Besides other lignocellulose waste resulting from agriculture, spent mushroom substrate is a major concern due to the high amount of waste, usually improper disposed. Also, sand-based mortars require the use of this non-renewable and exhaustive aggregate and problems of environment protection arise. The study aims to analyze the possibilities of sand replacement in mortars composition with grounded substrate. The ratio between cement and sand in the studied compositions was 1:1, 1:2, and 1:4. The hardened mortars are analyzed in terms of colorimetric changes, density decrease, mechanical strength, hydrophobic properties, and freeze-frost resistance. Thus, medium-light mortars for applications that requires moderate strengths, with ecological implications results when up to 15% of sand is replaced with spent mushroom substrate. The results can be used for a deepen research, considering also a detailed life cycle assessment of the waste and, secondly, combining the replacement material with other waste types.