Yes, you can waterproof any wood that has not already been treated. A good way to test this is to splash some water on it. If the water starts to bead up, the wood is treated and most likely doesn’t need another coating.

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. 

Yes, it is generally a very good idea to seal your deck after pressure washing. Power washing removes not only dirt and debris but also a thin layer of wood, leaving the surface exposed and more susceptible to weathering. Sealing is almost always needed after this process. After a general cleaning, sealing isn't automatically necessary if the existing sealant is still intact. You can test the surface by placing a few drops of water on it. If the water beads up, the sealant is working. If it soaks into the wood, it's time to apply a new sealant. If it has been a few years, it's wise to remove the old sealant, wash the deck, and reseal for maximum protection.

Ipe wood can last up to 75 years with minimal maintenance because its own oils help to preserve it. However, to get the most out of your Ipe wood deck, you should perform some routine maintenance, including regular cleaning, sweeping of leaves and debris, and rinsing spills with a hose. It’s also important to repair any deep scratches as soon as you spot them and reseal the deck annually to protect against scratches and scuffs.