Reason would tell you that hardwoods and softwoods are not everlasting and are susceptible to contraction and expansion due to their intrinsic property of being hygroscopic. Hygroscopy is a property wherein an object attracts and holds water molecules via absorption or adsorption at room or average temperature. Since wood is hygroscopic, it tends to absorb and adsorb moisture, depending on the changes in the weather or ambient environment.
So, if you want to dabble in woodworking but still wonder whether wood will expand or contract due to heat or cold, it will be good to note that wood expands or contracts due to cold or heat. Nevertheless, woods come in different species and varieties, meaning some are more susceptible to contraction and expansion due to cold or heat than others. But if you want to dig deeper into why wood expands and contracts due to cold and heat, it will be best to read on through this post.
Reasons Behind Wood Expansion and Contraction
The main reason behind the contraction and expansion of wood is moisture. Since wood is hygroscopic, it tends to absorb and adsorb moisture to attain equilibrium in its moisture content (MC) with the environment or humidity level. However, the air temperature also affects the moisture content or humidity content.
So, the seasonal changes impact the moisture content of wood, leading to its expansion and contraction. The rule is: the more significant the wood’s MC, the more likely the wood would expand. Aside from moisture, temperature plays a secondary role in wood expansion and contraction.
When the weather is dry, the temperature increases and moisture evaporates from the wood. Initially, the wood would exhibit thermal expansion and possible swelling, distortion, and warping. Nevertheless, wood will also exhibit shrinking over time.
Thus, the temperature is not the direct cause of the wood’s warping and distortion. The primary reason is the ambient humidity level and the wood’s MC. Besides, different wood species contract and expand differently.
Will Wood Expand During Summer or Winter?
Seasonal changes can cause wood expansion and contraction. As mentioned above, weather conditions do affect this alteration in the dimensions of wood secondarily. The reason is that moisture content in the air changes due to the seasons. Always remember that the higher the wood’s MC, the more probable the wood would expand.
Humidity affects wood. Thus, wooden floors usually contract during humid and warm summers. At the same time, during dry winters, they would expand, causing the loss or diminishing of the structural integrity of those ship-lapped boards. Sometimes wooden boards would crack due to these changes in dimensions.
When winter comes, for example, the atmosphere has around 76% humidity level; during summer, it is about 66%. This alteration in the atmosphere’s humidity level leads to the expansion and shrinking of wood. If this happens constantly, the wood will likely crack.
What Temperature Will Cause Wood to Warp?
Wood will likely warp if exposed to extreme hot or cold temperatures. Wood will not warp if exposed to temperatures ranging from 70°F to 72°F, given a 50% humidity level. However, wood will also likely contract under cold temperatures, and the constant expansion and contraction will lead to wood warping. You can remedy this problem by sealing the wood properly.
Wood will also contract under sweltering temperatures, causing wood fibers to expand because of thermal expansion, causing the wood to warp under constant changes in dimensions.
Do Warm Temperatures Affect Wood Contraction and Expansion?
Warm temperatures also occasion dimensional changes in wood. The humidity level, for example, changes when temperatures become warm. If the air outside is warm and dry, the atmosphere has less moisture content. But when temperatures become moist, the air carries high moisture content.
Wood will balance its moisture content when air is warm and dry outside by evaporating moisture. This evaporation of humidity leads to wood contraction or shrinkage. Loss of moisture from the wood fibers will lead to the shrinkage of the wood. If the air is moist and warm, moisture will get absorbed into the wood fibers, leading to expansion.
Does Humidity Have an Impact on Wood Contraction and Expansion?
As mentioned above, humidity is the main reason behind the contraction and expansion of the wood. It is not the high and low temperatures that mainly cause the contraction and expansion of the wood. When the outside temperature is hot, the MC content outside is high. Wood will try to achieve equilibrium by reducing its MC to equalize with the outside MC. When the wood reaches MC equilibrium, the wood’s expansion and contraction stop.
Similarly, when it is cold outside, the MC outside is low. The wood will try to achieve equilibrium between the outside and inside MC by releasing moisture into the air. Once equilibrium is achieved, the shrinkage will stop. The likely scenario is that the wood will expand if the air has a high humidity level. If the air has a low humidity level, the wood will shrink.
How Will Cold Weather Affect Your Wooden Furniture?
One question I often get asked about wooden furniture is how cold weather affects wooden furniture. My answer is relatively straightforward. Wood furniture gets affected by cold temperatures. Yet, this effect still boils down to how the furniture got built and what type of wood species it is.
The same principle that applies to wood contraction and expansion also applies to wood furniture. Wood furniture will expand if the moisture content outside of the wood is high. It will also contract if the moisture content outside the wood is low.
Nevertheless, suppose your furniture is made of sturdier species and is well-sealed and built. In that case, it will not exhibit remarkable expansion and contraction, especially if the furniture gets positioned inside the house. Most furniture will survive cold weather as long as the furniture doesn’t get wet.
How Will Warm Temperature Affect Wood Furniture?
Warm temperatures have no direct effect on wood. But warm temperatures will alter the ambient environment’s humidity levels, causing the wood to give off moisture to attain equilibrium between the wood’s internal and external MC.
Dry wood will tend to contract, while wet timber will likely expand. So, the factor that directly affects wood is the environment’s humidity levels. But the humidity levels of the environment are usually determined by the weather.
How Can You Prevent the Expansion and Contraction of Wood?
Wood movement or dimensional changes will ruin your wood projects and annoy you. Thus, when building a project, you must consider the potential wood movement and account for it, especially if you need precision. Of course, several factors affect wood dimensions, and thus, if you want to prevent the expansion and contraction of wood, you should know how to mitigate the effects of these factors.
The best way to keep dimensional changes of wood due to moisture is by entirely sealing your wood. You can apply multiple layers of liquid epoxy on the wood surface. But as a wise woodworker, you would instead account for the wood movement instead of ensuring wood will not move because there is no way you can prevent wood movement.
You can minimize wood movement by carefully selecting the wood species you will use. You can choose the wood that has been cut in a specific way and dried well. Below are the following methods you can employ to prevent wood movement:
Seal the Wood Properly
If you want to seal the wood to prevent dimensional changes, it will be best to seal it properly. Sealing wood can enable it to resist moisture and helps it avoid contact with outside air. You can use polyurethane resin and epoxy resin as a sealer. It will be best to apply many coats of epoxy resin to ensure the wood gets entirely sealed.
Sealing wood helps it resist moisture, preventing dimensional changes in the wood. When sealed, wood will not release or absorb water, given a certain level of humidity in the environment. Of course, small dimensional changes will happen even if you seal the wood. Allowing for small movements enables the wood to achieve MC equilibrium with the ambient environment.
During Extreme Weather, It Will Be Best to Disassemble Your Wood Furniture
When assembled, wood furniture will likely get affected by extreme weather conditions. If it expands or contracts, it may incur damages. Hence, it will be best to disassemble your furniture during severe weather. Otherwise, changes in dimensions might damage the wood, including the joineries.
Just imagine what will happen with the tenons and mortise and your dowel construction if the wooden joints expand or contract. They would tend to break due to the movements of wood. Thus, it is advisable to disassemble your furniture if you can to ensure it will not likely incur any damage due to the vicissitudes of the weather.
Secure the Furniture with Good Covers
You can drape your furniture with an excellent cover to prevent it from contacting water or moisture. This way, it will not absorb water or moisture from the environment. You can also put them inside storage boxes to protect them from the environment’s changing humidity levels.
Use Plywood for Your Projects as Alternative!
Plywood exhibits dimensional stability compared to solid wood. Thus, if you will have a project, it will be best to consider alternatives like plywood that is more dimensionally stable, especially in projects like windows, doors, and other parts of the house, which are more exposed to humidity level changes.
Choose Hardwoods That Are Not Likely to Expand or Contract!
Wood comes in various species ranging from very soft to very hard. If money isn’t an issue for you, choosing high-quality hardwoods for your projects will be best, especially if they get exposed to moisture or humidity. High-quality wood will not tend to take or lose moisture due to weather changes. Besides, it will help if you allow the wood to acclimate to the ambient environment where you will install it. This way, you can prevent abrupt and damaging dimensional changes in the wood.
Conclusion
Wood is excellent for many projects including furniture making and construction. Yet, wood is hygroscopic, meaning, it will absorb and adsorb moisture. Thus, wood tends to expand and contract, which can be a problem when you use them for your projects. As mentioned above, you got several ways to minimize the damaging effects of dimensional changes.
By following the abovementioned tips on how to minimize damages due to wood movement, you can prevent cracking, warping, and twisting of wood over time due to changes in weather and moisture levels.