Getting a paver patio right

The base is the patio. Pavers laid on thin or uncompacted gravel will rut and settle within a season no matter how carefully they were placed.

• No edge restraint. Without it the perimeter creeps outward and the joints open up. It is the cheapest part of the job and the one that holds it together.
• No slope. Fall about 1/4 in per foot away from the house or water will find the low corner and sit there.
• Buying exact. Colour varies between production batches. Buying short means the replacements will not match.

Pattern and waste

Running bond and stack bond waste about 5%. A 45° herringbone cuts every paver along both edges and wants 10%. Curves and circles want 10-15%, because a curved edge cuts every unit along it and the offcuts are shapes that fit nowhere else.

Herringbone is not only a look. Interlocking patterns transfer load sideways between units, which is why it is the standard for anything a car drives on; stack bond has continuous joints in both directions and sheds load poorly.

The base, which is the whole job

Four to six inches of compacted crushed stone for a patio, eight to twelve for a driveway, and it must be crushed stone WITH fines — 3/4 in minus, Class 5, road base. The fines are the point: they let the material lock together under a compactor into something that behaves like soft rock. Clean washed stone stays loose forever.

Compact it in lifts of 3 to 4 in rather than all at once. A plate compactor only densifies the top few inches, so a single 8 in lift is a firm crust over loose stone, which settles unevenly the first winter.

One inch of sand. Not three.

This is the most common paver failure and the most tempting shortcut, because sand is easy to spread and gravel is work. Bedding sand is exactly 1 in, screeded flat, never compacted before the pavers go down.

Sand does not compact. Under load it migrates sideways out from under whatever is being walked on, so a thick sand bed gives every footstep material to displace. Within two seasons there are ruts along the route people actually take, usually to the door, and the only fix is lifting the pavers and starting at the base.

It must be coarse, sharp, washed concrete sand. Play sand and mason's sand are fine and rounded, and rounded grains roll rather than lock.

How these numbers are worked out

Paver counts are the patio area divided by the paver's face area, plus 5% for cuts. Base and sand volumes come from the area and the depths above. Edge restraint is the perimeter.

The counts assume a rectangular patio laid in a running or stack bond. Curves, borders in a second colour, and herringbone all change the number, and the waste allowance is where that shows up. Anything carrying vehicles needs the deeper base and 80 mm pavers rather than 60 mm.