Mortar-based Chinking

Chinked log homes are built using a method which leaves a small gap between wall logs. To help prevent air leakage, moisture intrusion and insect infiltration, gaps are filled with a material which is initially pliable but which becomes solid as it cures. “Chinking” is the general term used to describe a number of materials which have been used for this purpose over the years.

For chinking, early homes used mud mixed with grasses, hog bristles or horsehair as binders. By the late 1920’s mortar was being used; a mixture of sand, lime and cement. Inspectors will see many older log buildings with mortar-based chinking which has been re-applied as owners strive to retain the original appearance.

Very white new-looking mortar like that in the photo to the left may indicate excessive levels of cement in the mix. Inspectors should probe for decay.

PROBLEMS WITH MORTAR-BASED CHINKING

Thermal Expansion and Contraction

Mortar-based chinking expands and contracts at a rate different from that of wood logs. Over time, this difference will degrade the bond between mortar and wood, and eventually chinking will detach from wood entirely. When mortar-based chinking is in this condition it sometimes looks intact from a distance, but can be lifted off logs easily, typically coming off in pieces 6” to 18” long.

Mortar is Brittle

Logs and mortar will expand and contract countless times over the years as they react to changes in temperature and humidity. Over time, mortar will develop cracks which freeze damage will enlarge. As this happens, mortar will break into increasingly shorter pieces.

Moisture Retention Problems

Historical mortar design mixes for chinking used sand, lime and cement, with cement kept to a minimum. It’s not unusual to find poor restoration attempts in which chinking mixes have been applied which have much higher proportions of cement than the original mix.

High cement-ratio chinking takes much longer to dry after becoming soaked from rain or snowmelt than the original chinking, and the higher moisture content levels may result in damage to logs from wood decay. Too much cement in the mix can cause wood to rot.

A more permanent method of attaching mortar-based chinking to log walls is to provide a backing similar to lathe. Expanded metal lathe has been used and has worked well.

The lath is cut into strips small enough to be pushed into spaces between logs and fastened with nails or staples. Once fastened into place, the mortar was applied to the lathe.

A number of backing materials have been used including chicken wire.

In the photo to the right, mortar-based chinking has been applied over diamond lathe, which can be seen where application was incomplete at a corner.

CHINKING and DAUBING

Occasionally when looking at older homes, inspectors may see spaces between log courses which were first filled with a solid material such as wood shingle scrap, ripped wood strips or even sticks and stones. With this method, it’s this solid material which is called “chinking” and the paste-like material, either mud or mortar, which was applied over the chinking and allowed to harden, is called “daubing”.

Courtesy of Permachink Inc.

The photos above show historic chinking. A wood strip can be seen where mortar has fallen away in the photo at the left. Logs in the photo at right never had daubing applied.

INSPECTION CONSIDERATIONS

A commonly-used rule of thumb is that when 30% of the chinking has detached, it’s time to completely strip and re-apply all chinking.
Detached chinking can sometimes be difficult to identify just by looking. Test the bond by hand.
Random areas which have mortar of a different color often indicate attempts by non-professionals at restoration. Probe wood around these ares for decay.

All photos not cited are courtesy of Kenton Shepard