Monday, April 30, 2007

Traditional Chinking

Years ago log cabin construction was made with handcrafted logs. The logs were straight and of durable first growth timber. The bark was skinned from the trees while green and was set aside for drying (seasoning). Some logs were pressure treated to resist weathering, insects and termites.

In constructing the old traditional cabin walls, the largest logs were placed at the bottom of the walls, tapering to the smallest logs at the top of the wall. The logs were reversed by placing the log top end of one log directly above the butt end of another log. This method insured a more uniform space between logs. This space between the logs was about two inches, with a minimum space of one inch.

After the logs were placed, chinking of the space between the logs proceeded. Six inch strips of expanded metal lath or heavy, small spaced wire fabric was placed on a diagonal between the logs. The metal strips were securely nailed to the bottom inside face of the top log and nailed to the top outside face of the bottom log. These metal strips were then covered by the mortar that ran continuously between the pgs for the length of each log.

The mortar my family used on our old cabin was a portland cement mortar mix; one bag of portland cement, 20% of lime by volume, and 3 cubic feet of loose plaster sand. These materials were mixed together dry. Water was added to produce a stiff mix. This mortar was allowed to stand for about one hour under a cover of wet cloth, then remixed. No additional water was added to the mortar.

The mortar was then ready to be placed for chinking. The mortar was simultaneously placed into the log spaces from both sides of the wall with compacting tools, pushing the mortar through the openings in the metal lath or wire fabric thus forming an anchor for the mortar.

The compacting tools were wood blocking about ten inches long with convex shaped face to produce a curved concave face to the chinking.

Feather edges against the logs were cut off with a trowel leaving approximately 1/4 inch shoulder on the top and bottom of the joint on both sides of the wall. Two to three hours later, the chinking and logs were painted with water glass (a sodium silicate solution). The water glass film began to peel and flake after several days and was removed with a dry rough scrub brush. The surfaces were then finished with sandpaper and finally stained. This sealed the walls from snow, wind, rain and animals.

In modern chinking (if used), the space between the logs is somewhat reduced. The space is filled with strip foam near the center of the logs and backer rods tight against the foam on each side. Then a synthetic chink is placed tight against the backer rods covering them, the foam and sealing against the logs. This new chink looks and feels like mortar. It is a permanent seal because of the elastic properties of the synthetic chink.
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