I heard an analogy recently that “Pressure treatment is to wood what embalming is to humans.” If that analogy is accurate (and I think it is), it’s all we need to know to understand the dangers of using pressure treated (PT) wood. Pumping toxic chemicals into wood–or into bodies–to extend the preservation lifetime has negative effects on the environment those chemicals will eventually come in contact with, not to mention health effects associated with workers handling such toxic chemicals.
But . . . you have a porch to build. And now you don’t want to use PT lumber? Luckily there are many alternatives. Below is not a 100% complete list, but only a quick and dirty list of what’s available these days . . .
Pressure-treated minus toxic chemicals
The kebonization process soaks wood in a specific alcohol that is a waste byproduct from sugar cane and the alcohol functions as a resin that guards the cell structure of the wood. Unlike PT lumber, there are no precautions beyond normal to work with this wood or to handle clean up.
Very similar to Kebony, but instead of using a byproduct of cane sugar, acetic acid is used. The process of acetylization transforms the cell structure of the wood so that it is does not shrink or expand a lot and is thus minimally affected by changes in moisture levels. The company argues that this feature makes Accoya more dimensionally stable than conventionally pressure-treated wood.
Glass fortified lumber
Lumber infused with sodium silicate (liquid glass) and heated up so it forms a glass-like cell structure, protecting the wood from fire, rot and insect damage. The process increases the strength and hardness of the wood and is good for ground contact applications.
Plastic decking material. Works great, doesn’t rot (but is plastic).
Wood is subjected to pressure and heat, driving out all the moisture. Though there is evidence that suggests it may not work as well as infusing the wood cells with substances (like Kebony/Accoya), it is attractive because there is no added product to the wood. As benign as acetic acid is, it is still a chemical. Downside is the energy intensity needed for the heat treatment, but it improves durability, stability and hardness of the wood. There are three main brands that have been developed: Retiwood, Thermowood and Platowood.
Ipe, Cumaru, Tigerwood, Garapa. All of these woods are rot resistant and often have very interesting patterns, making for a very unique deck. Unfortunately, exotic hardwoods are often from South American countries, not making it a locally sustainable solution. There is no argument that it is great decking material, but if you are concerned with rainforest deforestation, then perhaps some other alternative will suit you more.
Naturally rot-resistant North American woods
Black Locust, Eastern Red Cedar, Redwood, etc. Many trees have rot-resistant qualities, unfortunately many are prohibitively expensive to use given that they have been overharvested. If you choose these woods, be careful of your source. White oak is also a pretty good east coast wood to use, though it turns black rather easily with exposure to water. They build ships out of the material, so it is definitely rot-resistant, but it is not as stable as other materials over time.
Though not recommended for wood experiencing prolonged ground contact, treating wood with tung oil is an effective method for preserving exterior wood. Given that the oil only penetrates millimeters into the wood, it has to be reapplied often.
There are associated costs with using some of these “greener” products. Or maybe not? That’s where material reuse comes in. If you are creative enough, you can find cheap solutions. Find someone else making a deck and use their cutoffs (if you don’t mind short boards). Decking jobs are like tiling . . . often the customer will have several pieces left over . . . collect them from neighbors over time and voila! A new deck using materials that would have been thrown out!