Rammed earth (RE) materials with low greenhouse gas emissions have been developed as replacements for conventional construction materials. In this series, we examine the strength development, durability and sustainability, via life cycle assessment, of these new materials. In this paper, we present findings for material durability with and without the addition of the water repellent admixture, Tech-Dry ‘Plasticure’. Understanding of durability properties is essential to verify the suitability of the RE materials for building. The study assessed four distinct RE materials, all based on a substrate of crushed limestone: a control mix, cement-stabilised RE (the industry standard in Western Australia) and three alternative stabilisers, i) alkali-, ii) lime-, and iii) self-activated RE. The alternative RE stabilisers incorporated industrial by-products fly ash, ground granulated blast furnace slag and silica fume, in combination with sodium hydroxide, hydrated lime or no activator (respectively, by mix). Durability was assessed using initial rate of absorption, immersion and wire brush testing. Both with and without Plasticure, all materials either passed these tests or, where pass/fail criteria were unavailable, were found to be comparable to conventional building materials. Scanning electron microscopy and energy dispersive spectroscopy showed that greater maturity in terms of reaction of raw materials was associated with lower absorption. Those materials with Plasticure had lower initial rate of absorption than those without, especially in the case of lime- and self-activated RE. Plasticure was shown to improve durability properties of all tested RE mixes.