Stains penetrate wood best when it's cool and dry, so you want to avoid moisture. If the wood is wet upon application, or if it rains before the stain dries, the water will soak into the wood and displace the staining solution. This leads to a flaky and blotchy look, which is the opposite of a sumptuous even coat. Once the stain has fully cured, after about 3 days, rain shouldn’t cause you any problems.

Staining a deck with a rag is typically a better option than using a brush, as it helps the stain penetrate deeper into the wood. However, both brushes and rags are best reserved for detailed work because using these tools on an entire deck can require tediously crawling around on your hands and knees. A pad applicator, sprayer, or roller are preferred alternatives to applying stain over the majority of a deck. Use a rag for railings and other detailed work, and let the wood soak up as much of the stain as possible before wiping away drips or pools.

Two coats of stain are ideal for the best protection and aesthetic appeal. However, if your decking is made of particularly dense hardwood, you may only need one coat. If you want an intense color, two coats are ideal.

Ultimately, overapplication of stain can compromise the deck's appearance, durability, and longevity. It may result in an uneven finish, with excess stain pooling, dripping, or drying into thick patches. It can also obscure the wood's natural grain and texture, detracting from the desired aesthetic. Moreover, excessive staining may not fully penetrate the wood, leading to poor adhesion and premature wear. Additionally, thick layers of stain are prone to peeling, cracking, and blistering as they struggle to bond with the surface.