Stemmings plugs to quarries and mines in Africa


Stemming is one of the major effective parameters of open pit blasting. “Stemming plugs” are the new technological development on the increase of blasting efficiency without changing the feature of explosives. They are used in the stemming zone of the blast hole to increase the containment of the explosive gasses.

The drilling and blasting operations in open pit mining and quarrying are two important cost elements, which must be considered to reduce with new technological developments. Beside of the cost of blasting, another important effect of blasting to be considered is the fragmentation of blasted rock. It has a very big influence both on the performance of loading equipment and on the cost of primary crushing if the blasted pile is a raw material of a consecutive process.

VARISTEM is a manufacturer of blasting stemming plugs based in Pune. Globally, blasting stemming plugs have been a runaway success. Recently, the firm introduced the product to the Indian market.  

Advantages of using peri-stem blasting plugs in mining. Among the advantages of using VARISTEM’s peris-stem blasting stemming plugs are: Safety. VARISTEM ensures there is minimum to no flying rocks and air blasts. The plugs also allow consistent stemming heights with gas emulsions, saving in explosives with air decking.

In addition to eco friendly blasting and reduced blasted vibrations, VARISTEM’s increase in drilling patterns enables savings against expensive drilling costs. The improved blast fragmentation also leads to improved loading efficiency and reduced secondary breakage/mechanical breakage costs

Peri-Stem Blast Improvement / Blast Control Plugs are quickly becoming one of the most widely used and accepted stemming plugs in the industry. First introduced in 2011, they are now being used across the mining industry all over the world. These plugs enable management to explore new ways in cost reductions in both Drilling & Blasting arena, on a sustainable basis

Peri-Stem Plugs work by wedging the stemming material between the drill hole wall and VARISTEM plug. Upon detonation of the explosives, the plug is forced upward into the stemming material and locks. When the plug “locks,” the explosive gases and energy are prevented from venting through the drill hole, and instead are contained within the rock mass for milliseconds (ms) longer than non-plugged blasts.

Blasting is the first step in the aggregate and mining production process and the results happen in milliseconds! If you can make the rock smaller during the first step of the process, all other processes and phases will benefit.

With peristem, you get increased fragmentation and fracturing and cap rock breakage. This is while reducing fly rock and preventing contamination of Explosive Column Charge at the surface by avoiding direct contact of the Stemming material with the Explosive charge, thus resulting in better utilization of virgin and expensive explosive column charge

The peristem will not only ensure a reduction in air blast, stemming ejection, dust and noise, but also in oversized rock and Drilling and Explosive Charge by expanding Drilling patterns viz. Spacing and Burden

VARISTEM plugs are used in open cast limestone mines, underground and open cast coal mines, open cast granite, basalt stone quarry and iron ore mines. They are also used in construction and infrastructure projects like roads, railways, airports, canals, irrigation projects, building basement and hard rock excavation.

Following initial blast fracturing, the VARISTEM working with standard stemming materials, contains expanding gases to greatly improve blast fragmentation, providing major downstream savings. It is important to remember that blast containment is the key to mine savings, including crusher time, truck movement, ANFO or gas emulsions, and labor.

The University of Mines & Technology Ghana”, as well as the “Department of Mining Prince of Songkla University in Thailand” have independently studied fragmentation improvements using the VARISTEM STEMMING PLUGS, showing primary crusher output improved. In Thailand at the Mae Moh lignite mine, blasting vibration, shovel and crusher performance were specifically studied. Truck loading rates shovel was found to increase by 22.6%. Overburden crushing rate was increased by 37%, even though not run at full load. And vibration was reduced 37% to 63%, all confirming better blast containment. In Ghana, a gold operation saved 13% primary crusher time over a full year study. The complete studies can be read at

In studies, comparing standard rock stemming to stemming using the VARISTEM, it has been shown that following the blast, the time of stemming movement with standard stemming was 2.3miliseconds, while the VARISTEM held for 5.3miliseconds. And, with the movement, the stemming velocity of basic stemming was 481 meters per second, while the VARISTEM slowed the velocity to 280 meters per second. This confirms that the VARISTEM held the expanding gases, allowing the gas to move into the blast fractures and not up the drill hole. Most mines find an average reduction of 27% in fragmentation size. This containment also means that one can shorten stemming heights, allowing for better cap rock breakage.

One limestone operation in Canada found that using the VARISTEM in air decking they could reduce noise/vibration levels, and also achieve a reduction in explosive costs of approximately 12%. This is achieved using the VARISTEM in air decking, allowing shorter stemming heights, plus a reduction in explosives. Field studies confirm that air decking of 20% is possible without noticeable loss of blast fragmentation. And, if gas emulsions are used, this air decking allows inconsistent gas emulsion heights, while still achieving consistent stemming heights.

TH VARISTEM gear design allows for compression in varied drill holes, while also preventing any damage to the detonating cord. The durability of the VARISTEM resists the blast force/heat sufficiently long enough to accomplish its job of containment. While mainly destroyed during the blasting, its low cost allows single use blasting.

The full web site, showing all studies and videos, can be found at . The company will gladly work with any mine, providing sufficient samples to confirm their claims. They do ask that in evaluation of this product that a full study be made, as simply looking at a muck pile is not reliable. When studying crusher output, the proof of its value will be confirmed. There are distributors in various regions of the world, although presently in Africa, the VARISTEM would be supplied from the USA. The savings at the quarry will easily offset the low cost of this product. The supplier is searching for a working distributor to cover Africa.

Note, this firm also supplies a self fusing silicone tape used extensively in underground mining to keep electrical and communication connections free of dust and water. This pure silicone tape will stretch around any connection, bonding only to itself. So, if one wants to remove the tape, it is easily done without leaving any messy adhesive. Samples of this product can also be provided. The web site is


Please enter your comment!
Please enter your name here
Captcha verification failed!
CAPTCHA user score failed. Please contact us!