It is not always necessary to remove old stain before restaining a deck. If the previous stain is in good condition and is compatible with the new stain, you may be able to apply a new coat after thorough cleaning. However, if the old stain is in bad condition, flaking, or peeling, it is best to remove it completely to ensure an even surface and proper adhesion for the new coat. Staining over a damaged layer can lead to an uneven finish and poor penetration. For best results, test a small area first and consult the stain manufacturer's guidelines.

The longevity of paint on wood depends on factors like the quality of the paint, surface preparation, exposure to elements, and maintenance. Exterior paint on wood surfaces can last 5 to 15 years or more with proper care and maintenance. Interior paint tends to have a longer life span, often 10 years or more. Regular cleaning, touch-ups, and addressing any issues like peeling or cracking can extend the life of the paint. 

Deciding whether to stain or paint a pool deck depends on your budget, desired look, and the deck's material. Both options can work. Paint offers a wider variety of color options, provides excellent water resistance, and can last longer. However, it requires a primer and can eventually fade or peel. Stain is often cheaper, easier to apply, and penetrates the wood for a more natural look and longer-lasting finish. It also has great water resistance. The downsides are fewer color options and the need for a sealant. The choice can also depend on the deck material; for example, staining may be a better option for concrete as it bonds well and lasts longer than paint.

You should seal your deck every one to two years, but you’ll also need to clean and repair your wood deck throughout the seasons. You may want to hire a local house cleaning service to sweep and clean the deck thoroughly. These cleaning services cost around $50 per hour.

Inspect your deck at least once a year, and if you notice any damage or rot, expect to spend about $10 to $50 for simple DIY fixes or about $2,000 for professional repairs on more extensive damage.