That wet, greenish wood is packed with preservatives. It is a chemical cocktail meant to keep bugs and rot away.
When you buy pressure-treated lumber, it is often still soaking. It is like a sponge full of water and copper compounds.
Your stain is supposed to sink into the wood fibers. Instead, it sits on top of a chemical lake.
The Sticky Mess
Imagine painting a wet sponge. The paint just beads up and slides off. That is exactly what happens here.
The stain cannot bond. The wood is too busy pushing its own water out.
You end up with a patchy, sticky mess. It looks like a kid with a bad paint brush went wild.
