Pressure treated lumber marking codes (C) Daniel Friedman Deck & Porch Framing Lumber Preservative Treatments

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Preservative treated wood:

Health & environmental concerns when working with or using treated lumber: this article discusses deck framing lumber treatment methods, the use of pressure treated lumber, Health Concerns for Chromated-Copper Arsenate (CCA) Pressure Treated Lumber.

Advice for Existing Structures Built Using Chromated-copper Arsenate (CCA) Treated Lumber, Health Precautions for Alkaline Copper Quat (ACQ)-Treated Lumber, and Retention Ratings: Treatment Levels & Durability of Alkaline Copper Quat (ACQ)-Treated Lumber.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Guide to Pressure Treated Framing Lumber Methods, Chemicals, Durability, Health Concerns

Pressure treated lumber marking codes (C) Daniel FriedmanDeck framing lumber treatment methods. How to use pressure treated lumber. Health Concerns for Chromated-Copper Arsenate (CCA) Pressure Treated Lumber. Advice for Existing Structures Built Using Chromated-copper Arsenate (CCA) Treated Lumber. Health Precautions for Alkaline Copper Quat (ACQ)-Treated Lumber. Treatment Levels & Durability of Alkaline Copper Quat (ACQ)-Treated Lumber. Borate Treatment for Lumber & Deck Framing. Increased Corrosion Potential for ACQ and Copper Azole-Treated Lumber.

As described in Best Practices Guide to Residential Construction, Chapter Four, Best Construction Guide for Building Decks and Porches

Most builders choose pressure-treated lumber for the structural framework because of its low cost and high durability. At this time there are few viable alternatives.

However, composite and synthetic products are beginning to enter the market and are worth considering, especially for environmentally sensitive sites, such as wetlands or other applications where clients object to the use of treated lumber (see Table 4-1 shown just below).

[Click any image or table for a larger, more-detailed version.]

Pressure-Treated (PT) Lumber

The vast majority of residential decks were framed with lumber treated with chromated-copper arsenate (CCA) until 2004, when CCA was phased out and replaced primarily by alkaline copper quat (ACQ) and copper azole.

The treated lumber is typically Southern yellow pine in the eastern United States and hem-fir in the West. The more expensive and stronger Douglas fir is also used in the West, but it is more likely treated with the waterborne treatment ammoniacal copper zinc arsenate (ACZA).

Table 4-1 Deck Framing Materials (C) J Wiley, S Bliss

Incising Lumber for Treatment Penetration

Both Douglas fir and hem-fir are typically “incised” with surface cuts for better penetration of the treatment chemical. Even with incising, however, full chemical penetration is rarely achieved with these species, so the center of that wood remains vulnerable to rot, particularly in 4x and larger material.

With these species, effective field treatment of holes and cuts with a liquid preservative is essential.

Health Concerns for Chromated-Copper Arsenate (CCA) Pressure Treated Lumber

Despite CCA’s track record as an effective, economical wood preservative, its safety has long been questioned by health and environmental advocates. Their primary focus has been CCA’s heavy concentration of arsenic, a known carcinogen.

Although most experts agree that leaching of arsenic from CCA lumber is minimal and poses negligible health risks to end users, the industry acknowledges that CCA does pose risks to workers who handle the wet wood or burn scraps, and significant pollution around treating plants has been well documented.

Also see Wood Construction Products MSDS.

Phase Out of Chromated-copper Arsenate (CCA) Treated Lumber

In response to these concerns, manufacturers began a voluntary phase out in 2003 of all CCA treated lumber for noncommercial applications. Starting January 1, 2004, the Environmental Protection Agency (EPA) banned the manufacture of CCA-treated lumber intended to be used in residential settings, including retaining walls, decks, fencing, and playground equipment.

Pressure-treated shakes and shingles were exempted. CCA treatment will also still be available for plywood and heavy timbers used in commercial, industrial, and marine applications. Existing stocks of CCA-treated lumber were mostly depleted by the end of 2004.

Advice for Existing Structures Built Using Chromated-copper Arsenate (CCA) Treated Lumber

The EPA has issued no warnings regarding existing installations of CCA-treated lumber. However, for homeowners who are concerned about potential exposure to chemicals leaching out of the wood, researchers at the USDA Forest Products Laboratory (FPL) recommend periodically treating the pressure-treated lumber with a water-repellant or a semitransparent penetrating stain. Film-forming finishes, such as paints, are not recommended.

New Wood Preservative & Deck Lumber Treatment Chemicals: Alkaline Copper Quat (ACQ) and Copper Azole

Pressure treated lumber marking codes (C) Daniel FriedmanThe two main chemicals replacing CCA are the waterborne compounds alkaline copper quat (ACQ) and copper azole.

Copper azole Type B (CA-B) has largely replaced Type A (CBC-A) in the United States and Canada.

Both ACQ and copper azole perform as well as CCA and are free of any EPA-listed hazardous compounds.

As with CCA-treated wood, premium treated lumber is available with a factory-applied water repellant. With significantly higher copper content than CCA lumber, the new materials are 10 to 15% more expensive.

Of greater concern is the fact that the higher concentration of copper makes the lumber more corrosive to certain metals and metal coatings (see “Increased Corrosion Potential,” next page).

List of Wood Preservative Treatments & Methods

By 2016 Wikipedia (EN) listed about twenty different wood preservative chemicals or treatments and about fifteen different methods of applying these, including the following:

Chemical Preservatives for Wood

  1. Micronized copper technology
    1. Alkaline copper quaternary
    2. Copper azole
  2. Copper Naphthenate
  3. Chromated copper arsenate (CCA)
  4. Other copper compounds
  5. Borate preservatives
  6. PTI wood preservatives
  7. Sodium silicate-based preservatives
  8. Potassium silicate-based preservatives
  9. Bifenthrin spray preservatives
  10. Fire retardant treated
  11. Oil-borne preservatives
    1. Coal-tar creosote
    2. Linseed oil
  12. Other emulsions
    1. Light organic solvent preservatives (LOSP)
  13. Epoxy
  14. New technologies - Wood acetylation
  15. Natural preservatives
    1. Copper plating
    2. Naturally rot-resistant woods
    3. Tung oil
    4. Heat treatments
    5. Mud treatment

Application Processes for Wood Preservatives

  1. Non-pressure processes
    1. Brush and spray treatments
    2. Dipping
    3. Steeping
    4. Kyanizing
    5. Gedrian's Bath
    6. Preservative Precipitation
  2. Pressure processes
    1. Full-cell process
    2. Fluctuation pressure process
    3. Boucherie process
    4. High-pressure sap displacement system
  3. Incising
  4. Microwaving
  5. Charring

Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. Because Wikipedia and other website entries can be amended in real time, we cite the retrieval date of such citations and we do not assert that the information found there is always authoritative.

Health Precautions for Alkaline Copper Quat (ACQ)-Treated Lumber

Despite the lack of chromium, arsenic, or other hazardous chemicals, wood treated with alkaline copper quat (ACQ) and copper azole carry essentially the same handling instructions as CCA-treated materials. Workers handling ACQ and copper azole are still advised by the EPA to wear gloves or wash hands after contact, wear a dust mask when cutting, and not to burn the scraps. Like CCA-treated wood, it is not recommended for direct contact with food or drinking water.

Retention Ratings: Treatment Levels & Durability of Alkaline Copper Quat (ACQ)-Treated Lumber

While most CCA lumber was rated for ground contact, manufacturers are holding down costs with ACQ and copper azole by limiting treatment levels to the expected application of the lumber. For example, deck boards, 2x6s, and 4x4s at the lumberyard will typically have three different treatment levels (Table 4-2 below).

In most cases, lumber will be stamped or tagged with a designation such as “decking,” “above ground,” “ground contact,” or “PWF” (permanent wood foundation). Make sure the material purchased is rated for the intended application or one level higher.

Table 4-2: Pressure treated wood retention levels (C) J Wiley, S Bliss

Borate Treatment for Lumber & Deck Framing

Wood preservatives based on borate compounds have been used for decades abroad and are slowly becoming available in the United States. Borates are noncorrosive to metals and harmless to pets and humans, but they are very effective against insects and decay. Borate’s main limitation is its tendency to leach out of wood that is buried in soil or exposed to regular wetting, making it unsuitable for decks or other exterior applications.

New techniques to better fix the compounds into wood are under development, however, and may soon offer a viable alternative to copper-based treatments.

Increased Corrosion Potential for ACQ and Copper Azole-Treated Lumber

Because of their higher concentrations of copper, ACQ and copper azole are significantly more corrosive to aluminum, steel, and galvanized coatings than CCA (see “Galvanic Corrosion,” page 83). Preliminary tests have also shown that formulations with ammonia-based carriers (used for better penetration in heartwood species such as Douglas fir) are more corrosive than those with an amine or hybrid bases.

Many factors affect corrosion rates, but some studies have found ACQ-treated wood to corrode untreated steel up to four times faster than CCA and to attack galvanized coatings at twice the rate of CCA.

Biodegradable Wood Preservatives

A recent addition to wood treatments is Wolmanized® L3 is described as a low-impact, long-lasting preservative treatment with lasting resistance to termites and fungal decay. - Thanks to deck expert Mark Morsching, Everlast for this update, October 2010. (see Deck & Porch Products, Manufacturers) below.

Life Expectancy & Warranty Period for Treated Wood in Various Applications

We have moved this topic to PRESERVATIVE TREATED WOOD LIFE

Deck & Porch Resources, Products, Manufacturers: Where to Buy

Deck & Porch Wood Treatment Companies

Suppliers of Composite Structural Lumber for Decks & Porches

Composite Decking System Suppliers

Deck & Porch Industry Associations

-- Adapted with permission from Best Practices Guide to Residential Construction.

This article series discuss best porch & deck construction practices, including choice of framing materials, decking or flooring choices & installation, how to select and use deck and porch structural and flooring fasteners, actual deck & porch framing construction details & connections, deck joist & beam span tables, how to build leak-proof rooftop decks, construction of covered & screened porches, deck & porch railing construction & materials, choices of finishes and stains for decks & porches, and past & current deck lumber preservative treatments with related health & environmental concerns.


Continue reading at PRESERVATIVE TREATED WOOD LIFE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


See Rot-Resistant Deck Lumber & Flooring for a disucssion of lumber and flooring alternatives to preservative-treated wood.

Or see New Preservatives and Corrosion where we describe structural fasteners designed for use in pressure-treated lumber.

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