Special Order only. Allow 7-10 days shipping.
Closed Cell Foam Backer rod is used to fill most of the void in an expansion gap. Stuff it into the gap deep enough to leave a 1/4" space to allow a waterproof sealant like "Vulkem 45 Sealant" to fill in flush to the surface of the deck. This will prevent water from washing out soil from under your pool deck or concrete.
Vulkem 45 sealant is sold separately.