One of the most used building materials on Earth is wood, and the reason is quite apparent—it has several valuable properties like small bulk density, low heat conductivity, workability, relatively high strength, and many other properties. Despite its usefulness, it is fraught with one downside—its susceptibility to rot. This vulnerability to rot makes many construction stakeholders think twice about using wood. Moreover, many of them shift to the use of other materials that are more durable and lasting.
However, this apparent weakness of wood as a building material should not deter you from using it. Besides, there are many rot-resistant wood species that could last even for several centuries. These rot-resistant wood species are highly sought after by woodworkers and large corporations. Most of these rot-resistant wood species are expensive. Plus, many of them are overly harvested, making them very rare.
What is Wood Rot?
Since wood is a natural construction material, it is susceptible to rot, unlike concrete and other construction materials. Wood rot, however, means the wood will decompose over time, being biodegradable. The action of bacteria and fungi, for example, can make the wood deteriorate over time. Besides, termites and insects can gnaw on wood fibers causing the wood to decay.
Fungi thrive in humid environments. Thus, if you can keep wood dry, you can arrest the decomposition process of wood. But once moisture gains its foothold on the wood, microbial life will begin to thrive, causing the internal fibers of the wood to weaken and rot. Once the wood’s internal structures get damaged, it will disintegrate.
Why Does Wood Get Rotted Anyway?
Those who work with wood should understand the nature of wood. Besides, they know that the archenemies of wood are fungi and insects. Yet, insects can only get attracted to wood if the wood is wet. So, the first enemy that moves in to attack wood is the fungus.
Fungi are plants that carry chlorophyll. They are unable to manufacture their food like other plants via photosynthesis. As such, they thrive in taking food from materials like wood. They encroach into the very fibers of the wood and begin eating away the fibers of the wood.
Measuring Scale for the Level of Resistance of Wood Against Rot
As mentioned above, there are many species of wood, and each species exhibits a different level of resistance to rot. Some species are well endowed with tough fibers and higher density, making them almost impervious to rot.
Some carry complex chemical compounds that make them rot-resistant. These complex compounds are byproducts of long evolutions, allowing these wood species to develop ways to make them resistant to pests and moisture.
No standard scale is available or has been established to indicate the level of wood resistance to rot. Besides, experts only approximate the possible duration of a wood’s lifespan, given certain conditions. So, if a particular wood species is durable, it means it has greater resistance to decay. Thus, the measurement of wood’s resistance level to decay is still a qualitative measure or parameter.
How and What Makes Wood Rot-resistant?
Throughout the evolution of Earth, various species of wood have evolved that show high resistance to decay and rot. So, if you’re a woodworker, you would love to know these wood species. Wood types like Teak, Patagonian Rosewood, and many others show exceptional rot resistance. But what makes them resistant to rot? Below are some natural properties of these wood species that make them resistant to rot:
They Have Natural Oils
Most wood species with high resistance to rot exhibits a high level of natural oil that deters fungi and insects from damaging them. Aside from protecting themselves from insects and fungi, these natural oils also keep the inner fibers of the wood healthy and capable of quick expansion.
Enterprising people collect these natural oils and create stains and finishes to protect their wood projects. Examples of these natural oils are Tung oil and linseed oil. Hence, it is evident that these naturally occurring oils can likewise preserve the exterior of wood from damage due to fungi and insects.
The presence of these naturally occurring oils protects the wood from moisture damage. They ensure that moisture will not imbue the very fibers of wood, preventing the thriving of fungi and bacteria. Thus, if you would like to protect the wood with naturally occurring oils, you also need to reapply them intermittently to keep the wood protected.
They Secrete Extractives
Aside from the naturally occurring oils, wood quite resistant to rot also exhibit a high level of wood extractives or compounds that lower their susceptibility to decay. These compounds or extractives deter insects and fungi from inhabiting wood fibers.
These extractives occur naturally in the heartwood of the wood species. Examples of these compounds are resins and substances like triglycerides and polyphenols that ward off invasive organisms, preventing them from infesting the bark and fibers of the wood.
Harder Heartwood
When you cut a tree, you will discover it has heartwood and sapwood. Heartwood refers to the inner and more stable part of the wood. It is also the older part of the tree wood and differs from the younger sapwood.
Heartwood gets formed when the sapwood graduates from carrying water and nutrients. Heartwood is harder and darker than sapwood, and manufacturers use heartwood for producing furniture. Heartwood is more resistant to fungi and pests than sapwood because it is denser and more solid than sapwood.
The formation of the heartwood varies from one wood species to another. Some trees can form heartwood faster than other wood species. On average, a tree begins to form when the tree is almost ten to fifteen years of age. The formation process also goes on until the tree is living.
Pressure Treating Wood
One unnatural way of enhancing wood’s rot resistance level is by pressure treating it. After the pressure treatment of wood, the wood gains a certain level of rot resistance, making them more impervious to insect and fungi attacks. This method is a proven technique for extending the lifespan of the wood.
Wood, of course, shows pores, which are the breathing holes of the wood. These pores let air come out and allow moisture to come in, making the wood susceptible to the adverse effects of moisture.
When wood is pressure treated, it gets positioned inside a pressurized container. This container then gets filled with chemicals. The chemicals get pressurized into the very wood fibers. Then the wood is taken out of the chamber. The drying process lets the chemicals integrate with the wood fibers, making the board more resilient against harsh external factors.
Best Rot Resistant Wood Species
Rot-resistant wood species are often categorized into moderately rot-resistant, rot-resistant, and highly resistant to rot. Below are examples of the following given categories of rot-resistant wood species:
Moderately Rot-resistant
Some species of wood exhibit moderate resistance to rotting, and many woodworkers like to use this wood, especially in areas exposed to moisture. Below are some examples of moderately rot-resistant wood:
- Cypress: Cypress is moderately rot-resistant. It grows in a temperate region and consists of various coniferous tree species. Cypress usually grows in wetland areas of the U.S. It is durable, rot-resistant, and exhibits insect resistance.
- Redwood: We all know the giant Redwood of the Western United States, and these trees are mostly old-growth trees. The wood of these trees is moderately rot resistant.
- Old-growth Pine: Pines do not exhibit resistance to rot, but if you ever chance upon an old-growth Pinewood, you will notice that it is resistant to rot. You can find old-growth pinewood on old homes and shiplap siding.
Rot-resistant Wood
Aside from moderately rot-resistant wood, some wood species also get categorized as rot-resistant. Below are the well-known rot-resistant wood species:
- Old-growth Cypress: Old-growth Cypress comes with more heartwood, and this heartwood is rot-resistant. It is also harder and more durable.
- Western Red and Eastern White Cedar: Cedar has long been used for its resistance to rot. It is perfect for exterior applications. You can stain it with oil primer (stain blocking) to prevent bleeding of cedar before you paint it.
- White Oak: White Oak exhibits exceptional hardness. Thus, this wood has been used for a long time for doors, windows, and fine furniture. It also gets used as flooring.
- Old-growth Redwood: As mentioned above, old-growth Redwood belongs to those wood that exhibits rot resistance. Besides, it is pretty resistant to insect attacks.
- Pressure-treated Pine: You can quickly gain access to pressure-treated Pine because they are readily available. You can purchase it at home stores. This pressure-treated Pine shows remarkable resistance to insects and rot. Moreover, it accepts paint and stains well.
Extremely Rot-Resistant Wood
Some wood species exhibit extreme hardness. They are also very heavy and durable. Besides, they are sought-after wood species. Below are examples of these wood species:
- Mahogany: Mahogany is very hard and dense. Thus, termites and other insects will lose their teeth and leave this wood unscathed. This wood is likewise beautiful when finished. For this reason, many homeowners love to use this wood for their doors and furniture. It is also very expensive.
- Spanish Cedar: Spanish Cedar is very dense and hard. It is similar to Mahogany but less expensive than Mahogany. It is a perfect choice for exterior trims and windows because of its remarkable stability, though this wood is becoming rarer.
- Teak: Teak is another rot-resistant wood. For this reason, it is often used for decks and other applications exposed to moisture. You can leave this wood in its natural state outdoors without finish, and it will not decay. Nevertheless, it is challenging to work with and requires pre-drilling when fastening it.
- Ipe : Ipe is similar to Teak in its hardness. It is also perfect for porches and decks. Besides, it has a rich reddish color that gives it a rich and beautiful appearance. Ipe is a hardwood with a very high Janka hardness rating. It exhibits tight grain that prevents moisture from imbuing its very fibers. You can make this wood last a very long time if you oil it intermittently.
- Accoya: Accoya is pretty much decay-proof. This wood is a byproduct of treating Radiata Pine with chemicals to make it very stable dimensionally. The treatment process of this wood is referred to as “Acetylation.” Accoya is not a pressure-treated wood. Besides, it contains no harsh or toxic chemicals that could compromise your health.
Conclusion
Wood that is rot resistant is becoming rarer and rarer. Teak, for example, is expensive and rare. Ipe is also rare and expensive. Hence, many manufacturers pressure treat wood to make them more resistant to fungi and insects. These pressure-treated wood becomes excellent alternative to rot-resistant wood. Nevertheless, even if a wood species is known to be resistant to rot and insect, it will also help if you add a layer of protection to their bare surface to enhance their resistance to decay further.
After all, these wood species are still biodegradable.
By adding, for example, Tung or Linseed oil to the surfaces of these wood, you can further prolong their longevity and enhance their durability. Besides, if you stain them, you can improve their appearance while protecting them from the harsh elements of the outdoors. So, it will help if you keep a keen eye on your wood projects and engage in regular maintenance to ensure they would last longer than you expect.