A properly built log home won't be drafty, even if cracks develop in the mortar chinking. This is covered in-depth in the class, if you're interested in learning more about it. Mortar chinking will breathe and allow moisture to get out from between the logs, which is important.
Synthetic chinking is used a lot in "kit" log homes, a lot of which have to settle as the logs shrink over time - so it's necessary that the mortar flex. You're right about trapping moisture - not a good thing. Also, synthetic mortars have to be replaced periodically - which leads some people to think that the whole synthetic chinking movement is a money-making scam; they didn't have synthetic chinking 100 years ago, and they got along okay, I think. ;)
So, the answer is "it depends" - it depends on the type of log home you're chinking. If you're chinking a "kit" home, you would probably have to use synthetic; if you're building a home yourself using the methods taught by the association, you'll want to use mortar.
Does that help?







Is cement chinking really preferred over synthetic? It would really seem that concrete will develop cracks and allow drafts much faster than with synthetic. Whereas, the synthetic is thought to trap moisture, not allowing proper ventilation and causing rot.
I have no practical experience with either, and would really like some knowledgable information from some folks who have seen (and preferrably lived in) the differences between the two.