Why does the base matter so much on wet clay?
Clay soil holds water, swells when it is soaked and shrinks when it dries. A patio laid straight on top of it will sink in low spots and heave in others. Weeds and ants find the gaps, and water pools where it should run off.
A proper paver job removes the topsoil and soft material, then builds up compacted layers of crushed stone. That base spreads the load and lets water move through and away. The surface is then sloped slightly so rain runs off the patio and away from the house. Edge restraints lock the pavers in at the sides.
Cheaper jobs often skimp on depth and compaction. Ask any contractor you are considering how the base will be built, how deep it will be and how the patio will drain. A clear answer tells you a lot.

