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Wood Moisture & Why Bowls Crack as They Dry

When people bring me a fallen tree or a fresh-cut log, the first question they usually ask is, “Will it crack?” The honest answer is that wood is unpredictable. Some pieces behave perfectly, others try to split themselves open the moment they hit fresh air. It’s frustrating, but it also teaches you patience, skill and respect for the raw material when you work with greenwood.


I have the same argument with tree surgeons who expect firewood rates when I’ve no idea how the wood will move or if there are serious issues hidden inside the tree. Until it’s rough-turned or opened up on the bandsaw, nobody can say for certain what’s going on beneath the bark.


Understanding moisture is the key to understanding why bowls sometimes crack, why some survive, and why green wood behaves the way it does.


The bowl below is an Evergreen Oak that I picked up in 2016. I dried it a bit too fast and it cracked in typical fashion. You can see how much the wood distorted during the drying process, a good reminder of the tremendous forces at play as moisture leaves the timber. Learning to sense this ahead of time only comes with experience.


A twice-turned Evergreen Oak wooden bowl showing a typical drying crack along the rim and side wall
A Common Looking Crack in a Twice-Turned Bowl

If you’re thinking seriously about taking up woodturning and learning the ins and outs of drying wood and managing movement, I can guarantee there are aspects you haven’t yet considered.

I go into more detail about sourcing & processing greenwood in my post How to Process Logs for Woodturning. In case you are not convinced woodturning is right for you, my post So You Want to Be a Woodturner?, covers the parts nobody thinks about in the early days.


What Moisture Content Actually Means

Fresh hardwood can contain a surprising amount of water. A log that looks solid and dry on the outside may still be holding a huge amount of moisture inside the annual rings. When you cut into a fresh tree, that water has to escape somewhere and it almost always escapes through the endgrain first.


In fact, endgrain loses moisture up to twelve times faster than sidegrain, which is why cracks nearly always begin there.


As moisture content drops, it happens from the outside in. The outer shell dries and begins to shrink long before the inner wood does. The inside hasn’t moved yet, so the outer fibres pull against the wetter core. That internal tension is what causes cracks and distortion.


This is why slow, controlled drying is so important with the wood drying from the inside first and outside later.


If you want to dive deeper into preparing wood before it ever reaches the lathe, I cover this in my post How to Process Logs for Woodturning including how to break down a log to get the best yields and avoid unnecessary waste.


Why Wood Cracks During Drying

There are several reasons cracks form, and most of them come down to timing and moisture movement.


● Endgrain dries too fast - This is the number one cause. Endgrain acts like a bundle of straws, pulling moisture out much quicker than the sides of the log. If it dries faster than the rest, it splits.

● The sun and wind hit the exposed surface - A fresh breeze on a cut log can cause visible cracks within minutes on a warm day. Even in Ireland where the weather is mild, a bit of wind will do the damage.

● The wood wasn’t sealed or protected - If the bark is removed, or the ends are left unsealed, the log dries unevenly and tension builds far too quickly.

● Natural stresses inside the tree - Trees bend with the wind for decades, and this can leave built-in tension. Once you cut into that area, the wood sometimes twists, warps or splits even if you did everything right.

● Existing damage - Insect holes, heart rot, shakes and hidden cracks all make it harder for a bowl to survive the drying stage.


Wood is a natural material, and you simply cannot save every piece. But you can give every piece the best possible chance to survive until you are ready for it.


If you're new to turning, it also helps to understand that spindle wood and bowl blanks behave very differently, which I explain in my post Spindle Turning vs Bowl Turning: What’s the Difference?.


What I Do to Reduce Cracking

Every woodturner has their own approach, but these are the methods that work best for me.


1. Cover the Endgrain Immediately

This slows down the moisture loss so the wood dries more evenly. If the log is large, I’ll wrap it in bags or plastic tarp to buy more time before rough processing it.


2. Rough Turn Bowls Thick

A rough-turned bowl has thick walls so the wood can warp naturally without tearing itself apart. Once it dries, I come back months later and finish-turn it to its final shape.


3. Store Rough Bowls in a Cool, Stable Area

Away from heat, sunlight and airflow. Direct airflow is the enemy of green wood.


4. Seal the Wood Endgrain

As soon as the wood is cut to rough size or a bowl is rough turned, you can then seal it with an appropriate sealer like builders PVA glue. Watered down slightly makes it easier to paint on to the wood.


5. Weigh the Bowls as They Dry

A drop in weight can tell you how fast the moisture is leaving. When the weight stops changing, the bowl is ready for finishing. I look for an oval foot which is a good indicator.


6. Accept That Some Bowls Will Crack

Even with all the experience in the world, you will lose some pieces. It’s part of the craft.


Why Green Wood is So Unpredictable

Even two pieces from the same log can behave completely differently. One might dry perfectly, and the other might twist itself like a pretzel.


Reasons include:

● Different grain direction

● Closed knots

● Open knots

● Hidden stress

● Water pockets

● Variations in density

● Natural reaction wood from a tree that leaned during its life


This is why I always tell customers that I can try to make something from their tree, but nothing is guaranteed until the wood is fully dry. My page Fallen Trees has some more nuggets of information that may be handy to know.


Why Bowls Warp as They Dry

Warping is completely normal. In fact, many turners love the look of it. A 20 percent moisture drop will change the shape of almost any green bowl, especially when the grain direction changes across the piece.

The goal is to allow gentle, controlled warping—not cracking. Warped bowls can be beautiful. Cracked bowls usually end up in the stove. Although I do like a challenge in bringing some of these to life again.


How You Can Protect Wood Before Bringing It to Me

If you are dealing with a fallen tree and want me to make something meaningful from it, the best thing you can do is slow the drying down.

● Leave the bark on

● Keep the log off the ground

● Avoid the sun

● Avoid wind

● Put the log in a black bag or wrap it in plastic if possible

● Do not cut the ends away unless you know what you’re doing


Moisture management starts the moment the tree hits the ground. again, you can refer to my Logs for Woodturning post linked above for more detailed information.


Moisture Meters: Are They Worth It?

I used to use a moisture meter, several in fact but only as a guide in the early days. They can be handy for rough-turning decisions, but they’re not gospel. Wood density, species, temperature and grain direction can all throw readings off. Weight monitoring is often more reliable.


With more experience, I was able to tell by looking alone and most importantly time. Leave the wood long enough in the right conditions and it will be dry enough to work with.


Drying greenwood can be frustrating when you are trying to rush things and this is very difficult to do in the early days of becoming a woodturner. A lot of new turners give up early because they develop bad habits without realising it. I wrote more about this in Why Most New Woodturners Fail, and dust control is one of the biggest reasons.


Learn the Right Way From the Start

Woodturning is a tough craft in the beginning, but much like riding a bicycle, once you learn the basics you never forget them. Drying wood is the same, it’s as much an art as it is a science.


My honest advice to anyone thinking about taking up woodturning is this: take a lesson early and cut straight to the important stuff. There will still be plenty to learn along the way, but at least you’ll be starting with good habits instead of fighting bad ones.


If you’d like to learn in person, you’re very welcome to take a lesson with me here in Tralee. Visit my Woodturning Tuition page, see which option suits you, and I’ll help you get started the right way.


Final Thoughts

Wood moisture is the invisible force behind every successful or failed bowl. Once you understand how water moves inside the timber, you start to see why some pieces survive and others don’t. It’s also why handmade bowls carry so much value — every one of them has survived months of drying, tension and movement before it ever reaches someone’s home.


If you have a fallen tree and would like me to try turning a keepsake from it, feel free to get in touch. I’m always happy to take a look and tell you if the wood is viable.


Thanks for Reading,

David


About the Author

I’m David Condon, a woodturner and small business owner based in Tralee, Co. Kerry. I’ve been working with wood for most of my life at this stage — 11 years as a carpenter and over a decade running my own woodturning business.

During that time, I’ve worked with Irish hardwoods, taught woodturning, and run my workshop full-time. On this site, I share the same knowledge I pass on to my students — from choosing the right wood and tools to finishing techniques that make every project shine.


I have many related Woodturning Blog Posts if you'd like to stick around for a while.


© David Condon Woodcraft – All Rights Reserved.



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