Secondary Blasting and Boulder Breaking: Selecting the Safest and Most Economical Method
By Dr.-Ing. Vilem Petr
Petr Explosives Group
Oversized boulders can interrupt road, railroad, highway, excavation, quarry production, trenching, road construction, and material-processing operations. A boulder that cannot be loaded into a haul truck or accepted by a crusher must be reduced to a manageable size. This process is commonly called secondary blasting or secondary boulder breaking.
Available methods include:
- Intact excavation and removal
- Excavator-mounted hydraulic breakers
- Conventional explosives
- Propellant-based cartridges such as NXBURST®
- Expansive demolition grout
- Hydraulic rock splitters
- Diamond saws and wire saws
The method with the lowest purchase price is not necessarily the safest or most economical. A $36 cartridge, a $150 box of grout or a $500 breaker rental does not represent the complete cost of breaking and removing a boulder.
The correct comparison is the total installed cost, including mobilization, drilling, labor, equipment, materials, controls, cleanup, delays and possible rework.
Important cost disclaimer: All dollar amounts in this article are preliminary U.S. planning ranges and illustrative examples—not contractor quotations, guaranteed prices or published NXBURST® prices. Obtain current local quotations before making a project decision.
What Controls the Method Selection?
The assessment should consider:
- Boulder dimensions and estimated volume
- Rock type, strength, abrasiveness and natural fractures
- Required final fragment size
- Number and distribution of boulders
- Accessibility for drilling and heavy equipment
- Proximity to people, buildings, roads and utilities
- Noise, vibration, airblast and flyrock restrictions
- Applicable regulatory requirements
- Availability of qualified and authorized personnel
- Project schedule and production requirements
- Probability of achieving the required result on the first attempt
- Cost of rework, loading, hauling, crushing and disposal
No boulder-breaking method is universally superior. The best method safely provides predictable fragmentation with the lowest expected total cost.
Quick Economic Screening Guide
The following ranges are reasonable only for early planning. Difficult access, exceptionally strong rock, environmental controls, prevailing wages, remote mobilization or multiple unsuccessful attempts can increase costs substantially.
| Method | Illustrative fixed cost | Illustrative installed cost per boulder | Typical economic application |
|---|---|---|---|
| Intact excavation and removal | $0–$1,500 | $250–$2,000 | One or several movable boulders |
| Hydraulic breaker, equipment onsite | $0–$1,000 | $300–$1,200 | Approximately 1–10 accessible boulders |
| Hydraulic breaker, specially mobilized | $1,500–$5,000 | $500–$1,500 | Small project where other methods are restricted |
| Conventional explosives | $5,000–$15,000 | $150–$500 | Approximately 40 or more boulders in a suitable area |
| Propellant cartridges | $500–$4,000 | $150–$700 | Approximately 5–40 boulders or constrained sites |
| Expansive demolition grout | $500–$2,500 | $250–$1,200 | Small, noise-sensitive projects where time is available |
| Hydraulic rock splitter | $1,000–$5,000 | $300–$1,500 | Controlled splitting near sensitive structures |
| Diamond or wire saw | $2,000–$10,000 | $1,000–$5,000+ | Precision work where dimensional control is essential |
These ranges overlap because site conditions often exert greater control over cost than the selected product.
Rule-of-Thumb Recommendation
For preliminary screening:
- First ask whether the boulder can be excavated and removed intact. This can be the safest and least expensive solution.
- For approximately 1–7 accessible boulders, start by evaluating a hydraulic breaker, especially when the excavator is already onsite.
- For approximately 5–10 boulders near sensitive structures, compare propellant cartridges, expansive grout and hydraulic splitting.
- For approximately 8–40 boulders, propellant cartridges may provide a favorable balance of mobilization cost, speed and control.
- For approximately 40 or more boulders, conventional explosives may become more economical if blasting is legally and safely feasible.
- Where noise and vibration must be minimized, expansive grout or hydraulic splitting may be preferable, even if the work takes longer.
- Where the final cut must be precise, use a saw or specialized splitter rather than selecting the lowest-cost production method.
These thresholds are screening rules—not universal design boundaries. Actual break-even quantities must be calculated from project quotations.
1. Intact Excavation and Removal
Before breaking a boulder, determine whether it can be safely excavated, lifted, rolled, buried onsite where permitted, or transported to another location.https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQPe0j4Gru_Eku3CvTihYZiMwhODJIg-98ZnZqaoeikeeONhSXIsGLQPVtR&s=4
Advantages
- No drilling
- No energetic material
- No fragmentation or flyrock
- Potentially rapid when suitable equipment is onsite
- Boulder may have reuse or landscape value
Limitations
- Excavator or crane capacity may control feasibility
- Large boulders may require oversized transportation
- Hauling and disposal can be expensive
- Moving the boulder may disturb surrounding utilities or structures
- The receiving location must be identified
Planning Cost
- Equipment onsite: approximately $250–$750 per boulder
- Special lifting, trucking, or disposal: approximately $750–$2,000+ per boulder
Rule of Thumb
If a boulder can be safely lifted and transported using equipment already onsite, evaluate intact removal before drilling or breaking it.
2. Hydraulic Breakers
An excavator-mounted hydraulic breaker uses repeated mechanical impacts to fracture the boulder. It is usually the first breaking method considered when an excavator and compatible breaker are available.https://www.google.com/url?sa=t&source=web&rct=j&url=https%3A%2F%2Fwww.conquestequipment.net%2Fcompany%2Fblog%2Fhydraulic-rock-breakers%2F&ved=0CBYQjRxqFwoTCJD695_MvJYDFQAAAAAdAAAAABBp&opi=89978449
Advantages
- Simple mobilization when equipment is onsite
- No explosive or propellant cartridges
- Immediate visual control
- Suitable for isolated, accessible boulders
- Work can generally be stopped and restarted easily
Limitations
- Slow in massive, hard or abrasive rock
- Significant fuel consumption
- Breaker-point, excavator and hydraulic-system wear
- High noise near the breaker
- Dust and flying-rock hazards
- Cost increases when productivity is poor
Current rental guides illustrate why equipment size matters. One 2026 guide reports an average excavator rental of approximately $719 per day, with breaker attachments adding roughly $150–$300 per day; delivery, fuel, labor, and damage protection are additional. DOZR 2026 excavator cost guide
Example: Equipment Already Onsite
Assume:
- Breaker attachment: $250 per day
- Operator and excavator allocation: $900 per day
- Fuel and wear: $350 per day
- Cleanup: $200
- Production: 4 boulders per day
Total daily cost:
Cost per boulder:
If production falls to only one boulder per day:
This demonstrates why breaker productivity is the controlling economic variable.
Planning Range
- Productive fractured or weathered rock: approximately $300–$600 per boulder
- Strong massive rock: approximately $600–$1,500+ per boulder
- Special equipment mobilization: add approximately $1,500–$5,000
Rule of Thumb
Use a hydraulic breaker when:
- The equipment is already onsite
- Only a few boulders require treatment
- The rock responds efficiently
- Noise is acceptable
- There is room to position the excavator safely
Change methods when breaker progress becomes slow, tool wear becomes excessive or the machine cannot access the boulder.
3. Conventional Explosives
Properly engineered conventional blasting can rapidly reduce many boulders. The method has high production capacity and becomes more economical as fixed costs are distributed across more units. https://www.google.com/url?sa=t&source=web&rct=j&url=https%3A%2F%2Fbeezaasan.com%2Fslurry-explosives%2F&ved=0CBYQjRxqFwoTCIj0z_zMvJYDFQAAAAAdAAAAABA3&opi=89978449
Advantages
- Rapid fragmentation
- High production capacity
- Effective in large, strong and massive boulders
- Low incremental cost per boulder on large projects
- Suitable for quarries, mines and appropriate remote sites
Limitations
- Requires qualified and authorized personnel
- Subject to storage, transportation, security and use requirements
- May require permits, notifications, records and monitoring
- Can produce flyrock, airblast, vibration, fumes and noise
- May require blast mats and significant exclusion zones
- High fixed cost for only one or two boulders
- Greater public sensitivity near occupied areas
Illustrative Planning Model
Assume:
- Mobilization, planning and compliance: $8,000
- Number of boulders N
- Variable drilling, products, labor and controls: $300 per boulder
| Boulders | Total cost | Average cost per boulder |
| 1 | $8,300 | $8,300 |
| 10 | $11,000 | $1,100 |
| 20 | $14,000 | $700 |
| 40 | $20,000 | $500 |
| 50 | $23,000 | $460 |
| 100 | $38,000 | $380 |
Planning Range
- Fixed mobilization and compliance: approximately $5,000–$15,000
- Incremental cost: approximately $150–$500 per boulder
- Small urban or highly controlled work may exceed these ranges
Rule of Thumb
Conventional explosives normally become economically attractive when:
- Many boulders can be treated during one coordinated operation
- The site permits an appropriate exclusion zone
- Required personnel, storage and controls are already available
- Blasting is part of an existing quarry or mining operation
- The fixed cost can be distributed across approximately 40 or more boulders
Do not select conventional explosives solely because the material cost is low. Mobilization, compliance, and site control costs usually determine the economics of small projects.
4. Propellant-Based Cartridges
Propellant-based cartridges, including systems such as NXBURST®, use rapidly generated gas pressure to fracture confined rock. Their behavior, classification and regulatory treatment must not automatically be assumed to be identical to those of conventional high explosives.
Current manufacturer documentation and all applicable regulations must be reviewed for the specific product, application, and jurisdiction. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSEO17cUEXYbi7UPaXvSlo1qdB6hoQE0u79awYYuOJHbg&s=4
Advantages
- Useful for secondary breaking and controlled splitting
- Lower fixed mobilization cost than many conventional blasting operations
- Suitable where heavy-equipment access is limited
- Faster results than expansive grout
- Can reduce prolonged hydraulic-breaker operation
- Potentially competitive for small and medium-sized projects
Limitations
- Requires drilling and appropriate confinement
- Cartridge and drilling costs apply to every boulder
- Inadequate confinement can reduce performance
- Incorrect application can result in venting, incomplete fragmentation or unsafe conditions
- Product transportation, storage and use requirements must be verified
- Personnel must be appropriately trained and authorized
- Multiple treatments or rework can increase the cost
Cartridge Mass Is Not Price
The manufacturer’s online ordering page does not list a cartridge price. Eligible trained operators or customers must submit an order and receive confirmation. NONEX ordering information
Statements on that United Kingdom page concerning classification and purchasing apply to the manufacturer’s described product and jurisdiction; they are not a legal determination for a different product or U.S. jurisdiction.
Delivered Cartridge Cost
Example only:
- Box price: $1,500
- Shipping: $200
- Tax: $100
- Cartridges per box: 50
The illustrative delivered cost is $36 per cartridge. This is not a published NXBURST® price.
Narrow Direct-Cost Example
Assume:
- One cartridge: $36
- Drilling: $25
- Labor: $30
- Equipment: $20
The resulting $111 is only a narrow direct-cost subtotal. It excludes some or all of the following:
- Mobilization
- Initiation components
- Transportation
- Training and supervision
- Storage and inventory management
- Security and access control
- Monitoring
- Cleanup
- Rework
- Contractor overhead and profit
A planning estimate should not present $111 as a fully installed contractor price. A 120 g cartridge designation describes mass, not cost. The price cannot be determined from the cartridge weight.
Illustrative Installed-Cost Model
For comparison with complete contractor methods, assume:
- Fixed mobilization and project controls: $2,000
- Fully installed variable cost: $450 per boulder
| Boulders | Total cost | Average cost per boulder |
| 1 | $2,450 | $2,450 |
| 5 | $4,250 | $850 |
| 10 | $6,500 | $650 |
| 20 | $11,000 | $550 |
| 40 | $20,000 | $500 |
| 50 | $24,500 | $490 |
| 100 | $47,000 | $470 |
Planning Range
- Fixed project cost: approximately $500–$4,000
- Fully installed cost: approximately $150–$700 per boulder
- Complex drilling, multiple cartridges, difficult access, or rework can exceed $1,000 per boulder
Rule of Thumb
Propellant cartridges are often worth evaluating when:
- There are approximately 5–40 boulders
- Conventional blasting has disproportionate mobilization costs
- Hydraulic breaking would be slow or cause excessive equipment wear
- The project requires faster results than grout can provide
- Heavy equipment cannot readily access the boulder
- Site restrictions can be satisfied by a properly engineered cartridge application
5. Expansive Demolition Grout
Expansive demolition grout is a non-explosive material placed in drilled holes. As it cures, it gradually develops pressure and cracks the rock.https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcT27rd8JuaYpkI029fuarI1qXdle-exHQAYn0byktzZMQ&s=4
Advantages
- Very low noise
- Low vibration
- No explosive initiation system
- Useful near sensitive structures and utilities
- Controlled, gradual cracking
- Relatively low mobilization cost
Limitations
- Frequently requires substantial drilling
- Sensitive to product selection, temperature and field conditions
- Cracking may require many hours or longer
- Production schedules may be uncertain
- Mechanical completion may still be required
- Labor and drilling can exceed the grout material cost
A current retail example lists a 44-pound box of Dexpan at approximately $150. That price covers only the grout material—not drilling, mixing, labor, equipment, cleanup, or mechanical completion. Dexpan 44-pound retail listing
Illustrative Planning Model
Assume:
- Mobilization and setup: $1,000
- Drilling, grout, labor, and completion: $550 per boulder
| Boulders | Total cost | Average cost per boulder |
| 1 | $1,550 | $1,550 |
| 5 | $3,750 | $750 |
| 10 | $6,500 | $650 |
| 20 | $12,000 | $600 |
| 50 | $28,500 | $570 |
Planning Range
- Fixed cost: approximately $500–$2,500
- Installed cost: approximately $250–$1,200 per boulder
- Add downtime when the work controls the project schedule
Rule of Thumb
Use expansive grout when:
- Noise and vibration restrictions are strict
- The project is not schedule-critical
- Drilling access is good
- Only a small or moderate number of boulders requires treatment
- Gradual cracking is acceptable
- Additional mechanical separation can be provided if necessary
6. Hydraulic Rock Splitters
Hydraulic splitters apply controlled mechanical force inside drilled openings to separate rock.https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQ3X6bQxsmGq-DzVqdXJLQyVywnm-InYK4LJtsRmh7A7g&s=4
Advantages
- Low noise relative to impact breaking
- Controlled separation
- Limited disturbance to surrounding material
- Useful near structures and utilities
- Immediate results compared with expansive grout
Limitations
- Requires drilling
- Specialized equipment and operator
- May require repeated repositioning
- Less productive in some massive or poorly oriented rock
- Equipment access and reaction forces must be evaluated
Planning Range
- Fixed mobilization: approximately $1,000–$5,000
- Installed cost: approximately $300–$1,500 per boulder
Rule of Thumb
Evaluate a hydraulic splitter when vibration control is important but waiting for expansive grout is unacceptable.
7. Saw Cutting and Wire Sawing
Diamond saws and wire saws are used where precise dimensional separation is required. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTe10NfxH28XFY4o8TZLDEywn4eXn9VoH79iCHDKIrXog&s=4
Advantages
- High dimensional control
- Limited disturbance to surrounding material
- Appropriate for architectural stone and sensitive construction
- Reduced flyrock and airblast concerns
Limitations
- Specialized equipment and experienced operators
- High mobilization cost
- Slow production for routine boulder reduction
- Water and power may be required
- Blade or wire consumption can be significant
- Access around the boulder may be necessary
Planning Range
- Fixed mobilization: approximately $2,000–$10,000
- Cutting and separation: approximately $1,000–$5,000+ per boulder
Rule of Thumb
Use saw cutting when precision, surface quality, or protection of adjacent material is worth more than production speed.
Comparative Cost Example
For a consistent illustration, use these midpoint planning equations:
| Number of boulders | Hydraulic breaker | Conventional explosives | Propellant cartridges | Expansive grout | Splitter or saw |
| 1 | $1,150 | $8,300 | $2,450 | $1,550 | $3,900 |
| 5 | $3,750 | $9,500 | $4,250 | $3,750 | $7,500 |
| 10 | $7,000 | $11,000 | $6,500 | $6,500 | $12,000 |
| 20 | $13,500 | $14,000 | $11,000 | $12,000 | $21,000 |
| 40 | $26,500 | $20,000 | $20,000 | $23,000 | $39,000 |
| 50 | $33,000 | $23,000 | $24,500 | $28,500 | $48,000 |
| 100 | $65,500 | $38,000 | $47,000 | $56,000 | $93,000 |
These values illustrate a typical pattern, not universal prices:
- Hydraulic breaking is competitive for a few boulders.
- Grout can compete on small projects where time has little economic value.
- Propellant cartridges can become attractive at intermediate quantities.
- Conventional explosives can become least expensive at larger quantities.
- Sawing and specialized splitting are selected primarily for precision or environmental control.
Break-Even Rules From the Illustrative Model
Hydraulic Breaker Versus Propellant Cartridges
Under these illustrative assumptions:
- Hydraulic breaking is less expensive for fewer than approximately 8 boulders.
- Propellant cartridges are less expensive above approximately eight boulders.
Propellant Cartridges Versus Expansive Grout
Under these assumptions:
- Grout is less expensive for fewer than 10 boulders.
- Propellant cartridges are less expensive above approximately ten boulders.
Schedule requirements may move the practical break-even point toward propellant cartridges even at smaller quantities.
Propellant Cartridges Versus Conventional Explosives
Solve for \(N\):
Under these assumptions:
- Propellant cartridges are less expensive below approximately 40 boulders.
- Conventional explosives are less expensive above approximately 40 boulders.
This produces a useful preliminary screening rule:
| Illustrative quantity | Method to evaluate first |
| 1–7 boulders | Hydraulic breaker or intact removal |
| 5–10 boulders near sensitive areas | Grout, splitter or propellant cartridges |
| 8–40 boulders | Propellant cartridges |
| More than approximately 40 boulders | Conventional explosives, if feasible |
Economic Effect of Project Delays
Direct costs alone can lead to the wrong decision. Assume an excavation or quarry operation loses $4,000 for each day that a critical work area remains unavailable.
For 20 boulders:
| Method | Direct cost | Illustrative duration | Downtime cost | Total economic impact |
| Hydraulic breaker | $13,500 | 4 days | $16,000 | $29,500 |
| Conventional explosives | $14,000 | 2 days | $8,000 | $22,000 |
| Propellant cartridges | $11,000 | 2 days | $8,000 | $19,000 |
| Expansive grout | $12,000 | 5 days | $20,000 | $32,000 |
| Specialized splitting | $21,000 | 4 days | $16,000 | $37,000 |
In this example, propellant cartridges provide the lowest total economic impact. Grout has a reasonable direct cost, but the longer schedule makes it more expensive once downtime is factored in.
Probability of Rework
A low first-attempt cost is not economical when unsuccessful breaks are common.
Expected cost should include rework:
Example:
- First attempt: $500
- Estimated rework probability: 30%
- Rework cost: $800
The expected economic cost is $740—not the $500 first-attempt price.
Hidden Costs That Must Be Included
A complete estimate should include:
- Contractor and equipment mobilization
- Drill mobilization and drilling
- Drill bits, steel and consumable wear
- Excavator, breaker and compressor rental
- Fuel, maintenance and equipment depreciation
- Cartridge, explosive, grout or splitter materials
- Initiation components
- Qualified labor and supervision
- Training and familiarization
- Permits, transportation, storage and security
- Engineering and project documentation
- Barricades and access control
- Vibration, airblast or structural monitoring
- Traffic control and production interruptions
- Inspection and re-entry time
- Unsuccessful breaks and additional drilling
- Loading, hauling, crushing and disposal
- Contractor overhead and profit
- Potential claims and schedule delays
Safety and Economic Risk
A method with a lower estimated price can become the most expensive alternative if it causes an injury, equipment damage, regulatory violation, structural claim or extended shutdown.
Each method has hazards:
- Hydraulic breakers create noise, dust, flying chips and equipment hazards.
- Conventional explosives can create flyrock, airblast, vibration, fumes and security concerns.
- Propellant cartridges require correct product selection, confinement and authorized handling.
- Expansive grout can present mixing, temperature, pressure and premature-ejection hazards.
- Hydraulic splitters involve high-pressure equipment.
- Saw-cutting systems involve rotating equipment, electricity, water and blade or wire hazards.
The cost of controlling these hazards is part of the project cost.
Final Method-Selection Matrix
| Project condition | First method to evaluate | Alternative |
| Boulder can be moved intact | Intact excavation and removal | Hydraulic breaker |
| One accessible boulder, breaker onsite | Hydraulic breaker | Grout or propellant cartridge |
| Several boulders in hard rock | Propellant cartridges | Hydraulic breaker |
| Many boulders at an operating quarry | Conventional explosives | Propellant cartridges |
| Sensitive structures nearby | Grout, splitter or engineered propellant system | Saw cutting |
| Very strict noise limitation | Expansive grout | Hydraulic splitter |
| Schedule is critical | Propellant cartridges or conventional explosives | Hydraulic breaker |
| Heavy equipment cannot reach the site | Drilled cartridge, grout or portable splitter | Specialized cutting |
| Precise dimensional separation required | Diamond or wire saw | Hydraulic splitter |
| Highly variable or unknown rock | Trial treatment before full production | Hybrid method |
Final Recommendation
The safest and most economical method must be selected through a site-specific engineering assessment.
As a preliminary rule of thumb:
- Remove the boulder intact when it can be handled safely and economically.
- Use a hydraulic breaker for a few accessible boulders when suitable equipment is on-site.
- Evaluate grout or a hydraulic splitter where noise and vibration restrictions control the project.
- Evaluate propellant cartridges for intermediate quantities, difficult access, or schedule-sensitive controlled breaking.
- Evaluate conventional explosives for large quantities when blasting can be conducted safely, legally, and economically.
- Use diamond or wire sawing when precision is more important than unit production cost.
The 120 g cartridge designation is a mass—not a cost. The cartridge cost must be calculated based on the delivered supplier quotation. A narrow $111 direct-cost calculation should not be represented as a fully installed contractor price.
The final decision must compare:
- Direct breaking cost
- Mobilization and compliance
- Initial cash requirement
- Production rate
- Downtime
- Probability of successful first-pass fragmentation
- Rework and cleanup
- Safety, environmental and liability exposure
The lowest purchase price is not necessarily the lowest project cost. The best value is achieved when the selected method provides safe, predictable fragmentation with the least total economic impact.
All explosive and propellant-based systems must be evaluated and used only by appropriately trained and authorized personnel in accordance with current product documentation and all applicable federal, state and local requirements.
About Petr Explosives Group
Petr Explosives Group provides specialized engineering, consulting and professional education in explosives safety, propellant technology, secondary blasting, quarry operations, drilling and blasting, and high-speed diagnostic methods.
PETS training programs combine engineering fundamentals, regulatory awareness and practical field knowledge to help professionals plan safer, more compliant and more economical operations.
For information about PETS courses, secondary-blasting training or project-specific engineering assistance, contact Petr Explosives Group.
