I received a call today from a homeowner that was concerned that a stain they had purchased had damaged the wood on their deck. They used Cabot Australian wood oil, which is actually a pretty good product. The wood was darkening and looking stained. After having them send pictures and asking questions it was clear that the problem was  the application methods. One other problem that doesn’t help is that doing the project on the cheap and using Douglas Fir 2×6 instead of an actual decking is never going to last. First the deck was stained right after installation not allowing the wood to “cure”, dry and and be ready to accept stain deep into the material. Second, the stain was applied way too thick. Both of these things allowed stain to stay on the surface of the wood rather than penetrate. When stain remains on the surface it gathers contaminants and undergoes a chemical change and darkens and looks horrible. This also frequently happens when people re-stain a deck without adequately removing all of the old stain. The old stain will block the new from penetrating yielding the same unpleasant results. I recommend leting a deck or fence dry for 4-6 weeks and then make sure to wipe away any excess stain with a tack free cloth or apply more sparingly.