Timber & Wood Products: Preservatives, Binders, Fixing
Preservatives in Timber Products
While a comprehensive review is beyond the scope of this
document, a wide range of treatments is available, with varying
levels of human and environmental toxicity. Very toxic chemicals
have historically been introduced into our homes and buildings in
the cause of timber treatment such as DDT, Dieldrin,
Pentachloraphenol, Lindane, Tributyltin oxide and Arsenic.
Scientific understanding and public sentiment changes over time,
and we are using increasingly sophisticated treatments. The US
recently joined a growing list of countries in phasing out the use
of CCA treated timber (copper chrome arsenate) for most
applications (US EPA). Permethrin, organic zinc compounds, IPBC,
Dichlofluanid and Propiconazole are all less toxic than the earlier
treatments, although true health and environmental impacts will be
apparent only after many years of use.
Preservatives Used in the treatment of
Wood
Product
|
Use
|
Advantages
|
Disadvantages
|
(Boron/Fluorine products.)
|
Preservative, fungicide and insecticide. Dry pellet or liquid
form. Pellets moisture activated. For H1-H4 applications*
|
Considered largely benign/ very low toxicity. Commonly
available. Low initial cost.
|
As the products are water soluble, they leach out over timber
and *Must be replenished regularly (often 2-5 years) Widely used in
EU in exterior windows and similar applications, in Australia
primarily a maintenance product e.g. fence posts.
|
LOSP using linseed oil carrier
|
Preservative, fungicide and insecticide for H1-H3
applications
|
avoids use of white-spirit solvent, a greenhouse gas intensive
solvent.
|
May still use Tributyltin Oxide, often banned in marine
preservatives due to aquatic toxicity
|
(LOSP)
light organic solvent particles
|
Preservative, fungicide and insecticide for H1-H3
applications
|
Considered low-toxic, commonly available. Low initial cost. A
new formulation is available ('T2') that uses linseed oil instead
of white spirit, eliminating the greenhouse impact of white-spirit
off-gassing.
|
Not suitable for in-ground applications. Oil-based primer may be
required for painted applications (check with suppliers
instructions).
|
ACQ
(ammoniacal copper quaternary)
|
Preservative, fungicide and insecticide suitable for H1-H5
applications.
|
Highly effective. Contains no high toxicity arsenic/chromium
compounds. Can be burnt and mulched.
|
Poor availability for most applications now improving
slowly.
Slightly higher initial dollar cost.
Paintable.
|
Copper Azole
|
Preservative, fungicide and insecticide suitable for H1-H4
applications.
|
Highly effective. Contains no high toxicity arsenic/chromium
compounds. Can be burnt and mulched.
|
Poor availability for most applications now improving
slowly.
Slightly higher initial dollar cost.
Paintable.
|
CCA
(copper crome arsenate solution)
(tanalized) Available water/ oil base
|
Preservative, fungicide and insecticide suitable for H1-H6
applications.
|
Lowest initial dollar cost, paintable, highly effective. Oil
based variant offers improved resistance to surface weathering of
timber.
|
Cannot be safely disposed of except as landfill: highly toxic
smoke from burning, cannot be mulched. Not presently reusable for
timber products e.g. particleboards although research continuing.
Any shavings and offcuts must be disposed of as landfill.
Effectively prohibited in Japan and some European countries,
phase-out in US. Some research shows significant toxicity from
contact to treated timber to children under 6 years (Environmental
Working Group 2001)
|
PEC
(pigmented emulsified creosote)
|
Preservative, fungicide and insecticide suitable for in-ground
applications.
|
Emulsified form of traditional Creosote. Highly effective, lower
toxicity, may be disposed of by incineration.
|
Cannot be painted. Sill considered quite toxic, generally used
for agricultural applications.
|
Creosote
|
Preservative, fungicide and insecticide suitable for H4-H6
applications.
|
High efficacy.
|
High toxicity and restricted use (eg for farm posts). A known
carcinogen. Cannot be painted. Strong smelling.
|
*Applications are attributed 'Hazard' levels under Australian
Standards. These range from 'H1' (above ground, indoors and
protected) to 'H6', timber permanently in contact with salt water.
Windows are typically an H3 application (outside but not
in-ground), while fences (in ground contact) typically an H4.
Binder Toxicity
Many wood products today incorporate formaldehyde-based
glues. The IARC has classified formaldehyde as a
Category 1 'known human carcinogen' (IARC 2008). .
In many commonly used forms formaldehyde will offgas,
particularly in new products and in high heat and humidity.
Inhalation of formaldehyde vapors can cause fatigue, respiratory
irritation, allergic skin reactions and is a probable carcinogen
(IARC 2003).
Conventional interior grade products (plywoods, MDF's,
particleboards) typically use urea-formaldehyde glues, which are
relatively unstable and offgass consistentently over time.
According to the Australian CSIRO this offgassing is not stopped
for more than a matter of weeks by painting, varnishing or laminate
surfaces (Brown, pers. comm. 2003). These materials are a primary
contributor to formaldehyde emission concerns in buildings (Brown
2001).
Plywoods used for exterior and structural applications typically
use phenol formaldehyde (PF) resin. PF is a more expensive,
water-resistant glue, and a much more stable product that offgasses
at a much lesser rate than UF glue.
The US Green Building Council's LEED Credit for Composite Wood
on the other hand requires composite timber and agrifibre boards to
be free of any added UF products..
Fixing
The reclaimation of demolition timbers for use and
reprocessing as recycled timber is prevented due to the use in
recent decades of adhesive fixings. While deconstructability is
fundamental to reuse and high-value recycling, current glue &
nail practices will ensure this is in most instances impractical,
and repair difficult. It is critical wherever possible to use
fixings that facilitate deconstruction and high-value reuse.