Using pressure-treated lumber (PT) in home construction is very effective in reducing wood destroying insect activity, but it has the adverse effect of causing corrosion on most hardware and fasteners. Galvanic corrosion is an electrochemical process that occurs when dissimilar metals come into contact in the presence of moisture.
Can pressure treated wood be treated with galvanic corrosion?
Most pressure-treated wood is treated with chromated copper arsenate. The metal present in the treatment chemical (copper) is dissimilar to the metal roofing (steel). I would be concerned that galvanic corrosion could degrade the metal roofing or fasteners. Galvanic corrosion occurs when electrons move away from an anode toward a cathode.
How does pressure-treated lumber work?
When two opposing metals are placed together, a process called electrolysis happens, in which the harder metal attacks and erodes the softer metal. Pressure-treated lumber is often treated with one of two chemicals: copper azole (CA-C) or alkaline copper quaternary (ACQ), both of which contain copper (a harder metal).
What chemicals are used to pressure treat wood?
The two most popular chemicals for wood pressure treatment are alkaline copper quaternary (ACQ) and copper azole (CA), which are both active corrosion materials. Only two corrosion protection systems are recommended for use with these pressure treatment chemicals: hot-dip galvanized steel and stainless steel.
What type of corrosion protection should be used with pressure treated steel?
Only two corrosion protection systems are recommended for use with these pressure treatment chemicals: hot-dip galvanized steel and stainless steel. The hot-dip galvanized coating provides a thicker layer of zinc than other zinc-coated fasteners.
Can metal touch pressure treated wood?
Hot-dip galvanized steel can withstand the harsh chemicals and slow the corrosion rate. Common metal parts used with pressure treated wood are connector plates, joist hangars, bracing plates, and fasteners of all types.
How do you protect metal from pressure treated wood?
To prevent treated lumber from attacking flashing and fasteners, you'll need to make sure they're made with a harder metal than copper. Hot-dip galvanized or triple-zinc coated metals are great options.
Does pressure treated wood cause corrosion?
Using pressure-treated lumber (PT) in home construction is very effective in reducing wood destroying insect activity, but it has the adverse effect of causing corrosion on most hardware and fasteners.
What should I put between treated wood and metal?
The Metal Construction Association suggests that copper-containing preservative-treated lumber should ideally be separated from metal roof or wall panels and accessory materials using a polymeric membrane material between the metal panel and the wood substrate.
Does treated wood react with metal?
When using the new Pressure-treated wood – ACQ and CA, keep in mind that they do have a higher concentration of copper, which results in a chemical reaction that discolours and corrodes aluminum and some metal fasteners.
Can you put metal on treated wood?
Pressure treated wood does not work well with metal. The reaction to the chemicals in the wood and copper which is a dissimilar metal cause the metal to rust. It is recommended that you always use untreated pine or spruce stringers to attach the metal to.
Can I use galvanized metal with pressure treated wood?
Hot-dip galvanized or stainless steel fasteners, anchors and hardware are recommended by the Preservative Treated Wood Industry for use with treated wood.
Can I use galvanized bolts in pressure-treated lumber?
The treated wood industry specifies or recommends stainless steel and hot-dip galvanized products for use with pressure treated wood.
Will pressure treated wood eat aluminum?
Does Treated Wood Corrode Aluminum? Yes. Most of the new chemical treatments contain copper and should never come in direct contact with aluminum. Total failure caused by corrosion can occur in less than a year.
Can you wrap aluminum around pressure treated wood?
You can't wrap treated wood on your porch or screen room in aluminum.
Can you use stainless steel screws in treated lumber?
The wood treatment industry recognizes the corrosive nature of ACQ in relation to fastening systems, and recommends hot-dipped galvanized or stainless steel nails be used.
What can I put between aluminum and pressure treated wood?
Alternately, a rubber or plastic mat or sheet can be installed between the treated wood and aluminum to eliminate contact points.
Can galvanized steel be in contact with pressure treated wood?
Hot-dip galvanized or stainless steel fasteners, anchors and hardware are recommended by the Preservative Treated Wood Industry for use with treated wood.
Can you wrap aluminum over treated lumber?
You can't wrap treated wood on your porch or screen room in aluminum.
Can I use galvanized bolts in pressure treated lumber?
The treated wood industry specifies or recommends stainless steel and hot-dip galvanized products for use with pressure treated wood.
How does pressure-treated lumber interact with metal?
When two opposing metals are placed together, a process called electrolysis happens, in which the harder metal attacks and erodes the softer metal. Pressure-treated lumber is often treated with one of two chemicals: copper azole (CA-C) or alkaline copper quaternary (ACQ), both of which contain copper (a harder metal). If the treated wood is situated next to flashing or fasteners made out of a metal softer than copper—like aluminum—the copper in the treated wood will attack the softer metal.
What happens when two metals are placed together?
When two opposing metals are placed together, a process called electrolysis happens, in which the harder metal attacks and erodes the softer metal. Pressure-treated lumber is often treated with one of two chemicals: copper azole (CA-C) or alkaline copper quaternary (ACQ), both of which contain copper (a harder metal).
What metal is used to protect lumber from flashing?
To prevent treated lumber from attacking flashing and fasteners, you’ll need to make sure they're made with a harder metal than copper. Hot-dip galvanized or triple-zinc coated metals are great options. And remember: Because of its lower copper content, CA-C is a more user-friendly treatment material.
How much chemical treatment is required for ACQ?
CA-C coating requires 0.15 pounds of chemical treatment per cubic foot to achieve ground contact (treated to the point that the wood can withstand rot and decay even if it’s touching the ground or leaves), whereas ACQ requires 0.4 pounds of chemical treatment per cubic foot. Since ACQ has more copper, it’s more corrosive than CA-C.
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What is the G90 coating on wood?
Today all hardware for exterior PT lumber must have a minimum G185 rating (twice the G90 coating). The G90 coating is still allowed, but only in interior dry conditions. Stainless steel is the most resistant to this galvanic corrosion, but it comes with a hefty price tag at nearly 10 times that of galvanized steel.
What is CCA in wood?
New Wood Preservatives. In the mid 1930’s a compound known as CCA, or chromated copper arsenate, was invented as a preservative treatment for lumber. CCA was very effective at discouraging fungus growth and insect activity, but the arsenic content was determined to be a human health risk.
What is galvanic corrosion?
Galvanic corrosion is an electrochemical process that occurs when dissimilar metals come into contact in the presence of moisture. I frequently encounter this problem in moist basements when I see copper water lines being supported by steel hangers.
What is the rule of unintended consequences?
The rule of unintended consequences applies to home construction just as it does to many other aspects of life. By utilizing new technology or new techniques we solve one problem while simultaneously creating another. Using pressure-treated lumber (PT) in home construction is very effective in reducing wood destroying insect activity, but it has the adverse effect of causing corrosion on most hardware and fasteners.
Is ACQ corrosive or corrosive?
ACQ is the more corrosive of the two.
Is G90 coating still allowed?
The G90 coating is still allowed, but only in interior dry conditions. Stainless steel is the most resistant to this galvanic corrosion, but it comes with a hefty price tag at nearly 10 times that of galvanized steel.
Does pressure treated lumber cause corrosion?
Using pressure-treated lumber (PT) in home construction is very effective in reducing wood destroying insect activity, but it has the adverse effect of causing corrosion on most hardware and fasteners.
What is the standard for galvanized fasteners and hardware used with pressure treated wood?
So one way to address corrosion is by raising the standard for galvanized fasteners and hardware used with pressure-treated wood to G185 instead of the original G90.
What is a fastener used for?
As we all know, fasteners are used to hold things together.
What is protective coating?
The protective coating protects the metal underneath from getting in contact with water and the copper ions from the pressure-treated wood.
What is organic polymer?
Organic Polymer Coated Fasteners. A number of manufacturers developed organic polymer coatings for fasteners. The coatings are proprietary in nature but generally work in the same way. The protective coating protects the metal underneath from getting in contact with water and the copper ions from the pressure-treated wood.
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What is pressure treated lumber?
The use of Pressure-treated lumber (PT) is a well-known strategy to reduce the potential for deterioration and wood-destroying insect activity in lumber.
Is pressure treated wood corrosion?
Summary: Pressure Treated Wood and Corrosion of fasteners has received more attention in recent years. Enclosurists should be aware of the risk of galvanic corrosion of fasteners due to the copper used to preserve the wood. Keep this in mind during design, peer reviews, and repairs. Coated, and Stainless steel fasteners are recommended instead.
What chemicals are used to treat wood?
The two most popular chemicals for wood pressure treatment are alkaline copper quaternary (ACQ) and copper azole (CA), which are both active corrosion materials. Only two corrosion protection systems are recommended for use with these pressure treatment chemicals: hot-dip galvanized steel and stainless steel.
What is pressure treated wood?
Pressure treated wood is often used for construction areas that will be exposed to the weather or in high moisture areas. The chemicals used to treat this wood were revised in 2003 to remove some of the potentially harmful elements in the treatment. The change in chemical formulations increased the corrosivity of the wood when in contact with metal parts. The two most popular chemicals for wood pressure treatment are alkaline copper quaternary (ACQ) and copper azole (CA), which are both active corrosion materials.
Can you use hot dip galvanized steel on pressure treated wood?
Hot-dip galvanized steel can withstand the harsh chemicals and slow the corrosion rate. Common metal parts used with pressure treated wood are connector plates, joist hangars, bracing plates, and fasteners of all types. All of these parts should be either hot-dip galvanized or fabricated using stainless steel to withstand the corrosivity ...
What is the chemical used to treat wood?
Most pressure-treated wood is treated with chromated copper arsenate. The metal present in the treatment chemical (copper) is dissimilar to the metal roofing (steel). I would be concerned that galvanic corrosion could degrade the metal roofing or fasteners. Galvanic corrosion occurs when electrons move away from an anode toward a cathode.
What happens when electrons move away from an anode?
Galvanic corrosion occurs when electrons move away from an anode toward a cathode. This electron transfer causes the anode to degrade, while the cathode stays intact. If you remove one of the three components (the anode, cathode or electrolyte), you can prevent corrosion.
How does metal corrode?
A metal can corrode when minuscule amounts of electricity travel through an electrolyte connecting dissimilar metals. Water is an electrolyte. Since condensation is very likely to collect on the underside of metal roofing, you have an electrical conduit waiting to be plugged in. Most pressure-treated wood is treated with chromated copper arsenate. ...
Can you use untreated purlins on a metal roof?
The easiest way to avoid this potential problem is to use untreated purlins. If you insist on using pressure-treated purlins — for example, for termite protection — you could paint the purlins or the back of the roofing to break the electrical connection. Perhaps installing a plastic spacer or a strip of self-adhering roofing membrane between the metal and pressure-treated purlins would be a more practical way to separate the dissimilar metals.
Who is Paul Fisette?
About the Author. Paul Fisette. Paul Fisette is a wood technologist and former director of the Building Materials Technology and Management program at the University of Massachussets in Amherst, Mass. Advertisement.
What chemicals are used to treat wood?
The two most popular chemicals for wood pressure treatment are alkaline copper quaternary (ACQ) and copper azole (CA). These two chemicals are active corrosion materials. Two corrosion protection systems are recommended for use with these chemicals, hot-dip galvanized steel and stainless steel. All other systems do not have enough corrosion ...
What is pressure treated wood used for?
Authored by Dr. Tom Langill. Pressure treated wood is often used for construction areas that will be exposed to the weather or in high moisture areas. The chemicals used to treat this wood have been revised in 2003 to remove some of the potential harmful elements in the pressure treatment.
