Spotting some structural grading defects

[Don P]

I've been taking some pictures of lumber structural characteristics and defects as I come across them. I've then been looking them up when I get home. Thought some of you might like to look too.

The job I'm on now is a log cabin kit of Southern Yellow Pine. It has been loaded with compression wood.  A search on the forum will bring up several old threads if memory serves. Compression wood is abnormally weak and shrinks lengthwise considerably more than any normal wood.

From The Grader's Handbook,
Compression wood: Abnormal wood usually occuring in bands as a wide growth ring of hard, brittle wood that may be darker in color and smoother to the touch than the surrounding wood. It shrinks more than normal wood and is one of the principle causes of warp. It is prohibited if judged to be as damaging as other defects excluded from the grade. Guideline: If present with warp, allow only 1/2 as much warp as permitted for the grade. If the piece has dried without warping, judge the compression wood as not damaging.

One description I've heard that works for me is that it has a kind of peanut butter look, it also seems to me to appear dull and lifeless. My wife say tahini maybe, peanut butter never and what do I want anyway, animated wood.




The 8ft 2x10 in the picture fails several ways. The warp; in this case the warp presents itself as crook or sidebend. The maximum allowable crook in an 8' #2 2x10 is 3/16". Since it is present with a major compression band it should be limited to 3/32", in this board the grader apparently confused half and double  :. It also occupies more than 1/3 of the cross section of the piece, even though fairly centered I would consider this to be too much weakened to use in an application that called for #2 2x10 strength. I will likely use this as short jacks in a dormer roof. The stamp makes the inspector happy, I know the company graders are pushing things, this board is actually a #4 by the rules. The important thing is to make sure the real #2's in the load get to where they need to be and the lesser wood gets used where strength isn't the reason for the dimension. In the little dormer roofs the 2x10 dimension is for insulation, a 2x4 is strong enough for the short rafters.

The second picture is of the end grain of one of the cabin's logs. It shows several areas of compression wood scattered around it, logs like this are bowed toward the compression wood side. In this bit of endgrain there are 3 pretty large and 3 relatively small zones of compression wood.

[getoverit]

I have seen things like this too, especially large knots in pine lumber that would make the wood almost useless unless you cut the knot out.

I really do wish someone would go to war with the SPIB over this, but it looks like there isnt anybody around that has the money to fight them. In return, we all end up buying inferrior lumber from the box stores when we could cut and make our own better quality lumber.

[Don P]

Knots, especially in softwoods, are often the determining factor in calling the grade. When you first look at a board, scan it for defects, the worst one determines the grade of the board.

The total displacement of the knot in the cross section of the piece of wood is what you are trying to visualize. Remember branches grow from heart to bark, you have to understand where the timber came from in the tree and then you'll understand where the branch is going within the board. You are using your best judgement to describe how much sound, full strength wood remains after deducting the strength reducing defects.








These pictures are a white pine 2x4 with a simple through knot. The board is flat sawn. The handbook says "Knots; On wide face, measure both faces and average. On narrow face, estimate area occupied by knot and allow if equivalent to or less than knot at edge of wide face." This knot is covered by the first sentence, measure on both faces and average. That will give us the average knot diameter within the wood. For a #2 2x4  a centerline knot on the wide face can be as large as 2", an edge knot can be no larger than 1-1/4", holes from any cause can be no larger than 1-1/4". A true #2 is not a pretty board.

A #1 2x4 would be limited to a 1-1/2" centerline knot and 1" edge knot or hole. A #3 2x4 is limited to a 2-1/2" centerline knot and 1-3/4" edge knots or holes. If you look at the edge knot restriction, that is what I really try to remember, knowing the knot can get larger as it moves into the center of the board. If you look at those average edge knot allowable sizes and compare them to a 2x4's face, they occupy roughly 1/4 of the face for a #1, 1/3 of the face for a #2, and 1/2 the face for a #3.

Another way to think about grading that board, in your mind visualize the averge knot size. Now look at the board, can you put 3 more knots beside the existing one ... its not a #1. Can you fit 3 of that size across the face, its close, but I'd say yes, its a #2. If you could only put 2 knots that size on the face its a 3.

[Don P]

Here is why you need to look at all 4 faces and understand what the branches are doing within the wood. This small knot in a white pine 4x6 looks like an easy #1, maybe even Select Structural.


It had friends  ;D



You would sure want to know that was inside and allow for it before putting a heavy load on that timber. I'd give it a #2 instead of SS. In bending calculations it reduces this timber from 1050 psi to 575psi capacity. With the initial mental image of one small through knot vs the cluster that is in that timber you can see how that strength reduction makes sense. You don't grade from 1 face, consider ALL faces  ;).

[Don P]

We've been talking about spiral grain in another thread. Slope of grain is an important consideration in judging the strength of a timber. Severely angled grain can break across the board at very low loads. Spiral grain is one cause, sawing at an anle other than parallell to the bark is another. I'm not saying you must saw parallell to the bark or to firewood spiral grain, just keep an eye on the slope and account for it before using.

It can often be confusing to determine the slope of grain, flatsawn lumber can appear to have wild grain and yet the slope of the grain can be straight. The opposite can also be true.  I've taken a few pictures to show this I hope. These shots show checking that follows the slope of grain, checks follow the grain. Notice the checks and the "apparent" grain. This was a left spiral growing tree. If you look closely at your softwood lumber you can often follow the resin ducts to determine grain orientation also.

Select structural is limited to a 1in 12 slope of grain, so in 12" of length the grain cannot angle more than 1" from a straight line down the length of the board measured on the worst face.
Number 1 is limited to 1 in 10
Number 2 is limited to 1 in 8




Second log down, I'd swear its a hard right spiral at first glance, it has a left spiral, look at the checks.

[Don P]

Yesterday was the day for timberbreaks. I came home and took a couple more shots to round it out.
Timberbreaks and compression failures are not allowed above a #3.

First shot is a timberbreak in one of our 4x10 doug fir rafters, there were 3 along the same edge. I suspect this tree hit the ground hard or dropped across another. On the plus side the supplier brought out a replacement today. 24 hours on a 20' stick of west coast 4x10, I'm not complaining.


There are many compression breaks on my deck. Alot of pretty sketchy syp goes into radius edge decking. This shot is a compression wood failure. Remember that compression wood shrinks lengthwise more than normal wood. If it is bound alongside of good wood it will shrink and possibly bow the board. If it continues to shrink and the surrounding wood will not move any more, it tears across the grain.


Here is another. Juvenile wood surrounding the pith is often reaction wood. Same story as above, just in the juvenile core.


Hoping this is helpful.

[Fla._Deadheader]

I for one, am very glad you took the time to post this info. It really gives food for thought on how lumber is graded. Thanks, Don.

[isawlogs]

 I also am happy to read up on grading .. its been a long time since I saw this in a class room , you can keep on putting more on and you can rest assured you will have an avide reader .
  Thanks for taking time to do this Don . 

[getoverit]

I'm enjoying every post !! Keep them coming Don and THANKS !

[Don P]

Thanks guys,
I'll keep snapping and looking it up. Feel free to post yours. I was starting to think this was becoming my private diary  :D

[Nova]

I'll echo the comments of the others, this is very helpful.  Keep the lessons pictures coming and maybe I'll make a few less mistakes than  I would without this info.  Thanks.

[Don P]

I've been getting some pics of pitch recently, I think there's enough to cover some ground.
Pitch is unlimited in all grades, but, pitch is a softwood's bandaid, something happened to that tree. Look hard for the cause, sometimes the injury is not in that board though. Often the injury is not strength reducing

First couple are shots of pitch surrounding a separation between rings, looks like a debarking or lightning. I would use the shake rules for this. SS and #1 allow no through shakes away from ends, this goes through the piece. #2;at ends equal to splits (1-1/2 x nominal width) Shake away from the end may be through for 2 feet. Shake breaking into an edge may not be deeper than 3/4 the thickness. Surface shakes may be 3' long or 1/4 the length, whichever is greater.

This through shake went for about 4' on a 24' 2x10. The grader blew it, this is a #3. A #3 limits a through shake to 1/3 the length, an edge or end shake to 1/6 the length.



As far as I'm concerned the edgerman oopsed this one and the grader compounded the error.  There's some rafters that skirt the log gables, I can tie those to the walls. The rest of the pack was nice, straight, flat, good stuff.



Worm eaten pitch. Not allowed in SS or #1. Number 2 & #3 limits the area to the size of an allowable knot in that location of a timber of that width, measured on worst face. If there are any holes outside that allowed zone, assume the worm went travelling and #4 the piece. This chunk was turned into dunnage, good call. I know nothing of this critter and would like to know more, he must have a cast iron gut.


Pitch and bark pockets are usually smaller than allowable knots and are not limited by number. These ones are no sweat even in a SS. Use good judgement though, I've seen them rarely where they were so numerous they compromised the piece.


So for pitch, look for the cause and apply the rule for the defect. Sometimes it was just a missed buck  :D.

[getoverit]

While I was sawing some SYP today, I found a log with a pretty big pitch pocket in it. Matter of fact, I dont think I have seen one this big before in any lumber or log. It was a good inch wide and about a foot long.

what causes pitch pockets like this?

Also, I ran into one log that had been lever cut when it was felled. I noticed a strange pattern in the wood on the lever, but didnt pay much attention to it. When I cut about a foot off of the butt of the log, I found that the pattern had continued up that far. It kinda reminded me of a clover leaf. When I cut the log into lumber, the pattern didnt show up and was undetectable in the wood. The whole log had a reddish hue to it though. What caused this?

[Don P]

I don't know what causes them, I've heard some theories but don't think I oughtta write them down. I think they'll look dumber in print than in my head  :D
Anybody know?