Guide · Installation
How pavers are installed, base up
Pavers are installed by excavating well below the finished level, compacting an aggregate base in layers, screeding a thin bedding course, setting the units, restraining the edges, and locking the joints with sand. Roughly three quarters of the labor happens below anything you will ever see.
Almost every disappointing paver surface fails for the same reason, and it is never the paver. It is what was done, or not done, in the two days before the first unit was laid. Below are the beliefs heard most often at estimates, set against what a good crew actually does.
This matters more here than in most of the Valley. The Chatsworth foothills sit on the Chatsworth Formation, a body of Late Cretaceous sandstone that stands exposed at Stoney Point, and the USDA soil survey maps bedrock at the surface or within about 15 inches on those lots. Base work on ground like that is genuinely hard digging, which makes it the first thing a hurried installer quietly reduces.
Sand is present, but only as a thin screeded bedding course of about one inch. It exists to let each unit seat level, nothing more. Beneath it sits the layer doing the structural work: crushed aggregate, placed in lifts and compacted, six to eight inches deep for a patio and ten to twelve for a driveway. Set pavers on sand alone and the sand migrates, because sand is not a base, it is a levelling medium.
Depth follows use and subgrade, and beyond the right depth you are paying for stone that does nothing. What cannot be overdone is compaction. Aggregate has to go down in lifts of roughly three to four inches and be compacted between each one, because a plate compactor only influences so much material at a time. Twelve inches dumped in one go and rolled once is a worse base than six inches placed in two properly compacted lifts.
Sandstone shelf is excellent bearing material, and on a Chatsworth foothill lot you may well reach it. What you cannot do is set pavers on it. Rock arrives at an irregular surface, it does not drain evenly, and it gives you nothing to screed against. The shelf is broken back to a workable level, a graded aggregate layer goes over it, and that layer is compacted like any other. The rock saves you settlement worries. It does not save you the base.
Compaction happens at least three times on a proper job. The subgrade is compacted before any aggregate arrives. Each lift of base is compacted as it is placed. The finished paver field is compacted again after the joint sand goes in, which seats every unit into the bedding course and locks the joints. Skip the first and the whole assembly settles into soft ground. Skip the last and the surface feels loose underfoot within the season.
Edge restraint is structural, and on sloped ground it is the single most important piece of hardware on the job. Interlock only works while every unit is held against its neighbors. Free the perimeter and the outer courses spread, the joints open, and the spread works its way inward year by year. On a hillside approach the restraint is also what stops the entire field from creeping downhill under gravity and repeated vehicle loads.
Joint sand is what transfers load from one unit to the next, which is the entire mechanism of interlock. Weeds, meanwhile, almost never come up from below through a compacted base. They germinate in windblown debris that collects in an open joint from above. Chatsworth gets its share, because dry Santa Ana winds carry dust with them. Polymeric sand, properly set, fills the joint firmly, resists being lifted out in a wind event, and leaves seeds very little to take hold in.
The sequence, in order
- Mark and measure. Layout is set out on the ground, along with the finished levels and the fall for drainage.
- Excavate. Down to subgrade, which means the base depth plus the bedding course plus the thickness of the paver, below the intended finished surface.
- Prepare the subgrade. Compacted, and separated with geotextile where the soil below is soft or fine enough to migrate into the base.
- Place the base. Aggregate in lifts of three to four inches, compacted between each lift, and graded to the same fall the finished surface will carry.
- Screed the bedding. About one inch of bedding material, screeded flat and left undisturbed.
- Set the pavers. Laid to pattern from a straight reference line, with joints kept consistent as the field advances.
- Restrain the edges. Fixed along the whole perimeter before anything else happens.
- Cut, sand, compact. Perimeter cuts made, joint sand swept in, the field compacted, and the sand topped up and set.
| Surface | Compacted base | Paver thickness | Total excavation |
|---|---|---|---|
| Walkway | 6 in | 60mm | About 9.5 in |
| Patio | 6 to 8 in | 60mm | About 9.5 to 11.5 in |
| Driveway | 10 to 12 in | 80mm | About 14 to 16 in |
What that means on a Chatsworth lot
Read the table again with local ground in mind and the picture becomes clear. A driveway here calls for something like fourteen to sixteen inches of excavation across the whole approach. On the flats near Devonshire Street that is a straightforward morning's work with a machine. On a foothill parcel toward Twin Lakes or the rising ground below Santa Susana Pass, the trench may meet sandstone well before it reaches depth, and the dig moves from a bucket to a hydraulic breaker with the spoil hauled away rather than spread on site.
Two further local conditions shape the build. Equestrian parcels carry long rural approaches that see truck and trailer traffic, so base depth is decided by the heaviest vehicle that uses the drive, not by the family car. And on the steeper foothill lots, where slanted strata produce grades near thirty percent, drainage and edge restraint are designed before the pattern is even discussed, because on a slope those two details decide whether the surface is still true in ten years.
That sequence is the same on every paver surface in Chatsworth, and it is why a good contractor stands on the property before quoting. The figures in the Chatsworth cost guide hold up well, and the excavation line within them is the one that moves. If a driveway is what you are planning, the driveway page covers base depth, trailer loads, and hillside approaches in more detail.
Timber raises its own set of questions. Wood and wood-look surfaces in Chatsworth deals with those.
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The contractor walks the property, reads the surface, and gives you a fixed written price that accounts for what the digging will actually meet.
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