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I wrote the following article on the issues related to the changeover in pressure treated wood chemicals.

In recent years consumer advocacy groups joined forces with the Environmental Protection Agency (EPA) and the Consumer Product Safety Commission (CPSC) to convince the pressure treated wood manufacturers to stop using two chemicals that have been proven unhealthy to humans. This pressure treated wood has used in hundreds of thousands decks and playground equipment all across America.

In a voluntary agreement (due to bad news reports and their falling consumer confidence... they managed to avoid an all out ban), the pressure treated wood manufacturers agreed to stop using harmful chemicals in the production of pressure treated lumber. These chemicals included, Chromate Copper Arsenate (CCA), Ammoniacal Copper Arsenate (ACA), and Ammoniacal Copper Zinc Arsenate (ACZA).

Pressure treated wood is infused with chemicals to preserve the wood that is in direct contact with the earth and in direct exposure to the elements. It is most often used in residential exterior construction, decks, and children's playground equipment. The agreement became effective on December 31, 2003.

Since December 31, 2003 the following chemicals are out:


  • CCA - Chromate Copper Arsenate
  • ACA - Ammoniacal Copper Arsenate
  • AZCA - Ammoniacal Copper Zinc Arsenate

So in keeping with the "out with the old and in with the new" philosophy, the pressure treated lumber manufacturers adopted a whole new witches brew of chemicals to continue their production. And with the use of new chemicals have come new issues, the most prominent of which is the fact that the new wood immediately starts to rust and decompose all of the old style metal brackets and securing fasteners. This leads to deck collapse.

The most popular new preservative treatment is a new chemical known as Alkaline Copper Quaternary (AQC). Who knows exactly what this is actually composed, but you sure wouldn't want to sprinkle it on your Frosted Flakes in the morning. It remains to be seen if the new chemicals will pose harm to kids playing on the pressure treated wood playgrounds.


  • AQC - Alkaline Copper Quaternary

When evaluating decks, the December 31, 2003 date becomes very important because, for about a year after the implementation of the new products, there was a real mix-up as to what hardware could be used with the new treatment formulas. The existing stock of fasteners were still being used by builders who had an old box sitting in their storage room and they were unaware of the corrosion issue. The new fasteners would work with the old wood, but the old fasteners would not work with the new wood.

Manufacturers of fasteners have come out with new product lines that are AQC compatible, but there are no special markings. To make things worse, the new wood looks just like the old wood, except that there is an identification label sticker on the butt ends. The drawback for inspectors looking at wood decks is that we do not get to see the butt ends because they are butted up against other deck framing members. This leaves us looking for signs of corrosion at the fasteners and brackets.

The rapid rusting of the fasteners and the flashings will be the sure source of deck failures in the future, yet these collapses could be averted with regular deck inspections.

There is also an issue with the flashings used for deck installations. Flashings for decks are the metal sections that sit behind the exterior home finish and brings water out and over the attaching point of the deck to the home. By directing the water away from the home it helps prevent deterioration to the framing at the deck attaching points. 

Fasteners and brackets are the metal bolts, screws, nails, and joist hangars used to hold the deck together and secure the deck to the home. These include anything metal related to the deck. If you were to see rust and corrosion, then you should start asking questions about the when's, how's, and what's, related to the deck construction. Try to determine when it was erected to see if fastener to wood incompatibility is even a possibility.


The corrosive nature of the new pressure treated lumber is activated when water hits the wood and the chemicals leach onto the fasteners. This corrosion can cause the fasteners to fail and the flashings to leak. Water entry leads to rot, which then causes the main deck ledger connecting points to come loose and fail. I guess the future deck failures will require two questions to be immediately answered:

  • 1) Did this deck fail because of incompatible fasteners and treated lumber?
  • 2) Did this deck fail because of water entry due to corroded flashings?

Once these questions are answered, then the regular questions can be addressed:

  • 1) Did they use any flashing?
  • 2) Did they bolt the ledger? Or did they just nail the ledger to the home?
  • 3) Is there direct earth to wood contact?
  • 4) Is the substructure adequate for the size and use of the deck?
  • 5) Was the deck professionally built, or was it a Weekend Warrior Harvey Homeowner special?

One thing is for certain, and that is decks have become part of the American lifestyle and they are going to continue to fail due to poor design, inadequate supports, long term rot, and now add to the list, fastener to pressure treated wood compatibility.



CPSC - NOV 2003 - Q&A's For CCA Pressure Treated Lumber

CPSC Denies CCA Ban Petition - Nov 2003

CPSC FACT SHEET - Feb 2003 - Chromated Copper Arsenate (CCA) -Treated Wood Used in Playground Equipment

CPSC Consumer Product Safety Review - Spring 2004 - PDF

CPSC Outdoor Playground Safety Handbook - Aug 2005 - PDF

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