Stemming plugs for better blast containment: Varistem


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




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