Does Cedar Shrink? (5 Key Wood Moisture Insights)

Safety First: A Woodworker’s Prime Directive

Before we even begin discussing the intricacies of cedar and its shrinking habits, I want to emphasize something paramount: safety. I’ve seen too many accidents in my years working with wood, from minor cuts to serious injuries involving heavy machinery. Whether you’re a seasoned logger or a weekend firewood enthusiast, prioritizing safety is non-negotiable.

Always wear appropriate personal protective equipment (PPE). This includes:

• Eye protection: Safety glasses or a face shield are crucial to protect against flying debris.
• Hearing protection: Chainsaws and other power tools can cause significant hearing damage over time. Earplugs or earmuffs are essential.
• Gloves: Protect your hands from splinters, cuts, and abrasions.
• Steel-toed boots: Prevent foot injuries from falling logs or dropped tools.
• Chainsaw chaps: If you’re using a chainsaw, chaps are a must-have to protect your legs from accidental cuts.
• Hard hat: For any work involving falling trees or overhead hazards.

Never operate machinery under the influence of drugs or alcohol. Ensure your equipment is in good working order and that you are properly trained in its use. Be aware of your surroundings and potential hazards. And most importantly, don’t be afraid to ask for help or advice if you’re unsure about something. Woodworking and logging are rewarding pursuits, but they demand respect and a commitment to safety.

Does Cedar Shrink? (5 Key Wood Moisture Insights)

The question of whether cedar shrinks is deceptively simple. The short answer is yes, all wood shrinks as it dries. However, the degree of shrinkage, the rate at which it shrinks, and the consequences of that shrinkage are all crucial factors that determine how you work with cedar, especially in applications where dimensional stability is critical. From building durable outdoor furniture to crafting intricate woodworking projects, understanding cedar’s moisture behavior is key to success.

I’ve spent years felling, milling, drying, and working with various types of wood, including a significant amount of cedar. I’ve learned firsthand the hard way – through warped boards, splitting panels, and projects that simply didn’t hold up over time – the importance of understanding wood moisture content. In this article, I will share my insights on cedar shrinkage, drawing from my experiences and providing you with a practical guide to managing moisture in your cedar projects.

1. Understanding Wood Moisture Content (MC)

Before diving into cedar specifically, let’s establish some fundamental concepts about wood moisture. Wood is hygroscopic, meaning it readily absorbs and releases moisture from the surrounding environment. The amount of moisture in wood is expressed as a percentage of its oven-dry weight, known as the Moisture Content (MC).

• Green Wood: Freshly cut wood has a very high MC, often exceeding 30%. In some species, it can even reach over 100% (meaning there is more water than wood fiber by weight). This wood is very heavy and prone to significant shrinkage and warping as it dries.
• Air-Dried Wood: Wood that has been allowed to dry naturally in the air will reach an Equilibrium Moisture Content (EMC) that depends on the relative humidity and temperature of the surrounding environment. In most regions of the US, air-dried wood will typically reach an MC of 12-15%.
• Kiln-Dried Wood: Wood that has been dried in a controlled environment (a kiln) can be brought to a lower MC, typically between 6-8%. This makes it more stable and suitable for interior applications.
• Oven-Dry Wood: Wood that has been dried in an oven at 212°F (100°C) until it reaches a constant weight has an MC of 0%.

Why is MC important?

Wood shrinks as it loses moisture below its Fiber Saturation Point (FSP), which is typically around 28-30% MC. Above the FSP, the water is primarily in the cell cavities and doesn’t affect the cell walls. Below the FSP, the water begins to evaporate from the cell walls, causing them to shrink. This shrinkage is not uniform; it’s greater in the tangential direction (around the growth rings) than in the radial direction (towards the center of the tree). This differential shrinkage is what causes warping, cupping, and checking.

My Experience:

I once built a beautiful cedar deck using lumber that I thought was adequately air-dried. However, after a few months of exposure to the summer sun, the boards started to cup and twist dramatically. I realized that the lumber, while seemingly dry on the surface, still had a high MC in the core. The sun’s heat caused the moisture to evaporate rapidly, leading to uneven shrinkage and the resulting distortion. This taught me a valuable lesson about the importance of properly drying wood and understanding its moisture content throughout.

2. Cedar Species and Shrinkage

Not all cedar is created equal. There are several species of cedar, each with its own characteristics and shrinkage properties. The most common types include:

• Western Red Cedar (Thuja plicata): This is the most widely used cedar, prized for its durability, workability, and beautiful reddish-brown color. It has relatively low shrinkage compared to other softwoods.
• Eastern Red Cedar (Juniperus virginiana): Despite its name, this is actually a juniper. It’s known for its aromatic properties and resistance to insects. It has moderate shrinkage.
• Spanish Cedar (Cedrela odorata): This is a tropical hardwood, not a true cedar. It’s commonly used for cigar boxes and humidors due to its ability to regulate moisture. It has relatively low shrinkage.
• Alaskan Yellow Cedar (Callitropsis nootkatensis): Also known as Nootka Cypress, this is a strong and durable wood with a yellow color. It has low shrinkage and is resistant to decay.

Shrinkage Values:

Wood shrinkage is typically expressed as a percentage of the green dimension. Here are some typical shrinkage values for different cedar species (from green to oven-dry):

Note: These values are approximate and can vary depending on the specific tree, growing conditions, and drying methods.

Insight: Western Red Cedar generally exhibits lower shrinkage than Eastern Red Cedar, making it a more stable choice for applications where dimensional stability is critical. Spanish Cedar and Alaskan Yellow Cedar also offer excellent stability.

3. Measuring Moisture Content

Accurately measuring the MC of your cedar is essential for predicting its shrinkage and ensuring the success of your projects. There are two primary methods for measuring MC:

• Moisture Meters: These electronic devices use electrical resistance or capacitance to estimate the MC of wood. They are convenient and provide quick readings. There are two main types:
  • Pin Meters: These have two pins that are inserted into the wood. They measure the electrical resistance between the pins. They are relatively inexpensive but can leave small holes in the wood.
  • Pinless Meters: These use radio frequency signals to measure the moisture content without penetrating the wood. They are more expensive but non-destructive.

• Oven-Dry Method: This is the most accurate method for determining MC. It involves weighing a sample of wood, drying it in an oven at 212°F (100°C) until it reaches a constant weight, and then calculating the MC using the following formula:

  MC (%) = [(Wet Weight - Oven-Dry Weight) / Oven-Dry Weight] x 100

Using Moisture Meters:

When using a moisture meter, it’s important to:

• Calibrate the meter: Follow the manufacturer’s instructions to calibrate the meter for the specific species of wood you are measuring.
• Take multiple readings: Moisture content can vary within a single board. Take several readings in different locations and average them to get a more accurate assessment.
• Consider the wood’s temperature: Moisture meters are typically calibrated for a specific temperature. If the wood is significantly warmer or cooler, you may need to adjust the reading.
• Avoid measuring near knots or defects: These areas can affect the accuracy of the reading.

My Experience:

I initially relied solely on a pin-type moisture meter, thinking it was sufficient. However, I encountered inconsistencies in my readings, especially with thicker lumber. I then invested in a pinless meter and started using the oven-dry method to verify my measurements. I discovered that the pin meter was often inaccurate, particularly when measuring wood with a high MC gradient (i.e., a significant difference in moisture content between the surface and the core). The pinless meter provided more consistent readings, and the oven-dry method served as a reliable benchmark. Now, I use a combination of all three methods, depending on the situation.

Case Study:

I once had a client who insisted that his cedar siding was “perfectly dry” because his pin meter read 12%. However, when I took a core sample and used the oven-dry method, I found that the core MC was closer to 20%. This difference explained why the siding was cupping and warping after installation. The client was skeptical at first, but the evidence from the oven-dry test convinced him that the wood needed further drying before it could be used.

4. Drying Cedar Properly

Proper drying is crucial for minimizing shrinkage and preventing defects in cedar. There are two main methods:

• Air Drying: This is the traditional method of drying wood. It involves stacking the lumber in a well-ventilated area and allowing it to dry naturally.
  • Stacking: Stack the lumber with stickers (thin strips of wood) between each layer to allow air to circulate. Use dry stickers of a consistent thickness (typically 3/4″ to 1″).
  • Orientation: Orient the stack so that the prevailing winds blow through it.
  • Covering: Protect the stack from direct sunlight and rain with a roof or tarp.
  • End Sealing: Seal the ends of the boards with a commercial end sealer or paint to prevent checking (cracking).
  • Weighting: Place weights on top of the stack to help prevent warping.
• Kiln Drying: This is a faster and more controlled method of drying wood. It involves placing the lumber in a kiln and circulating heated air to remove moisture.
  • Schedule: Kiln drying requires a specific schedule of temperature and humidity to dry the wood evenly and prevent defects. These schedules vary depending on the species and thickness of the wood.
  • Monitoring: The MC of the wood is carefully monitored throughout the drying process.
  • Stress Relief: At the end of the drying cycle, the wood is often subjected to a stress-relief process to reduce internal stresses.

Air Drying vs. Kiln Drying:

My Air Drying Setup:

My air drying setup consists of a covered shed with open sides to allow for good ventilation. I stack my lumber on concrete blocks, using 1″ x 2″ hardwood stickers spaced about 2 feet apart. I apply a commercial end sealer to the ends of the boards as soon as they are cut. I also weigh down the top of the stack with concrete blocks to help prevent warping. I monitor the MC of the lumber regularly using both a pin meter and a pinless meter.

Kiln Drying Considerations:

If you plan to kiln dry your cedar, it’s best to consult with a professional kiln operator or follow a recommended drying schedule for the specific species and thickness of your lumber. Improper kiln drying can lead to severe defects, such as honeycomb (internal checks) and case hardening (a hardened surface that prevents the core from drying properly).

Strategic Advantage:

While kiln-dried cedar is generally more stable and suitable for indoor applications, air-dried cedar can be a more sustainable and cost-effective option for outdoor projects. Air drying also allows the wood to retain its natural oils and resins, which can enhance its durability and resistance to decay.

5. Working with Cedar’s Shrinkage

Even with proper drying, cedar will still experience some shrinkage and expansion as its MC changes with the seasons. Understanding how to account for this movement is crucial for building durable and long-lasting projects.

• Design Considerations:
  • Allow for Expansion and Contraction: In large panels or assemblies, design joints that allow for movement. This can be achieved using sliding dovetails, floating tenons, or expansion gaps.
  • Orient Grain Direction: Pay attention to the grain direction of the wood. Wood shrinks and expands more across the grain than along the grain. Orient the grain so that the movement is less noticeable or less likely to cause problems.
  • Use Quarter-Sawn Lumber: Quarter-sawn lumber is cut so that the growth rings are perpendicular to the face of the board. This makes it more dimensionally stable than flat-sawn lumber.
• Joinery Techniques:
  • Avoid Restrictive Joints: Avoid using joints that rigidly constrain the wood, such as fully glued mortise-and-tenon joints.
  • Use Floating Joints: Floating tenons or loose tenons allow for movement in the wood without compromising the strength of the joint.
  • Use Screws and Bolts: Screws and bolts allow for some movement in the wood and can be tightened as needed to compensate for shrinkage.
• Finishing:
  • Apply a Moisture-Resistant Finish: A good finish can help to slow down the rate of moisture absorption and release, reducing the amount of shrinkage and expansion.
  • Finish All Surfaces: Apply finish to all surfaces of the wood, including the back and edges, to prevent uneven moisture absorption.

Case Study: Building a Cedar Chest:

I once built a cedar chest for a client who wanted to store delicate fabrics. I knew that cedar’s aromatic properties would help to protect the fabrics from moths, but I also knew that I needed to account for the wood’s shrinkage and expansion.

• Wood Selection: I used kiln-dried Western Red Cedar for the chest because of its dimensional stability and resistance to decay.
• Joinery: I used floating tenons to join the sides, top, and bottom of the chest. This allowed for movement in the wood without compromising the strength of the joints.
• Lid Design: I designed the lid to be slightly oversized, with a rabbeted edge that fit into a groove in the top of the chest. This allowed the lid to expand and contract without binding.
• Finish: I applied a clear, water-based finish to all surfaces of the chest to protect it from moisture.

The chest has been in use for several years now, and it has held up beautifully. The joints are still tight, and the lid fits perfectly. This is a testament to the importance of understanding wood moisture and accounting for its movement in your designs.

Practical Next Steps:

1. Invest in a good moisture meter: A reliable moisture meter is an essential tool for any woodworker.
2. Learn to identify different cedar species: Understanding the characteristics of different cedar species will help you choose the right wood for your projects.
3. Practice air drying lumber: Experiment with air drying your own lumber to gain a better understanding of the process.
4. Design projects that account for wood movement: Incorporate design features that allow for expansion and contraction.
5. Experiment with different joinery techniques: Try using floating tenons, sliding dovetails, and other joinery techniques that allow for wood movement.
6. Apply a moisture-resistant finish: Protect your projects from moisture with a good finish.
7. Continuously monitor your projects: Check your projects periodically for signs of movement or distortion.

By understanding the principles of wood moisture and applying them to your work, you can build durable and long-lasting projects that will stand the test of time. I hope this guide has given you a solid foundation for working with cedar and managing its shrinkage. Remember to always prioritize safety, take your time, and enjoy the process of working with this beautiful and versatile wood.

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