Maya Ellison
Cordwood masonry is a popular construction method, with some opting to build their own homes using this technique. However, one of the challenges of cordwood construction is managing moisture to prevent wood rot and mould. One proposed solution is to cover cordwood with clear plastic sheets to speed up the drying process. This method is similar to a passive solar wood-drying kiln, creating a greenhouse effect that draws out moisture. While this approach can be effective, adequate ventilation is crucial to prevent trapped moisture from causing rot and mould issues.
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What You'll Learn
- Plastic sheets can create a greenhouse effect, drying wood faster
- Wood must be dried to 12% moisture content to avoid shrinkage and rot
- Hardwoods are not ideal for cordwood due to swelling and cracking
- Cedar is the best wood for cordwood due to low shrinkage and rot resistance
- Plastic roofing can prevent water from migrating up cordwood walls
Plastic sheets can create a greenhouse effect, drying wood faster
Plastic sheets can indeed create a greenhouse effect, drying wood faster. This is a well-known method for drying wood, with many people discussing its effectiveness online.
The process involves creating a frame and covering it with plastic sheeting, which can be an affordable way to dry wood. The plastic sheeting should be high-quality, UV-resistant, and durable. It is also important to ensure that the plastic is not pulled too tightly, as it needs some flexibility to withstand wind and weather conditions. Sealing any gaps with duct tape or adhesive can improve insulation and help maintain a stable temperature.
Some people have suggested that covering wood piles with plastic can create a "greenhouse effect" on hot sunny days, drawing moisture out. However, others have warned that without proper ventilation, the moisture will condense, leading to rot and mould. One person suggested building a frame and draping it with clear plastic, then using a fan to exhaust the warm, moist air through an exhaust port.
Covering just the top of a woodpile may be a better option, as it allows air to circulate while keeping rain off the wood. This method has been found to be successful in drying wood quickly. Another suggestion is to use rigid, waterproof roofing with a sufficient drip edge to prevent water from running down the sides of the stack.
Overall, while plastic sheets can create a greenhouse effect to dry wood faster, it is important to provide adequate ventilation to prevent mould and rot.
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Wood must be dried to 12% moisture content to avoid shrinkage and rot
Wood is hygroscopic, meaning that it exhibits a strong attraction to water. This means that moisture influences the strength of the wood. As humidity increases, so does the moisture in the wood, causing it to expand. As humidity decreases, the moisture in the wood decreases, causing it to shrink.
Woodworkers want to use pre-shrunk wood to avoid issues with shrinkage and warping after the wood has been used. The ideal moisture content for wood varies depending on its intended use and the average humidity of the environment in which it will be used. For example, wood used for indoor structural timber needs to be around 20% moisture content or less. Wood with a moisture content of 8% will still shrink and may be more prone to warping.
To avoid shrinkage and rot, wood must be dried to a moisture content of around 12%. This is because wood will eventually adopt the same moisture level as the air around it. If wood is installed in a less humid environment than it was dried in, it will lose moisture and shrink. For example, wood with a moisture content of 12% that is introduced to an environment with 20% relative humidity will eventually reach a moisture content of 4%, causing it to shrink.
To dry wood, some people suggest covering wood piles with clear plastic to create a greenhouse effect that draws out moisture. However, this method must be done carefully to avoid trapping moisture, which can lead to rot and mould. Instead, it is recommended to provide ventilation for warm, moist air to escape.
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Hardwoods are not ideal for cordwood due to swelling and cracking
Cordwood masonry is a beautiful natural building method. However, when it comes to choosing the right wood for cordwood, hardwoods are not ideal. This is because hardwoods are dense and have a tendency to swell, which can cause mortar joints to crack. This can lead to walls being pushed out of plumb and even knocked apart.
Indeed, hardwoods are more prone to expansion and contraction than softwoods, and this can cause problems in cordwood construction. If a hardwood log experiences extreme contraction, gaps can form between the log and the mortar, providing an ideal breeding ground for moisture, mould, bacteria and fungi to enter and spread. On the other hand, if a hardwood log expands too much, the swelling could push the mortar apart and buckle the wall.
These issues can be mitigated to some extent by following certain methods. For example, building off of grade and using a pressure-treated bottom plate can help to prevent moisture from seeping into the mortar and causing the wall to swell. Using larger mortar joints can also help to manage the pressure created when hardwoods swell. However, these extra steps may not always be feasible or effective, and it is important to note that hardwoods can still swell during high humidity.
Therefore, softwoods are generally recommended for cordwood construction. Cedar, in particular, is considered ideal due to its rot and pest resistance, as well as its ability to dry out on its own if it gets wet. Other softwoods, such as tamarack, can also be used but may require additional steps such as splitting and drying to prevent them from behaving like hardwoods.
In addition to choosing the right type of wood, there are other considerations for ensuring the success of a cordwood project. Properly dried logs, for example, are less likely to shrink dramatically and create gaps for moisture to enter. Covering wood piles with clear plastic sheets can help speed up the drying process, although adequate ventilation must be provided to prevent moisture buildup and promote the escape of warm, moist air.
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Cedar is the best wood for cordwood due to low shrinkage and rot resistance
When building with cordwood, it is important to consider the type of wood being used. The best type of wood for cordwood is one that is naturally rot-resistant, disease-free, decay-resistant, insect-resistant, soft, and has a low shrinkage rate and a high R-value.
Cedar is a popular choice for cordwood due to its low shrinkage and rot-resistant properties. Cedar is a softwood species native to the western regions of North America. It contains natural oils and resins that protect it from moisture damage and decay caused by fungi and other microorganisms. These oils give the wood a distinctive aroma and colour, ranging from light brown to deep red or reddish-brown. Cedar is also lightweight and has a pleasing colour, making it an ideal choice for cordwood construction.
Other types of wood can also be used for cordwood, such as pine, tamarack, and aspen. However, it is important to consider the volumetric shrinkage rate of the wood, as some woods may shrink more than others. For example, red alder has a volumetric shrinkage of 12.6%, while cedar has a volumetric shrinkage of 7.2%.
It is also important to properly dry the wood before using it for cordwood. This can be done by placing the wood in the sun or using a passive solar wood-drying kiln. Additionally, covering wood piles with clear plastic sheets can help speed up the drying process by creating a greenhouse effect on hot sunny days. However, it is crucial to provide ventilation to prevent moisture buildup and the growth of mould and rot.
Overall, cedar is an ideal wood for cordwood due to its low shrinkage, rot resistance, pleasing colour, and aroma. With proper preparation and drying, cedar can provide a successful and stable cordwood building material.
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Plastic roofing can prevent water from migrating up cordwood walls
Plastic roofing can be an effective way to prevent water from migrating up cordwood walls. While cordwood construction has a long history, dating back over a thousand years, it requires careful planning and maintenance to ensure its longevity.
One of the critical challenges in cordwood construction is protecting the structure from moisture damage. The end grain of the logs used in cordwood walls is particularly susceptible to water absorption, which can lead to issues such as rot, mould, and fungal growth. To mitigate this, it is essential to keep the log ends dry and protect them from exposure to rain and snow.
Plastic roofing provides an effective barrier against water infiltration. By extending the roof overhang to at least 16 inches, or even further if possible, you can create a protective cap that shields the cordwood walls from splashback. This simple measure helps to control moisture damage and prevent water from migrating up the cordwood walls.
Additionally, plastic roofing made from materials such as EPDM roof membrane or rubber membrane can be used in earth-sheltered cordwood buildings. These materials create a waterproof barrier that protects the structure from water infiltration, ensuring that the cordwood walls remain dry.
However, it is important to note that proper ventilation is also crucial when using plastic roofing. While plastic can help keep water out, it can also trap moisture inside, leading to condensation and potential mould issues. Therefore, adequate ventilation is necessary to allow warm, moist air to escape and prevent moisture buildup within the cordwood structure.
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Frequently asked questions
Plastic under cordwood can help to dry the wood, but only if it is adequately ventilated. The plastic creates a greenhouse effect, which draws out moisture. However, if the moisture is not allowed to escape, it will condense and cause rot and mould.
Cedar is the best wood to use for cordwood due to its low shrinkage rate, insect and rot resistance, light weight, high R-value per inch, and pleasant aroma. Other softwoods can be used but are more prone to insect infestation and should be treated with a borax solution. Hardwoods should be avoided as they tend to swell and crack mortar joints.
The ideal moisture content for cordwood is 12%. Drying your logs to this level ensures that they will be stable in the wall and less likely to crack due to expansion.
The time it takes to dry cordwood depends on the local climate and the time of year. In hot and dry weather, logs can dry out in a matter of hours or days, while in more humid conditions, it can take weeks or months.
