How to Waterproof Stairs

Prepare the stairs by removing all items from them and cleaning off all visible debris. Use a sturdy broom to sweep away dirt and dried mud from the surface of the stair steps, or treads. Brush away spider webs, trapped leaves and other items from the undersides of the stairs and from railings.

Spray the stairs with water from a hose, using a sprayer attachment that provides a strong stream of water. While the stairs are still wet, scrub their wood surface with a deck cleaner solution, following the manufacturer’s instructions for mixing and applying the solution to the stairs. Use a stiff-bristle brush to work the solution into stubborn areas of stains and greasy spots. Rinse off the deck cleaner, along with all loosened soil and other debris, after the amount of time recommended by the deck cleaner's manufacturer. Allow the stairs to dry completely.

Apply deck sealer to the railings with a paintbrush. Deck sealer is a waterproofing solution. Use a thin coat to avoid unsightly drips and smears. Allow the first coat of deck sealer to dry completely, following the recommended drying time on the deck sealer's label. Follow the first coat of deck sealer with a second coat to provide adequate coverage.

Apply the deck sealer to the stairs. Use a paint pad to spread the product over the horizontal surface areas, and use the paintbrush to work the solution into cracks and along the sides and front of the stairs. Let the first coat of deck sealer dry thoroughly before applying a second coat.