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Building log cabin with green logs

Started by Nsp0005, December 24, 2018, 11:30:59 PM

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arky217

Quote from: firefighter ontheside on December 27, 2018, 09:32:31 AM
Some of my logs are over 40 feet long and maybe 20" diameter at the big end.  There is almost no visible checking anywhere in the house.  That is because of the saw kerf that is run down the middle of the joint.  I would look for a foam gasket that has adhesive on one side.  Place that close to the inner edge and close to the outer edge.  When the house is done, use a caulk like Big Stretch and run a bead along the outer seams and you should not need it inside.



I'm building a small (12'x12') log cabin out of green southern pine using sort of the same strategy.
Using approx. 10" logs, I'll be milling 3/4" off the tops and bottoms.
This leaves the log 8.5" thick with a 5.5" wide flat on top and bottom.

Then I'll cut a kerf 3.5" deep on the bottom to help prevent checking. I'll use a modified butt & pass
method in that I'll drill a 1/2" hole thru the top log and 5" into the bottom log. Then I'll enlarge the
hole in the top log to 5/8".

Then I'll drive a 13" length of 1/2" rebar so that's it's recessed 1/2" into
the top log. This way the rebar will be tight in the bottom log and will allow the top log to settle and
stay snug to the bottom log.

But I have a question about using a 1/8" thick x 5.5" wide strip of sill foam between the logs.
I plan to lay down the strips as I assemble the logs since the logs should stay snug to each other
which would make it hard to wedge in the foam strip after assembly.

But the question is, will the foam strip hinder the purpose of the kerf cut by sealing it off.
Perhaps I should forget about the foam strip and just caulk the outside joints after assembly.

I would like to use the foam strip but not at the cost of checking.
What do you think?
Arky217

Don P

Foam really needs somewhere to live to be able to recover. It doesn't recover if smashed flat. You also don't really want it creating dimension.
Centered on the bottom flat, straddling your kerf, run a power planer a couple of passes up the length of the underside of the log, creating a plowed out wide, shallow groove. Stick the foam in that, then it doesn't interfere with log height and the foam is not crushed. Flat faces  become convex as the timbers dry, this will keep the logs bearing on the outer edges of the plowed groove. Fastening the logs down with screws in counterbored pilot holes lets you get them tighter to begin with, something I've never been able to do with any dowel type connector, pins, spikes, rebar. At least take that out of the gapping equation. Allthread drilled in as you go can allow you to keep tightening the stack later.The foam will not prevent the drying stress from concentrating on that weakest radial part of the log, it is a stress concentration point rather than a drying point.

arky217

Quote from: Don P on April 21, 2019, 08:12:39 PM
Foam really needs somewhere to live to be able to recover. It doesn't recover if smashed flat. You also don't really want it creating dimension.
Centered on the bottom flat, straddling your kerf, run a power planer a couple of passes up the length of the underside of the log, creating a plowed out wide, shallow groove. Stick the foam in that, then it doesn't interfere with log height and the foam is not crushed. Flat faces  become convex as the timbers dry, this will keep the logs bearing on the outer edges of the plowed groove. Fastening the logs down with screws in counterbored pilot holes lets you get them tighter to begin with, something I've never been able to do with any dowel type connector, pins, spikes, rebar. At least take that out of the gapping equation. Allthread drilled in as you go can allow you to keep tightening the stack later.The foam will not prevent the drying stress from concentrating on that weakest radial part of the log, it is a stress concentration point rather than a drying point.
Very good answer; thank you.
I like the idea of using a power planer as you suggested;
I didn't realize that the flat surfaces would become convex as they dried.

Another thought occurred to me about my intended plan on enlarging the hole in the upper log
so that it will settle down on the rebar as the logs shrink.

I intended to redrill the 1/2" hole in the upper log to 5/8" to accomplish this,
but what with the possibility of the logs twisting or otherwise deforming as it shrinks,
I now wonder if I should increase the size of the hole in the upper log to 3/4"
to make sure the upper log will stay down on the lower log and not bind up on the rebar.

What do you think ?
Arky217

Don P

The convex flat surface is a result of the shrinkage difference between radial and tangential grain. Tangential shrinkage is about double radial. The center of a boxed heart timber is radial and the outer edges are tangential grain.

If the rebar is free in the upper log and there is no "head" on the fastener... what is it doing? It isn't helping to draw things down during assembly or holding down a twist, and it isn't helping with uplift. Is this just a loose lateral restraint? If you want to hold the upper log down on the lower log I think you'll have more luck with allthread from bottom to top in loose holes with a big plate and nut top and bottom. I doubt you can crank the entire stack down fully tight but certainly much more than just the weight of the stack.

Stephen1

One other item to think about is the length of your wall. From what I had studied when I built my place was no log wall should be longer than 20' as they have tend to spring out, or in. An interior wall or a corner is recommended. It might also be different with rebar or log screws every 2'
DonP might weigh in on that.
 I was told at the time that 3/4' shrinkage for every foot of wall height. 
DonP I understand after reading your post what you are talkiing about with the flat logs. Mine is A scribe home so a height shrinkage rate is increased.
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kantuckid

This thread coincides with my current interests. FWIW, My stacked log walls of 6" thick SYP was spiked every 2 feet using 12"x 3/8" dia, 100d nails, beat into 5/16" pre-drilled augered holes per the instructions from Carolina Log homes kits who I sort of copied some but built from scratch.
Log building always have challenges with the settling over time unless kilned or western dry logs. 
I just measured a log end beside me from 1979 and it measures right on 5 3/4" thick, circle sawed to 6" originally. Sawmilled logs even when band sawed will make you check your wall corners height as you go for variances! Never built a kit but would think they are much less of an issue as you build to stay all the same height. 
Too cold to heat my shop or sawmill for little old me so I'm chasing down EWP logs for my walls today on the cell phone. One guy has 50,000BF of EWP but runs 36-48" at the butt diameter which if I sawed into 6" "D: logs- I'd have a bunch of lumber I don't need off the sides. Said he had another stand of 30,000BF EWP  thats smaller but got cut off so we'll see what pans out. I need 5,000 BF yield of 6" thick D logs best sawed from 9-12" logs. He's the same guy that reneged in October on sawing my wall logs as too busy logging to saw much. 
Kan=Kansas;tuck=Kentucky;kid=what I'm not

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