A wood treating plant changed hands in Georgia in early 2024, and the deal quietly expanded pressure-treated lumber capacity across the Southeast. An Alabama distributor bought the facility and its associated assets in Ringgold, Georgia, and announced it would treat a full range of pressure treated wood at the site with MCA, a modern copper-based preservative. The buyer, founded in 2006, already served customers in 19 states with treated and untreated lumber plus aluminum railing and composite decking.
Consolidation has already reshaped the equipment rental landscape, and the same playbook now runs through wood preservation, where regional plants are being bought, expanded, and retooled for newer chemistries. For builders, the practical questions are simpler: what gets treated, how the treatment works, and which grade belongs in which part of the building. This article explains the process, the preservatives, the stamps, and the applications that decide whether treated lumber earns its place.
What Pressure Treating Does to Wood
Pressure treating pushes preservative deep into the wood so the protection survives cutting, weathering, and years of ground contact. The process happens inside a horizontal steel cylinder at a treating plant, and the result is lumber that resists fungal decay and insect attack for decades in the right exposure.
How a Treating Cylinder Works
The process inside the cylinder follows five steps:
- Lumber is stacked on carts with spacers between layers so preservative can reach every face.
- The carts roll into a horizontal steel cylinder that seals at one end.
- A vacuum draws air out of the wood cells.
- Preservative floods the cylinder under high pressure and drives deep into the cell structure.
- A final vacuum recovers excess solution, and the lumber rolls out to drip and dry.
Retention measures how much preservative stays in the wood, usually expressed in pounds per cubic foot. Penetration measures how far it travels from the surface. Both numbers appear on the treatment stamp and both determine the use category the lumber qualifies for.
The practice dates to the 1930s, when railroads treated ties to extend service life. Residential use grew after World War II, and the chemistries moved from creosote and CCA to the copper systems in use today.
Finishing and Storing Treated Wood
Freshly treated lumber arrives wet and needs to dry before paint or stain will adhere. Finish materials deserve the same care, and smart storage methods for preserving wood finishes keep cans stable between jobs. Stack treated lumber off the ground, separate the layers, and cover it loosely so air moves while rain stays out.
Preservatives Compared: MCA, ACQ, and CCA
Modern residential treatment relies on copper-based preservatives. The two most common are MCA, micronized copper azole, and ACQ, alkaline copper quaternary. The older chemistry, CCA, chromated copper arsenate, left the residential market in 2003 after the industry withdrew it.
| Preservative | Active chemistry | Typical use | Notes |
|---|---|---|---|
| MCA | Micronized copper and azole | Residential decks and fences | Light color, lower corrosivity |
| ACQ | Copper and quaternary ammonium | Ground contact, freshwater | Brown-green, use rated fasteners |
| CCA | Copper, chromium, arsenic | Industrial and agricultural | Restricted from residential |
| Borate | Boron salts | Interior, insect-prone areas | Not for exterior wet exposure |
Micronized copper is ground fine enough to stay suspended in water, and azole adds a fungicide. ACQ keeps copper in solution instead, which gives ACQ-treated lumber its darker green-brown cast and its higher corrosivity.
Color is a rough guide, not a spec. MCA lumber often carries a light tan or green cast, ACQ runs darker, and weathering grays both over time. The end tag, not the color, is the document that matters.
Regional Capacity and Supply
Regional capacity follows demand. The Southeast gained a treating plant when an Alabama distributor acquired the Georgia facility, and a separate operator announced plans to expand its Louisiana facility to serve the shed and trailer markets. When treating capacity grows near a market, freight drops and lead times shorten.
Corrosivity and Fasteners
Copper-based preservatives accelerate corrosion of plain steel fasteners. Hot-dipped galvanized or stainless hardware is the standard for ACQ and MCA lumber, and connectors, hangers, and joist straps need the same rating. The treatment stamp often lists the required fastener class.
Where Treated Lumber Earns Its Place
Treated lumber handles the parts of a building that stay wet: decks, fences, retaining walls, sill plates, porch framing, and anything that touches concrete or soil. It also shows up in utility trailers, portable barns, pallets, and crates, where exposure to weather and cargo moisture is routine.
Ground Contact and Above-Ground Grades
Use categories run from UC1, interior dry, to UC4B, ground contact in severe climates. Above-ground lumber resists decay but rots quickly if buried, so the grade has to match the exposure. Ground-contact grade carries roughly double the retention of above-ground grade in most preservatives.
Treated wood also carries cost advantages in the right application. A ground-contact post rated for 40 years costs a fraction of a stone or steel equivalent, and the installed cost stays competitive because local crews already know how to cut and fasten it.
Marine applications sit at the top of the exposure ladder. Salt water attacks wood fast, and the treating industry rates marine-grade piles separately, with retention levels well above ground-contact grades.
The load path runs from the treated sill plate into the concrete foundation, and that joint is only as good as both materials. The concrete side depends on the local ready-mix market, where cement companies across the United States supply the slabs and footings that treated members bear against.
Fastener and Connector Selection
Choose connectors rated for the preservative. Galvanized hangers and screws labeled for treated lumber hold up, while electroplated hardware fails within a few seasons in ground contact. Stainless steel is the safe call for marine and high-moisture sites.
Reading the Stamp: Retention, Penetration, and Standards
Every bundle of treated lumber carries an end tag printed by the treating plant. The tag records the preservative, the retention, the use category, and the year of treatment, and it is the warranty document for the product.
What the End Tag Tells You
- Treating company and plant code
- Preservative type and retention level
- Use category and exposure rating
- Year of treatment
Retention by Exposure
Above-ground deck boards commonly carry 0.15 pounds per cubic foot of copper-based preservative, while ground-contact members run 0.40 or higher. Match the number to the job: a higher retention costs a little more and buys a lot more service life in wet soil.
Third-party inspection agencies audit treating plants against AWPA standards. The stamp is only as good as the inspector behind it, and reputable plants display the agency’s mark alongside their own.
Water and the Treating Process
Water chemistry influences how evenly a preservative penetrates, because the treating solution is waterborne. High-iron or acidic supply water can complicate the mix, the same reason a homeowner with corrosive well water researches treating acidic well water before it damages pipes and fixtures.
Treated Wood in the Building Envelope
Inside the envelope, treated lumber shows up at the points most exposed to moisture: sill plates on concrete, floor joists over crawlspaces, and wall framing near grade. Getting these details right keeps the structure dry for decades.
Crawlspace and Foundation Details
Floors over crawlspaces put treated lumber in a damp environment, and treating a crawlspace as a conditioned space changes the moisture load those members see. Sealing the crawlspace and adding vapor control lets the framing dry out instead of cycling between wet and damp.
Termite shields and capillary breaks add a second line of defense above the treated members. A metal shield between the foundation and the sill plate blocks the path insects use, and a sill gasket seals the joint.
Cutting, Drilling, and Field Treatment
Cutting and drilling expose untreated wood at the heart of the member. Field-applied preservative, usually copper naphthenate, coats cut ends and drill holes, and it is required on ground-contact cuts in most jurisdictions. Brush two coats on the end grain and let the first dry before the second.
Choosing Treated Wood for the Job
The right purchase starts with the exposure, not the color. A deck board, a fence post, and a sill plate need different retentions, and the end tag tells you which one you are buying.
A Selection Checklist
- Match the use category to the exposure, above ground or ground contact.
- Confirm the preservative suits the region’s termite and decay pressure.
- Buy from a plant with a current, legible end tag.
- Store bundles off the ground and covered loosely until install.
- Use fasteners and connectors rated for the preservative.
Disposal rules matter. Treated wood should not be burned, because the preservative concentrates in ash. Most jurisdictions accept it at construction and demolition landfills, and some mills now recycle it into composite products.
Seasonal buying smooths the price. Treating plants run year-round but builders buy in bursts, so early orders in late winter lock in lower freight and steadier supply.
The interface between wood and masonry deserves attention too. Where treated members meet foundation walls, understanding and treating damp masonry keeps the joint dry and stops moisture from wicking into the framing.