What is Pressure Treated Wood?

When you are considering undertaking an outdoor project like a deck frame or wooden fence, the first material most homeowners consider is treated wood. This popular type of timber is used in everything from planter boxes to swing sets. It’s ideal for structural applications on your property, and in this guide, we’re going to explain what it is and talk about the pros and cons of pressure treated wood as a building material. 

Pressure Treated Lumber Explained

As the name implies, pressure-treated wood is lumber that has been “treated” with chemicals that make it resilient outdoors. Lumber is inserted into a large pressurized chamber where a solution is forced deep into the core of the wood.The amount of solution used varies depending on what it’s rated for. The chemicals used to treat this special type of lumber can also vary to a degree as well, but typically involves alkaline copper quaternary, otherwise known as ACQ. Micronized copper azole or MCA is also an option but can be more expensive.

The chemicals used in the process enable pressure treated wood to remain highly resistant to the elements. They can keep termites from treating your lumber as lunch while blocking rot and decreasing the rate at which wood decays naturally. If you plan on using ACQ treated lumber, you’ll want to stick to hot-dipped galvanized steel nails or plated screws as the chemicals can cause hardware to deteriorate over time.

Types of Pressure Treated Wood

While all treated wood is created with the same general process, there are actually two types of pressure treated wood to consider for your next project. In most cases, this lumber will either be rated as AG or GC.

Above Ground Pressure Treated Wood

AG stands for above ground pressure treated wood. It’s geared for use with projects that don’t come into direct contact with the ground, so you’ll want to keep at least 6” of clearance between AG pressure-treated lumber and the ground.A few of the more popular applications for above ground pressure treated wood include fencing, trim boards, deck railing, or trellises. You can even use AG lumber for above ground decks on the second story of homes. It’s best suited for areas that can be replaced or maintained easily as these boards are as saturated as the next option.

Ground Contact Pressure Treated Wood

When you need to put a piece of wood into the ground or in direct contact with it, GC pressure-treated wood should be the only option on your shopping list. This lumber has twice the amount of preservatives infused within the core so that it can be used above or in contact with the ground outside.Common uses for ground contact pressure treated wood include framing for outdoor projects like decks, sheds, and gazebos. This wood is perfect for fence posts, sill plates, step stringers, and raised garden beds as well. On average, you can expect to pay a bit more for CG wood, but the difference could be minimal depending on where you shop.

Pressure Treated Wood Safety

While you may have found your way to our site to find out what pressure treated is, there’s a good chance you’ve also heard bad things about this product when it comes to safety. Simply put, the chemicals used to treat this type of wood are toxic, so you’ll need to take a few precautions when working with pressure treated wood.

Regardless of whether it’s AG or GC wood, you’ll want to wear a dust mask when cutting or drilling any type of pressure-treated lumber. Eye protection and gloves are a must as well, and it’s a good idea to work in a way that allows you to clean up sawdust easily. Sucking it out of the grass with a shop-vac is not ideal.

If you’re using pressure treated wood as a material for garden beds, you can line the inside with plastic to create a barrier between the soil and wood. Keep the bottom open for drainage and pre-drill any screw holes to prevent potential splits or cracks. When done, you’ll want to clean up thoroughly and wash your work clothes. 

Scraps from pressure treated wood should be handled differently as well. Sawdust and any scrap pieces of wood from your project need to be bagged and sent to a landfill. While some cities and counties will pick up construction debris curbside, you don’t want to set pressure treated wood scraps out with the trash.

Pressure Treated Wood FAQ

Q: When did manufacturers stop using Arsenic in pressure-treated wood?

A: In 2003, the environmental protection agency and lumber manufacturers came to an agreement to stop producing CCA pressure treated wood that contained arsenic. 

Q: Can I burn old pressure treated wood?

A: Burning pressure treated wood can release toxic fumes into the air, so you should always dispose of this type of lumber at a landfill where it can be handled properly.

Q: Can pressure treated wood be sanded?

A: Yes. You can sand pressure treated timber as need, but be sure to good dust mask, gloves, and eye protection.

Q: Is it safe to use pressure treated lumber indoors?

A: While there are types of pressure treated wood that have been approved by the EPA for indoor use, it’s not advised as the wood is more expensive and heavier than untreated lumber that’s used indoors.

Q: Why is some pressure treated wood green?

A: The color is caused by a chemical reaction from copper in the preservative used. It will fade over time outdoors as the wood dries out.

Q: Can I paint pressure treated wood?

A: Yes, but you will want to make sure it’s completely dry before attempting to paint or stain it. If water still beads up on the surface of the wood, it will need to dry out before it can be coated.

Q: Should you treat the cut ends of pressure treated lumber after it has been cut?

A: Even though this wood has been treated to hold up outdoors, you should always seal any end cuts when working with this lumber as those areas will have less preservatives.