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Safety Cue
Task-specific safety guidance for ordinary work hazards.
Chapter 5
Install and Compact a Gravel Base for Pavers
Install and compact an approved aggregate base to the specified thickness, support, slope, and finished elevation for paver installation, using an accepted excavated and compacted subgrade from Chapter 4.
Field Cue System
These cues appear at the point of work. They identify safety, code, manufacturer, and measurement issues before they become rework or hazards.
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Critical Safety Cue
Serious injury, utility strike, or major damage is possible.
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Field Safety Cue
Practical work-area safety: footing, slopes, traffic, and housekeeping.
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Code Alert
Local requirements vary. Verify permit, inspection, and jurisdictional rules.
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Manufacturer Cue
Follow product-specific instructions for materials and components.
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Measurement Cue
Clearance, layout, elevation, and reference-point guidance.
Job Overview
This chapter qualifies you to install and compact the aggregate base course that carries the paver surface above it. The finished work product is one compacted aggregate base, placed in approved lifts, over an accepted subgrade, at the specified compacted thickness, slope, elevation, and edge extension, with density or proof checks completed and documented.
You will confirm the subgrade acceptance and base specification, inspect delivered aggregate, place and compact the base in controlled lifts, verify thickness, elevation, and slope on a grid, correct deficient areas, protect the accepted base from traffic and weather, and document the completed installation.
This chapter depends directly on the accepted, compacted subgrade produced in Chapter 4. Every later paver, wall, path, and drainage chapter in this book depends on the base you install here: Chapter 6 screeds bedding sand directly from this base's accepted elevation, and no paver, cap, or drainage component installed later in this book may rest on a base that has not passed the acceptance standards in this chapter.
Skills You Will Demonstrate
- HC-025 — Select base aggregate compatible with the project specification, load, and drainage requirements.
- HC-026 — Place gravel in controlled lifts not exceeding the specified maximum lift thickness.
- HC-027 — Compact the base using equipment, pattern, and pass count appropriate to the specified aggregate.
- HC-028 — Maintain the specified compacted base thickness across the project area.
- HC-029 — Verify base slope against the approved drainage direction and value.
- HC-030 — Inspect base stability, including density, proof, or deflection checks where specified, and document acceptance.
Where This Skill Fits
The aggregate base is the structural layer of a hardscape system. Bedding sand is a thin setting layer, not a substitute for a properly compacted base; a base that is thin, loosely compacted, out of slope, or contaminated with fines will settle, rut, or pond regardless of how carefully the pavers above it are installed. This chapter is where the base's thickness, compaction, and slope are locked in before any bedding sand is placed.
The same lift-thickness, compaction, and elevation-verification discipline taught here recurs in the gravel-path base of Chapter 11, the wall leveling pad of Chapter 12, and the base repair work of Chapter 18. Learning the base-installation sequence correctly here prevents the most common cause of hardscape failure addressed later in this book.
Scope and Intended Use
This chapter covers:
- confirming subgrade acceptance and the approved base-aggregate specification, including required compacted thickness and maximum lift thickness
- inspecting delivered aggregate for gradation, contamination, segregation, and moisture
- protecting the subgrade from rutting during delivery and placement
- placing and moisture-conditioning aggregate in controlled lifts
- compacting each lift using the specified equipment, pattern, and pass count
- checking lift thickness, density, and elevation after each lift
- correcting low, high, loose, pumping, or segregated areas
- verifying final elevation, slope, and edge extension on a grid
- performing density, proof, or deflection checks where specified
- protecting the accepted base from traffic, rain, and contamination
- documenting aggregate, lift count, moisture, passes, tests, and final readings
This chapter does not authorize the learner to:
- place base aggregate over a subgrade that has not passed the Chapter 4 excavation and subgrade acceptance standards
- substitute a different aggregate gradation, thickness, or compaction target than the one stated in the approved base-aggregate specification
- place bedding sand or pavers over a base that has not passed this chapter's thickness, elevation, slope, and stability checks
- operate compaction equipment near foundations or fragile structures without observing the vibration limits and separation distances identified in this chapter
Any base condition that fails inspection in this chapter must be corrected and reinspected before Chapter 6 bedding-sand work begins.
Reference Conventions
Establish these references before base installation begins, and record them on the base installation record.
| Term | Definition |
|---|---|
| Compacted lift thickness | The finished thickness of one aggregate layer after compaction, as stated in the approved base-aggregate specification |
| Maximum loose lift thickness | The maximum thickness of uncompacted aggregate that may be placed before compaction, as stated in the approved specification or manufacturer instructions |
| Total compacted base thickness | The full specified thickness of the finished, compacted base, measured from the accepted subgrade elevation to the top of the base |
| Edge extension | The distance the base extends beyond the finished paver edge, as stated in the approved specification |
| Base slope | The finished slope of the top of the base, matching the approved drainage direction and value |
| Proof-rolling | A visual or instrumented check for pumping, rutting, or deflection under a moving load, performed only where specified |
Base Installation Record
Before placing aggregate, record the base specification directly on the base installation record:
Aggregate type and gradation: ______ Specified compacted thickness: ______ Maximum loose lift thickness: ______
Required slope and drainage direction: ______ Edge extension: ______ Compactor make/model and rated pattern: ______
Date placed: ____________ Installer name: ____________
Prerequisites
- A subgrade that has passed the Chapter 4 excavation and subgrade acceptance standards, with the acceptance record available
- An approved base-aggregate specification stating gradation, compacted thickness, maximum loose lift thickness, and edge extension
- An approved drainage plan or layout stating the required base slope and drainage direction
- A plate compactor or roller matched to the specified aggregate, inspected and in working order, with manufacturer instructions on hand
- Delivered aggregate on site, inspected and accepted for gradation, contamination, segregation, and moisture before placement begins
Common Field Fundamentals
Every aggregate base in this book, from a straight walkway base to the Chapter 20 capstone patio base, is built using the same lift-and-compact sequence: confirm the subgrade and specification, place a controlled lift, compact it, verify thickness and elevation, and repeat until the total specified thickness is reached. Skipping a lift check or compacting an oversized loose lift is the most common cause of a base that looks finished but is not structurally sound.
Subgrade and specificationAccepted subgrade, aggregate gradation, compacted thickness, maximum lift thickness
Delivered aggregateGradation, contamination, segregation, moisture inspected before placement
Lift placement and compactionControlled loose-lift thickness, moisture conditioning, overlapping compactor passes
Elevation and stabilityGrid elevation checks, slope verification, density or proof checks where specified
Stop-Work Conditions
This chapter requires the installer to halt base placement, rather than continue to the next lift, whenever a condition falls outside what the approved specification and this chapter's checks can resolve.
HC-025 – HC-030
Aggregate Base Installation / Compaction Qualification
Aggregate Base Installation and Compaction
A. Finished Base Specification
Deliverable: one compacted aggregate base installed over an accepted subgrade, at the specified compacted thickness and maximum lift thickness, matching the approved slope and drainage direction, extending the specified edge distance beyond the finished paver edge, with density, proof, or deflection checks completed where specified and a completed base installation record.
B. Base Installation Record Schedule
| Record | Required Content | Source |
|---|---|---|
| Subgrade acceptance | Chapter 4 acceptance date, elevation, and slope confirmation | Chapter 4 record |
| Aggregate inspection | Gradation, contamination, segregation, moisture at delivery | Field inspection |
| Lift record | Loose thickness, compacted thickness, moisture, and pass count for each lift | Field measurement during placement |
| Elevation grid | Elevation readings at each grid point relative to the fixed reference | Field measurement |
| Slope verification | Measured slope compared against the approved drainage direction and value | Field measurement |
| Stability checks | Density, proof-roll, or deflection results where specified | Field test |
| Corrections | Any low, high, loose, pumping, or segregated area found and corrected | Field inspection and correction record |
| Protection record | Measures taken to protect the accepted base from traffic, rain, and contamination | Field record |
C. Governing Document Checklist
- Chapter 4 subgrade acceptance record: confirms the subgrade this base is placed on has passed excavation and subgrade acceptance.
- Approved base-aggregate specification: confirms gradation, compacted thickness, maximum loose lift thickness, and edge extension.
- Drainage plan: confirms the required base slope and drainage direction.
- Manufacturer compactor instructions: confirm the rated pattern, pass count, and vibration limits for the equipment in use.
D. Acceptance Standards
| Check | Standard |
|---|---|
| Subgrade acceptance | The subgrade record confirms Chapter 4 acceptance before any aggregate is placed; a subgrade exposed to rain, traffic, or standing water since acceptance is reinspected for softness before placement |
| Aggregate inspection | Delivered aggregate matches the specified gradation and shows no contamination, segregation, or moisture outside the range needed for proper compaction |
| Lift thickness | No loose lift placed exceeds the maximum loose lift thickness stated in the specification or manufacturer instructions |
| Compacted thickness | Total compacted base thickness at every grid point meets or exceeds the specified compacted thickness |
| Elevation and slope | Elevation at every grid point and the measured overall slope match the approved drainage plan and value within the stated tolerance |
| Edge extension | The base extends the specified distance beyond the finished paver edge at every point along the perimeter |
| Stability | Density, proof-roll, or deflection checks, where specified, meet the stated pass/fail standard with no pumping, rutting, or deflection beyond the stated limit |
| Protection | The accepted base is protected from traffic, rain, and contamination until Chapter 6 bedding-sand work begins |
E. Preparation — Confirm Specification and Inspect Aggregate
- Confirm subgrade approval and base-aggregate specification. Review the Chapter 4 acceptance record and the approved base-aggregate specification, and record the compacted thickness, maximum loose lift thickness, slope, and edge extension on the base installation record.
- Verify required compacted thickness and maximum lift thickness. Confirm the number of lifts needed to reach the total specified compacted thickness without exceeding the maximum loose lift thickness in any single lift.
- Inspect delivered aggregate for gradation, contamination, segregation, and moisture. Reject and document any delivered load that does not match the specified gradation or shows visible contamination or segregation.
- Protect subgrade from rutting during delivery. Route delivery vehicles, carts, and wheelbarrows on planked or protected paths across the subgrade, and stage aggregate away from the excavation edge.
F. First Lift — Placement and Compaction
- Place aggregate in controlled quantities. Dump and spread aggregate in measured quantities across the project area rather than in a single uncontrolled pile.
- Spread the first lift evenly beyond the paver edge as specified. Rake the first lift to the specified loose thickness, extending to the required edge-extension distance beyond the finished paver edge.
- Maintain the approved slope while spreading. Use string lines or a laser level referenced to the fixed reference point to guide the rake or screed to the approved slope.
- Moisture-condition aggregate where required. Add or allow moisture only as stated in the specification or manufacturer instructions, and record the moisture condition before compaction.
- Compact using the specified plate compactor, roller, or rammer. Operate the equipment stated in the specification, sized to the aggregate and lift thickness.
- Overlap passes and follow the approved pattern. Overlap each compactor pass according to the manufacturer's stated overlap distance and direction.
- Keep compaction equipment clear of foundations and fragile structures where vibration limits apply. Use hand-operated equipment in place of the plate compactor within the stated separation distance.
- Check lift thickness, density, and elevation. Measure the compacted lift thickness at spot-check locations and record the result on the lift record before placing the next lift.
G. Subsequent Lifts and Final Elevation
- Add subsequent lifts. Repeat placement and compaction in additional lifts, each not exceeding the maximum loose lift thickness, until the total specified compacted thickness is reached.
- Do not place overly thick loose layers. Split any lift that would exceed the maximum loose lift thickness into two or more compacted lifts.
- Fill low spots with approved aggregate. Add specified aggregate to any area found low on the elevation grid, and recompact before continuing.
- Trim high spots rather than covering them with bedding sand. Remove excess compacted material from any high area rather than allowing bedding sand in Chapter 6 to compensate for it.
- Compact edge, corner, drain, and utility areas. Use equipment appropriate for confined areas to achieve the same specified compaction at edges, corners, drain openings, and utility penetrations.
- Check final elevation on a grid. Measure elevation at every grid point stated in the project specification, relative to the fixed reference used throughout the project.
- Verify final slope and transitions. Compare the measured slope against the approved drainage plan and confirm smooth transitions at every edge and interface.
- Perform density, proof, or deflection checks where specified. Conduct the required test using the stated method and record the result against the stated pass/fail standard.
H. Correction and Protection
- Correct loose, pumping, segregated, high, or low areas. Remove and replace or recompact any area failing the elevation, slope, or stability checks, and reinspect the corrected area before continuing.
- Protect the accepted base from traffic, rain, and contamination. Cover, barricade, or otherwise protect the accepted base until Chapter 6 bedding-sand work begins.
- Document aggregate, lift count, moisture, passes, tests, and final readings. Complete the base installation record with every lift's thickness and moisture, the final elevation grid, slope verification, and stability-check results.
Common Site Inspection
Review every base installation using the same checks regardless of project type.
- Subgrade check: confirm the Chapter 4 acceptance record is on file and the subgrade was reinspected if exposed to rain or traffic since acceptance.
- Aggregate check: confirm delivered aggregate matches the specified gradation and shows no contamination, segregation, or unacceptable moisture.
- Lift check: confirm no loose lift exceeded the maximum loose lift thickness and every lift's compacted thickness was measured.
- Elevation and slope check: confirm final elevation at every grid point and the measured slope match the approved drainage plan.
- Stability check: confirm density, proof, or deflection checks were performed where specified and met the stated standard.
- Protection check: confirm the accepted base is protected from traffic, rain, and contamination before Chapter 6 begins.
Complete the Aggregate Base Installation Worksheet in the Inspection Checklist section below before beginning Chapter 6.
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Failure Points and Troubleshooting
Cleanup
This chapter ends with a completed, documented base installation record and a protected, accepted base, not a visually finished surface alone.
- Remove excess aggregate, spillage, and debris from adjacent surfaces, drains, and vegetation
- Store the base installation record with the Chapter 4 subgrade acceptance record and the approved base-aggregate specification
- File lift-record photographs and elevation-grid photographs alongside their corresponding worksheet entries
- Cover or barricade the accepted base to prevent traffic, rain intrusion, or contamination before Chapter 6 begins
- Retain the complete base installation record for reference throughout the remainder of this book, including the Chapter 20 capstone
Field Terms
- Compacted Lift Thickness
- The finished thickness of one aggregate layer after compaction, as stated in the approved specification.
- Maximum Loose Lift Thickness
- The maximum thickness of uncompacted aggregate that may be placed before compaction.
- Total Compacted Base Thickness
- The full specified thickness of the finished, compacted base measured from the accepted subgrade.
- Edge Extension
- The distance the base extends beyond the finished paver edge, as stated in the approved specification.
- Base Slope
- The finished slope of the top of the base, matching the approved drainage direction and value.
- Proof-Rolling
- A visual or instrumented check for pumping, rutting, or deflection under a moving load, performed only where specified.
- Segregation
- Separation of coarse and fine particles within an aggregate load, resulting in inconsistent gradation.
- Grid Elevation Check
- A series of elevation measurements taken at regular intervals across the project area relative to a fixed reference.
- Fixed Reference
- The single permanent point, established in Chapter 1, from which every elevation and slope measurement is recorded.
- Density Test
- An instrumented measurement of compacted soil or aggregate density compared against a stated pass/fail standard.
Skill Check
- Why must the subgrade acceptance record from Chapter 4 be confirmed before any aggregate is placed?
- What is the difference between loose lift thickness and compacted lift thickness, and why does exceeding the maximum loose lift thickness cause a compaction failure?
- Name three conditions that would cause delivered aggregate to be rejected before placement, and explain why each condition affects the finished base.
- Why is bedding sand not a substitute for correcting a low or high area in the compacted base?
- What must be verified before operating a plate compactor directly next to a foundation or fragile structure?
- Why must elevation and slope be checked on a grid rather than at a few convenient points?
- What is the difference between a visual inspection and a density, proof, or deflection test, and when is each appropriate?
- What must happen before a base that fails a stability check is considered acceptable for Chapter 6?
- Why must the accepted base be protected from traffic and rain before bedding sand is placed?
- Why does every later chapter in this book depend on the base installation record produced in this chapter?
Competency Rubric
| Competency | Independent Pass Standard | Not Demonstrated | With Assistance | Independently |
|---|---|---|---|---|
| HC-025 | Selects base aggregate matching the approved specification's gradation, load, and drainage requirements before placement begins | |||
| HC-026 | Places every lift of aggregate at or below the specified maximum loose lift thickness, recorded on the lift record | |||
| HC-027 | Compacts each lift using the equipment, pattern, overlap, and pass count stated in the manufacturer instructions and specification | |||
| HC-028 | Maintains the specified compacted base thickness at every point on the elevation grid, correcting any deficient area before proceeding | |||
| HC-029 | Verifies final base slope against the approved drainage direction and value within the stated tolerance | |||
| HC-030 | Performs required density, proof, or deflection checks, corrects any failing area, and documents complete base acceptance |
Mark one column per competency. Only Demonstrated Independently awards the competency; Demonstrated with Assistance authorizes additional supervised practice but does not complete the requirement.
Inspection Checklist — Aggregate Base Installation Worksheet
| Record | Finding | Deficiency (if any) | Prerequisite / Corrective Action | Status |
|---|---|---|---|---|
| Subgrade acceptance confirmation | ||||
| Aggregate inspection | ||||
| Lift 1 record | ||||
| Lift 2 record | ||||
| Additional lift record(s) | ||||
| Elevation grid | ||||
| Slope verification | ||||
| Edge extension check | ||||
| Density/proof/deflection check | ||||
| Protection measures |
Base acceptance decision: ______ (Accepted / Conditionally Accepted / Rejected) Conditions or reasons: ____________
Date: ____________ Installer name: ____________ Reinspection date (if applicable): ____________
Performance Check
With the base placed, compacted, and every record on the Aggregate Base Installation Worksheet completed, review the finished base against the Acceptance Standards table and confirm that the subgrade acceptance is on file, delivered aggregate passed inspection, no lift exceeded the maximum loose lift thickness, total compacted thickness and elevation meet the specification at every grid point, slope matches the drainage plan, edge extension is maintained, required stability checks pass the stated standard, and the base is protected from traffic, rain, and contamination. If any item is incomplete or a deficiency remains unresolved, correct it and reinspect the affected area before beginning Chapter 6.
Project Closeout
You have completed the fifth chapter in the hardscaping sequence: installing and compacting a gravel base for pavers. This chapter required you to select compatible base aggregate (HC-025), place gravel in controlled lifts (HC-026), compact the base (HC-027), maintain design thickness (HC-028), verify slope (HC-029), and inspect base stability (HC-030).
You now have a uniform, stable, compacted aggregate base at the approved thickness, slope, elevation, and edge extension. That base carries directly into the next chapter: screeding bedding sand from this base's accepted elevation using screed rails set to the exact bedding thickness the paver installation requires.
Retain the completed Aggregate Base Installation Worksheet, lift records, elevation-grid readings, and stability-check results. You will reference this exact base record throughout the rest of this book, including the Chapter 20 capstone.