Although log houses enjoy a mystique of durable low maintenance, those not made from woods very resistant to decay will require regular maintenance, unless pressure treated deep into the wood. I am always amazed how books on log houses spend 20 sections on building with logs and generally no more than two pages on maintenance. Generally speaking, a log exterior in the humid South will need a preservative applied nearly every year, and in the North it will need one about every three years to be safe. There are many such preservatives on the market.
Fungicidal preservatives are usually copper naphthenate or zinc naphthenate. Oil-based penetrating stains are mostly linseed oil with colors added if desired. Some log house devotees claim that plain linseed oil, regularly applied, serves the purpose except in very humid, warm regions where mildew is a constant threat. But all that sounds like high maintenance to me and so outside the purview of this guide. Also remember that woodpeckers (the pileated woodpecker is most harmful) and boring insects love to make holes in logs.
