A paver patio is three layers, and the calculator above handles the two underneath. Get these right and the pavers on top stay flat for decades. Get them wrong and no amount of care with the pavers themselves will save it.
The two layers
The base is compacted crushed stone with fines — four to six inches for foot traffic, eight or more for vehicles. This is the layer that carries load and it must be compacted in lifts of three to four inches.
The bedding is exactly one inch of coarse concrete sand, screeded level and left loose. Its only job is to let each paver seat evenly.
Why the sand layer is one inch
Sand does not carry load. Any more than an inch and the pavers settle into it unevenly over the first year, which is what produces a rippled patio.
If your base is not level enough to work with a one inch bedding layer, the fix is to level the base — not to add more sand.
Slope for drainage
A patio needs to shed water away from the house, about a quarter inch of fall per foot of run. On a 12 foot patio that is three inches of drop from the house edge to the outer edge.
Build the slope into the compacted base, not into the sand.
Edge restraint
Without a restraint along the open edges, the outer pavers creep outward and the joints open up. Plastic edging spiked into the base is the common solution and it is not optional on a patio that gets used.
Compact in lifts, and rent the right machine
Base stone has to be compacted in layers of three to four inches. Dumping eight inches and running a plate compactor over the top compacts the top three and leaves the rest loose.
A plate compactor is the right tool for paver base and it can be rented by the day. A hand tamper works for a small area and is genuinely hard work beyond a few square metres.
Lightly wetting the stone before compacting helps the fines pack. Saturating it does the opposite — wet base pumps rather than compacts.
Excavating deeper than you think
The excavation depth is the base thickness plus the sand plus the paver thickness, measured down from the finished surface you want.
For a typical patio that is six inches of base, one inch of sand, and two and three eighths inches of paver — close to ten inches of digging. Under a driveway it is more.
And the excavation extends beyond the paved area, usually six inches past each edge, because the base has to support the edge restraint. Both of these add to the soil volume you will be removing.