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We have rolled through several discussions where the topic briefly passes through soundboard wood that has a crushed internal structure. It usually centers around redwood - which seems particularly prone perhaps because of the massive trees.

I think I experienced this recently with WRC. I bought some perfect looking 4x4 cedar fence posts several years back and decides to split them and saw them into multi-piece tops. (As an aside, an almost complete waste of time. My average yield out of a "good" 8' long 4x4 post is the equivalent of 1 single D size top.....)

Well - I was burning some of the scraps from 2 such sawed up posts. When breaking them over my knee - the slices out of the 1 post would snap straight across the board nearly clean with nearly no shards. The other exhibited classic "green stick fracture" - where the each layer breaks sequentially and delaminates into 10,000 long jagged knives. (The "good" redwood did the same)

This got me thinking about the discussion of crushed internal structures caused by the weight of the tree mushing the wood. That likely - the one which simply broke straight across suffers from this malady - though it still seems to tap quite reasonably well and it sure feels like it breaks at nearly the same level of smash across my knee (precision calibrated whack of course )

BUT .... This got me thinking of the classical luthiers discussions that there is cedar and then there is cedar - and they ran into a lot of cedar that really didn't make spectacular instruments but they couldn't put their arms around why not.

And then - if this happens in redwood and in WRC - how about Spruce too? I have broken some spruce that just snapped in half - but I never thought anything of it.

Would taking a thin long slice off the edge of a soundboard blank and breaking it - just to see how it fractures tell us anything worthwhile (maybe ...) Does it exhibit the green stick fracture or does if just snap straight across more or less clean. Then - would this tell me anything particularly useful about the sort of top it will make other than being perhaps susceptible to cracking crossgrain.

Might this give some insight into why some spoundboard wood has such low damping while other pieces of the same have much higher damping.... Perhaps there are degrees of mushing.

Thanks

Truck: Never heard this mushing theory before. Wood that has cracks across grain are usually referred to as having falling shakes. The damage being done when the tree hit the ground, across another log, stump, etc. Have seen it in Mahogany but have not seen it in WRC but IIRC have seen it in Redwood which no doubt you know is quite brittle. As to the Spruces, have not seen it but I would guess possible and least likely in Sitka due to it's grain structure even though they are massive trees. All mostly speculation on my part of course.
Tom

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A person who has never made a mistake has never made anything!!!

Out of curiosity, I dug into my stack and sacrificed a couple ugly tops just to see....

Now I understand why Al Carrurh makes careful distinction between "compression" wood and "reaction" wood.

True compression wood is the stuff that's been mushed by the tree. It crumbles or snaps easily with only a small, light bend. It's useless for a soundboard or any structural use on a guitar. I found some of this stuff in some spruce tops. It's not the fat summer growth wood racing stripes we are used to calling "compression wood".... This looks almost like shiny brown or silvery stains as if someone poured lacquer on a blotch in the wood and it almost crumbles when you bend or twist it.

The danger I found is that wood near the blotchy mushed compression wood was also damaged - but it wasn't obvious if you split out the compression blotch until you broke it. It broke much easier than unaffected wood but not as easily as the badly mushed blotchy stuff.

Reaction wood on the other hand has the characteristic thick late wood. When bent - it acts just like normal wood. In the spruce I have - the stuff almost bows to 50% of its original length before it lets go. When this stuff breaks - the break follows runout like any normal break. When sawed out - a strip of reaction wood typically bows or will be found shorter than the rest of the plank because of the built in tension.

2 very different beasts. Reaction wood should make a guitar just fine. Compression wood - not so much.
Thanks

Interesting. I don't think I've ever seen wood like that before. Can you take a photo of it?

The reference on this is "Growth Stresses and Strains in Trees" by Richard R. Archer, Springer-Verlag, 1987, ISBN 3-540-16406-5 or 0-387-16406-5. The subject comes up on pg. 88, under "Inelastic Growth Stress Effects" and mostly concerns problems with hardwoods. Still, it does seem to me that I've seen similar issues in redwood in particular, which makes some sense since the trees are so big. It's possible that this is less of an issue with softwoods because they lay down reaction wood on the compression side, where hardwoods build reaction wood on the tension side.

Here's a pic...



The brown stain area is the "Compression wood" - it stands out because it looks much more shiny than the spruce around it - almost as if someone spilled oil or lacquer into the top wood... but its still just as shiny when sanded... It's not just a brown streak in the grain...

When you flex it - it crumbles.

Notice - there is some heavy late wood "Reaction" wood nearby... That stuff is fine when it's flexed... It's totally different than the crumbly mushed wood...

Thanks

The type of felling shakes and compression fractures I've seen in softwoods are characterised by crumpled grain lines forming a local zig-zag pattern, with a crack originating from a surface, perpendicular to the grain, penetrating the wood. Often this is accompanied by local discoloration due to water/fungi getting into the wood at the crack location.

What you have there, John, appears to me to be some type of biochemical degradation, which may have originated from a compression crack/felling shake, but that wouldn't be my first guess. I'm thinking more along the lines of the early days of normal rot. Was this wood sourced from storm-fall recovery or similar, where the wood can be lying around for a while before being collected?

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Trevor Gore wrote:
"I'm thinking more along the lines of the early days of normal rot."

I'm agreeing with Trevor on this.

We have White Pine on out property, and it is subject to 'red rot' that looks like that. Usually it sets in if the trunk gets damaged, say by being hit by logging equipment. I've seen similar damage in spruce as well, although not in the tree. I'm not sure what causes it; I'm thinking that it might be a fungus.

Not rot or shake. I have seen both of them.

The pic looks like a dark brown stain. In real life it's not really brown - just way more shiny.

This stuff is quite hard and dense feeling and it splits out like nothing is wrong. It's only when you flex it that it just breaks with almost no force.

Wood wise - this came out of a really cheap billet I got in 2009 and just got around to sawing. I have not seen tops with this sort of big shiny spots in them (I found one or two others - but the shiny spots are tiny in comparison and those were firewood grade tops) Probably because the sawyers know the wood is not useful structurally.

Anyway - if you see tops with spots that are very glossy/shiny - reject them.

Thanks

This thread actually has a mis-named title. The proper descriptive word or term is "collapsed cell". It happens in Cedar and redwood when drying at a high temperature, and generally in thicker cuts. It is a breakdown of the cell walls.
I have never actually seen it, because we don't dry with heat. But a producer/customer I supplied with about 7000 guitar tops worth of sitka spruce block for guitar tops every month for 14 yrs, also cut some cedar for a couple years, and did have that happen in his kiln. It never happened to the spruce.

There are a couple of other terms used in this thread that are off base.
Whoever gave names to some of these wood attributes, ya gotta scratch your head.
Compression wood is a characteristic in softwood trees, like spruce, pine and fir. I have seen it in Yellow cedar but not red cedar.
Has nothing to do with getting smashed. But everything to do on how and where a tree grew. A spruce tree with an offset heart will have either compression wood or hard grain in the quadrant of the tree with the most meat.
The pic is of a tiny tree, but the principle is the same as the 4-5' diameter trees I work with. There is tremendous timber bind in it. It warps really bad. It's very heavy and dense.

Another commentor suggested the compression wood was responsible for a board breaking, clean and easy, describing a shearing type of break. That is "brash". And that is the beginning stages of rot. Hardwoods with spalt will tend to be "brash".

I discoloration caused by rot, or brashness is spruce, will also display a sunkeness kinda look as the cell structure collapses in drying.

The pic I see above, looks to me like a knot bleed. It is a high pitch resin patch of fiber. It may be from an uphill knot, but other things can cause it. I would presume by what i see that there could be significant grain slope in that band of growth. The other side of the board and the next cut will display the same characteristic, but towards the ends as the pitch flows and followed that section of fiber.

As John hints in his original post, this is a continuation of a sporadic ongoing conversation. Some of the terms used may not be standard, but that is due, at least in part, to the inadequacy of the standard terms. We're due for what the old Chinese philosophers called a 'rectification of names'.

"Compression wood is a characteristic in softwood trees, like spruce, pine and fir. I have seen it in Yellow cedar but not red cedar."

Hoadly in his "Understanding wood" talks about 'reaction wood' on pp 36-39. Softwoods form reaction wood on the on the compression side, and hardwoods on the tension side, in general. Thus reaction wood on softwoods is called 'compression wood, and on hardwoods it's 'tension wood' (I don't have to tell you that).

Some tone wood suppliers talk about 'compression GRAIN' as a separate thing. This is softwood with abnormally heavy latewood lines, often from low down in the trunk, that is not reaction wood. Such wood tends to be dense without a commensurately high young's modulus for bending along the grain. I see it commonly in Douglas fir and redwood, and often enough in the spruces. It does not show the usual interlocked grain of reaction wood. The term is unsatisfactory in some respects, as it is too much like 'compression wood'. It threw me off the first time I ran into it, too, but maybe we're stuck with it.

Another reference I use is "Growth Stresses and Strains in Trees" by Archer, Springer-Verlag, 1987, ISBN 3-540-16406-5. He talks about the fact that new wood typically is pre-stressed s the tree grows, so that it is under tension relative to the wood under it. This necessarily puts the wood further in the trunk in compression. He points out that the in the heart of large hardwood trees the combined residual stress plus the weight of the tree can exceed the compression stress limit of the wood. This can make the wood there subject to brash fracture as, in a sense, it's already 'broken'. Some users of 'stump' rosewood have noted a tendency of it to fracture across the grain when bending when there is no evidence of 'wind shake'.

I have seen redwood that has, for lack of a better term, a 'crushed' look, with irregular curvature to the grain lines, which are also irregularly spaced, In my experience this wood is weak in bending, denser than it 'should' be, and has high damping. I speculate that this is, in fact, crushed wood. That's what the OP was asking about.

One could speculate that softwood trees can, in some sense, 'hijack' parts of their normal mechanism for forming reaction wood in compression when there is a particularly large load on the trunk that is not asymmetric, and does not require buttressing against a lean. Maybe they just make those really heavy latewood lines it that case. Archer pints out that trees can react very quickly to changes in loading for whatever reason. That would help explain why, as he quotes Jacobs as saying: Conifer may be utilized to the pith, whereas in hardwoods of similar durability the layers near the pith are brittle and frequently have to be discarded" (p 89).

Yes, it is. I just re-read the Hoadley section on compression wood, and your statement makes no sense at all. Compression wood is described as having heavier latewood, and that is the same as 'compression grain'. You seem to be insistent on confusing definitions.

On very rare occasions, I have encountered red spruce that meets that description. In every case, it was caused by rot. It is not compression wood, compression grain, or reaction wood. It is rot.

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John

john Arnold wrote:
"You seem to be insistent on confusing definitions"

I'm just trying to make sense of a lot of the stuff that gets posted on these lists. I didn't make up the term 'compression grain' to refer to wood with heavy latewood lines, and, as I said in my post, I found it confusing too. OTOH, I do often see softwood samples that show especially dark/thick latewood lines that don't show any sign of the interlocked grain of 'reaction wood'. These samples are denser than they 'should' be given their measured stiffness, so there would seem to be some use in having a term to refer to wood of that sort, and that's what the folks who use it seem to mean. So... As I say, we need a session of 'rectification of names' so we're all talking about the same thing.