Treated vs. Untreated Wood: A Comprehensive Guide

You have heard about pressure-treated wood or timber, but what is it really? Here at Trex, we deal not only with composite but also timber decks. Besides composite, people have several choices for their deck build. One of the most common hardwood materials is pine. Cedar runs a close second, with redwood being another popular choice.

Even though Trex Australia specializes in composite, our decks have timber undersides. As a proprietor, I have many years of experience with multiple types of timber and can tell you with certainty that using pressure-treated lumber is the way to go. Using joist tape and pressure-treated timber will help increase your deck’s lifespan and protect it from the damage caused by natural elements. We’ll check out the pros and cons of using timber for decks and other various outdoor uses.

 Treated vs. Untreated Wood

As mentioned, pressure-treated lumber will have more resilience and durability than untreated lumber. Pine, among a few other materials, is one of the main types of hardwood used in deck building. Pressure-treating your pine will protect it from harsh temperatures, direct sunlight, moisture, rot, and insects, such as termites. When timber is used inside for cabinetry and similar indoor woodworking projects, it doesn’t have to be pressure-treated.

Applications of Pressure-Treated Wood

Pressure-treated timber is perfect for outdoor use, such as decks, fencing, gazebos, pergolas, and garden beds. The pressure-treating process guards against rot and other issues that accompany a structure’s outdoor use. Ground contact, like with playground structures, can lead to further mould damage, so protecting your timber is essential to prevent this.

What is Pressure-Treated Wood?

Pine (or fir) is sourced from the land then taken to a treatment facility. At the facility (or plant), it’s then treated with chemicals that prevent it from rotting, warping, and becoming infested with termites. Timber treated with these chemicals will be safeguarded from extreme temperatures, which will increase its longevity.

Pre-treating timber for playgrounds, marina docks, and decks involves chemicals that could potentially keep the timber in relatively good shape for three or four decades. The average well-maintained timber deck can last quite a few years, though it probably won’t last several decades!

How is Pressure-Treated Wood Made?

The timber is likely already in planks from the mill where it was sourced. At the treatment facility, the planks are then loaded by forklift onto a conveyor and into a large steel cylinder called a vacuum pressure vessel. Air is removed from the cylinder using an industrial pump, and thus the timber, too.

The vacuum pressure vessel is then filled with wood preservatives that are forced deep into the lumber material. The cycle length and pressure levels are adjusted to the type of timber being treated. Then, the cylinder is drained. Afterwards, the timber is removed from the vessel and placed on a drip pad at the lumber yard for one to two days (around 24 to 48 hours).

Potential Environmental Impact

There are some chemicals involved in the pressure-treating process. For a while, CCA or chromated copper arsenate, was used in the timber treatment method. CCA provides ultraviolet protection and resistance to moisture damage and insect activity. It’s an effective preservative, but it has had some negative effects on the environment. This includes the risk of arsenic or other contaminants leaching into the soil. Nearly two decades ago, the Australian Pesticides and Veterinary Medicines Authority (or APVMA) restricted the use of this particular preservative for certain outdoor applications where the incidences of human contact were highest. (Handrails, benches, playground equipment, and the like.)

ACQ, known as alkaline copper quaternary, is more widely used today. This chemical helps shield against moisture, a wide range of temperatures, and insect infestation. ACQ has been deemed to be better for the environment than CCA, but a major drawback is that ammonia compounds are released into the air during this process. Therefore, using gloves, dust masks, and eye protection is very important. Additionally, fasteners made of copper, stainless steel, or hot-dipped galvanized steel to prevent corrosion are necessary when installing timber that’s been pressure-treated with ACQ.

Benefits of Pressure-Treated Wood

Homeowners who use timber outside for decks, playgrounds, pergolas, and other similar structures should use either pressure-treated timber or composite. Other types of hardwood don’t need to be pressure-treated, such as cedar, ipê, and redwood. Pine, by far, is the most common material used in decking and for a variety of other outdoor projects due to its cost-effectiveness and ease of obtaining.

To get the most out of your pressure-treated timber deck, it is recommended that you have regular cleanings, check your deck routinely for potential maintenance issues, and seal it. Using a sealant is necessary to ensure your deck has a long life. It will also protect it from direct sunlight, moisture, and rot. Staining or painting your deck is another way to keep it in top shape.

Besides rot and insect resistance, pressure-treated timber won’t split as easily, and warping will be minimal. It’s also flame-retardant, as the chemicals will slow down the heat from affecting the material. The lifespan of treated timber ranges from about 10 to 15 years, sometimes even longer. Although timber treated with wood preservatives is more expensive, it is ultimately worth it.

What is Untreated Wood?

Untreated wood or timber has yet to have this chemical process applied to it. Most hardwoods used for indoor purposes are cedar, oak, and maple. They are utilized primarily for DIY woodworking projects. Timber furniture such as bed frames, chairs, dining tables, bookshelves, and the like are prime examples. Wainscoting, which is panelling that’s usually in the lower part of a room or hallway, is another indoor application of untreated timber.

Because it is not exposed to the elements, this type of timber does not need to be chemically treated. Some people may opt to kiln dry it, but it’s not necessary for the aforementioned timber types. Furthermore, when cared for properly, the natural beauty shines through. Timber furnishings and cabinets can last an extremely long time. Attractive woodworking projects, such as dressers, desks, cabinetry, and mantles, will complement home décor and give a natural ambience to whatever setting they are adorning.

Choosing Between Treated and Untreated Wood

Your type of project will guide your decision to use pressure-treated versus untreated timber. The general rule of thumb is to use untreated timber for indoor projects and treated lumber for outdoor use. Regarding outdoor use, there are many options for durable materials.

Most people will build their decks either with composite or timber, so it is a wise idea to do research and see what will function best for you. Take into consideration the climate, as that will be a factor in your choice. Whatever you decide, Trex is always standing by with sustainable and beautiful composite.