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. 

Hot, intense sunshine can cause your stain to dry too quickly, which could lead it to look uneven or patchy. If you’re staining the deck during hotter months, it’s best to do it in the morning or evening once the wood has had time to cool down. If you’re staining in cooler weather with less sunshine, the time of day won’t make as much of a difference.

Yes, you must thoroughly clean your deck before staining. If you don't, dirt, debris, grease, and mildew can get trapped between the wood and the new stain. This not only looks unsightly but also prevents the stain from penetrating the wood properly, reducing its ability to protect the deck from weather and UV rays. As a result, the stain won't last as long or look as good. Any existing mold or mildew left untreated can continue to grow beneath the new stain, potentially leading to wood rot and structural damage. Always wait at least 48 hours after cleaning for the wood to dry completely before applying stain.

The plastic in composite decking boards protects them enough that you do not need to paint them to prevent warping. In fact, painting composite decking voids the warranty of some manufacturers. Painting can also increase maintenance on the deck, as you must paint regularly to keep it looking its best.