Gravel under pavers
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The gravel under pavers is a pavement base, not a drain and not a decorative layer. Three thicknesses get mixed together in one order: the compacted base, the bedding sand, and the joint sand. They are three materials. This page keeps the published depths next to the examples this site already calculates. It does not replace those tools.
Base depth by use
ICPI Tech Spec 2, the February 2020 file, says base thickness depends on traffic, soil, drainage, and climate. Sidewalks, patios, and pedestrian areas should be a minimum of 4 inches (100 mm) after compaction over well-drained soils. A residential driveway on that soil should be at least 6 inches (150 mm). Colder climates and continually wet or weak soils should be at least 2 to 4 inches thicker. The 2022 application guide, the file CMHA hosts as Tech Spec 10, states walks as 4 to 6 inches, driveways as 6 to 8 inches, and streets as 8 to 12 inches, and it says a designer should review anything heavier. The short homeowner guide repeats the 4 inch pedestrian minimum.
This site’s worked pad is 12 by 16 feet. Four inches is 12 × 16 × 4 ÷ 324 = 2.37 cubic yards and 3.20 short tons at 1,600 kg/m³. Six inches is 3.56 cubic yards and 4.79 short tons. A walk the 2022 guide puts at 6 inches, or a driveway it puts at 8 inches, is a different depth in the same calculator. Type that depth.
| Use | Tech Spec 2 (Feb 2020 file) | 2022 application guide | 12×16 at 1,600 kg/m³ |
|---|---|---|---|
| Patio or walk | Minimum 4 in after compaction | Walks 4 to 6 in | 4 in is 2.37 yd³ and 3.20 short tons |
| Residential driveway | At least 6 in | 6 to 8 in | 6 in is 3.56 yd³ and 4.79 short tons |
| Cold, wet, or weak soil | Add at least 2 to 4 in | Thicker than the range, with a design review | Add the extra inches on the calculator |
What the base is made of
Tech Spec 2 says specifications used for aggregate base under asphalt are adequate under pavers. If no local specification exists, it points to the grading in its own table. The 2022 guide says the same thing and names ASTM D2940 when there is no local, state, or provincial standard. Both are describing a dense-graded base, the material that packs. On this site that order is the paver gravel calculator, whose own note calls for 3/4 inch crushed stone with fines or dense-grade aggregate. The tons above use the page’s 1,600 kg/m³ start, about 1.35 short tons per cubic yard. The page also says crusher run is often ordered heavier, near 1.43 tons per yard. Change the density when the ticket says so. Do not change the depth to fake a heavier stone.
Clean #57 is a different product. The French drain gravel guide is where that open stone belongs. It will not compact into the structural course these ICPI files describe. A washed chip on top of a dense base is a look, counted as its own layer, and it is not the base.
Bedding sand
Bedding sand sits between the compacted base and the pavers. ICPI Tech Spec 17, the February 2018 file, says to screed it loosely to 1 inch to 1-1/2 inches (25 to 38 mm), compacting to about 3/4 inch to 1-1/4 inches. The CMHA guide specification says a nominal 1 inch, and it says not to use limestone screenings, stone dust, or mason sand conforming to ASTM C144. Tech Spec 17 wants ASTM C33 concrete sand. The homeowner sheet describes the installed sand as between 3/4 inch and 1-1/2 inches.
This site’s paver sand calculator starts at that 1 inch. Over the same 12 by 16 feet, 192 square feet, 1 inch is 0.59 cubic yards and 0.80 short tons at 1,600 kg/m³, and 32 bags of 0.5 cubic feet. An inch and a half is 0.89 cubic yards and 1.20 short tons. The paver-gravel page already says the 2.37 yard base does not include this sand. Order it on the sand page. The 1 to 2 inch note on that page covers the screed Tech Spec 17 describes. A 3 inch sand bed is not that spec.
Compaction lifts
Finished depth and a lift are different. Tech Spec 2 says to compact in 4 to 6 inch lifts with a 7,000 lbf reversible plate, and to use thinner lifts with a 5,000 lbf machine. The 2022 guide says lifts are typically 4 to 6 inches and depend on the machine. Neither file treats a 6 inch driveway as one loose dump.
Pedestrian areas and residential driveways should reach at least 98 percent of standard Proctor density, ASTM D698. Constant vehicular traffic should reach at least 98 percent of modified Proctor, ASTM D1557. The paver-gravel page already says a single 6 inch loose dump will not finish at 6 inches. The depth you type is the finished thickness. Run the calculator once for that total, or once per lift if the loads arrive separately. Do not add the loose height on top of the compacted height.
The 2022 guide also sets the paver thickness that sits on this stack. Pedestrian use and residential driveways are 2-3/8 inch (60 mm) pavers. Pavements with more vehicular traffic are typically 3-1/8 inch (80 mm). That thickness is the paver, not the gravel and not the sand.
Joint sand is the third material
After the pavers are laid, the joints get sand. On this site that count is the polymeric sand calculator. A 10 by 10 foot patio of 4 by 8 inch pavers, a 1/8 inch joint, and a joint depth of 2.375 inches at 100 lb/ft³ is 0.90 cubic feet, 89.50 pounds, and 2 bags of 50 pounds. The 2.375 inch depth is the 2-3/8 inch size for a 60 mm paver, filled to about 1/8 inch below the top. An 80 mm paver at 3.125 inches on the same patio is 117.76 pounds and 3 bags. That is joint sand. It does not build the inch of bedding, and it does not replace the base.
How many units cover the patio is the paver calculator. Ten by ten feet of 4 by 8 inch pavers set tight is 450.00 pavers, 4.50 per square foot, or 495 with 10 percent for cuts. The same face with a 1/8 inch joint is 429.65 modules before waste, which is the module the polymeric page uses. Count the pavers there, the base on the gravel page, the bedding on the sand page, and the joints on the polymeric page.
Sources
- ICPI Tech Spec 2, Construction of Interlocking Concrete Pavements, the February 2020 file. Base thickness by use, 4 to 6 inch lifts, and 98 percent Proctor.
- ICPI Tech Spec 10, Application Guide (2022 PDF on cmha.org). Walk, driveway, and street ranges, lift thickness, bedding sand at 1 inch, and paver thickness.
- ICPI Tech Spec 17, Bedding Sand, the February 2018 file. Screed thickness and the concrete-sand grading.
- CMHA guide specification, pavers on an aggregate base. Nominal 1 inch bedding sand, and the note against mason sand and screenings.
- ICPI homeowner guide. The 4 inch pedestrian minimum and the 3/4 to 1-1/2 inch sand note.
Frequently asked questions
How deep is the gravel under a patio or a walkway?
Tech Spec 2 says sidewalks, patios, and pedestrian areas should have a minimum of 4 inches after compaction over well-drained soils. The 2022 application guide says walks are 4 to 6 inches. This site’s 12 by 16 foot example at 4 inches is 2.37 cubic yards and 3.20 short tons at 1,600 kg/m³. Four inches is that example, the bottom of the published range, not a code for a wet yard.
How deep is the base under a residential driveway?
Tech Spec 2 says at least 6 inches after compaction on well-drained soil. The 2022 guide says driveways are 6 to 8 inches. The same 12 by 16 foot pad at 6 inches is 3.56 cubic yards and 4.79 short tons at 1,600 kg/m³. Cold, wet, or weak soils: Tech Spec 2 says add at least 2 to 4 inches.
How thick is the bedding sand?
Tech Spec 17 says to screed bedding sand loosely to 1 inch to 1-1/2 inches, compacting to about 3/4 inch to 1-1/4 inches. The CMHA guide specification says a nominal 1 inch. This site’s 12 by 16 foot example at 1 inch is 0.59 cubic yards and 0.80 short tons. An inch and a half is 0.89 cubic yards and 1.20 short tons. That sand is not in the gravel total.
How thick is a compaction lift?
Tech Spec 2 says 4 to 6 inch lifts with a 7,000 lbf reversible plate, and thinner lifts with a 5,000 lbf compactor. The 2022 guide says lifts are typically 4 to 6 inches. Pedestrian areas and residential driveways in both files go to at least 98 percent of standard Proctor, ASTM D698. Constant vehicular traffic goes to at least 98 percent of modified Proctor, ASTM D1557. The depth you type is the finished depth. A single 6 inch loose dump will not finish at 6 inches.
Is polymeric sand the bedding layer?
No. Polymeric sand is the joint after the pavers are laid. On this site’s polymeric calculator, a 10 by 10 foot patio of 4 by 8 inch pavers, a 1/8 inch joint, and a 2.375 inch depth at 100 lb/ft³ is 89.50 pounds and 2 bags of 50 pounds. The 2.375 inch depth is the joint in a 60 mm paver, filled to about 1/8 inch below the top. It is not the inch of bedding sand, and it is not the gravel base.
Which stone is the base?
Tech Spec 2 says the aggregate base used under asphalt is adequate, and if there is no local spec it points at its own base grading. The 2022 guide points at ASTM D2940 when no local base spec exists. That is a dense base with fines, the product the paver-gravel page calls 3/4 inch crushed stone with fines or dense-grade aggregate. Clean #57 is the open stone in the French drain guide. It does not pack into this course. The paver-gravel tons at 1,600 kg/m³ are the starting density. A crusher-run ticket nearer 1,700 kg/m³ belongs in the density box.
How many pavers go on that base?
The count is the paver calculator, not this page. A 10 by 10 foot area of 4 by 8 inch pavers set tight is 450.00 pavers, or 495 with 10 percent for cuts. A 1/8 inch joint drops the count to 429.65 before waste. The base under those pavers is still the gravel calculator, and the inch of sand is still the paver-sand calculator.