•Realizes the value-added reuse of waste sandstone resources.•Micron quartz grains <150 µm can improve compressive strength and ASR property.•Provides a convenient method in testing ASR.•S-sand produced from sandstone by-product can be used as high-quality fine aggregate. The construction industry is facing a shortage issue of river sand, therefore broadening new sources of fine aggregate is imminent. This paper demonstrates the feasibility of a recycled sand from sandstone waste in mortar manufacturing by comprehensive assessment of workability, mechanical properties, water absorption, alkali silica reaction (ASR). The recycled sandstone sand (S-sand) has a smoother microscopic morphology and better particle size distribution than river sand (R-sand). Fine particles smaller than 150 µm in R-sand usually contain a large amount of impurities (such as clay) and are considered harmful. However, the S-sand containing ∼15.7% µm quartz grains <150 µm significantly improves the mortar performance in terms of compressive strength and ASR property. At the same water to binder ratio, the mortar using the S-sand shows worse workability than that using R-sand but a slight increase of water to binder ratio or adding water reducer improves not only the workability but also mechanical properties. For the ASR test, the S-sand shows potential uncertain risk as per ASTM C 1260. Using calcined clay or fly ash to replace 25% cement can effectively inhibit expansion risk. The compressive strength is reduced due to ASR, however, as the ASR progresses, it is somehow restored. This study also finds the good linear relationship between length change of mortar bar and mass change, which can be used to predict the sand ASR property. The results showed that S-sand produced by waste sandstone by-products can be used as high-quality fine aggregate.