To prevent air and humidity from entering the space or chink between logs in a log cabin, it is necessary to fill them with a sealant.
This is called chinking.
PVC plastisols are used to chink modern log cabins. Sometimes it is desirable to implement older techniques using locally available materials, particularly for historical cabins.
A mix of equal parts of pure clay and sand with straw added to hold it together is said to work very well. Some skill is required when applying the clay chink to avoid rainwater runoff.
Alternatively, a mix of two parts of clay, one part of sifted wood ash or hydrated lime, and 1/2 part of salt with water is said to work much better than cement, which tends to crack over time.