Do I need to seal pressure-treated wood before staining?

Why pressure-treated wood needs to dry out first

Pressure-treated lumber is forced full of a water-based preservative at the mill, which means a brand-new board can be carrying a lot of moisture. If you stain over that moisture, the stain can't soak into the wood fibers properly — it just sits on top, and you'll see it peel or flake off within a season.

That's not a sealer problem, it's a moisture problem. The fix is time, not an extra product.

How to tell if your deck is ready

Don't guess based on the calendar alone — lumber moisture content varies a lot depending on how it was stored and the weather since it was installed. Two reliable ways to check:

• Water bead test: sprinkle a few drops of water on the wood. If it beads up on the surface, it's still too wet. If it soaks in within a minute or two, it's ready.
• Moisture meter: the more accurate option. You're looking for readings under 15% before staining.

Sealer vs. stain: what's actually different

These get used interchangeably, but they're not the same job:

• Sealer is typically clear or near-clear and its only job is blocking water penetration. Some pressure-treated wood is sold "pre-sealed," which refers to the factory preservative, not a separate product you apply.
• Stain adds color/UV protection on top of some level of water resistance. Most exterior deck stains already include water-repellent properties, which is why a separate sealing step is redundant for most pressure-treated decks.

If you want maximum protection, some people apply a clear water repellent a year or two after staining, as a top-up — but that's maintenance, not a prerequisite.

My recommendation

Wait for the wood to test dry, do the bead test in a few spots, and go straight to a quality exterior deck stain. Skip buying a separate sealer for new pressure-treated lumber — you'd be paying for a step the wood already did at the mill.