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Long-Term Performance

Not everyone is convinced that the new micronized products are an improvement over the older solubulized versions. Their chief critic is ACQ manufacturer Viance, which has charged that MCQ-treated posts buried in the ground suffered extensive decay in testing funded by Viance. Manufacturers of micronized products counter that Viance’s studies are biased and not representative of the MCQ products they are selling.


Continuous in-ground stake testing of traditional CCA lumber goes back 70 years. Newer formulations are holding up under similar testing, but some have only a four-year to 10-year track record.

With formulas changing so rapidly, can contractors rely on the labeling to ensure that the wood is going to survive as well as the old CCA lumber? Yes and no, say experts. Stan Lebow, the Forest Products Laboratory’s top authority on treated wood, says, “There’s just no way we can have as much confidence in the newer formulations until they’ve been in service for many decades. This doesn’t mean they’re not effective — it just means there’s no substitute for real-time, in-service experience.”

What we can do, says Lebow, is look at factors we know are relevant to the lumber’s performance, such as the treating chemical’s lab-established potency against bugs and rot. “All the new formulations have shown efficacy in these tests, and concentrations used [to treat lumber in the market] are above those thresholds,” he notes. “Unfortunately, it’s impractical to make these determinations for all types of wood-attacking organisms, so the tests are typically run against a subset of the most common organisms.”

Leaching of preservatives is another factor that’s hard to assess, Lebow points out. “All the newer formulations do have some mechanism of stabilizing the preservative in the wood, although it’s a different mechanism than for CCA. As with decay and insect testing, we are not yet able to confidently apply the results of our laboratory leaching tests to predict leaching in real-world exposures.”

Varying exposure conditions in the real world also complicate performance. “We know the same piece of treated wood will last much longer in Montana than Florida, and much longer above ground than in ground contact,” says Lebow. “But we don’t know exactly how much longer.” Throw in rain, snow, sun, leaf and plant litter, or salt air, and the long-run performance of a piece of wood is hard to predict.


Although incising helps, treatments often do not penetrate to the center of a timber.


A 2-by member.


Experts recommend field-treating all cuts with a copper-based penetrating wood preservative such as Jasco Termin-8 or Wolman’s CopperCoat.

And keep in mind, says Lebow, that treating chemicals — whether CCA, ACQ, or the newer types —may not penetrate to the heartwood of large timbers, especially in hard-to-treat Western wood species. So when you cut posts or beams in the field, especially for a structurally important role, you should field-apply a preservative to the cut end. Copper naphthenate (with at least a 1 percent concentration of copper) is the most common formula for that, says Lebow.

Hardware Choices

At this point, the IRC allows only four fastener materials for use with any copper-based preservative treated wood: copper, silicon bronze, stainless steel, and hot-dipped galvanized treated according to ASTM Standard A153 (steel bolts 1/2 inch or greater in diameter are excluded). Of these, only stainless steel and galvanized steel are widely available. But effective this year, the ICC-ES has published an updated “Acceptance Criteria” — AC257 — that will allow other fasteners to earn evaluation reports qualifying them as alternatives to the accepted fasteners.

The AC257 standard involves driving the test nails being tested into pieces of treated lumber alongside hot-dipped galvanized nails, placing the pieces into a saltwater spray chamber, and then comparing the results, both visually and by weighing.

There are already hundreds of fasteners on the market — with a variety of ceramic, phosphate, polymer, and mechanically plated or electroplated zinc or other metal coatings — that are advertised as “approved for” or “compatible with” treated lumber. At this time, it’s up to the buyer to ask what testing was done and what approvals are in hand. But now that AC257 is in effect, many of these products are likely to gain their building code Evaluation Service listings in the next year or two.

Even before the development of the AC257 test, some fastener makers were working hard to demonstrate that their products were compatible with ACQ lumber. Take FastenMaster’s popular LedgerLok structural screw (, which is used to attach deck ledgers and make structural connections. LedgerLok is made of heat-treated carbon steel with a zinc plating plus an epoxy and Teflon surface coating. The product does carry an ICC evaluation report, ESR-1078, which you can download from the company’s Web site or from the ICC site ( But that report addresses only the screw’s structural strength — it specifically states, “This evaluation report does not address fastener corrosion when the fastener is installed in chemically treated wood.”

Nevertheless, FastenMaster endorses the use of LedgerLok screws with ACQ lumber or any other treated wood, except in coastal locations within 1,000 meters of the ocean. That recommendation, says FastenMaster technical manager Mark Guthrie, is based on an older accepted test method for corrosion in metal fasteners and hardware, AWPA Standard E12. LedgerLoks and other FastenMaster coated screws were tested according to the E12 protocol in a lab at Michigan Tech: Ten fasteners were screwed into untreated lumber, CCA wood, and two types of ACQ wood; then the wood samples were exposed to salt solution and heat in a corrosion-acceleration chamber. Compared with galvanized lag bolts and galvanized nails, the LedgerLok screws showed no visual deterioration in the coating and lost less than 1/2 percent of their original weight.

And, says Guthrie, who handles callbacks for FastenMaster, field results bear out the testing: He has never seen a LedgerLok screw with significant corrosion in any kind of treated lumber in actual use conditions. Guthrie says that FastenMaster is pursuing the process of getting the LedgerLok tested under the new ICC standard AC257. But he says it may take a while: “There are very few labs currently set up for it.”

Within a year or two, though, contractors should have a reasonably wide selection of approved fasteners to choose from, backed by ICC evaluation reports. But will those fasteners hold up in service on your deck? There’s no way to really know, says John Kurtz, executive vice president of the International Staple, Nail, and Tool Association (ISANTA). Kurtz has been working for years with committees trying to develop testing standards for fastener corrosion in treated wood. “Corrosion is a very complex subject, and there are many variables,” he says. “No one has figured it out well enough to be able to say, this behavior in a test will translate into three years or 12 years or 100 years of performance in a particular exposure in a particular part of the country or climate. It’s a best effort, but there is no guarantee.”

The best rule for anyone willing to pay the price of caution is probably this: When in doubt, use stainless steel. All the research testing shows that Type 304 and Type 316 stainless steel are practically immune to corrosion by any kind of copper-treated wood.

Simpson Strong-Tie, for example, advises stainless steel for any coastal exposure, or any situation where there might be an unusual chemical stress (such as next to swimming pools, where chlorine may be a factor). Simpson’s Ed Sutt looks at the judgment call this way: “You need to weigh where it is important to get the job done and where it is important to do the best job. So, for instance, if you’re in a harsh environment and you don’t want to spend the money for stainless on the whole job, maybe that critical ledger connection is where you should consider using stainless, to reduce the risk. Or where you attach handrails — that’s not the place to save money. But when you are attaching the deck boards, maybe that’s the place where you want to save money — because that’s not necessarily as critical.”

Hangers and Connectors

AC257 is the ICC test standard for nails and screws in contact with treated lumber. So far, there’s no comparable test for hardware connector straps, joist hangers, or post bases, and no way for hardware suppliers to get specific code listings that apply to using their product with treated wood. For now, contractors have to rely on the recommendations of the wood treaters and the hardware makers. Simpson’s advice, based on extensive testing, is posted online at For USP’s guidance, see

In essence, the manufacturers call for increasing corrosion protection as exposure conditions grow more harsh. In protected dry locations, they recommend G-90 galvanized hardware (with a coating of .90 ounces of zinc per square foot of surface area). For wet exterior locations, this gets bumped up to a G-185 galvanized product (with 1.85 ounces of zinc per square foot), such as Simpson’s Zmax product line or USP’s Triple Zinc line. But in severe exposures (including, says Simpson, “exposure to ocean salt air, large bodies of water, fumes, fertilizers, soil, some preservative treated woods, industrial zones, acid rain, and other corrosive elements”), the recommendation is for Type 303, 304, 305, or 316 stainless steel connectors and fasteners.

Simpson’s “high exposure” category, it’s worth noting, includes some types of treated wood — such as formulas containing a lot of ammonia, or wood that has been treated to unusually high retentions. Quality control is an important factor in the corrosiveness of treated lumber; if a given batch has more chemical than usual or has not dried fully, for instance, it could be rougher on fasteners. There may not be any easy way to determine this, unfortunately — so if you’re thinking conservatively, you may want to go ahead and spend the money for stainless steel.

Looking to the Future: Beyond Copper

While copper is a highly effective wood preservative — without the severe toxicity of arsenic and chromium — it’s not necessarily the last word in wood preservation. For one thing, it’s got its own environmental issues; in fact, three countries in Europe have already outlawed copper-based wood preservatives because of copper’s toxic effect on some aquatic life.

Many U.S. companies are looking beyond micronized copper and working on new formulas that contain no copper — or any other metal, for that matter. For example, there are carbon-based formulas, made up of combinations of commercially available fungicides and insecticides originally developed for agriculture and already approved by the EPA for use by farmers. And there are borate-based formulas, mostly designed for use in dry indoor locations, but including one system approved for outdoor use above ground.

Carbon-based formulas. When they first hit the market, the carbon-based wood preservatives were called “organics.” Fair enough: Complex carbon polymers are known in chemistry as “organic molecules” and the science of making them is called “organic chemistry.” But confusion arose about the other, completely opposite meaning of “organic” in the marketplace — the one that refers to natural farming without the sort of chemical pesticides used in these formulations. So the EPA told wood treaters to find another term, and the marketers came up with the less controversial “carbon-based.”

So far, there are two carbon-based brands on the market: Ecolife, from Viance (, and Wolmanized L3, from Arch Treatment Technologies ( Ecolife uses the insecticide imidacloprid, paired with the fungicide DCOI, commonly called isothiazolone. L3, pronounced “L-cubed,” also contains imidacloprid, but with the same “triazole” fungicides used in Arch’s copper azole product, tebuconazole and propiconazole. So far, neither carbon-based brand is listed for ground-contact applications, although at least one vendor is reportedly working on getting that listing.

As a rule, carbon-based preservatives are much less corrosive than copper-based products. (The carrier used to dissolve the chemicals, however, might still be corrosive, cautions Mike Freeman.) Another big advantage of carbon-based products is appearance. They start out the color of natural wood, and they’re easy to paint and stain. But those benefits haven’t proven as popular as the vendors had hoped. “I thought people would jump at the chance to have a carbon-based preservative in their wood, and sales have been okay, but not as great as I expected,” says Arch executive Huck DeVenzio. “I do think it’s the wave of the future,” he adds.

Ironically, some customers seem to miss the green tint they associate with traditional treated lumber. “Some customers wanted the wood to have some color so they could tell the difference between treated and untreated wood,” says Freeman. “They want that green shade. And guess what the treaters are using to tint the wood? Copper.”

On the other hand, for uses where paintability is key, the neutral color is a plus. “People making molding and trim love it,” says DeVenzio. “People who make outdoor furniture, or storage sheds — they really like the natural look too.”

Borate-based formulas. The other new entry into the field is preservatives based on boron, a mineral that effectively controls both insects and fungi and is widely considered benign to humans and other mammals. Experts say borate is no more toxic to humans than ordinary table salt; homeowners can buy nearly 100 percent pure boric acid off hardware-store shelves in the form of roach-control products like Roach Prufe.

All three of the big players in wood treating have borate-based products for above-ground applications protected from the weather: Arch’s SillBor (, Osmose’s Advance Guard (, and Viance’s TimberSaver ( But because borates are very water-soluble and readily leach out of wood, none of those products are effective for outdoor use. After just one season in the rain, preservative levels would be too low to protect the lumber.

More appropriate for deck builders is a product called ES+Wood, from Wood Treatment Products, ( This treatment uses disodium octaborate tetrahydrate, a water-soluble borate compound, plus a penetrating polymer binder that seals the borate into the wood and keeps it from leaching out. ES+Wood is not code-approved for ground contact, but it’s available for use as deck framing, decking, railings, and trim, as well as playground and recreational equipment. It carries a 40-year transferable warranty (limited to materials only) against damage by termites or fungal decay.

Ted Cushman writes about construction from his home in Great Barrington, Mass.