Applying a sealer or topcoat after staining wood is highly recommended, though not always strictly required. A sealer protects the wood from moisture, UV rays, and weather-related issues, which is especially important for outdoor surfaces like decks and fences. It also enhances the stain's durability, prevents fading over time, and gives the wood a cleaner, more professional-looking finish. For some indoor applications, a sealer may not be necessary, depending on the type of stain used and the level of protection needed. It's always best to check the stain manufacturer's recommendations and consider the wood's intended use and exposure when deciding whether to apply a sealer.

Waterproof paint creates a barrier to hold back moisture, but it doesn’t eliminate the source of the water. If you hire a basement waterproofing contractor, many will tell you that waterproof paint is only a temporary solution. On average, you can expect it to last from six months to two years in a wet basement before deteriorating.

There are more pros than cons when staining a deck. Deck stain is more affordable than paint, it protects the wood and allows the natural textures to shine through, and it can revive the appearance of your home. However, deck stain also requires prep work (sometimes days or more), carries more upkeep than a painted deck, and can fade over time if not cared for. 

Applying too much sealer to a deck might seem like extra protection, but it can cause more harm than good. Wood is a porous material with a limited capacity to absorb liquids. When you go overboard with sealer, the excess can't soak in and instead forms a film on the surface. This leftover layer is prone to peeling, cracking, and trapping moisture, ultimately defeating the purpose of sealing in the first place.