I know way back there was issues with Thompson's if you didn't do all sides of the boards with moisture coming out of the ground, into the wood, and trapped under the top layer of water seal.
Cetol seems to work pretty good. I've reapplied this a few times at my Grandpa's place in Shuswap, both on siding and his deck. You have to do it every few years, but it looks really good.
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