If your patio was flat in the fall and lumpy by spring, the stone probably isn't the problem. Frost is lifting it from underneath. In Connecticut it happens every winter, and whether a patio survives it comes down to one thing you never see: what's under the stone.

We've built and repaired patios across Fairfield and Litchfield County for three generations. Here's what's happening, how to spot it early, and what goes under a patio that stays level.