Pressure Treated Lumber: Part 2

If you're building an outdoor structure this summer, there are critical things to know about using the new pressure-treated lumber. In fact, manufacturers have posted tear sheets all over home centers and hardware stores, hoping we'll read them.

Some of them even use the word 'critical'.

Here's the reason: If you use the wrong fasteners to build your deck or play set with the new pressure-treated lumber, the fasteners will fail before the lumber does.

Errant Current

Since January 1, 2004, the old arsenic-laced pressure-treated lumber has been replaced in home centers and hardware stores with new copper-based preservatives - either ACQ (alkaline copper quaternary compound) or copper azole. There's way more copper in the wood than there used to be, and copper can cause problems when it interacts with other metals.

Let me explain.

You know how crews are always renovating the Statue of Liberty? That's because the two metals she's made of (iron armatures for the internal supports, covered by a copper skin) set up a mild electrical charge, and turn her into a huge, weak electrochemical battery cell that corrodes like crazy.

Any two metals will have some kind of galvanic interaction, but the farther apart they are on the Galvanic Table (a fascinating document that offers conversational fodder for ANY social circumstance), the worse the corrosion will be.

This means that when you build a deck and use plain carbon steel fasteners in copper-treated lumber, the fasteners can corrode 5 times faster than they're supposed to, because of the interaction of the two metals.

Screw Scruples

This is a real issue for fastener manufacturers. They've been rushing to test their products to make sure they hold up in the new lumber.

Here are the recommended fasteners, in order of effectiveness:

• #304 or #316 stainless steel
• Hot-dipped galvanized fasteners that meet the American Society for Testing and Materials (ASTM) standard of A153 or A653
• Polyester-coated fasteners like DuraGrip

The reality is that most consumers won't choose stainless steel because it's 6 times as expensive as hot-dipped or polyester-coated fasteners. (i.e. One #8 stainless steel 3-inch screw costs 63 cents. A comparable DuraGrip screw costs 8 cents.)

Hang it All

If you buy joist hangers or any of the Simpson Strong Ties that are standard in deck construction, don't choose the plain old galvanized ones. You have to choose Simpson's Zmax line, which is hot-dipped galvanized.

TIP: Sometimes the displays get messed up with stock in the wrong places. Make sure each piece you choose from the bin has the word Zmax plus the identification code number (which contains a Z) right on the sticky label.

Never use carbon steel nails to affix Zmax hangers and ties. Then you'll be combining steel nails and zinc hangers with the copper in the lumber - an electro-chemical nightmare for you Galvanic Table enthusiasts.

NOTE: Not all manufacturers' specs for "hot-dipped galvanized" are the same, so you should consult their product handbook, which may be hanging nearby or available from the service desk. For example, most of the bulk nails and screws available at The Home Depot are made by the B.C. company Tree Island. Their "hot-galvanized" moniker actually means "hot-dipped galvanized to ASTM153 standards". Some manufacturers don't match this high level with their 'hot-galvanized' products.

Once you've got chosen your fasteners, here are other hints for building with the new pressure-treated lumber:

1. There are several grades of pressure-treated lumber. Each board should bear a stapled-on label identifying its grade. 'Ground contact' means the lumber is designed to be in contact with the ground (i.e. posts) 'Marine grade' means it can go underwater. 'Above ground' means it shouldn't be in contact with water or ground.
2. Use an end-cut preservative. This is really important. If you don't protect freshly cut ends, it really compromises the life of your structure. Paint cut ends with one of two wood preservatives available: Copper napthenate, for cut ends that will be in contact with the ground, and zinc napthenate, for cut ends that will be exposed to air only.)
3. Never put copper-treated lumber in contact with aluminium (i.e. flashing or door frames.) The aluminium will corrode. Use nylon spacers to maintain at least 1/4" distance between the wood and the aluminium. Or use a polyethylene barrier (10 mils thickness minimum).
4. ACQ and CA lumber fades quickly to a sandy brown, so don't use green coated screws unless you're going for some bohemian decorative effect.
5. If you have questions about working safely with pressure-treated lumber, visit www.ptw-safetyinfo.ca or call 1-866-679-0957.