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Author Topic: Why are there indentions in the wood  (Read 511 times)

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Offline flatrock58

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Why are there indentions in the wood
« on: September 16, 2017, 09:52:33 am »
We just got back from Yellowstone and I noticed that a lot of the wood in the park had rows of marks or indentions in the wood.  I have seen this before on other park boardwalks.  Can anyone tell me what the purpose of the indentions might be? 

I did see a lot of standing dead timber in the park.  What a waiste of wood.  It seems like the wood doesn't  rot out there since there were lots of trees on the ground that looked solid.


 
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Offline scsmith42

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Re: Why are there indentions in the wood
« Reply #1 on: September 16, 2017, 10:04:40 am »
I always thought that the indentations were to allow the solutions used in pressure treating to penetrate deeper into the wood.
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Offline flatrock58

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Re: Why are there indentions in the wood
« Reply #2 on: September 16, 2017, 10:41:36 am »
That might be scsmith42, but I don't see them in most of the pressure treated wood around here.
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Offline TKehl

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Re: Why are there indentions in the wood
« Reply #3 on: September 16, 2017, 12:27:06 pm »
Ahh... the mark of the wide mouth bark beetle.   ;D

Could it be as simple as offering better traction when the boards are wet?
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Offline Crusarius

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Re: Why are there indentions in the wood
« Reply #4 on: September 16, 2017, 01:49:09 pm »
I think its a great spot for rot to start with water pooling in them.
I knew what I thought I meant.

Offline bluthum

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Re: Why are there indentions in the wood
« Reply #5 on: September 16, 2017, 02:11:34 pm »
I forget the term for that process but it is intended to help the wood take in more preservative.
It isn't considered necessary for SYP but is for the western softwoods.

Oh, maybe it's called incising....

Offline Don P

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Re: Why are there indentions in the wood
« Reply #6 on: September 16, 2017, 02:43:19 pm »
Yup, incising, used on western woods like dougfir that don't take up preservative readily. Southern pine is like a bundle of big bore soda straws. Incising reduces bending strength by 15%. But rot reduces it by 100%. It is not easy on the eye, it was hard to get used to using it when I was out there.

Offline GeneWengert-WoodDoc

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Re: Why are there indentions in the wood
« Reply #7 on: September 17, 2017, 09:18:50 am »
Indeed, these are the man-made slots made in wood that is not permeable enough to accept an adequate amount of wood preservative when being pressure treated.  There are very precise specifications for the amount of preservative that must be in The outer inch or so of the treated piece of wood.  The slots help the preservative penetrate into the wood.  More preservative is required for pieces in contact with the ground than for pieces above ground.  The process of making these slots (done with sharp knives usually on a roller) is called incising, and the treated wood is called incised.  As mentioned Douglas-fir is known to be quite impermeable, along with spruce.

Although incising weakens the wood, the design values used for wood are often 1/6 of the actual strength, so a 15% loss is not an issue.
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Offline flatrock58

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Re: Why are there indentions in the wood
« Reply #8 on: September 17, 2017, 03:49:35 pm »
Thanks, for the response.  I guess that makes sense.  Just had no idea that other soft woods would not take preservative under pressure.  Didn't look like they needed much preservative out west from what I saw.  lots of untreated wood around that did not look like it was rotting.
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Offline Don P

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Re: Why are there indentions in the wood
« Reply #9 on: September 17, 2017, 07:34:41 pm »
Actually southern pine heartwood doesn't accept preservative chemicals either, the extractives and resins in the heartwood block the cells. You can see this when you cut a piece of treated that contains heartwood and look at the end, there won't be much or any green in there.

One example of this, those landscape timbers sold at the big box stores are really just peeler cores from plywood manufacturing. When they've spun the log between centers until they can no longer peel off any more veneer they are left with a small cylinder of heartwood. They plane 2 flats on it, throw it in a treatment chamber and "treat to refusal" (look at the tag). The heartwood refuses immediately so there is really no treatment inside and no treatment level like .25lbs per cu ft or a use category, UC, listed on the tag for that southern pine heartwood. The spec for foundation grade syp specifies no heartwood for this reason, they want preservative to the bone.

The 15% reduction comes into play on something like a floor joist on a deck. I just went to the span calc on the awc website, the folks who make the building code span tables. the calc is here;
http://awc.org/codes-standards/calculators-software/spancalc
I set it up the way I would check the allowable span for a #2 dougfir 2x10 floor joist 16" on center in wet service. Without incising the allowable span would be 15'7", then I clicked the incised lumber tab and the allowable span dropped to 13'11". If you look at the design values it lowered the allowable design values for stiffness, bending strength and shear strength. So do pay attention to the reduction in spans if using incised lumber. The regular span tables for those woods unincised can get you into trouble at inspection time.
http://awc.org/codes-standards/calculators-software/spancalc

Offline GeneWengert-WoodDoc

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Re: Why are there indentions in the wood
« Reply #10 on: September 21, 2017, 12:16:03 am »
When buying properly treated lumber or timber, the grade stamp is the grade after drying but before treating.

The pressure treating tag or stamp has strict quality requirements, so treating to refusal is not a legitimate treating process for structural wood and cannot be stamped or graded with the required above ground or ground contact stamp.  Home Depot does not sell treated to refusal pieces at the store I go to, but sells legitimate treated pieces.

Note that to get preservative into syp, it must be first dried before it can be treated to retain the required level of preservative. Note that 95% of all syp is kiln dried.  About half is then pressure treated.

Regarding syp heartwood, it is highly decay resistant.

The amount of veneer cores that are made into lumber is very small compared to the amount of syp sawn from logs that is treated.  In fact, due to warp of lumber from heart-centered cores, many cores are sold as-is for posts.

To clarify:  For decking, often the span is 16" to 24" so a span loss due to incising is not an issue.  The molding piece at the top of the picture is also not structural, so incising strength loss is not an issue.
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