Paver Base and Bedding: What Goes Under Pavers

A paver patio is not a surface. It is a stack of five layers, and the two questions that bring most people here, how deep and what material, belong to the layers nobody sees once the job is done.

The stack, in the order it goes in:

1. Subgrade. Native soil, stripped of organics, cut to slope and compacted.
2. Base. Four to twelve inches of compacted crushed aggregate, set by what drives on it.
3. Bedding. One inch of coarse washed sand, screeded level and left loose.
4. Pavers and edge restraint. The wearing surface, plus what stops it spreading sideways.
5. Joint sand. Swept into the gaps, which turns loose units into a pavement.

Each layer fails in its own way, and nearly every failure surfaces looking like a problem with the pavers.

Start below the base: the subgrade

Excavation depth is everything above it added together, measured down from the finished surface: base, plus 1 inch of bedding, plus paver thickness. A 4-inch patio base under 60 mm pavers is about 7 3/8 inches of digging.

Strip all topsoil and organic material out of that excavation. Roots and buried sod decompose and leave voids, and a void under a compacted base becomes a dip two summers later. Dig soft spots out and replace them with compacted base material rather than bridging over them.

Then compact the exposed soil, before any aggregate goes down. The base spreads load; the soil carries it, so a perfect base over loose soil passes the settlement straight up to the surface. Several passes with a plate compactor at proper moisture is the minimum, and 95 percent of standard Proctor density is the figure commonly specified where vehicles are involved. Run a loaded wheelbarrow over it: if it ruts, the soil is not ready.

On clay or soft soils, lay geotextile separation fabric between soil and base. It stops base stone punching down into the soil and wet fines pumping up into the base. Fabric is not a weed barrier and not a substitute for depth. A soil face left more than about a foot high at the patio edge is a wall rather than a slope, and the retaining wall calculator covers those.

How deep the base goes

Base depth is set by load, not by the pavers or the size of the patio.

What uses the surface	Compacted base depth
Patio or walkway, pedestrian only	4 in
Patio or walkway over clay, or in a hard-freeze region	6 in
Driveway, passenger cars and light trucks	8 in (6 in on firm, well-draining ground)
Driveway taking an RV or delivery trucks	10–12 in

These are the conventional residential figures, and every one assumes a competent subgrade: firm soil that drains, stripped and compacted as above. Over soft clay or a high water table, extra base depth is a patch rather than a fix. Anything repeatedly carrying real vehicle loads deserves a designed pavement section rather than a number from a table.

What the base is made of

The material that works is a well-graded crushed aggregate: angular pieces with fractured faces that interlock, across a spread of sizes down to fines that fill the voids between them. It sells as crusher run, road base, dense-graded aggregate, 3/4 inch minus, Class 5, or GAB depending on the region.

A uniform washed stone such as #57 is the wrong choice here. Its permanent voids are what make it drain, and exactly why it never firms up under a paver. The gravel calculator sets out that drainage-versus-compaction trade-off in full.

Permeable interlocking pavement is the one real exception: it uses open-graded stone through the whole stack because the voids are the stormwater storage. That is a designed system, not a swap inside a conventional build.

Compacting the base in lifts

Place the base in lifts of 3 to 4 inches loose and compact each one before the next goes on. A rental plate compactor only densifies the top few inches: tip in 8 inches at once and you get 3 good inches sitting on 5 loose ones, which consolidate later, under the patio. An 8-inch driveway base is three lifts, not one. The stone wants to be damp rather than dry or saturated.

Base is specified, ordered against, and inspected as a compacted depth, so the loose volume you buy is larger than the finished thickness: roughly 5 inches of loose aggregate to finish at 4 compacted. That is not a waste factor and does not replace one. Material waste factors explains why compaction, waste, and settling are three separate allowances a single job can need at once.

Compacted volume is square feet × depth in inches ÷ 324 = cubic yards, and the paver calculator runs it for base, bedding, and pavers together. Check depth against a string line as you go, because a base 3 inches deep in one corner reads as perfectly flat.

The bedding layer: one inch, not a levelling course

On the finished base goes 1 inch of coarse washed concrete sand, the gradation usually specified as ASTM C33. Screed it against rails set to the finished grade, pull the rails, fill the grooves by hand. The tolerance normally quoted is plus or minus about a quarter inch, and it should not exceed roughly 1 1/2 inches anywhere. Leave it uncompacted: it gets compacted through the pavers when they are vibrated in.

What bedding sand is not, and this is the most common way a competent-looking patio fails, is a levelling layer for a base that was never properly graded. Extra sand in the low spots consolidates further under load than thin sand elsewhere, so the base’s low spots reappear at the surface a season later instead of immediately. No amount of sand fixes a base that was not compacted.

Mason’s sand and play sand are too fine and rounded, so they migrate. Stone dust and limestone screenings hold water. Work off the laid pavers rather than walking on the screeded bed.

The pavers, and the edge restraint that holds them

Paver thickness is a load decision like base depth. Sixty millimetres, about 2 3/8 inches, is the pedestrian unit; 80 mm, about 3 1/8 inches, is the vehicular one. A 60 mm paver in a driveway cracks regardless of what is under it.

Pattern is structural as well as visual. Herringbone is the standard for vehicular work because the interlocking angles resist the twisting and braking forces that shove running-bond courses apart. It also costs more in cuts, which is why the paver calculator carries 15 percent for herringbone against 8 percent for running bond. Pavers go down on the untouched bed, and the field is then vibrated with a plate compactor over a protective pad.

Edge restraint is where base dimensions stop being only about depth. The paver calculator covers why an unrestrained field comes apart at its border. What that page does not cover is where the restraint anchors: it spikes into compacted base, never into bedding sand, which is far too loose to hold a spike through a frost cycle.

That requirement reaches back to the excavation. The base has to run past the paver field at full depth, roughly 6 inches beyond for pedestrian work and 12 inches for a driveway, or there is nothing solid under the edging. A trench cut to the exact patio outline has already lost the edge, and it is lost with a shovel on day one, weeks before anyone is holding a piece of edging. Plastic or aluminium with 10-inch spikes at about one per foot is the usual answer; a mortared soldier course is the permanent one, and the concrete calculator sizes that small pour.

Joint sand: the layer that makes the field one piece

Joint sand is swept in, vibrated, topped up, and vibrated again until the joints are full for their whole depth. A joint full at the surface and hollow below transfers no load between pavers, so the interlock is not there.

Regular joint sand is cheap, fine, washed, and dry. It works, and it washes out: heavy rain, a pressure washer, and ordinary runoff all take it, and open joints let in weeds and ants.

Polymeric sand carries a binder that sets when wetted, buying a joint that resists washout, weeds, and ants and stays full. It costs several times as much and is far less forgiving to install:

• Pavers and joints must be dry when it is swept in. Damp joints set the sand before it reaches full depth.
• The paver faces must be blown completely clean before any water touches them. Residue hardens where it sits, and textured pavers hold it tenaciously.
• The watering is a specified sequence, not a soaking. Too much floats the binder out into a surface film; too little leaves loose sand under a thin crust.
• Most products state a minimum joint depth, commonly an inch or more. Shallow joints over a high bedding course will not hold it.
• Rain inside the cure window ruins a fresh application.

It is also not a repair for a failing perimeter: if sand keeps vanishing, look at the edge restraint and at where the water runs.

Slope: the one dimension every layer shares

A patio needs fall away from the house, conventionally 1/8 to 1/4 inch per foot, roughly 1 to 2 percent. Across a 12-foot patio that is 1 1/2 inches of drop at the shallow end of the range and 3 inches at the steep end. The 1/4 inch figure is safer next to a building.

Slope is established at the subgrade and carried up through every layer in parallel: excavate to it, grade and compact the base to it, screed the bedding to it. You cannot build the base flat and create the fall in the bedding sand, because the fall would have to come out of a sand thickness that is fixed at an inch.

Two checks before you set the finished height. Building codes require ground to fall away from a foundation, and a paved surface hard against the house counts as part of that grade, so confirm the figure with your building department. And the finished surface has to sit below door thresholds, weep holes, and any damp-proof course, because a patio level with a threshold drains into the house. Where the ground falls toward the building, the answer is a channel drain piped to daylight rather than a flatter patio.

Reading the stack backwards

When a paver surface goes wrong, the symptom usually names the layer:

• Edges spreading, joints opening at the perimeter first. Edge restraint, or no base under it to spike into.
• A dip in the middle of the field. Organics or a soft spot left in the subgrade, or a lift that never got compacted.
• Joint sand that keeps washing out. Water running across or under the field, which is a slope problem.
• Seasonal heave that recovers each spring. Water trapped in the base over frost-susceptible soil.

The layer that almost never turns out to be at fault is the one people shop for hardest. Pavers are the part you choose; the base decides how long the choice lasts.