Chinked log homes are built using a method that leaves a small gap between wall logs. To help prevent air leakage, moisture intrusion and insect infiltration, gaps are filled with a material that starts out pliable and becomes solid as it cures. “Chinking” is the general term used to describe a number of materials that have been used for this purpose over the years.
Early homes used mud mixed with grasses for chinking, with hog bristles or horsehair used as binders.
By the late 1920s, mortar made up of a mixture of sand, lime and cement was being used. Inspectors may see many older log buildings with mortar-based chinking that has been re-applied as owners strive to retain their homes’ original appearance.
Thermal Expansion and Contraction
Mortar-based chinking expands and contracts at a rate different from that of wood logs. Over time, this cycle degrades the bond between the 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 inches 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 develops cracks that freeze damage will enlarge. As this happens, mortar will break into increasingly shorter pieces.
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 that have a much higher proportion of cement than the original mix. A 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 level may result in damage to the 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 lath. Expanded metal lath has been used and has worked well.
The lath is cut into strips small enough to be pushed into the spaces between the logs and fastened with nails or staples. Once fastened into place, the mortar is applied to the lath.
A number of backing materials have been used for this purpose, including chicken wire.
Modern chinking sealant material is typically acrylic and designed to remain flexible after it cures, allowing it to stretch and compress without breaking as logs expand, contract, bow and twist. Buying chinking in 5-gallon buckets is far less expensive than buying it in tubes. It’s usually applied with a bulk gun (pictured at right). Modern chinking is basically caulk that is chemically designed for durable exposure to the weather.
Chinking is manufactured in a number of textures and colors and is usually formulated to either give the appearance of old-style, mortar-based chinking or to blend in with the wood.
It’s also designed to be resistant to damage from ultraviolet (UV) radiation, which can be a problem with long-term exposure to sunlight.
Many defective applications are not visible until they fail. Confirmation of proper chinking methods related to such conditions should be disclaimed by inspectors in their reports, as well as verbally explained to clients.
- Two-point adhesion: To allow maximum flexibility, chinking should be adhered to both upper and lower logs but should have a middle section of uniform thickness that is free-floating and not bonded to the wood. This is usually achieved by installing foam backer rod or plastic tape into the joint between the logs before the chinking is applied. Proper application may be difficult to verify visually.
- Blistering: Improper backing materials, such as colored foam boards or extruded polystyrene, can cause blistering. Excessive moisture in the logs can also cause blistering.
- Telescoping: Poor installation of the backer material can show through once the chinking has cured.
- Thin application: Chinking applied too thinly will tear. This is sometimes a problem where round backer rod has been used. A good rule of thumb is that the chinking should be a minimum of 3/8-inch, but this is often difficult to confirm. Tears less than a foot long can be caulked. Tears exceeding 1 foot should have the chinking cut out and replaced.
- Inadequate bead width: A good rule of thumb is that the width of the chinking bead should be one-sixth of the log’s diameter. An 8-inch-diameter log is calculated 8 ÷ 6 = 1.3 inch, so the chinking bead should be 1-5/16 inch wide. Significantly smaller beads throughout should be brought to the client’s attention, with a recommendation for a specialist’s evaluation.
- Incompatible finishes: Some adhesion failures are caused by the application of chinking to a log finish with which it’s not compatible. Logs with oily or waxy surfaces do not allow for a good bond with chinking sealants. Inspectors need not give reasons for adhesion failures but only state that they exist and recommend a specialist evaluation or repair by a qualified contractor.
- Tooling: Tooling the chinking bead compresses it to the wood surface and helps ensure a good bond at the bead edges where the chinking is thinnest. Un-tooled chinking should be called to the client’s attention as potentially shortening the lifespan of the chinking system.
- New chinking bonded to existing mortar: Although it’s not recommended, new chinking applied over existing mortar is not in itself a defect. However, a bond-breaker, such as plastic tape, must be applied to existing mortar, and areas of missing mortar must have a backing material installed. Both these conditions will be difficult for inspectors to verify and are another reason to disclaim hidden chinking conditions.