Larch as a PT alternative.

[Dave Shepard]

I'm thinking about developing some larch products as an alternative to PT lumber. I've heard that it lasts very well untreated in many applications, but seldom see it actually used anywhere. Even if it isn't on par with PT, and I don't really have a lot of respect for PT's longevity anyway, not having a treated product will appeal to a lot of people around here. Black locust is a good alternative, but supply of straight sound logs is not great, and it is not a friendly wood to saw and process. I'm wondering if the qualities I'm looking for in larch are common to all varieties, or just a specific one. There are several varieties growing in the US, and I have not tracked down exactly what is growing in my area. Aside from the sawdust being very irritating, the larch I have sawn saws very well, stays straight, and the tiny knots have not presented as a defect in the products I have made.

[Chuck White]

About 8 years ago, we put 4x4 Larch poles in the ground untreated to support a volley ball net.

Early this Spring, one of them finally fell, so we pulled the other one also.

So, they'll last a while, but are not to be considered permanent.

If you have access to creosote to soak the ends in, then they should last many years!

[Skidder Kev]

IMO I think it is,  we did a job for the region, we had to construct a 300 foot rasied walking path through a low area in a bush which floods in the spring.  They wanted larch used 1 for how long it last and 2. they figured rough cut larch wouldn't get as slippy as PT.   wew saw it after 2 winters in it still looks great but only time will tell.


 

kev

[Clark]

As far as species are concerned there are only two native species that amount to anything. Larix laricina is the eastern variety (tamarack) and Larix occidentalis is western larch.

Tamarack is the one of the few species around here that has notable rot-resistant properties. There is a very slight color difference between the outer (sap) wood and the inner (heart) wood. I don't care for the terms sapwood or heartwood as they typically only differentiate between two colors in a log, lumber, etc. There may or may not be a difference between the rot resistance of those two colors. Granted, there are some species (Doug fir, for one) where that difference in color is a difference in other properties. I do not know if that holds true for tamarack.

Clark

[Dave Shepard]

About 8 years ago, we put 4x4 Larch poles in the ground untreated to support a volley ball net.

Early this Spring, one of them finally fell, so we pulled the other one also.

So, they'll last a while, but are not to be considered permanent.

If you have access to creosote to soak the ends in, then they should last many years!

My neighbor put three 4x4 posts in for his mailbox last winter. He has given up. I guess PT is allergic to snow plows. :D

[Chuck White]

Beautiful walkway Kev. 

[clww]

Gorgeous walking path.

[Skidder Kev]

Thanks guys I felt pretty good when it was done but all the credit should got to my bosses bro.   Anyways I'm not trying to hijack this thread I just used it as a example of how we used it and why.  plus everyone loves pics. 
thanks again
Kev

[hunz]

This question may be common knowledge, but I'll ask it anyway. Has your state, and/or the IBC/UBC qualified larch as a naturally durable species? I know here in NC, I was scanning the building codes when I first found out B.L. was a code permitted alternative. To be honest its a shame that white oak can't be considered a n.d.s.

[SwampDonkey]

You can try it, but it won't last like tight ringed white cedar. I know dead snags of tamarack don't stand long, while cedar stands there for a long time.

[barbender]

I think larch does ok as long as it isn't in soil contact. It rots quickly if it's touching the ground. But, a lot of ACQ PT lumber is not rated for ground contact either.

[beenthere]

This question may be common knowledge, but I'll ask it anyway. Has your state, and/or the IBC/UBC qualified larch as a naturally durable species? I know here in NC, I was scanning the building codes when I first found out B.L. was a code permitted alternative. To be honest its a shame that white oak can't be considered a n.d.s.

hunz
Here is a chart that separates out the resistance to decay for different woods. A lot of testing (i.e. making stakes and putting them out in test areas around the country over many years and recording the results) so the data are pretty good.
http://www.plantra.com/Portals/0/docs/average-heartwood-decay-resistance-usda-forest-service.pdf

[mikeb1079]

beenthere that's a great reference chart, thank you   :laugh:

[grouch]

Here is a chart that separates out the resistance to decay for different woods. A lot of testing (i.e. making stakes and putting them out in test areas around the country over many years and recording the results) so the data are pretty good.
http://www.plantra.com/Portals/0/docs/average-heartwood-decay-resistance-usda-forest-service.pdf

Thanks for that link!

It says under the title, "Table taken from Wood Handbook: Wood as an engineering material -  General Technical Report 113 - USDA Forest Service". I couldn't stand the mystery wondering what else might be in that report, so went searching and found Wood Handbook Wood as an Engineering Material Centennial Edition from USDA Forest Products Laboratory. Whew. Bit off more than I can chew.

[beenthere]

Yep, that one is plumb full of about everything one might want to know about wood.

Past member Tom (may he RIP) used that book as a resource quite often.

[grouch]

A follow-up...

The chart linked to by beenthere has a footnote "a" stating "Exceptionally high decay resistance". That footnote applies to black locust, red mulberry and osage orange, among the domestic (US) woods. I think I can personally attest to one of those.

About 35 or 36 years ago I was heating with wood. During a search for suitable firewood I came across a gnarly looking dead tree with most of the bark already gone. The wood was still sound so, armed with my then-trusty 16" Echo chainsaw I attacked. More sparks flew than chips. I replaced the chain and tried again. More sparks, little cutting. With more than a little aggravation, I laid into it with a double-bit ax from a local hardware store (long since extinct). I swear I can still feel the tingling in my elbows.

Having never encountered such stuff before, I described the tree to some locals who told me it was Osage orange.

Fast-forward to 2015-01-13:
[Edit: Oops, forgot to state size -- it's about 16" DBH]







How's that for decay resistance?

(And now the universe is going to implode -- reply #13 above was my 13th post on FF and I just noticed that every image posted in this reply contains 13 in the file name).

[SwampDonkey]

Never used the exact book in college, but one with similar data and now out of print was Textbook of Wood Technology, and now there is Hoadley with more current info. Of course the Handbook gets revised quite often. I reference my book and the handbook a fair bit, but Tom really liked the Handbook for a reference for sure. 

It's also funny how knowledge changes about wood as well. I have a formula for a certain calculation we used for fibre saturation point that actually holds well for our native species of wood in NB, but not so well for all the commercial species there is data on. It makes a wrong assumption about volume loss from shrinkage. Not all the intercell voids in cell walls from bound water loss collapse or at the same degree.

[Brucer]

I've had some experience with Western Red Cedar, Douglas-Fir, and Western Larch. I've noticed that in contact with the ground, in all three species the sapwood decays much more quickly than the heartwood.

WRC lasts longer than the other two. Most of my raised garden beds are made from 1-1/2" WRC, heartwood only. After 8 years the decay had penetrated about 1/2". The outside was fine, being exposed only to the weather. The oldest ones are now 16 years old and I had to start replacing them.

I just pulled out a Larch stump last year. I'd cut the tree down a dozen years earlier. The sapwood was gone -- not a trace. The heartwood was decayed and full of worm holes about 3" into the wood. Beyond that the wood was absolutely sound.

The cover on my spring was made from three layers of D-Fir T&G, laminated at 90 degrees. It was still sound enough to hold my weight after 30 years, but at 40 years was beginning to collapse. There was no protective material on top of the wood, so over the years dust, tree needles, and leaves had built up on it and between the layers of wood. Had the previous owner bothered to cover the top with roofing material, it would probably still be sound.

Whatever the species, wood doesn't just suddenly decay all at once. The decay is gradual and the wood loses strength over a long period of time. While D-Fir & W. Larch don't last as long as WRC, they are much stronger and my continue to serve their function as long as Cedar would.

Keep in mind as well that wood will not rot if it's moisture content is kept below 19%. Sometimes you can extend the life of an untreated wooden structure by designing it so it won't trap and hold water. For example, I never fasten decking directly to the joists or stringers. I always put strips of asphalt roofing material on top of the joists (not roofing paper -- either roll roofing or cut up shingles).

[FarmingSawyer]

You can try it, but it won't last like tight ringed white cedar. I know dead snags of tamarack don't stand long, while cedar stands there for a long time.

I've been impressed with how many EWC I've been able to salvage from the forest floor. The sap would is gone and the heartwood is perfectly sound. I've milled up some already which has been clear with a tight ring pattern and amazing color you don't get in fresh cedar.

[SwampDonkey]

When I worked on the west coast, western red cedar and yellow cypress, dead or alive, was counted as volume as long as it was solid and intact for most of the way up. They were actually estimated for height based on close by live ones. You recorded a height to what it would be if alive. I saw some huge cedar on the ground, cut in the 40's. Sap wood gone to mush, supporting hemlocks, but the heart was sound with that sweet western red cedar smell like it was fresh sawn. These were 6 to 8 feet diameter logs, in the middle. I also saw cedar you thought was dead because the sapwood was mostly gone with salal vines living off it. But was the sapwood all dead? Nope. On the back side was most often a strip of live bark, and supporting sapwood, that was like a vine itself supporting (feeding it) a candelabra-like branch with green leaves. :D

[FarmingSawyer]

When I lived on an island off the coast of Washington the old sawyer I worked for stumbled on a 24x24 cant in the woods. He remembered sawing it in the 60's--some 30 years earlier. He was an avid beachcomber and scavenged logs throughout the San Juan Islands. He grabbed the log this cant came from and sawed it up to see what it was. And then put it in "storage" until he could figure a use for it. We put the cant on the mill. The outside was soft and pulpy, black with age. The old boy couldn't quite remember what it was, but it didn't break when he dropped it with the loader.

He scrapped the cant with the blade and peeled off the outer layer of funk and inside, as solid and bright as the day he first milled it, was Alaska Yellow Cedar. Almost clear and quite stinky. We milled some into 24' 2x6 for the plates of my house, and then cut some 2x4 and 1x. I used some as slats for a bed and made some rose trellises out of some. As far as I know, those trellises are still holding those roses up 20+ years later. I think he sold some of the clear pieces to a boat builder and some was made into oars. I wish I had access to a log/cant like that again!