Wood stain does go bad, but it will last in the can for between three and six years, provided you use proper storage techniques. Storing wood stain in open containers or in extremely low or high temperatures will cause your wood stain to become unusable much more quickly. Water- and latex-based wood stains typically last for just two to four years, while oil-based wood stains can last for three to six years.

Staining or sealing a cedar deck or fence is highly recommended to extend its lifespan and protect it from the elements. While cedar is naturally resistant to mold and mildew, it is not impervious to damage from moisture, sun exposure, splintering, fading, and rot over time. Applying a protective finish creates a shield that preserves the wood's strength and appearance, potentially extending its life by five to 10 years.

When choosing a finish, it's helpful to understand the difference between a sealer and a stain. A sealer sits on top of the wood, whereas a combination stain and sealer soaks into the top layer. Because it penetrates the wood, a stain generally offers better protection against UV damage and rot and lasts significantly longer. For the best results that also preserve the wood's natural color, consider using a near-translucent stain.

To maintain protection, plan on reapplying the stain or sealer every two to three years, either as a DIY project or by hiring a professional.

You can apply stain over peeling stain, but it’s not a good idea. Your old stain will get in the way of your new stain bonding to the wood, so you’re likely going to see the same issue again shortly after application. Your best option is to sand off the old stain and clean the surface thoroughly before applying new stain.

Whether you can paint over your existing paint depends on what’s on there. Most of the time, you’ll want to sand down or scrape off the paint that’s currently coating your surface. Epoxy paint, for example, won’t let new paint stick to the surface. Latex paint is more forgiving and will accept a new coat, but a primer is recommended if you’re switching colors.