Pressure treated wood is basically treated by submerging it in a liquid solution that is toxic to bacteria, fungi, and bugs (it has a lot of copper, and sometimes some other things), then pressurized to shove the solution into the wood. I’ve glazed over a ton of details, but the solution shoved into the wood prevents the bugs, fungi, and bacteria that normally rot wood. That’s also why most pressure treated lumber is that weird green color.
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