Selleys Marine Flex Adhesive Sealant can be used on boats, pools and spas, where you need a waterproof seal or bond, even underwater It can be applied and will cure under water no need to drain your pool or spa. Compared to traditional polyurethanes it provides a more durable seal and bond with superior UV resistance. It is powered by Sil-X advanced polymer technology and is sandable when fully cured. Not suitable for PP, PE or PTFE. Critical seals/repairs underwater should be regularly checked and repaired if required. Not for polycarbonate and Perspex underwater. The Gelcoat must be lightly sanded prior to product application.