Why Do Timbers Split and Crack? (2023)

Eric Morley on why timbers split and crack, how long it takes timber to dry, where to get dry timbers, and why gunshots in the night are nothing to be afraid of when you understand wood checking and splitting.

What Causes Wood to Crack?

Wood Checking Does!

Splits and cracks (known as wood checks in the industry) occur when wood shrinks as it dries. Wood shrinks roughly twice as much along with the growth rings (radially) as it does across the rings (tangentially). It is this uneven shrinkage that causes checks to develop.

Why Do Timbers Split and Crack? (1)

Is Wood Checking Bad?

Here at Carolina Timberworks, we think of them as wrinkles in a cotton shirt. It proves the timber is real. Checks are what make a solid timber look different from a boxed beam. Look at the reclaimed timber below. It is impossible to predict where a check will appear in timber. It is the check that gives this reclaimed Oak timber so much of its character and a big part of what makes it completely unique and different from any other beam in the world.

Why Do Timbers Split and Crack? (2)

Ever Heard the Song of the Wood?

Have you ever taken a hot loaf of artisan bread out of the oven, and put your ear to it? If you do, you’ll hear the song of the bread–pops and crackles as the crust shrinks, cracks, and dries.

Walk into a timber framer’s shop one winter evening when everyone has gone home for the day. Throw another log into the woodstove, and listen carefully. If there are green (wet) timbers arrayed on sawhorses, within a few minutes, you’re likely to hear the song of the wood – a symphony of pops and cracks as wood checking occurs.

(Video) Prevent Your Boards From Splitting- STOP Cracks in Their Tracks!

If one night, asleep in your newhome, you’re awoken by a loud crack a little like a gunshot. Don’t worry. Roll over and go back to sleep. It’s just your timbers singing to you. That’s wood checking in action.

Why Do Timbers Split and Crack? (3)

Why Does Wood Shrink?

It sometimes surprises people to learn that roughly half of a living tree’s weight is water. Let’s consider a 24’ long Douglas Fir log that measures 34” diameter at the large end and 14” at the small end as an example. This hypothetical green (wet) log would contain a little over 1 ton of water or about five 55-gallon drums of water.

Sometimes when we drive a chisel into green (wet) timber, water spurts out of the wood. Wood is hydroscopic – meaning it’s like a sponge in that it can absorb, hold and release water. When freshly cut, approximately half of a tree’s weight is water. The photograph below shows water in a freshly cut Cypress timber–and how the timber is drying from the outside in.

Why Do Timbers Split and Crack? (4)

How Long Does It Take a Timber to Dry?

It’s not exactly a fast process. It depends on the humidity of the environment in which the timber is located, but one rule of thumb is that timber air dries about one inch per year. Thus a 12” x 12” timber would take about six years to dry to the center.

How Dry Will the Timber Become?

A timber will eventually air dry to the Equilibrium Moisture Content (EMC) of its environment. The EMC is the point at which wood is neither losing nor absorbing water. A timber’s moisture content is determined by the atmospheric humidity of the timber’s environment.

(Video) Repairing cracks and splits in timber

That environment varies, of course. Is the timber located inside, or outside? What part of the country is it located in? What time of year is it? For example, in the dry mountain air of Denver, the outdoor EMC of wood exposed to the outdoor atmosphere in July is 9.4%, while New Orleans is 15.3% (Forest Products Laboratory: Equilibrium Moisture Content of Wood in Outdoor Locations in the United States and Worldwide, August 1988).

How Wet (or Dry) Are My Timbers?

Since we can’t see the water in the wood, moisture meters are used to measure moisture content. Inexpensive moisture meters measure the surface moisture content which works ok for 3/4” boards, but not 8” thick timbers. Professional moisture meters use electromagnetic scanning to read the moisture in the wood, not on the surface of the beam.

Why Do Timbers Split and Crack? (5)

What is the Average Moisture Content in the U.S.?

The majority of the U.S. has an 8% average moisture content, the Southeast and California coastal areas have an 11% average moisture content, and the Southwest desert areas are closer to 6%.

Most Timber Frames Are Built From Green (Wet) Wood

It is impractical (it takes years) to air dry timber, and we humans are an impatient species, so for the last two thousand years, people have been building timber frames from green (wet) timber. Yes, green timber will shrink, check, and sometimes twist as it dries, but timber framers and engineers understand and account for the movement. Checks begin on the exterior surface of the timber and almost always stop at the heart (center) of the timber, and are almost never a structural concern.

By the way, if a crack were to develop all the way through a timber (splitting it into two separate pieces), it would be called a split and might be cause for concern.

Learn more about timber framing all the ways timber can be used here.

(Video) Timber Checking Explained - Cosmetic Repair Method

Why Do Timbers Split and Crack? (6)

How Much Does Green (Wet) Timber Shrink as It Dries?

Shrinkage depends on the species, but more than you may think!

Since many timber frames are built from Douglas Fir, let’s start by looking at a 12×12 Douglas Fir (Coastal) timber. This particular green (wet) Douglas Fir timber, dried to a final moisture content of 8%, would be expected to shrink a little less than 9/16” on each face from 12” x 12” to a final size of 11-7/16” x 11-7/16”.

Western Red Cedar shrinks less: The same size timber in Western Red Cedar timber would shrink a bit less about 5/16” to 11-11/16” x 11-11/16”. Finally, how about a species with a high shrinkage rate, like White Oak? It would be expected to shrink a bit less than 3/4” to slightly larger than 11-1/4” x 11-1/4”.

6 Ways to Minimize Problems with a Green (Wet) Wood in a Timber Frame:

  1. Specify Free-Of-Heart-Center instead of the less expensive Boxed Heart grade.
  2. Apply a wax-based end sealer to the end grain to slow the drying process. We use Anchorseal, available at https://uccoatings.com/products/anchorseal/.
  3. Utilize housed joinery wherever possible.
  4. Drawbore pegged joints.
  5. The slower the wood cracking when drying, and the more gradual the process, the better (i.e., the worst thing you can do is enclose the timber frame and immediately turn on the heat or air conditioning full blast.)
  6. Do not apply a film-forming finish (i.e., polyurethane) to the greenwood.

I Don’t Want Wood Checking or Cracks in My Timbers. What Are My Options?

Don’t build with solid timber. Instead, ask us to price glulam beams for the timber frame, or to fabricate box beams from well-dried new or reclaimed lumber.

If you’re ok with some checks, but would prefer to avoid some of the characteristics of green lumber, consider purchasing your timber like you do your high-quality organic cotton t-shirts–pre-shrunk. There are two ways to buy dry beams: new timber that’s been dried in a kiln, or reclaimed wood that’s dried slowly and naturally for 50 or 100 years during its previous life as a barn or warehouse.

Where to Buy Kiln Dried Timbers?

We offer two types of kiln-dried timber: Conventionally kiln-dried (KD), and Radio Frequency Kiln Dried (RFKD). Conventional kiln drying dries about the outer 1” or so leaving most of the timber wet. The other method, RFKD, is similar to a giant microwave and dries timber to the core.

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What you need to know about RFKD timber is that it currently works only on Douglas Fir, it is dry to the core, and it is more expensive. It is, however, not as dry as conventionally kiln-dried hardwood flooring or lumber (6-8% moisture content). For example the driest grade of RFKD timber measures 15% or less moisture content 3” in from the surface of the timber.

What About Using Reclaimed Wood in Timber Frame Construction?

Reclaimed wood beams that have naturally air-dried for 50-100 years during their previous life as a barn, factory, or warehouse are often completely dry to the core and the driest timbers available anywhere. It’s not easy to hand-scribe and connects irregular, twisted, and non-square reclaimed beams so the finished timber frame appears to have always been one frame.

We think a timber frame built from reclaimed wood is everything that today’s sleek, mass-produced, technology-saturated culture isn’t. It celebrates the cracks and character and dirt and all the other marks that time, weather, and use leave behind.

Why Do Timbers Split and Crack? (7)

Interested in learning more about timber framing? Check out our


How do I keep my timbers from splitting? ›

You can keep wood from splitting by applying a sealant or stabilizer, using a salt paste, applying varnish, applying paintable wax, or applying boiled linseed oil. Those methods will help you to keep wood from splitting when nailing, screwing, drying, cutting, and sawing.

Is it normal for wood beams to split? ›

While extreme loading or improper notching/boring can cause a wood post (more rarely) or beam to split, usually the splits or cracks found in wooden posts and beams are due to shrinkage as wood dries, occur along the grain, and do not raise a structural concern.

When should I be worried about cracks in beams? ›

Checking cracks do not normally run all the way through a log or beam - which is a reason that they're not normally a structural concern unless the crack appears at a location that compromises a structural connector.

What is crack timber? ›

Cracks or checks occur when wood shrinks as it dries. Wood shrinks roughly twice as much along the growth rings as it does across the rings and it is this uneven shrinkage that causes checks to develop. Checking can be controlled in smaller sized 4/4 -10/4 lumber, because it's easier to dry.

Why does my wood keep splitting? ›

Splits and cracks (known as wood checks in the industry) occur when wood shrinks as it dries. Wood shrinks roughly twice as much along with the growth rings (radially) as it does across the rings (tangentially). It is this uneven shrinkage that causes checks to develop.

Do cracks in wood get worse? ›

Even after proper kiln-drying and varnishing, wood still responds to temperature and moisture. Wood will bend and twist, and cracks will get longer and wider. Untreated cracks can cause a flat tabletop to warp or, in extreme cases, separate from the bases or legs.

What is it called when wood splits? ›

Wood splitting (riving, cleaving) is an ancient technique used in carpentry to make lumber for making wooden objects, some basket weaving, and to make firewood. Unlike wood sawing, the wood is split along the grain using tools such as a hammer and wedges, splitting maul, cleaving axe, side knife, or froe.

At which point is the wooden beam most likely to crack? ›

Diagonal tension is the main cause of the crack. Near the supports is where this crack is most likely to be seen. The shear force due to all loads is likely to occur at supports.

Is split wood a problem? ›

None of these splits or cracks in the timber will affect it's structural integrity or inherent strength. If however, it concerns you I recommend the use of a good quality timber treatment as this will restrict the moisture both entering and leaving the wood.

Why do fence posts split? ›

Timber is a naturally porous material and as such can absorb or release moisture depending on the weather conditions. This natural process is generally not detrimental, but some movement in the timber may be unavoidable. This can include splitting, warping & twisting.

Does pine wood crack easily? ›

Because pine lumber has a low moisture content, its spaces fill with air as the wood dries out during seasoning. This makes the wood less dense and easier to split. It's why pine and other cone-bearing trees are considered softwood.

Why do beams crack? ›

When the tensile stresses in the beam exceeds the tensile capacity, the concrete cracks. After this point the tensile force is transferred completely to the steel reinforcement. In a concrete beam, the crack widths and their distribution is mainly controlled by transverse reinforcement, or simply the stirrups.

How do you strengthen a timber beam? ›

Hence, timber or glulam beams are often strengthened by bonding with fiber-reinforced polymer (FRP) layers or steel plates on the tension side of the beam. Such strengthening will increase the flexural strength and stiffness and will result in a ductile failure mode.

Does linseed oil prevent wood from cracking? ›

Wooden boards and logs can be treated with linseed oil to prevent them from splitting or cracking. Linseed oil is a natural product that easily penetrates deep into the wood, forming a strong seal on the surface and reducing the loss of moisture.

Does wood Crack in heat? ›

Avoid excess heat or dryness, as this can cause wood to split and crack. Be sure to keep your furniture away from heat sources such as fireplaces or radiators.

How long does linseed oil last on wood? ›

Maintenance will have to be done about once a year or according to the wear of the finish. Dry looking or discolored wood is a good indicator that you need to reapply a light coat of oil. Simply clean the surface with a damp cloth, let dry completely and apply the oil, wiping all excess oil after 5 minutes at most.

How do you treat splitting wood? ›

If this happens, carefully apply some wood glue into the crack or break and use clamps to hold the pieces together until it fully dries. If you have the time, it's best to leave the clamps on for up to 24 hours to ensure the glue has dried and sealed the break.

Should oak beams crack? ›

The simple answer is they are totally natural and nothing to worry about! As oak dries out it shrinks across the grain and develops splits and cracks, sometimes also called 'shakes'.

How do you fill cracked timber? ›

  1. Ensure surfaces are clean and dry and remove any rotted timber and fix split timber firmly before filling. ...
  2. Apply Polyfilla Exterior Timber firmly using your filling blade. ...
  3. Sand back to a smooth, even surface and paint with a quality exterior water or oil-based paint, or stain and clear varnish.

How do you keep wood from cracking when spreading? ›

There are ways to stop cracks in wood from spreading. A good solution is to use wood filler or wood putty to fill the cracks or use sawdust and wood glue. You can also use epoxy resin to fill cracks in wood from getting bigger.

Does pressure treated wood split? ›

Another issue Pressure Treated lumber can experience is called checking, which means that the wood splits and splinters. But both twisting and checking can be minimized, if you follow some simple steps.

Does wood lose strength over time? ›

Paul Fisette responds: The general rule is that the mechanical properties of wood show little change over time. In short, the aging of wood, unlike that of cheese, does not make it better. Nor does it improve its strength.

What causes timber to warp? ›

In damp or rainy conditions, moisture is absorbed into the wood causing swelling. When timber dries, it shrinks. With every wet and dry cycle this process is repeated. When one part of a timber board dries and consequently shrinks faster than another area, the wood is stressed and warping occurs.

Are cracks in log homes normal? ›

Cracks in your logs can cause some serious problems. However most cracks are nothing to worry about. It is natural for wood to crack or check as it dries and this is actually part of the charm of a log home. It's that rustic, weathered look that makes them unique.

What is a shear crack? ›

Cracks in beams due to increased shear stress

Cracks in concrete beams due to increase in shear stress appears near the support such as wall or column. These cracks are also called as shear crack and are inclined at 45 degrees with the horizontal.

What is flexural crack? ›

Flexural crack cracking occurs where the bending moment stress is at its maximum. Shear crack cracking occurs where the shear stress is at its maximum.

Is it normal for cedar posts to split? ›

This is so common in timbers that there is a term for it called “Checking” which can seem to have the appearance of a split or a crack. Checking is a more common trait in Cedar timbers. A few of our clients still prefer Cedar especially in a Natural finish for its inherent beauty with knots.

Why do 4x4 posts crack? ›

Pressure and moisture are the big crack culprits. New wood is wetter inside than many homeowners realize. Not only is there natural moisture, but lumber is often treated with chemicals to prevent rot. As the sun dries your new wood fence, it sucks out moisture, putting pressure on wood fibers.

Why do posts crack? ›

The cracks are as natural as the wood itself and keep the post from twisting out of shape, particularly for pressure treated lumber. The arrows show splits in a pressure treated post. Structurally they are not a problem. Without them the post would twist and bend out of shape.

Do wooden sleepers crack? ›

It is completely normal for wood of all types to split as it contracts and changes in response to the weather, and it is common for many splits to appear over time. However, it is unusual for a split to reach the centre of the sleeper over a long enough distance to affect the structural integrity of the sleeper.

Do fences warp in hot weather? ›

The same goes for the summer when materials can expand in the hot weather. And if your fencing is not flexible enough to allow for expansion, it can lead to cracked or warped boards. Another way that your fence can become damaged is actually via your pathway or the area in which its foundation is set.

What's the hardest wood to split? ›

1. Australian Buloke – 5,060 IBF. An ironwood tree that is native to Australia, this wood comes from a species of tree occurring across most of Eastern and Southern Australia. Known as the hardest wood in the world, this particular type has a Janka hardness of 5,060 lbf.

What wood is easiest split? ›

White, Yellow, or Paper or Gray Birch burn at medium to high heat levels and burn fairly well. These woods are easy to split, do not smoke much or release many sparks.

What is the disadvantages of pine wood? ›

Pinewood has good moisture resistance than most other woods and it is significantly resistant to decay and rotting. The only problem with pine wood is it dents and scratches easily because of being softwood.

How do you dry wood so it doesn't crack? ›

You can dry wood without cracking by applying a sealant, stabilizer, or salt paste before drying. Finally, you can apply boiled linseed oil or let logs dry as boards to avoid cracking when drying. Treating wood with stabilizing solution keeps wood from cracking when drying.

How do you keep wood from cracking when spreading? ›

There are ways to stop cracks in wood from spreading. A good solution is to use wood filler or wood putty to fill the cracks or use sawdust and wood glue. You can also use epoxy resin to fill cracks in wood from getting bigger.

How do you keep Live Edge wood from splitting? ›

The best way to keep wood from splitting as it dries is by using a commercial sealant such as an anchor seal. These sealants can be applied to the open ends of logs and prevent them from drying and shrinking in contact with the air.

How do you keep landscape timbers in place? ›

Rebar. Rebar is the best option for staking single or layered timbers to the ground. You can use it alone or in conjunction with landscape spikes and screws, but it does require predrilling.

Does linseed oil prevent wood from cracking? ›

Wooden boards and logs can be treated with linseed oil to prevent them from splitting or cracking. Linseed oil is a natural product that easily penetrates deep into the wood, forming a strong seal on the surface and reducing the loss of moisture.

Does vinegar preserve wood? ›

With this in mind, believe it or not, a bit of canola oil and vinegar makes a brilliant wood sealant, protecting wood from burrowing insects, wear and water. As well as this, this can be reapplied to revitalize the wood, something that won't work without sanding off varnish.

Is linseed oil good for wood? ›

Yes– linseed oil is an extremely popular finish for wood cutting boards and wood kitchen products. It is non-toxic and food friendly.

How do you treat splitting wood? ›

If this happens, carefully apply some wood glue into the crack or break and use clamps to hold the pieces together until it fully dries. If you have the time, it's best to leave the clamps on for up to 24 hours to ensure the glue has dried and sealed the break.

What to use to fill wood cracks? ›

Wood putty or wood filler sticks are easy to use and effective for covering over wide cracks in indoor and unstained wood. For a quick fix, a mixture of wood glue and sawdust seamlessly blends in small cracks and gaps in assembled furniture. Purchase epoxy to handle larger gaps, such as on outdoor projects.

Will epoxy stop wood from splitting? ›

In addition to its filling capabilities, the epoxy resin also acts as an adhesive. That means it will hold the crack sides together to prevent further damage of the wood.

Why is my new deck wood splitting? ›

Decking splits as it dries. As the water evaporates from the wood in the sun, the surface wood shrinks cracking around the un-shrunk core wood or fasteners. The solution to prevent decking from splitting is controlling the pace the wood dries and providing room around the fasteners for the decking to shrink.

Does live edge wood need to be dried? ›

As a general rule of thumb, you should let your live edge slabs air dry for 1 year per every inch thick they are. Then, they should be kiln dried. You'll want them to be at most 20% moisture level when they are going in the kiln.

How long do landscape timbers last? ›

Pressure-treated timbers are typically what you use for a timber retaining wall. The fun fact about pressure treated wood is that it is warrantied – but putting it in continuous contact with the ground voids the warranty. Even so, you can reasonably expect to get anywhere from 10-20 years out of a timber wall.

Should you seal landscape timbers? ›

If left unsealed, these ends would allow moisture inside, quickly diminishing the timber's life and quality. This is why it is crucial to seal and coat the exposed ends of pressure-treated landscape timber.

How long does it take for landscape timbers to rot? ›

I have used "treated" landscape timbers for 40 yrs and they normally last a long time... 15-20 yrs. More recently, I installed 55 of them for different landscape projects. Many are rotting within 4-5 years.


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