Soil is the most important part of the construction work. Siltstone has a high durability when dry and will decrease on wet condition. Cement stabilization chosen to increase durability of siltstone. The specific objective of this study was to investigate the value of slake index (Is) on siltstone due to the drying and wetting cycle. The amount of cement used in this study was 10% using dry and spray mix using method. Two kind of sample was used in this test, sample size of the UCS mold test which broke into fragments and sample size half of triaxial mold test with a weight of 40-60g approximately. The results of this study indicate that the addition of cement can decrease the degradation rate caused by weathering on siltstone. Sample with UCS mold were broken and the spray mixing method obtained higher durability than half triaxial samples and dry mixing method.