The Summary Traditional jointing sand washes out during heavy rains, allowing water to penetrate the subgrade and destroy the patio's structural integrity from the bottom up. Polymeric sand fixes this by utilizing water-activated bonding agents to create a flexible, high-PSI joint that repels moisture, stops weed growth, and prevents insect tunneling. Attempting a DIY polymeric sand installation often fails due to under-watering, which creates a fragile surface crust that sha