Hairline Cracks in Oak

Jak3

Jacob
Senior User
Would you use material with hairline cracks?

These are some blanks for a glue up that will become the top of a plant/candle stand, and I noticed one of them has some hairline cracks. Even though I have plenty of thickness to plane them out I worry they might reappear. I'm not worried about them weakening the piece but I certainly dont want them to show in the top. Should I get some other material?


What causes this? This wood was air dried. All from the same board but not all of them exhibit cracks.

Useable or firewood?


 

ehpoole

Ethan
Corporate Member
DQ
The hairline cracks can occur during drying (especially if too aggressive) but another common cause is wind shake damage in a tree that has been subjected to either an extreme wind event (such as a severe hurricane) or repeated bouts of high wind that create stress cracks within the tree from being shaken repeatedly, as can a severe impact event like a car crash or a very large heavy tree impacting the affected tree while falling which imparts a shockwave through the wood. The tree usually survives and heals over the damage, but the cracks remain behind since they are in the “dead” wood of the tree and typically fill with pitch/sap that then drains out when the trunk is cut. So there are multiple possible causes.

While I would not use such boards for critical structural elements that would be under stress, they are perfectly fine for many projects if you don’t mind the aesthetics. Just analyze your design to judge how much stress your design is likely to apply along the axis of the cracks and then ask yourself what the absolute worst possible outcome would be if it did split all the way through on that board (which is unlikely without some real stressor). A lot of the projects we make have very limited stresses involved and would not be dangerous even if catastrophic failure occurred while other projects do present potential dangers or have extreme stresses.

Another option to deal with the problem is to support the split so it can not grow by either laminating a layer of good wood on top (even better if it’s grain ran perpendicular, or at least at some reasonable angle, to the fault...or use plywood which is well suited to the task with its alternating grain) or by using tricks like “bowties” to prevent the split from propagating any further.
 

kelLOGg

Bob
Senior User
DQ
Here's an interesting article about "wind shake" by Gene Wengert, an expert on most things wood.

 
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Chilihead

Chilihead
User
I have a bunch of red oak and much of it has similar cracks in it. Often the crack does run through aboard, so, as others have already mentioned, be mindful of that when structural concerns are there. I've have very good luck filling these cracks with epoxy. It does double duty helping to reinforce the wood and giving me a smooth flat surface face. Epoxy planes and scrapes well, and in those small cracks, it is not too noticeable.
 

Jeff

Jeff
Corporate Member
DQ
These are some blanks for a glue up that will become the top of a plant/candle stand,
Those look to be pretty small (even zooming on your pics) and probably shallow as well so use the boards even if the tiny cracks don't come out after planing. They're not a show stopper as is. Epoxy is very good for filling cracks and voids but those look so small that it may not be worth trying.
 

JimD

Jim
Senior User
DQ
Just one of the many basically cosmetic things to think about as you select boards for different portions of the project - in my shop. Almost all projects are very overbuilt (does a table top need to be 3/4 or more hardwood to support a plate?). So while there is a structural impact of a crack it is normally not important.

I also notice these around knots sometimes. I didn't read the attachment and I agree that wind damage is a possible cause but I think the wild grain around knots is a potential cause too.
 

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