In underground mining, tampings are an inert material packed above the explosive charge in a blast hole to seal the hole, confine explosive energy and improve fragmentation while reducing flyrock, airblast and dust. They are often made from crushed rock, sand, clay or dolomite-based products such as OGM’s graded sinter and bentonite blend.
What is tamping in mining?
Tamping in mining is the process of packing material tightly into a charged blast hole to seal the explosive and control how the energy is released into the rock. The material used is called tamping or stemming material.
What are tampings made of?
Tampings are usually made from inert, non-explosive materials such as:
- Crushed rock or gravel
- Sand or soil
- Clay-based compounds
- Engineered products (like capsules or dolomite–bentonite blends)
OGM Mining Supplies manufactures tampings using crushed and screened metallurgical-grade dolomite (graded sinter) combined with Ecca bentonite clay. The dolomite chips wedge in the hole, while the bentonite seals voids and carries the chips.
Is tamping the same as stemming?
Yes, in most mining and blasting environments “tamping” and “stemming” refer to the same concept: filling the space above an explosive charge in a blast hole with an inert material to confine energy and prevent gases from venting straight out of the hole.
What is the purpose of tampings in underground blasting?
Tampings are used to:
- Contain explosive gases so more energy goes into breaking rock
- Improve fragmentation and reduce oversize rock and sockets
- Reduce flyrock and airblast, improving safety on the face
- Stabilise the collar of the blast hole, helping to prevent blowouts
- Support more predictable, repeatable blasts
How do tampings affect blast performance?
Good tampings increase resistance at the top of the blast hole, forcing energy into the rock where it is needed. This can:
- Reduce air overpressure by more than 90% in some designs
- Improve fragmentation and mucking efficiency
- Reduce fines when the blast is correctly designed
- Improve overall energy efficiency, so explosives work harder on the rock, not the air
Why is low-silica tamping important?
Many mines are increasingly focused on respirable crystalline silica, a known health hazard when inhaled over time.
OGM’s tampings are designed with dolomite-rich, graded sinter and reduced quartz content, following Mintek recommendations. The formulation aims to keep total crystalline silica below 5% by mass, helping:
- Reduce potential silica dust exposure during handling and blasting
- Support compliance with occupational health standards
- Improve long-term worker health protection
How are tampings used in an underground blast hole?
While exact procedures depend on mine standards, a typical sequence looks like:
- Drill the blast hole to the designed depth.
- Load explosives and initiation system.
- Place a suitable plug or start layer (depending on the design).
- Add tampings in measured layers above the charge.
- Compact each layer to eliminate voids and ensure a tight seal.
- Leave the planned free face collar (if required by the design).
OGM’s dolomite–bentonite tampings are designed to flow and compact easily, giving a dense, consistent stemming column.
Are tampings safe for miners and the environment?
Properly designed tamping products are inert and non-explosive. OGM’s tampings:
- Are made from naturally occurring minerals (dolomite and bentonite)
- Are designed to be totally inert in normal use
- Do not release harmful chemicals into surrounding rock or water
- Can be removed from misfired holes using standard on-face tools, water and air, according to site procedures
This supports safe handling, storage and use underground.
How do I choose the right tamping material for my mine?
When choosing tampings or stemming material, mines typically consider:
- Hole diameter and depth
- Rock type and structure (hard rock vs softer seams)
- Explosive type and energy
- Ventilation and dust control requirements
- Health and safety standards, including silica-control policies
- Ease of handling and delivery to the face
OGM Mining Supplies helps underground mines in South Africa and abroad select between its products (e.g. OGM Caps and Kgwahla) and can provide custom blends to suit specific geologies and blast designs.
Who supplies tampings for underground mines in South Africa?
OGM Mining Supplies, based in Vereeniging, is a dedicated manufacturer and distributor of tampings for underground mines across South Africa, offering:
- Locally manufactured, low-silica tamping products
- Customised blends and technical guidance
- Delivery nationwide and selected international supply options
