot at a
point 300 mm (12 in.) from any edge. Plywood 16 mm (5/8
in.) or less in thickness shall be sampled through the full
thickness. Plywood over 16 mm (5/8 in.) in thickness shall
be sampled from the lower grade face to 16 mm (5/8 in.)
depth. Borings shall be tested for penetration by the
appropriate procedure described in AWPA Standard A3.
Penetration in a charge of plywood shall be acceptable if 90
percent of the veneers are penetrated. The charge shall be
rejected if less than 90 percent of the veneers inspected are
penetrated. A veneer shall be considered penetrated if there
is evidence of penetration into the wood substrate of the
veneer. Penetration of lathe checks alone does not qualify as
acceptable penetration of a veneer. For PTI preservative, a
penetration surrogate shall be added to the treating solution
at concentrations not to exceed 500 ppm boron.
b. Glued Laminated Timbers (Treated after gluing).
See Tables 1A/1B. For glued laminated material treated after
gluing, more than one boring may be taken from the same
piece, but no more than one from the same lamination unless
there is an end joint separation or there are an insufficient
number of separate laminations. For UC4 members more
than 480 cm 2 (75 in ) cross section at the ground line, every
member in the charge shall be bored for penetration. For
UC4 members 480 cm (75 in 2) or less in cross section at the
ground line, 20 members per charge shall be bored for
penetration. Should the charge contain less than 20
members, every member shall be bored. Where only 20
members in a charge are bored for penetration, the sizes of
those members checked shall be representative of the sizes
in the charge.
c. Glued Laminated Timber Treated before gluing. See
Tables 2A/2B. The bonding quality for glued laminated
timber manufactured from treated laminates may or may not
have been evaluated by the AWPA composites committee.
Such bond quality for a glued laminated beam is required to
be qualified in accordance with ANSI A190.1. Specifiers
and end-users of treated composite wood products should
consult with the treater and/or composite manufacturer
regarding the availability of preservative treatments.
2
2
- 99 -
T1-15
USE CATEGORY SYSTEM: PROCESSING AND TREATMENT STANDARD
Page 28 of 38
© 2015
d. Structural Composite Lumber (LVL, PSL).
sampling zone for assay shall be:
All Wood Species
Member Dimension
Under 50 mm (2 in.) thick
50 mm (2 in.) thick and over
Number of borings/charge:
The
Standardized for Each
Commodity
0 - 15 mm (0.0 - 0.6 in.)
0 - 25 mm (0.0 -1.0 in.)
The retention determination shall be made on a percent by
dry weight basis and then converted to a weight/volume
basis using the appropriate density value according to AWPA
Standard A12. Penetration shall be 63 mm (2.5 in) in
products 125mm (5.0 in) or more in thickness, or half the
thickness of the product in the narrow dimension, whichever
is less. For determination of penetration, a core shall be
taken from the wide strand face of PSL or perpendicular to
the gluelines in an LVL product from 20 pieces in each
charge. If 80% of all strands show evidence of penetration
within the assessment zone, the charge shall be accepted.
e. Mechanically Fastened Timbers. Treatment of
Laminates treated before assembly for Mechanically
Fastened Timbers must meet the assay and penetration
requirements in T1 Section A for the final use category of
the composite product assembled from them.