This paper aims to recommend a new supplementary preconditioning procedure that can accelerate the degradation process of concrete specimens when exposed to sulfate attack. Several specimens obtained from 30 and 60 MPa (4.4 and 8.7 ksi) strength concretes were tested. Expansion, mass change, and ultrasonic pulse velocity measurements were conducted for specimens subjected to two primary methods of presaturation using sulfate solution and desiccators, then immersed in sulfate solution. A complementary microstructural analysis was also carried out to define the degradation mechanism. When compared to the control method, which had the same immersion conditions without primary presaturation, test results showed an important acceleration of the degradation process with the use of supplementary preconditioning in desiccators. In addition to the remarkable acceleration in the degradation process, the microstructure study confirmed that the degradation mechanism of concrete specimens subjected to supplementary preconditioning by desiccators reflected the field observations in sulfate attack environments.