Caution needed when using pressure-treated wood

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Caution needed when using pressure-treated wood

© The Ottawa Citizen 2008

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Steve Maxwell

Saturday, April 19, 2008

 

 

 

Arsenic isn't an element that enjoys a good public relations image. That's

why the American and Canadian lumber industries voluntarily halted consumer

sales of all pressure-treated wood containing arsenic-bearing chemicals four

years ago.

Trouble is, the new, arsenic-free, pressure-treated lumber also presents

hidden hazards that too few people realize. If you're planning to build an

outdoor project this spring, you need to understand crucial details for your

work

to endure. And don't assume that every builder understands the seriousness of

this issue.

Safety rules for handling and building with the new breeds of lumber read

the same as for old wood, despite the freedom from arsenic. According to

Environment Canada, avoid using the new pressure-treated lumber where direct

food

contact is possible.

Keep it away from animal food storage bins, water troughs and compost bins.

Wear gloves and long sleeves when working with pressure-treated lumber, and

put on a dust mask when cutting it. Wash your hands after working with the

product, and especially before eating, drinking or smoking.

Launder work clothes separately before reuse, and never burn

pressure-treated wood scraps. Of all the safety rules -- new pressure-treated or

old -- the

no-burn requirement is the most important.

Besides rules for safe handling of pressure-treated lumber, there's a

structural issue, and it has to do with a chemical interaction that's not

obvious.

A substance called alkaline copper quat (ACQ) is one of the most common wood

preservative compounds that keeps new kinds of pressure-treated lumber from

rotting.

ACQ relies on copper to be effective, not arsenic, and this is where

structural problems can occur if you're not careful. When the copper in

pressure-treated wood gets wet and comes in contact with certain kinds of metal

nails,

screws and joist hangers, it accelerates the corrosion of these fasteners.

The first signs of trouble show up as rapid staining of the wood surrounding

these fasteners, often within just a few weeks of construction. And within a

few years, the choice of inappropriate fasteners will cause premature deck

failure as nails and screws are reduced to crumbly iron oxide.

Hot-dipped galvanized nails and screws offer the minimum level of corrosion

protection required by today's modern lumber. Stainless steel is even better,

though there's a problem. It's not always easy to know the makeup of

fasteners just by looking at them. In fact, you can't tell what you've got just

by

sight.

At a minimum, the safest approach is to use fasteners specifically labelled

for use with ACQ lumber. You should also make a distinction between two kinds

of joints in your outdoor projects: joints that remain accessible after

construction, and those that you can't ever get at once the project is

complete.

Inaccessible joints should be fastened with the more costly, reliable

stainless-steel screws or nails. You can afford to use less expensive,

hot-dipped

fasteners on joints where additional nails or screws can be installed years

later, if the first fasteners fail.

Aluminum flashing is another area you need to consider when using

pressure-treated wood. Aluminum is especially vulnerable to corrosion when in

contact

with copper-rich lumber. That's why it's essential to use copper flashing

anywhere near pressure-treated wood.

Handle today's pressure-treated lumber properly and it'll deliver excellent

results for a long, long time.

Steve Maxwell is technical editor of Canadian Home Workshop magazine. Send

questions to _www.stevemaxwell.ca_ (http://www.stevemaxwell.ca) .

© The Ottawa Citizen 2008

 

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