Growth Stress End Checking

Log characteristics can cause checks to open up, even when ends are coated and drying conditions are correct. February 19, 2006

We sawed some wide (more than 14") walnut and some wide (more than 14") quarter sawn white oak in the heat of August. I know that’s not the best time, but the logs were going bad fast.

After sawing we sticker and stack inside our metal building which heats up plenty in the sun. This is great for air drying but can be too fast for the thicker turning blanks we sometimes cut. Anyway, after 5 weeks the widest walnut all has an end check right in the center of the board while none of the white oak does. Both were anchor-sealed properly. Oddly, some of the white oak has blue stain on its sapwood, suggesting that the drying is too slow. This may be because there is no wind inside, so air flow is low but heat is high.

I am surprised it happened this way since white oak prefers to dry slowly and walnut is usually so well behaved. Maybe the oak has still not lost its free water yet and the walnut is already losing bound water? I know that I must be drying both too fast but the white oak is not showing defects because it cannot release its water as quickly. I am just looking to learn what is happening here. Next time I will cover outdoors and keep things slow to start when sawing in the late summer.

Forum Responses
(Sawing and Drying Forum)
From contributor D:
Here is my take - the walnut is drying and the white oak is not. The white oak may have a thin shell dried hard if your metal building was as hot as metal buildings around here. Cut an end off and see.

From contributor J:
I would also add that being quarter sawn the oak is a little more stable than the flat sawn walnut and might be able to stand a little harsher drying, but my guess is that maybe a bacterial infestation in the white oak may be causing the excessive moisture content.

From contributor L:

On your walnut, is it an end check or end split that extends couple of inches up to 8" into the board? I don’t have many problems with walnut end checking but sometimes I get these long splits. Just from observation the splits are caused by tension wood.

From Gene Wengert, forum technical advisor:
My guess is that you have excessive tension stress (natural stress in the tree; also called growth stress) in the walnut. End coating does not prevent checking associated with this stress; end coating prevents checking caused by rapid drying of the ends of the lumber.

From the original questioner:
Yes, what I am seeing is a longish 3-6" plus end split. So it’s the nature of the log I chose then right? I do not remember sawing obvious pith-off-center leaners, so I am not sure how to prevent this in the future. But a 14" wide board ripped into two is still saleable.

From contributor L:
If you sawed to close to the juvenile core wood, that will sometimes also cause splits like were talking about.

From Gene Wengert, forum technical advisor:
It is not preventable - it comes with the log. Oftentimes the greatest stress seems to be in 16" to 20" diameters. Some species have a lot more growth stress than others. As Contributor L states, it is more common to see such stresses near the center of the log, but you will see them at all locations.