Why is my brick patio sinking?

A brick patio, especially one that's sand-set rather than mortared to a slab, depends entirely on a properly prepared and compacted base, typically a gravel base topped with bedding sand, to stay level. If that base wasn't compacted to enough depth during the original build, or if drainage wasn't graded away from the patio, water pools on and around it and gradually washes finer material out from underneath, leaving voids that the brick above eventually sinks into. The brick itself is rarely the problem; it's just following whatever's happening in the layers underneath it.

Freeze-thaw makes this worse here than it would be in a drier or milder climate. Repeated freezing and thawing pushes and resettles loose or saturated soil under a patio, and a patio built directly on native soil without adequate excavation and base depth is especially prone to that seasonal movement over the years, even if it looked level when it was first laid. A patio can hold level through several dry summers and still start sinking once a couple of wet, hard-freeze winters work on a marginal base.

When we're called out to a sinking patio, we check whether it's a localized low spot or a broader base failure across a wider area. A localized dip can often be fixed by lifting the affected brick, correcting the base underneath, and relaying it to match. Widespread sinking usually means the base itself needs to be rebuilt with proper compaction and drainage slope before the brick goes back down.

• Base material wasn't compacted enough during original installation
• Poor drainage letting water pool and erode material from underneath
• Freeze-thaw cycles shifting loose soil beneath the patio
• Tree roots growing under the patio and disturbing the base
• Original base too shallow for the soil conditions on site