LumberAisle
TheUltimate
Outdoor
Notoxins?
Noplastic?
Nokidding.Thermally
modifiedwood
maybethe bestthingsinceslicedcedar.
he holy grail of outdoor woods:
rot-resistant,weather-resistant,
insect-resistant,strong,and
dimensionally stable. And to make the
quest more challenginge, let's add
beautiful, non-toxic, and sustainable.
Impossible, you say?Well take a look at
thermally modified wood. That elusive
and legendary pefect wood for outdoor
projects might be closer than you think.
The end-product is a lightweight,
strong, durable, stable, and chemicalfree wood. The prccess imparts a dch
brown color that permeates the board
and a pleasantly sweet,baked smell
The wood is machined into deck
boards, siding, or dimensional lumber
after undergoing the prccess, and most
of its tendency to wary gets left behind
continued.on page 2)
Beyond kiln-drying
The idea of thermally modifying wood
is nearly as old as toolmaking. Early
hunters heated wooden spea$ over the
fire to harden them. But it wasn't until
the 1990sthat Scandinavian wood
processo$ and kiln manufacture$,
such asStellacOy, took the processinto
the lab for closer scutiny. The resulting
technology has been employed for
years in Europe, but is only recently
making its way into North American
rctail markets via such comoanies as
RadianceWood Products (rtdiancewood.com), Ecovantage (ecoprem,com),
Bay Tree Technologies (purewoodproducts.com),and Northland lotest
Products (cambiawood.com).
The thermal modification process
(seeillustration ct ngl,t) starts where
kiln-drying l&ves oft subiecting the
wood to temperaturesnear 500' F. This
"bakes" the sugarsin the wood, making
it unpalatable 1o rct-inducing microbes
and wood-munching insects. Components in the wood's cell walls that
normally absorband teleasemoisture
become permanently water-insoluble
during thermal modification. Robbed
of ready moisture, the wood becomes
not only less vulnerable to decay by
biodegrading, but also more dimensionally stableand resistantto warping.
And, iust like those spearsof old, the
wood hardensas the cell structureis
transformed.
Kiln-driedwoodwith a moisturecontent
rangingfrom 14-19%entersthe computercontrolledthelmalmodificationkiln.
Initial heating:Thetemperatureinside
the kiln risesto212"F,theboilingpointof
water.
Preconditloning.ld drying: Theheat
continuesandsteamis introducedto
slowlybringthe dryingwoodto a uniform
7-896moisturecontent.
Therm.l llodltlcEtion: Asthe
tempeaature
of the kiln booststo 480' F,
the increased
heat"bakes"the sugatsand
tanninsinthewoodmakingtheminedible
to microbesandinse<ts.Thewoodda*ens
andhardens.
Condltlonlngrsteamonceagainis
introducedto stabilizethewoodand
preventit from dryingcompletelyinthe
high heat.
CoollngrComputers
slowlylowerthe
temparatureofthe kilnto minimize
stresses
onthewoodasitcools,Only
24-48hoursafterit entered,thewoodis
readyto b€ removed.
WOOD m.g.z l n€
Marc h20l
LumberAisle
Environmental impact
The thermal-modificatlonprocess
works on any speciesof wood, but most
manufacturers utilize Southern Yellow
Pine becauseof its low price and
sustainabiljty. The chemical-free
processleavesbehind no chemical
waste at the kiln and nothing toxic to
led. h lr om th e w o o d i n to )o u r b a rk yard soil.
One manufacturer, RadianceWood
Products,carriesthe green aspecta step
further by adding a resin-bascd,
volatile-organic-compound-freefinish
calledOne TIME in the factory.Bond
Distributors, maker of One TIME
recorln.rendsref inishing with their
product within sevenyeals.
Thermally modified wood weighsso
little, a truck can hold more than two
times the number ofboard feetcompared
wood, savingfuel and
to pressure-treated
reducingemissions.(Although the latter
is offsetsomewhatby the increasedfuel
necessaryto heatthe kilns.)
Waiting for the
other shoe to droP?
H erei l i \, but i l \ morel i ke d moLLati n
that
than a work boot: The.process
leavesthe wood harder also reducesits
splitting resistance;severalmanufactul'
ers recommend predrilling screwho1es,
especiallynear the endsof boards.The
wood becomesmore vulnerable to UV
light, fading to a silver-grayfasterthan
unmodified wood, so refinishingis
everYYearor two.
nec€ssary
One other caveat:Becausethe process
is fairly ne\'\,,most products have not
yet been certified for ground contact.
So for now, you'll still need to build
your deck framework with pressuretreated lumber. That's why most
manufacturers are focusing their
product lines on 5/4 deck boards,posts,
balusters,and railings, rather than
standarddinlensionallumber'
Availability and cost
Currently, thermally modified wood is
making its way into lumber yards and
specialty decking stores,with limited
inroads into home centers.lts cost
lands somewherebetweenthat of cedar
decking and composites.Warranties
ranE etrom 20 ro l0 ) edr \ .Wdt ch lnl
increasedavailability and possibly
lower oricesascomPanie5rev uP
produition and disiribution..|
How thermally modified wood stacks up against other outdoor materials
WOOD magazine
March 201