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Best Practices in Wood Waste Recycling Click here for printable PDF version Quality Specification for Mulch
Material: Wood Waste
Issue: Clear communication is necessary between wood waste processors and potential purchasers regarding the characteristics and quality of mulch made from recycled wood. For mulch products, the critical characteristics may include:
Failure to satisfy quality expectations for these characteristics can lead to lost business.
Best Practice: This best practice recommends that suppliers (processors) of wood waste derived mulches and potential customers come to a clear understanding of quality requirements. Written product specifications should be developed and made available to purchasers of mulches to enable them to use the products properly and effectively.
The appropriate specifications for mulch products will vary significantly from region to region depending on consumer expectations and the quality of competing products. Within a given locale, the appropriate specification will also vary depending on the type of application, and on the price of the wood waste product versus the prices of competing products.
Provided below are general specifications for two grades of mulch made from wood waste. The low-grade mulch is appropriate for very limited applications where the appearance of the material is not critical. The high-grade mulch is more appropriate for a broader range of applications, for competitive marketplaces, or as a feedstock for colorizing to create a premium mulch product.
Wood Species There are typically
no
limitations
on
the
acceptable
types
of
tree
species
or
on
the
softwood-hardwood
mix
for
this
product,
except
to
the
extent
that
these
may
affect
the
visual
appearance
of
the
mulch.
For
some
applications,
however,
it
would
be
important
not
to
include
certain
varieties
such
as
Black
Walnut
and
some
Cedars
as
these
contain
compounds
that
inhibit
plant
growth,
whereas
in
other
cases
these
species
may
be
acceptable
or
even
desirable
for
these
same
characteristics.
Size Distribution Low-Grade High-Grade · Length: 1 - 2” (25-50 mm) max. 1” (25 mm) · Overs: (> 2”), max. 25% (> 1”), max. 5% · Thickness: Not critical Not critical · Width: Not critical Not critical · Fines: Varies * Varies * * Acceptable
fines
content
for
mulches
depends
on
the
application
and
local
standards. An excessive amount of fines can prevent rainfall
from
infiltrating,
causing
ponding
and
related
problems
in
rainy
areas,
although
in
“spot”
applications
this
would
not
be
a
problem. Fines content for high-grade mulches could
be
as
high
as
15
to
30%,
depending
on
local
markets
and
the
visual
impacts
of
the
fines. Acceptable
Geometry A coarse/shredded material
is
typically
acceptable
or
even
preferable
over
of
a
chipped
material.
Maximum Allowable Contamination
Levels ** Low-Grade High-Grade Rot:
5% 1% Bark Not
critical
5%
Dirt, rock, sand 10% 1% Metals
1% 0.2% Plywood
5% 0.25% Particleboard 3% 0.25% Wood with laminates 2% 0.25% Plastics
0.5
Trace Painted wood 1% 0.25% Treated wood 1% 1% Other non-wood materials 1% Trace **Allowable contamination levels
are
highly
dependent
on
local
market
conditions
and
on
the
actual
visual
impact
of
the
contamination.
Color/Brightness There is typically
no
brightness
requirement,
but
color
may
be
an
aesthetic
consideration.
Moisture Moisture content
is
typically
not
critical.
Implementation: In the course of adapting processing systems to produce a mulch, wood waste processors must work with potential buyers (and with actual customers on an ongoing basis) to determine consumer expectations and satisfaction. Wood waste processors should manage their compliance with printed specifications through a consistent QA/QC program that both controls incoming material before processing and continuously tests finished products for compliance with specifications and consumer expectations.
Benefits: Providing a consistent and quality mulch will improve the marketability of the processor’s product(s), potentially increasing both the price and volume of the material sold.
Application Site: This Best Practice applies
to
wood-waste
processing
facilities.
Contact: For more information about this Best Practice, contact
CWC,
(206)
443-7746,
e-mail
info@cwc.org.
References: 1. Hoeck, Jack. Rexius Forest Products, Eugene, OR. 2. Sargent, Bob. Rainier Wood Recyclers, Kent, WA. 3. Hlavka, Rick. Green Solutions, South Prairie, WA
Issue Date / Update: March 1997
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