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edowens
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# Posted: 11 Mar 2014 11:30am
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Is there any problems using center cut 8x8 green D logs when building a small cabin? we may not have time to get these dried all the way be fore the building starts at most maybe 1 year of air drying and a month in a solar kiln. So any thoughts? by the way not worried about shrinkage as this has been worked out.
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bldginsp
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# Posted: 11 Mar 2014 02:05pm
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Twisting could be a major issue, if the timbers have severe spiral grain.
If the spiral is greater than 1 in 30 on left hand spiral logs, or greater than 1 in 20 on right hand spiral logs, the likelihood that they will twist while drying is high. The log cabin building trade is well familiar with this, see the Int. Assoc. of Log Builders guidelines on use of logs.
Other than that its best not to seal up green timbers behind sheetrock or other finishes which will trap the moisture.
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edowens
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# Posted: 11 Mar 2014 02:32pm
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Ok I don't understand the left/right spiral thing could you explane better? also these will be pinned together every 2ft I do understand the twisting part just not how you figure the spiral ,I've done some checking at the log builders site but haven't found it yet. I'll be checking on how long it will take to kiln dry (solar) for an 8x8 beam. Thanks Ed
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bldginsp
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# Posted: 11 Mar 2014 02:51pm - Edited by: bldginsp
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Draw a line on the log parallel to its axis, next to a drying crack. Measure 30 inches of this line. Measure from the ends of this 30 inches, perpendicularly,to the crack. Is the difference more than an inch? If so, use that log only as a post or in short sections horizontally.
Pinning the log will not stop twisting.
Look for log building standards on the ILB site.
I don't know how long a solar kiln will take to dry lumber, but generally log builders build green and let it dry. If you avoid severe spiral grain it's not a problem
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Nirky
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# Posted: 11 Mar 2014 03:42pm
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From the Log Home Builder's Association forum, people who have been teaching log home building for over 30 years:
"The International Log Builders Association out of Canada talks about right hand and left hand twist in their standards. Mostly I believe this has to do with whether shaped logs will try to move and lift your structure after it is built. If you are shaping the logs and attaching them with 1/2" rebar every 24" there is very little concern about the logs moving and twisting after the structure is built. I've known builders to pull their logs into alignment with a 5 ton come along and then pound in the rebar and there wasn't any movement after they were done. It's a different story with hand crafted logs which may only have a through rod every 4 to 6 ft and the hole for the rod is oversized by 1" or more. Too much twist causes them to move around and can be a big problem."
"My Eucaliptus Saligna logs over here in South Africa are known for bending. It is a very highly stressed wood. Its a fact - not all logs are as straight as you would like them to be. I have used a 6 ton chainblock (close to capacity) to encorage logs into the correct places, rebarred them and let go with the chainblock. To quote Skip,"it ain't going nowhere".
If you rebar it as tought, you won't have any problems."
"We built with englemann spruce from BC and we had some right and left twist logs. No problems here."
So to summarize, their builders have found using 1/2" rebar into a 5/8" hole pinned every 24" the logs will stay in place. loghomebuilders(dot)org
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bldginsp
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# Posted: 11 Mar 2014 03:48pm
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I'm not an experienced log builder, but its not hard to find photos of log walls where a twisted log lifted those above it and created a gap. Log builders use the logs with severe spiral, they are just very careful about where they use them. Some species are worse than others.
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Don_P
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# Posted: 11 Mar 2014 11:44pm
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There was my question, Species?
White pine that has air dried for a year is getting pretty close to equilibrium, White oak dries at something more like glacial speed. I've metered the core of a red oak 8x8 5 years out and it was approaching EMC. An uncontrolled kiln can make matchsticks out of large timbers due to the moisture gradient. most damage is done above 40%
Look up the log from the end and notice the spiral direction, if it is like a common screw or bolt thread it has a right hand spiral, if it is spiralling to the left, well its a lefty. Right hand is more common typically and a stack of right hands will all move in the same direction as they achieve equilibrium. A righty over a lefty will open as they both dry twisting in opposite directions.
Some trees, like a white oak start life typically spiralling right, striaghten up as they mature and spiral ledft as they get old. A gum spirals one direction for a few years , then the other, then back, then back again, over and over, creating "interlocked" grain. If you need some boat propellers out of gum, I'm your man... but when you get one that dries flat and use it as a pinned tension spline it will not split.
I'm not much for rebar, we used threaded fasteners and impacts to draw things down dollar bill tight, the closer to in service moisture content you start, the better the building will perform, and the easier it is to cull logs that would have shown themselves too late if they had been used dead green.... but I have kicked the birds out and built the next day, just not the best idea.
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edowens
Member
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# Posted: 12 Mar 2014 11:25am
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Great info guys thanks, I'll be using fur and pontarosa pine , I also plan on routing a 1/2 x 3/4 on both top and bottom then adding a 1 1/2 in. strip of good plywood between each board for an air stop along with some sort of caulking. We will be going up next weekend and more than likely buy the 60 acres we have been eyeing for sometime .
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Nirky
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# Posted: 12 Mar 2014 02:35pm
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About Ponderosa pine, it isn't the preferred wood to build a log home from because it biodegrades--rots--more quickly than other softwoods when exposed to the elements. If you do use it, you may want to design your roof to overhang as much as possible to keep the rain off. Oil/stain can also add a little to its lifespan.
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Don_P
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# Posted: 13 Mar 2014 07:43am - Edited by: Don_P
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I've not built with these woods so cannot comment on Nirky's experiences. One general way logs and large timbers dry that might be informative. Wood shrinks tangentially, tangent to the growth rings, or around the circle, about twice as much as it does radially, in the direction, like spokes on a wheel , radiating through the center. what this means in a boxed heart timber like the logs you describe, is that the dried timber ends up with convex sides, a plump box. When you stack these dried timbers they bear on the fat centers and are gapped at the inside and outside edges. One way I've "fixed" this tendency is to take a power planer and make a pass or two down the center bottom of each log making a wide relief channel about 3" wide and 1/8" deep. This lets the curve on the top of the log below ride up into that relief and gets the bearing back onto the outer edges.
I'm not a real fan of cutting a groove into the top face of a log as any water that does get into the lateral joint can then drop into that groove and get deep into the log to cause trouble.
I do like a groove cut into the bottom edge immediately after sawing, this encourages the drying check to form on that bottom face where it is in a draining orientation rather than forming randomly on one of the exposed faces or the upper edge.
For rot and insect protection I'm a fan of using borate, boron, a very low mammalian toxicity element commercially sold under the names of Timbor, or BoraCare. A low cost way of making it is to buy the agricultural soil nutrient Solubor and mixing it at a rate of 1 to 1.5 lbs per gallon of water and dipping, spraying or painting the wood liberally, very liberally, with it, soak it in deep. The last 50 lb bag I bought was getting close to $100. I have a dip tray I made with 1x sides and a plywood bottom all assembled with construction adhesive and many nails then caulked and painted inside. I take wood and timbers right off the sawmill and roll them in the tank for several minutes per side, then lift them over the tank and slip sticks under them for them to drip back into the tank for a few minutes before stickering them to dry. Work over a plastic sheet on the ground or an area that is not a ground problem. Although this is a soil micronutrient you don't want a random concentrated spill. In between dip sessions I drain and store the borate in 5 gallon buckets. Use it all up, it's best place is within the wood.
Oh, and as just about always it seems, there is now an "official" standard. Standard on the Design and Construction of Log Structures, ICC 400, available through the ICC website. dense, full of technical jargon but also some very good details... and some that stink. I was in on the commentary phase of its' development a few years ago as were many others... the suits won. But if we don't speak up they don't even know you're under their heel.
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