The use of naturally occurring wood as a construction material can be traced back to the beginning of civilization. However, under certain situations wood being an organic material undergoes degradation. By such situations, we mean wet conditions or termite attacks. With the advancement in technology, as different kinds of preservative treatments evolved, wood can be protected from these pest attacks and also humidity attacks. Treated wood has long been in use outdoors. When there is a high risk of attack by pests or fungi, they are also used indoors. In this article, we will concentrate more on borated treated lumber and pressure treated lumber and try to differentiate closely between the two.
Need For Wood Protection
Before proceeding further, let us first investigate the need for such treatments with regard to wood.
As said earlier, naturally occurring wood is biodegradable. As a result, when prone to fungi and insect attack, they can be broken down. Fungi attacks wood when it stays wet for too long as fungi depend on water for growth. Though building may be well protected from these outside elements, excessive water exposure is still a threat which is arguably unavoidable. While outdoor wood can get wet easily, indoor wood may also get wet as a result of moisture from any leaks. Also, insects like termites which thrive in mild to hot climates, pose threat to wood in most parts of the US and Canada. Now, there are wood species that have their own protection mechanism against these fungi and insect attack. Trees like yellow cedar, white cedar, red cedar, etc. do have some kind of resistance against fungal and insect attack. However, there are a lot of other tree species who are more viable to these attacks. This is disadvantageous when it comes to their use in constructional activities. Painting wood may be considered as an option, but may not offer full protection from both fungi and insects. However, with proper treatment of the wood, you can tackle the situation. Involving well established technologies, treated wood has been in use since over 60 years. They are found to be safe and effective in their application area.
Treatment Procedure: Other Pressure Treatments Vs. Borate Treatment
Now as we already have mentioned regarding the availability of different preservatives for wood. The usage of a particular preservative mainly depends on the intended usage of the lumber. The most common treatment for lumber makes use of chromated copper arsenate, also known as CCA. Other preservatives like ammoniacal copper quat or ACQ and copper azole or CA were later introduced to replace the use CCA for certain residential applications. In the clearer picture, up until 2004, CCA was the main chemical preservative used in pressure-treated lumber, but due to health concerns, the EPA banned it in the residential market because of health concerns. Later on, copper became the main ingredient used in the treatment of lumber.
Treated wood has been in use for over a decade. Their use is mostly in outdoor applications with CCA, ACQ or CA being the popular choice for common exterior or wet applications such as fences, roofing, batten strips and sill plates. While, borates are generally preferred for indoor uses such as framing lumber.
The treatment procedure involved in the application all these preservatives remains the same, that is these preservatives are carried by water into the wood, under pressure. For this, wood products are initially loaded into a chamber. Now, a combination of vacuum and pressure are used to drive the above said preservative chemicals into the wood. As wood is impermeable, use of pressure becomes necessary. Due to this, treated wood is commonly called pressure–treated wood. So pressure treated wood is a generalized term.
Now with most pressure treatments, partial penetration is the only possibility in most wood species. So actually, the treatment creates some sort of an envelope protection. So if this envelope is breached, say like when lumber is cut at the construction site, the untreated wood will get exposed which may require further use of treatment preservatives on field. To avoid this, some pressure processes also involve incising the wood. This will make way for better penetration of these preservative chemicals when treated in the chamber. However, this is not the case with borate treated lumber. Here no incising is required.
Pressure Treatment of Lumber: Important Things to Know
So we have seen how pressure treated lumber is more or less of a generalized term. Using pressure in the treatment of wood becomes necessary as wood is impermeable. Different chemical preservatives are used in the pressure treatment of wood like CCA, ACQ, CA and bortaes. This offers the necessary protection to the wood from rot and insects. Hence pressure treatment of wood is significant for wood structures which are exposed to moisture as well as insects. Hence, decks, fences, railings, garden beds, playground equipment and other wooden structures need to be pressure treated for protection from these elements.
Pressure Treated Wood Is Not Suitable For All Applications
As pressure treated wood is acted upon by preservatives, making it resistant to rot and insects, you may think of it as an all purpose construction material. However, this is not the actual scenario. You need to be aware of the fact that pressure-treated wood can be applied for several uses but this does not make it suitable for use in all applications. Chemicals in pressure treated lumber are found to be corrosive to untreated steel and this pertains to the need for galvanized fasteners. Some framing materials like pine, spruce, fir, etc., when encapsulated behind sheathing and siding, are less susceptible to rot and insects. Hence these inexpensive choices of lumber are better preferred than pressure treated wood for interior works. Also, treating lumber causes it to well with moisture which then leaches out as the wood dries. This can cause warping and shrinking of wood making it not suitable for fine woodworking projects. Another issue is that the preservatives used in the pressure treatment of wood may leach from the wood over time. They may penetrate the water or soil around them. As you know leached copper is a threat to aquatic life and hence pressure treated lumber is not good for marine applications like for use in piers and docks. Another concern is regarding the use of pressure-treated wood for playground structures. In general, arsenic-free pressure-treated wood is considered safe option for children to be around in a play environment. However, some guidelines may suggest that children shouldn’t be around the sawdust created during the construction process. Also, pressure treated lumber, though not considered a threat to be used in raised garden beds, organic growers may disagree.
Painting Pressure-Treated Wood Is Difficult
Pressure treated lumber has the ability to retain a good amount off moisture. So with moisture content within the wood, it would be difficult for paint and opaque stains to penetrate the way as with other typical materials. Weak bonds are formed, resulting in the paint getting peeled off or sloughed off. Also, when the pressure-treated wood dries, the lumber shrinks causing the paint to crack and flake. Better option would be to use clear stains and sealers or else you need to wait for the wood to dry completely, which can take months.
Durability Of The Pressure-Treated Lumber Depend On The Concentration Of Chemical Treatment It Has Undergone
The pressure treated lumber, used for aboveground applications, where the wood does not touch the ground like those in fence slats, railings, framing lumber, etc. contain fewer chemicals. Hence they might last for around 10 years, that too with proper care and sealing. For pressure treated lumber suitable for contact with the ground, commonly used for pressure-treated posts and some framing, there is a greater amount of chemical treatment. Hence, they will last much longer, say for up to 40 years or more in some cases.
Precautions To Be Followed When Using Pressure Treated Wood
With the banning of arsenic treated pressure wood by EPA in 2004, the products available today are expected to be completely safe. However for DIYers, it is better to take some precautions. Wearing a mask when cutting or drilling pressure treated wood is a smart move. Also, you need to ensure proper ventilation and it is better to perform such activities outdoors. Also remember to dump any scrap wood left over with care. It is also not recommended to burn pressure treated lumber as the chemicals vaporized can enter your body through eyes, nose, and mouth. This may cause health hazards in some situations. So it better to avoid the occurrence of such situations.
How Borate Treatment Of Lumber Differs From Other Pressure Treatments?
So let us see how borate treated lumber differs. In Borate treatment of lumber, the chemical preservative in use is sodium borate. The preservative is actually water soluble. As a result, it is mobile in the wood and has the ability to diffuse throughout the wood in the presence of sufficient water. So when the wet wood leaves the treatment chamber, sodium borate continues to spread deeper into the lumber until it is dried for use in construction use. Once dried, with the absence of water, no further movement of borate happens and wood becomes stable. So borate treatment can be seen as providing a deeper shell of protection than other preservatives which offer only envelope protection. With the possibility of borates to spread throughout the entire cross section of the lumber, it is ensured that even if wood is cut at the construction site, there is little less concern as to exposure of the inadequately protected wood.
It is found that the diffusion property of borate works well even with hard to pressure treat wood species like Douglas fir. However, borate treated lumber is intended to be used in applications not involving constant water exposure. This is because, borates being diffusible, the presence of water can make it move out of wood. So if placed in a continuous stream of water, the preservative will migrate out and this leaves the wood unprotected.
Significance Of Borate Treated Lumber When Compared To Other Pressure Treated Lumbers
Naturally occurring salts, borates result from the combination of oxygen and boron. They are found as mineral deposits around the world. In the United States, the deserts of California have them in abundance. They find application in hand soap powders, laundry boosters, contact lens cleaners, eye washes, cosmetics, ceramics, medicines, etc. among many others. Harmless to human health, borates are considered for use as wood preservatives for interior wood works. Also being inorganic, there are no volatile organic compounds causing air pollution and harmful odours.
There are two different types of borates used as wood preservatives: sodium borate and zinc borate. Sodium borate (specifically, Disodium octaborate tetrahydrate or DOT), is used for treating lumber and other solid wood products. Zinc borate, having low solubility borate, is mainly used in the treatment of wood composites. Borate treated lumber usually retains the color of the wood. While with other pressure treated lumbers, it tends to change the color of the wood.
Borates are very effective at inhibiting insects and fungi. They act by disrupting the digestive process of the insect which causes it to starve. With fungi, they act by preventing their enzymic activity at the cellular level. If we observe in detail, for a broad range of insects and fungi, about 0.2% borates by weight in lumber is sufficient enough to keep them under check. However, for termites you may require a higher level of preservative. The level of preservative depends on the termite species. If you consider the case of Formosan subterranean termite, which is one of the world’s most economically significant pests for wood products, it requires approximately 2% borates by weight in lumber. After biting the borate–treated lumber, the termites will spread the chemical through their large colonies. This happens during their grooming activities in the nest. The termites upon sensing that the consumption of the borate treated wood is dangerous to the colony’s health will move on and find a better source of food.
Now, the borate–treated wood will look and handle just like untreated wood. It is generally colourless, though some treating facilities may add a colourant just for the sake of identification. As is the case with any other wood, it can also be drilled, sawn, glued and finished. Also, it is recommended that all mechanical fasteners can be used. It is also found that borate–treated wood can be used in contact with other types of building material. However, for cut ends and holes, you may have to use field preservatives or else the wood will still be at risk of biodegradation.
Mostly used indoors, borate–treated wood can still be used for some outdoor applications with adequate protection from the rain. However, this may require it to be painted with a primer coat and two top coats of exterior grade paint. Varnishes and penetrating stains are not found to provide adequate rainwater protection for the borates.
It is better to keep the borated treated wood dry and covered when used in construction. However, no significant losses in chemicals have been reported when exposed to limited moisture levels.
Also, in most municipalities, borate–treated wood waste can be disposed in the same manner as untreated wood. You may have to check with the local regulations to guarantee the same.