Hi John,
Here are a few pointers in doing log homes.
First The type of sealer you have been using contains linseed oil, Linseed oil comes from Flax, (It's like a wheat) because it's a natural product it contains sugars & starches, Mildew love to eat sugar & starches, Thats one of the reasons these products turn dark and fail. They are easily stripped off, With a sodium hydroxide based stripper, always apply from bottom to top, this way the cleaner does not run down and burn in. Then wash from top to bottom, wash with light pressure, after washing especially with a stripper you will notice the wood is dark, then you spray on a neutralizer such as Oxalic acid, you will see the wood return to it's natural state almost immediately. The water temp question is up to you, we wash all our log homes with cold water, Let the stripper do the work. The sprayer to use would not be an airless I would suggest the Deck Boss or the deck hand or even a pump up sprayer, And the only sealer I would put on your log home would be Ready Seal, It penetrates immediately, looks beautiful, no runs, no lap marks it's foolproof, it can even rain immediately, does not contain linseed oil, It contains peraffinic oil,It will last for years and whats more important, you will be a hero, and get many more log homes, believe me there fun and easy, If need to chat further please give us a call @ sun brite.
Good Luck Chris Detter
See Y'all in Las Vegas/PWNA wood school