If you have an aluminum pontoon boat, you'll want to keep it in good condition by sealing the hull. This will protect it from salt water and sun damage. You can use a special paint or epoxy designed for aluminum boats, or you can use a regular sealant like silicone caulk. Whichever option you choose, be sure to follow the manufacturer's instructions carefully.
Preparing the surface of your pontoon is critical for ensuring that the sealant adheres properly. Start by sanding down the entire hull with fine-grit sandpaper. Wipe away any dust with a damp cloth, then let the surface dry completely. Once it's dry, apply a primer specifically designed for aluminum surfaces. This will help the sealant to stick better.
Once the primer is dry, you're ready to apply the sealant. If you're using caulk, cut off the tip of the tube at a 45-degree angle and position it against the hull so that there's a small gap between the edge of the tube and where you want to start caulking. Apply even pressure as you move along, filling in any gaps or cracks as you go. Make sure not to overfill them - just fill them enough so that they're sealed shut. If you're using paint or epoxy, follow the manufacturer's instructions for application (usually brushing or rolling on).
Let your pontoon dry thoroughly before taking it out on the water again - this will usually take 24 hours for caulk and 48 hours for paint or epoxy