repair of checking cracks in heavy wood timbers (post and beam)

[PSUengineer1]

Wood shrinks as it dries. Shrinkage responses cause anomalies in the appearance of wood known as checks and splits. The attached photo shows a 6"x6" wood timber that has checking. Brighter color wood within area of checking (above right hand side of knot) could be argued as being "recent" based on its color.

2 things:

1. checking does not affect structural integrity of member.. agree? even if it was possibly made worse by recent movement of structure?
2. how do you repair check cracks if they have recently worsened? Epoxy? Looking for repair recommendation.

Thanks.

 

[CANPRO]

That doesn't look that bad to me. The repair, if required, depends on the nature of the loading. Taking a guess from the picture - it looks residential, and my not even be structural. My initial thought is maybe measure the cracks and check back in a few months to a year. I think any repair here would be purely cosmetic.

 

[dik]

concur... you can fill the 'cracks/checks' if you like... I'd use epoxy injection to maintain/improve strength if felt necessary. Has there been a change in the environment to cause the additional checking?

Dik

 

[PSUengineer1]

@ dik.... no change in environment, house was struck by a vehicle

 

[dhengr]

PSUengineer1:
That looks like a very nice mellow piece of interior paneling/trim and I don’t think I would do a thing to it. Anything you do to it will change its natural aging and coloration process, and it will stick out like a sore thumb, it’ll look like hell. A 6x6 wood timber for interior trim, really?, how is that member loaded and stressed? Watch it, over time, and see if it really grows in a significantly dangerous way, otherwise, that’s the nature of the beast. Next time, use a concrete beam, instead of a wood timber. Concrete splits following a different grain pattern, maybe a more appealing pattern to you , but cracks nonetheless. And, just as with timber the cracking patterns in other materials are pretty often a function of the material characteristics.

This is a pretty subjective matter and pretty much requires some individual inspections and considerations for each problem which rises to some (critical) level of cracking/checking. Generally speaking, a nice long, longitudinal, fairly straight check down the center of a column, a compression member, should not appreciably change the cap’y. of the column, no real change in P/A. The check should not be completely through the timber; and it should not slope out, following the grain, to one of the faces. But then, this latter sloped grained member should probably never have been graded for a compression or bending member in the first place. These latter conditions can lead to buckling of two thinner members, like a poorly interconnected built-up column member; or a diagonal compression/shearing/sliding failure following the sloped crack. You will see a lot of timber checking in old timber industrial bldgs. without much apparent deleterious effects.

This same central check in bending members could have significant detrimental affects where shear and horiz. shear stress are high, less so where shear is low; and of course, it would be akin to putting two 3x6's face to face, in the plank bending orientation and wondering why they aren’t the same strength as a good 6x6. I’ve seen a number of articles on this over the years, and there have been testing programs and reports on these issue to develop grading criteria, but I have no quick easy links for you, sorry. A number of Wood/Timber design text books cover some of this, grading rules do too, and I think “The WOOD Handbook, Wood as an Engineering Material,” USDA, Forest Products Lab should have something. There just aren’t any simple, exact rules and formulas for this problem.

 

[PSUengineer1]

@dhengr:

this is not a trim piece. It is a 6x6 horiz member in a frame (post and beam construction). Loading is axial. Would you apply epoxy if the contractor had it ready? would you add pins or screws? thanks.

 

[dhengr]

PSUengineer1:
Is it axial tension or compression, and what stress level? Does the checking run out into the regions of the end connections, and what are these connections, and how are they affected by the cracking, if at all? I can imagine a car impact causing some member stresses which might make that crack grow a bit, particularly at the irregular grain structure of a knot. But, the real crack may not be so new, as that it was just opened a little more to expose some wood surfaces which hadn’t seen much dust and smoke yet. How deep into the member is the real open part of the check? I would use vert. through bolts, near the member face we can see. Then plug the holes with some (flush?) dowels which mimic the dowels at the joints. Take some bar clamps and a couple 2x4 blocks 12-16" long to protect the timber, and see if you can start to squeeze that crack closed. If that isn’t fairly easy to do, I probably wouldn’t do anything. If I used any epoxy, it would be very sparingly, and way back in the crack. Then, I would stop tightening the bolts when the epoxy squeezed out to within .25" of the face, and then leave it alone. I hesitate with the epoxy because that is such a beautifully colored finished face/surface, and you can’t play with epoxy without get it all over the place. I would not have these same qualms about a less exposed or industrial situation. You might get by with some of the newer structural screws about 4.5"-5" long installed from the top and countersunk. I don’t really see that crack as a problem if it doesn’t grow any more. Were any of the framing joints loosened or whacked out of alignment?

 

[oldestguy]

Leave it as is. Opening and closing will occur with moisture changes. As an example the wall has had some "patching" that looks like hell. Don't make it look worse.

 

[Ron]

Agree with dik...you can inject epoxy. Works well. Used it for repairing a pedestrian bridge at "a major theme park near Orlando" ()

 

[dik]

Have to take care... some repairs can be ugly...

Dik