Understanding the nuances of wood is crucial for anyone working with timber, whether you’re a carpenter, a builder, a furniture maker, or simply a homeowner maintaining a wooden structure. One significant timber defect to be aware of is “shake.” This article delves into the complexities of shake, exploring its various types, causes, effects on wood strength and appearance, and methods for identifying and mitigating its impact.
Defining Shake: A Timber Defect
Shake, in the context of timber, refers to a separation or crack along the grain of the wood. This separation can occur between the annual growth rings (also known as ring shake or cup shake), or it can radiate outwards from the center of the tree (known as heart shake or star shake). It’s a naturally occurring defect that can significantly affect the structural integrity and aesthetic value of lumber.
Unlike splits, which are typically caused by drying stress and extend to the outer surface of the wood, shake often remains within the log, making it less obvious. Detecting shake requires careful inspection, and understanding its potential impact is vital for selecting appropriate timber for different applications. The severity of shake varies; some shakes may be hairline cracks, while others can be substantial separations extending several inches or even feet.
The presence of shake doesn’t automatically render a piece of timber unusable. However, it must be carefully evaluated to determine its suitability for a specific purpose. In some cases, affected timber can still be used for non-structural applications or in situations where the shake doesn’t compromise the load-bearing capacity.
Types of Shake in Logs
Shake manifests in various forms, each with its own characteristics and implications for the wood’s usability. Identifying the specific type of shake is essential for accurately assessing its impact.
Ring Shake (Cup Shake)
Ring shake, sometimes called cup shake, is characterized by the separation of wood fibers along the growth rings. Imagine the tree’s annual rings peeling apart from each other. This type of shake often occurs in a curved pattern, following the contours of the growth rings, hence the name “cup shake.”
The extent of ring shake can vary considerably. In some cases, it may only affect a small portion of a growth ring, while in others, it can extend around the entire circumference. The severity of ring shake directly influences the timber’s strength, making it weaker in bending and shear.
Ring shake can be particularly problematic because it may not be immediately visible on the surface of the log or lumber. The separation occurs within the wood, making it difficult to detect without a thorough inspection.
Heart Shake
Heart shake, as the name suggests, originates from the heart or center of the tree and radiates outwards. It appears as a series of cracks that extend towards the outer edges of the log. These cracks can be short and relatively insignificant, or they can be long and deep, significantly weakening the timber.
Heart shake is often caused by stresses within the tree as it grows and ages. Environmental factors and the tree’s internal structure can contribute to its development.
The pattern of heart shake can vary. In some cases, the cracks are relatively straight and uniform, while in others, they are more irregular and branching. The shape and extent of the cracks are influenced by the wood’s grain and the stresses it has been subjected to.
Star Shake
Star shake is a variation of heart shake, characterized by multiple cracks radiating outwards from the center of the tree, resembling a star pattern. This type of shake is often more pronounced than typical heart shake, with a greater number of cracks extending further into the wood.
Star shake can severely compromise the structural integrity of the timber, making it unsuitable for load-bearing applications. The numerous cracks weaken the wood in multiple directions, making it susceptible to splitting and failure under stress.
Identifying star shake is crucial for avoiding its use in critical structural components. Careful inspection of the log ends is necessary to detect the characteristic star-shaped pattern.
Pith Shake
Pith shake is a specific type of shake that occurs around the pith, the soft, central core of the tree. It involves the separation or cracking of the wood fibers immediately adjacent to the pith.
While pith shake may not extend as far into the wood as heart shake or star shake, it can still weaken the timber, especially if the pith is large or the surrounding wood is weak. It can also create a pathway for decay and insect infestation.
Pith shake is often associated with juvenile wood, which is the wood formed in the early years of the tree’s growth. Juvenile wood is typically less dense and weaker than mature wood, making it more susceptible to shake.
Causes of Shake in Timber
Shake is a natural phenomenon that can result from a combination of factors affecting the tree’s growth and environment. Understanding these causes can help in selecting timber from sources where shake is less prevalent.
Environmental Factors
Environmental conditions play a significant role in the development of shake. Extreme temperature fluctuations, particularly rapid freezing and thawing, can cause stresses within the wood that lead to cracking.
Similarly, periods of drought followed by heavy rainfall can also create stresses that contribute to shake. The wood expands and contracts as moisture levels change, and these movements can cause separations along the grain.
Wind exposure can also be a factor. Trees exposed to strong winds may develop internal stresses as they resist the force of the wind, potentially leading to shake.
Growth Stresses
As a tree grows, it experiences internal stresses. These stresses are caused by the addition of new wood cells and the expansion of the trunk. Uneven growth rates, caused by factors such as sunlight exposure or soil conditions, can lead to imbalances in these stresses.
These internal growth stresses can be significant, and they can exceed the wood’s tensile strength, resulting in shake. The type and severity of shake are often related to the specific growth patterns of the tree.
Fungal Decay
Certain types of fungal decay can also contribute to shake. While not a direct cause, fungal infections can weaken the wood fibers, making them more susceptible to separation along the grain.
Fungal decay often occurs in areas where the wood is exposed to moisture for extended periods. The decay process breaks down the wood’s cellular structure, reducing its strength and increasing the likelihood of shake.
Age of the Tree
The age of the tree can also influence the likelihood of shake. Older trees are generally more prone to shake than younger trees. This is because they have been subjected to more environmental stresses and have had more time for internal stresses to develop.
Additionally, older trees may have accumulated more fungal decay or other forms of damage that weaken the wood and make it more susceptible to shake.
Impact of Shake on Timber
The presence of shake can have several negative consequences for the timber’s structural integrity, appearance, and overall usability. Understanding these impacts is essential for making informed decisions about timber selection and application.
Structural Weakness
The most significant impact of shake is the reduction in structural strength. The separations along the grain weaken the wood, making it more susceptible to failure under load. This is particularly critical in load-bearing applications such as beams, columns, and rafters.
Ring shake reduces the wood’s resistance to bending and shear, while heart shake and star shake can compromise its tensile strength. The severity of the weakening depends on the type, extent, and location of the shake.
Timber with significant shake should not be used in structural applications where its load-bearing capacity is critical. Using affected timber in such situations can pose a serious safety risk.
Reduced Aesthetic Value
Shake can also detract from the aesthetic appeal of timber. The cracks and separations can be unsightly, especially in applications where the wood is visible, such as furniture, paneling, and trim.
Even minor shake can be noticeable and detract from the overall appearance of the wood. The presence of shake can also make it more difficult to achieve a smooth, even finish.
In applications where aesthetics are important, it’s best to select timber that is free from shake or has only minor, inconspicuous shake.
Increased Susceptibility to Decay
Shake can create pathways for moisture and fungal spores to penetrate the wood. These pathways accelerate the decay process, further weakening the timber and reducing its lifespan.
The cracks associated with shake provide ideal conditions for fungal growth. The moisture trapped within the cracks creates a favorable environment for decay organisms to thrive.
Protecting timber with shake from moisture is crucial for preventing decay. Proper sealing and regular maintenance can help to extend the lifespan of affected timber.
Waste of Material
Timber affected by shake often results in a higher degree of waste during processing. The presence of shake may require the removal of large portions of the log or lumber, reducing the overall yield.
This waste can increase the cost of timber and contribute to resource depletion. Selecting timber from sources where shake is less prevalent can help to minimize waste.
Identifying Shake in Logs and Lumber
Detecting shake requires careful inspection and a keen eye. Knowing what to look for is essential for accurately assessing the extent and severity of the defect.
Visual Inspection
The first step in identifying shake is a thorough visual inspection of the log ends and the surface of the lumber. Look for cracks or separations along the grain.
Examine the end grain carefully for signs of heart shake, star shake, or ring shake. The characteristic patterns of these types of shake can be readily visible on the end grain.
Also, inspect the surface of the lumber for any cracks that run parallel to the grain. These cracks may indicate the presence of shake within the wood.
Sounding
Another technique for detecting shake is sounding. This involves tapping the log or lumber with a hammer or mallet and listening to the sound it produces.
A solid, clear sound indicates that the wood is sound and free from internal defects. A dull, hollow sound may indicate the presence of shake or other internal voids.
Sounding requires some experience to interpret the sounds accurately. It’s often used in conjunction with visual inspection to confirm the presence of shake.
Dye Penetration Tests
In some cases, dye penetration tests can be used to detect shake. This involves applying a colored dye to the surface of the wood and allowing it to penetrate into any cracks or separations.
After a period of time, the surface of the wood is cleaned, and the dye that has penetrated into the shake becomes visible. This technique can be useful for identifying hairline cracks that are not readily visible to the naked eye.
Moisture Meter Readings
While not a direct indicator of shake, moisture meter readings can sometimes provide clues. Areas of high moisture content within the wood may indicate the presence of shake, as the cracks can trap moisture.
However, high moisture readings can also be caused by other factors, such as fungal decay or improper drying. Therefore, moisture meter readings should be used in conjunction with other inspection techniques.
Mitigating the Impact of Shake
While shake cannot be completely eliminated, its impact can be mitigated through careful timber selection, processing techniques, and proper design considerations.
Timber Selection
The first step in mitigating the impact of shake is to select timber from sources where shake is less prevalent. This may involve choosing specific tree species, harvesting techniques, or geographical locations.
Some tree species are naturally more resistant to shake than others. Similarly, certain harvesting techniques, such as careful felling and handling, can minimize the risk of shake.
Selecting timber from well-managed forests can also help to ensure that the trees are healthy and less prone to defects.
Processing Techniques
The way timber is processed can also influence the impact of shake. Proper sawing techniques can minimize the risk of shake spreading or worsening during processing.
For example, sawing logs in a way that minimizes internal stresses can help to prevent the cracks from widening. Proper drying techniques can also reduce the risk of shake developing or worsening.
Slow, controlled drying is preferable to rapid drying, as it reduces the stresses that can lead to cracking.
Design Considerations
When designing structures or furniture using timber, it’s important to consider the potential impact of shake. This may involve avoiding the use of timber with shake in critical load-bearing areas or designing the structure in a way that minimizes stress on the affected timber.
For example, if timber with shake is used in a beam, it may be necessary to provide additional support to compensate for the reduced strength.
Sealing and Protection
Protecting timber with shake from moisture is crucial for preventing decay. Applying a sealant or preservative can help to prevent moisture from penetrating the cracks and promoting fungal growth.
Regular maintenance, such as reapplying sealant or preservative as needed, can help to extend the lifespan of affected timber.
In conclusion, understanding shake in logs is crucial for ensuring the safe and effective use of timber. By understanding its types, causes, impacts, and methods of identification and mitigation, you can make informed decisions about timber selection and application, maximizing its value and minimizing potential risks. Careful inspection and proper handling are key to working effectively with timber that may be affected by shake.
What is shake in logs, and how is it defined as a timber defect?
Shake refers to a separation or crack within the wood of a tree, typically running parallel to the annual growth rings or medullary rays. This separation weakens the wood structure and reduces its overall strength and usability. It’s considered a timber defect because it compromises the integrity and performance of lumber sawn from the affected log.
Different types of shake exist, each categorized by its orientation and cause. Ring shake follows the growth rings, heart shake radiates from the center of the tree, and star shake resembles a star pattern. These defects can occur due to various factors, including tree growth stresses, environmental conditions like wind or frost, or fungal decay that weakens the wood fibers.
What are the different types of shake, and how do they differ?
The primary types of shake are ring shake, heart shake, and star shake. Ring shake (or cup shake) is a separation between annual growth rings, creating a circular crack within the log. Heart shake radiates outwards from the pith (center) of the tree, often following the medullary rays. Star shake, as the name suggests, consists of several heart shakes forming a star-like pattern.
The differences lie primarily in their orientation and the pattern they create within the wood. Ring shake impacts the log’s ability to resist bending forces, while heart and star shake compromise its splitting resistance. The severity and location of each type affect the log’s suitability for different applications, influencing grading and processing decisions.
What causes shake to occur in trees?
Shake can be caused by a variety of factors, both environmental and biological. Growth stresses within the tree, particularly in fast-growing species or those subjected to strong winds, can contribute to the formation of shake. Sudden changes in temperature, such as severe frosts, can also create internal stresses that lead to cracking and separation within the wood.
Biological factors, such as fungal decay, can weaken the wood fibers, making them more susceptible to separation and shake formation. Insect infestations can also contribute to the problem by creating pathways for decay or weakening the wood’s structural integrity. The specific cause often depends on the tree species, its growing environment, and its overall health.
How does shake affect the strength and usability of timber?
Shake significantly reduces the strength and usability of timber. The separations within the wood weaken its ability to withstand bending, compression, and shear forces. Lumber with shake is more prone to splitting and can be structurally unsound, particularly when used in load-bearing applications.
The presence of shake also affects the timber’s appearance and workability. It can create unsightly defects that detract from its aesthetic value and make it more difficult to process, shape, or finish. Depending on the severity and location of the shake, the timber may be downgraded, rejected for certain uses, or require special processing techniques.
How can shake be identified in logs or lumber?
Identifying shake in logs involves careful visual inspection. Look for cracks or separations along the ends of the log, paying close attention to the growth rings and the central pith. The presence of loose bark or raised areas on the log’s surface can also indicate underlying shake. Sometimes, a dull thud when struck can indicate internal separation.
In lumber, shake is visible as splits or separations running parallel to the grain. The type of shake can be determined by observing its pattern – ring shake will follow the growth rings, while heart and star shake will radiate from the center of the board. The severity of the shake is assessed by its length, depth, and frequency within the lumber.
Can shake be prevented or controlled in timber production?
While completely preventing shake is difficult, certain silvicultural practices can minimize its occurrence. Selecting tree species that are less prone to shake and managing stand density to reduce growth stresses can help. Proper pruning techniques can improve tree form and reduce wind exposure, lowering the risk of shake caused by wind damage.
Careful harvesting and handling practices can also play a role. Avoiding damage to trees during felling and transporting logs gently can prevent the exacerbation of existing weaknesses. Properly drying lumber after sawing is crucial to prevent further cracking and warping, which can worsen the effects of shake.
Are there any specific applications where timber with shake should be avoided?
Timber with shake should be avoided in applications where structural integrity is paramount. This includes load-bearing beams, columns, and rafters in construction. The presence of shake compromises the wood’s ability to withstand stress, increasing the risk of failure. Avoid using timber with significant shake in critical structural components.
While not suitable for structural applications, timber with minor shake may be acceptable for non-structural purposes such as paneling, siding, or decorative elements. In these cases, the aesthetic impact and potential for further degradation should be carefully considered. Utilizing shorter lengths can sometimes mitigate the effects of shake in these applications, but careful inspection remains crucial.