How can you clean a log home in an environmentally sound way?
The first thing to try when cleaning a log home is simple soap and water and a good scrub brush. If you try this route try to find a very environmentally friendly soap - one that you wouldn't mind leaking into your well or septic system. This can be a bit hard to find but there are some that are not horrible.
You could even try just water and a great scrub brush. Don't worry about getting the wood wet, only the outer layers will truly soak up the water and that will evaporate relatively quickly.
A traditional tried and true way to clean is using solvents. It is relatively fast and not very expensive, but when you think about how much toxicity you are letting seep into the ground surrounding your home it is something you may not want to do unless truly necessary.
Even then I would question if there is not another way. Whoever is doing the work would also suffer a lot of toxic exposure. Really a big no-no!
A very low tech way to accomplish the job is to sand the wood either by hand or with a small sander. This is cost effective and achieves a beautiful and smooth surface, but it is very time consuming and laborious.
Also your wood will tend to soak up a lot more stain when you have finished sanding than if you simply scrub the surface.
Pressure washing is often an acceptable method that produces a nice clean surface. It is relatively easy and inexpensive and the powerful water does not damage the wood. This is a good answer because it can use only clean water and not introduce chemicals into the ground.
A current and effective method is called Corn Blasting (or Cob Blasting). This method is safe for your log homes as opposed to sand blasting which can really damage the surface of wood.
Cob blasting has evolved into a very popular, solvent free finish removal system. The method uses a modified sand blaster and a large air compressor to blast your surface with ground up corncob at a very high velocity and relatively low volume. Coverage one can expect from a 40-pound bag of corn can vary from 40-50 square feet up to 150+ square feet.
While the corncob won't rough up your log surface to the extent a sand blaster will, it also won't leave your home with a "hand-sanded" finish. You can always choose to buff or sand your log surface lightly after a cob blasting to minimize the effect of blasting.
I hope this helps! And while you are cleaning, check your logs for any gaps in the chinking! Best of luck.