My crack: expansion joint between the pool deck and the coping ( the stone immediately surrounding the pool) This is the area needed to fill this crack above my tile below the coping...? After putting in a filler to bring the expansion joint within 1/2" several other posts use polyurethane products. A pool service tech recommend Boss Silicone - any experience as to this product? Would it be any better to use a marine grade product like 3M 5200 fast cure sealant on my application. Being in AZ with more swim season & heat than the average- will silicone based products provide the best waterproof & flexible seal?