Has anyone ever heard of a post or other timber checking so dramatically that it became a structural hazard, or of one actually busting in half, or houses falling down....or is this mostly an aesthetic issue?

I know that I have culled many a timber that probably would have brought down a frame had it been used, but those are obvious and I couldn't imagine how anyone would have let one like those get by.

I have also seen many old frames with very large checks. I tend to believe that most timbers withhold their structural integrity once checked and dry in the frame.

Thoughts?

TG,
We had to replace a 10"x16" timber spanning 25 feet and supporting 12 feet of second floor because of severe spiral grain checking. The beam was a bit undersized for the load, but I don't think it would have failed if it had been straight-grained. The timber had a boxed heart, and if it was green enough to have no surface checks when it delivered from the mill, I could see how the spiral grain could have been over looked.
Regards, Chris

Freshly cut green wood is often endgrain sealed with Anchor seal, though I haven't yet heard of timber framers doing it to timbers cut for a frame. If you end grain sealed when you cut timbers, wouldn't it reduce checking? Isn't that desireable? It will dry slower. Will that cause problems with finish items installed then? Endgrain sealing on a frame that wasn't going to be put up right away would seem like it could be beneficial, no?

We use anchor seal on all end grain we cut, even inside mortises. It also helps at raising time, as the tenons are "greased". You're right about not getting it on the finished surfaces, as it will inhibit the finish from soaking in. CB.

I think I read somewhere on the forestry forums. Something like 75% of the moisture loss from a timber goes out the end grain.....

Anchor seal mitigates that loss by plugging the end grain to slow down moisture loss....


Good question TG...I'm interested to see what the response are to that question....

Spiral checking on green wood can be detected if you know what you're looking for (mind you, I only know soft woods, so can't speak for all species).

The checking created by lack of end seal hasn't seemed to be, in my experience, a source of structural concern, though I would never cut a frame without using it. My rule is to end seal any exposed end grain 1" and over, sloped tenons, and inside mortises.
Land Ark makes a nice product, though expensive....

No, my thoughts are those checks that were a topic of discussion on another thread recently (I'm too lazy to link to it, computer bogging down and I think you all know which one I'm talking about) where the guy's post was checked to the center of an 8x8...I saw that and wasn't so concerned; I've seen some fine, strong timbers with such checking (I was more concerned about the girt not snugged up to the housing)
So that got me thinking about this topic. We hear a lot about unsightly checking and how to avoid it (proper drying, kerfing the backsides, end seal..) but I honest to God have never heard of an actual structural failure due to extreme checking.

Spiral checking aside - that goes into the category of things to cull before the frame is cut.

Just plain old big fat check running down the length of the timber to the heart.
That's what I'm after.

I thought about posting this in the engineering forum, but wanted to see what the general consensus might be.

Duuhhh....the other thread I was referring to is Post Checking...right below this one...

I'll second or third watching out for spiral checking. I've seen a few barn timbers with spiral checking that most definitely ruined the timber.
How does TG see spiral checking in a green timber??
Spiral grain can often be seen easily in the bark of the tree...

Hhmmm...How does she see it?

Well, to be honest, it really depends on how green 'green' is.
By the time a timber gets to me it has usually been felled and sawn for a few days, if not weeks. And depending on the weather it may have already started to dry some.
Thus it gives me a bit of an advantage when I go over my timbers.

Spiral grain can be detected in the tree before being sawn, but that is different from spiral check. A timber with spiral grain wouldn't even make it to the saw.

Spiral check happens mostly in straight grained timbers, and can depend on such factors as speed of growth (varying yearly growth can cause a timber to dry in some funky ways, fighting against itself), or how the timber has been sawn.

I don't know exactly how I do it...I just know wood.
The Culling Queen.
The Timber Goddess.

But I'm sure I miss some, as well (*disclaimer*)

The check follows the grain, spiral grain causes spiral checks, straight grain checks straight. The "cleavage plane" if you want to call it that, is along the rays or resin ducts in the wood. Those are the cross grain cells that transport from bark to heart and are a natural weak spot. you can follow grain direction in softwood by watching the direction of those ducts or in hardwood by following the "chicken scratches' of the rays.
Just thought, lumber graders have a small pocket tool, a pick, that follows the grain and shows spiral. Should we try to source them?

There used to be a shear value assumption in the NDS for a checked timber and increases for unchecked material. That was changed a couple of ewditions ago, well they had also blown the math.

Never seen a timber check through although I've seen lumber do it. A timber typically checks to the heart.

I've used this tool you mention, yet no one was able to tell me the name of it.
A small brass device that flips open and has a little nail on the tip.
I was told in grading that it measures the 'slope' of the grain, and will not detect spiral checking...

I have to remember to take more pics, for today I had the perfect example of a straight grained larch timber with said spiral checking, which I come across sometimes.

Too bad I have a 3 day weekend and I'm not going to be at work tomorrow..sitting on the beach instead ....

Yup, that's the tool, I don't know the name either, they showed us in a grading class how to use it.

here's how I understand checking; As the timber shrinks, the drying shell is shrinking around a still green and swollen core. When this drying stress exceeds the woods strength perdendicular to grain, it splits. Wood is far stronger with the grain than perpendicular to it. What I think you are proposing is that the wood is splitting diagonally across the length of the cells. The picture I'd like to see would be to cut a firewood length of the checked larch then to split the firewood right beside the check to show the grain orientation. I hope we can agree that firewood splits with the grain? I'll bet the check and the split is in the same plane, the wood will not split across the check.

That said I can think of a notable exception where I often see cross grain breaks at 90 degrees to the grain, across the board.
When we lay 5/4 southern pine decking. The decking is often made from heart pieces that include juvenile wood. When we screw the board down it is restrained from bowing. The mature wood alongside of the juvenile core restrains the wood also. It is pretty common to see an unrestrained piece on a pile bow like crazy. It is also common to see a piece screwed down on a deck checked, cross grain in the juvenile zone as that wood shrinks lengthwise. That is not what we're talking about here though, they are graded as "compression failures" or "timber breaks" and are limited to the lower grades.

What you are proposing would stand grading on its head, its opposed to I was taught in grading school and have seen in my experience. If you can get tension perp failures in the grain direction, we got biiig problems That is another thought. How many are using accredited graders as required by code in most places? Should the Guild be having graders teach sessions at events? The '06 code has tightened up a notch on that front, that will only continue.

I don't entirely disagree with you, believe me, but that is the way its heading. But, checking does show the direction of the true "grain" of a piece of wood. When you split that piece of checked firewood I can about guarantee it will cleave in the plane of the check, that is how the timber will fail. If you see a diagonal check across a timber, measure the slope of that check and use that as the slope of grain in determining the allowable stresses that the engineer will use in determining the timber"s strength. These are sympathetic jobs not an either or, a good grading gives the engineer what he needs to design safely.

As far as whether to trust the TPI grader, or the engineer... I'd rather you were trained and approved to gradestamp your own At the end of the day, after you have worked the timber, that is the true grade. You are ultimately the grader no matter what the timber was to begin with. If the engineer assumed a #2 strength and you gave him a timber with #3 sloped checks, the timber is weaker than designed. A mortise across from a knot could weaken the timber more than intended, or not, knowing the allowables lets you keep the strength up to the engineer's assumptions. I attended TPI's grader training class, and feel I did bring more to the table than many of the "real" graders that are on the line stamping what I cull around at the sawbench every day. I can't change that, the training did give me a better eye, I learned alot. I think it is worthwhile for a woodworker to know the rules and the whys. Being well trained as a group might help when your local enforcement of these codes tightens.

i've been curious about the distinction Phleps makes between "left hand' and 'right hand' spirals, where a clockwise spiralling grain (looking up the tree) "should be rejected for building purposes" ??!!!1 how could this matter? more checking? twisting? white spruce with spiral grain does seem to check big. of the two big checked logs in our house (white pine) one is a strong left hand check, the other straight. any experience with this?

there are two crabapple braces (4X6) going up in the frame (tomorrow!!) and i'm a little concerned about them. my buddy (out of whose backyard the tree came) did some reflective carving on a waste chunk remaining and it checked pretty huge. mind you he had left it on his deck in the direct sun, but eventually the wood will get warm and dry out in any case. only the crabapples can really know what it's made of.

From what I've read... Softwoods tend to start with a left spiral which changes to more vertical or right spiral as the tree matures. Hardwoods tend to start with a right and move towards a straight or left spiral.

From what I've worked with... I tend to, seem to, think, I have more trouble with lefties in softwoods. They are rarer, catch my eye and so I probably look at them harder.

What I speculate... in softwood the lefty is often a juvenile with all the troubles that accompany immaturity. Shrinking from duty in any direction possible, not able to hold up their end of a job, rigidly stubborn as all get out.

Restrictions on lefties is being written into log codes that are moving through the ICC in the last draft as I recall. Several authors have claimed a scientific basis for this. Mackie claims lefties are proven to be weaker and inferior. The grading instructor looked at me like I just fell off the truck when I asked there. I have asked if anyone knows of this research to back up what is being written into law. Thus far I haven't seen any. As I said, I'm not sure I disagree, just would like to see some backup.

Whenever lefties and righties come up I think of gums and elms and other interlocked grains. The tree grows righty for awhile, then lefty, then back again. I guess it depends on when you fell it

This piece of old heart pine crossed my path today. Looking at the growth rings I would say "its a straight grained tree". As it checks it shows that the straight appearing cylinders that were being laid down were. But in this case they were also rotating left around the tree. It was a straight tree but mildly twisting left.

Nice photo Don. Had this not have checked already, would you have noticed the spiral grain? One often assumes that the grain (direction of cells) is parallel to the grain (surface appearance or figure.) I have heard the left vs. right bit on the spiral, and still have trouble comprehending why one would be stronger than the other.

I seriously doubt I'd have noticed it in green. Slope of grain, especially what I'd call "local slope of grain" near joinery can be a biggie strengthwise. You know real quick with a drawknife, chisel or slick. Apologies to BB and Eric C, Derek's had the jukebox in my head singing "Riving with the King" all week .

I would like to hear more on the righty lefty thing as anyone comes across it.

"From what I've read... Softwoods tend to start with a left spiral which changes to more vertical or right spiral as the tree matures. Hardwoods tend to start with a right and move towards a straight or left spiral."

Cool topic. I find it interesting how trees grow and timber moves. I wonder too what the reasons are for the spiraling trends. Would the sun changing in the sky through the seasons effect this?

Anyone, are the points where these right to vertical or left to vertical, etc. at a general point on the tree?

Hi Christopher, Don, et al,

I was in a 5 bay barn at Ockley in Surrey yesterday and observed that this 18th century barn had been constructed using nearly all "reused timbers" many of which were of much greater antiquity.

One of the major observations made was how both spiral grain and straight grained timbers had been employed for the main jowl posts in this barn with both left and right hand spiral in evidence on separate post timbers.

Up until this moment I had always considered spiral grain timbers to be bad news but I may just have had a change of heart. Where large spiral grained timbers are left fairly intact by the conversion process e.g. boxed heart with some wane, then the checks developed on these timbers tend to be multiple small surface checks rather than one large check through to the heart as per straight grain timbers.

I noticed that the jowl on a straight grained post had developed a huge long check about 5 feet long down a line from where the teazle tenon meets the tie beam and wall plate. This rather obvious and predictable plane of weakness failing was not repeated on the spiral grain timbers where loads are conducted down the grain, rotating as they go and thus tending to prevent an obvious plane of weakness from developing that coincides with the geometry of the piece concerned.

Critical observations are important as is factual analysis when determining best practice.

Mr Phleps arguments may well hold true for log buildings where a rotating timber might lift and entire wall but this might not necessarily be a relevant concern in a timber frame especially where a timber might be free to rotate - e.g. a main post at a barn door which only has mortice and tenon connections on one side.

Regards

Ken Hume

That is interesting, I have usually attributed those kinds of checking differences to different species rather than grain orientation within a species. For instance red pine, our cousin of scots pine, tends to check with many smaller checks where eastern white pine tends to relieve its drying stresses in one or two major checks. I'll start paying more attention to grain orientation and checking within a species. I don't think mild spiral is a huge deal as long as the grain within a piece doesn't become too short and weaken it. In the round the grain never "runs out" and is fairly balanced. As we saw or hew a timber we cut across the grain and also create places for the stress to concentrate as it dries. Thanks Ken, more to think about.

My experience is with log more than heavy timber, a lefty in a wall of righties is trouble, its unwrapping in a different direction from the rest of the wall and hard to keep put.

Mo,
The switch from juvenile to mature wood is gradual and in pines is normally considered to happen around the 20 year old period. Nature varies alot as does the age of a part of the tree. To drop in one more level of magnification, individual cell walls are made up of several layers of microfibrils, bundles of filaments. The S2 or middle and thickest layer of the cell wall is the one of most interest usually. In juvenile cells the microfibrils align at an angle to the upright axis of the tree, they are slanted at an angle of up to around 30-40 degrees. As the tree matures the MFA comes more in line with the axis of the tree. This is below "grain" level but I think it does have an effect on grain, or the orientation of cell to cell up the tree. I suspect this is due to the proximity of the apical meristem and its auxins. As the tip moves farther away from a section it "matures" and produces straighter alignment, further away yet and the spiral reverses. (That's all pure speculation on my part)

The MFA does affect shrinkage and direction. Shrinkage occurs as the water bound between the microfibrils leaves the cell walls. This is the "bound water" as opposed to the "free water" that is within the cell lumen and doesn't affect shrinkage as it leaves. As the water leaves the microfibrils can move closer together, this is the level where shrinkage occurs. If the fibrils are oriented vertical the wood shrinks in width and thickness...normally. If the wood has a large proportion of juvenile or reaction cells with a steep fibril angle the wood shrinks lengthwise as it dries. If a board has juvenile wood along one edge and normal wood along the other, the board bows as it dries. If the grain spirals the board twists.

Wealth of knowledge, much thanks. What an extensive subject!

Don, do you know of a good book to read regarding what you are talking about. Something that would not require a chemistry or biology degree, but at the same time provide the information. I have learned a little about material science (trees, metals, etc.) so I would not be completely in the dark with terms.

Thanks, mo

An index to the Wood Handbook is here;
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

The search function on the FPL site links to thousands of research documents.

"Forest Products and Wood Science", Haygreen and Bowyer is a good one. There is a course description and syllabus with good slides here;

http://legacy.ncsu.edu/WPS202/syllabus.html

I was lucky enough to work around students from this curriculum interning in the wood industry for some years, they thought we were teaching them, they were giving us a good basic wood tech education.

Hoadley's "Understanding Wood" is another good book.

I was bumping around in the computer looking for a labelled cutaway pic of a cell, no luck yet, but I found a short piece I wrote several years ago for another forum that skates on the edges of some of what we've been talking about, off topic but hopefully it'll be neat to you too. Wood's cool, and plumbers don't get to burn their mistakes. Feel free to bring us back to the topic if anyone wants to

Reaction Wood

Reaction wood is formed when, for some reason, the main stem of the tree is not vertical. It is the wood formed by the tree in trying to right itself. In softwoods compression wood is formed on the underside of the leaning stem. In hardwoods tension wood is formed on the upper side. If the center of the stem is considered the point of rotation, compression wood is pushing up on the stem or tension wood is pulling the stem upright. Imagine pulling on a stem, the bottom, compression, side would become shorter as the upper, tension, side would lengthen. I find this analogy helps me understand other characteristics of this wood.

Compression Wood

The underside of most branchwood is compression wood, holding up the branch. Weeping or drooping branches would be an exception. Compression wood contains more lignin and less cellulose than normal mature wood. Lignin is what makes cells stiff, or strong as in a strong column. Individual compression wood cells, or tracheids, are typically shorter by almost a third, blunt or even folded on the ends, and rounder in section. It is normally about equal in strength to normal wood, although denser. Compression wood shrinks about ten times more lengthwise than normal wood, 1-2% vs 0.1-0.2%, this is its major drawback. Compression wood tracheid walls typically contain a primary later of somewhat random microfibrils followed by the fairly horizontal S-1 layer, this is relatively normal. The major ply of the cell wall, the S-2 layer, that controls most properties such as shrinkage, lays at a much flatter angle than normal. As bound water leaves the spaces between the microfibrils and they draw closer to one another this causes more lengthwise shrinkage than in cells having a more vertical microfiber angle.

Tension Wood

Tension wood is trying to right the stem from the upper side of the pith, by pulling on, or restraining, it. Tension wood is low in lignin, high in cellulose. Cellulose is the long, straight chained, glucose polymer in wood. This makes a cell that is strong but supple. This analogy can only be taken so far as in reality tension wood is weaker than normal wood, so should not be used in critical structural applications. In cross section tension wood cells walls are thicker than normal, often with the inner secondary cell walls detached from the primary layer. In the secondary layers is an abnormal, thick, gelatinous layer. The fibers in this layer are arranged nearly vertically. Again the analogy of the cable being pulled taught with fibers straightened out or pushed to a flatter angle as in compression wood. Often this gelatinous, or G, layer us pulled loose out of the "shell" of the primary cell wall and dangles there as a tough fibrous "fuzz" that heats saw blades and makes a flat smooth finish very hard to attain. Shrinkage is high in tension wood but for a different reason than in compression wood. Since the inner layers of the cell wall detach so frequently the orientation of the primary layers' microfibrils determines the direction shrinkage will take. This is typically a more horizontal angle than that in the secondary lamellae of normal wood, so the longitudinal shrinkage in tension wood is greater than in normal, although normally about half that of compression wood.

For the topic we started on... Chapter 4 of the wood handbook starting at 4-28 is a good read, really the whole section on Natural Characteristics Affecting Mechanical Properties is worth reading. Notice fig 4-4.

The slides on the NCSU site covering softwood rays and resin canals are good too.

While I was looking at those slides another couple of wood tech things came to mind. First as you look at rays and tracheids you are looking at the plumbing of a tree, tracheids, vertical softwood cells, take care of up and down movement. Rays take care of the heart to bark transport among other duties.

Second, you probably know that wood shrinks about half as much radially as it does tangentially. While looking at the rays, notice the grain direction they have within the wood. They don't want to shrink lengthwise and so reduce shrinkage in the radial direction. The microfibrils winding around the pit pairs on the radial faces of the cell wall are another reason.

Hi Don,

Great replies. Clearly you have been burning the mid night oil on your researches.

A thought for consideration.

With a spiral whole timber if this comes under significant tension then the tendancy would most likely be for the checks to open up as the timber starts to straighten itself.

Would the opposite be true i.e. if a timber is under compression e.g. a post would this tend to close up its checks and hold itself together as loads increase ?

Regards

Ken Hume

Thanks for the kind words Ken,

One other neat factoid I came across while reading some time ago. Archers seek tension wood, that rubbery G layer makes a more elastic bow. They've been seeking out tension wood for alot longer than we've had microscopes. I'd appreciate it if you kind of kept an eye out for where the oldtimers used spiral grain, were they "placing" it?

Thinking about a spiral grain compression member, I think I'd rather have spiral in compression than tension or bending. I think we're talking about loads that would be way above "allowable". Would it tend to buckle sooner in a taller more slender column than straight grain? Kinda like trying to push a slinky down, it wouldn't take as much for it to squirt out the side?

I guess with a short enough column maybe checks might move a little, but then would you crush whatever is delivering that load before the checks think about closing?

The Japanese have been using relief cuts for centuries and maybe millenium. On an overhead beam, the cut would be on the top, on a post it would be against the wall.

Does that make a well built house a boat?

The closest I dare hope to get to either one is a Grumman canoe and an Airstream trailer.

Motorhomes float not and it takes a biiig tractor to fish em out.

The relief cut works if its put in early, before the check finds another place to relieve the drying stress. I built a log home that had been kiln dried, then their planing equipment also relief cut it... the check had already happened.

I was reading last night, not sure if or how it applies. A concrete column can be reinforced either by standing vertical rebar and placing individual loops of rebar around it or by spiraling a continuous rebar up the vertical rods in the column. The spiral column is slightly stronger.

TOIVO...............THE REASON YOU REJECT LEFT HAND SPIRAL LOGS IS THAT THEY WILL TWIST LIKE A BARBER POLE.IN A CONVENTIONAL LOG WALL THIS CAN POP THE LOG RIGHT OUT OF THE WALL.IN A TIMBER FRAME APPLICATION,ONCE MILLED THE LOG COULD TWIST AND CAUSE STRUCTURAL PROBLEMS.
[1]IN A MORTIS TENON APPLICATION IT COULD BRAKE THE JOINT AND PIN.
[2]IF YOU PLACED INTERIOR AND EXTERIOR CLADDING ON THEN IT TWISTED YOU WOULD GET AN UNSIGHTLY BUMP IN THE WALL.
[3]IF IT WAS USED AS A SILL OR TOP PLATE IT COULD HEAVE THE WALL OR RAFTERS
[4]IF USED AROUND WINDOW AND DOOR ROUGH OPENINGS FOR FRAMING.IT COULD JAM OR BREAK THE WINDOWS OR DOORS.
[5]ETC.

CORDWOODGUY