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Why was moisture a problem for early ammonium nitrate explosives?

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coal miner loading a drill hole with an explosive — explosive A coal miner loading a drill hole with a water gel explosive called Tovex.

Moisture was a significant problem for early ammonium nitrate explosives because the substance is highly hygroscopic, meaning it absorbs moisture from the environment too readily. This tendency to pick up water hindered the development of effective nongelatinous mixtures during the late 19th century.1

Because ammonium nitrate is also highly soluble in water, its exposure to moisture could compromise the stability and performance of the explosive product. To address this, early solutions included coating the ammonium nitrate with substances like paraffin to repel water. Modern methods for achieving water resistance include the use of water repellents, such as calcium stearate, or ingredients that form a protective gel on the surface of the explosive to slow water penetration.12