Try the above link that I tried to insert.
It is a totally waterproof sealant that bonds to most any material that it is placed on. Wipe down the plastic surface with a cleaner first to create a good bond with no dirt or grease. I use TSP as a cleaner and it also etches the surface of anything that is glossy and opens the pours of smooth sufaces to allow it to be able to bond to the sealant when it is applied. TSP is used by painters to etch the surface of glossy items so that paint will stick to the surface and not peel off. TSP (tri sodium phosphate) can be found in most paint departments of hardware stores.
The product that would work is: 116 Vulkem Polyurethane High-Performance Sealant
Here is the description:
Vulkem 116 One-Part, High-Performance Polyurethane Sealant One-Part Grainy Textured Finish Primerless Adhesion on Most Common Construction Surfaces Durable and Flexible Seal Features and Benefits: Vulkem 116 has demonstrated superior primerless adhesion to porous substrates for 30 years, and is the choice for sealing expansion joints in commercial construction applications. It can be used exterior or interior with adequate ventilation. Vulkem 116 is also suitable for certain water immersion applications. Vulkem 116 is also rated for 25% movement capability. Vulkem 116 Sealant is a one-part moisture curing, gun grade polyurethane sealant. Vulkem 116 is durable, flexible, and offers excellent performance in moving joints. No primer is required on most construction materials, and it applies with conventional caulking guns. It is an excellent general purpose sealant designed for use in precast, masonry, glazing, window frame perimeters and similar types of construction joints. Suitable for continual immersion in water with the appropriate primer. Designed for exterior and interior use. The light grainy texture has proven very popular for matching textured substrates like stucco and masonry, and for smooth metal storefront joints the light texture blends and hides tooling marks and the wavy effect that is inevitable when tooling sealants. Color: Bronze Contents of Cartridge: 10.1 fl oz (300 ml) Vulkem 116 Color Chart Joint Design: Vulkem 116 may be used in any vertical or horizontal joint designed in accordance with accepted architectural/engineering practices. Joint width should be 4 times anticipated movement, but not less than 1/4" (6.4mm). Joint Backing: Closed cell or reticulated polyethylene backer rod is recommended as joint backing to control sealant depth and to ensure intimate contact of sealant with joint walls
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