It is known that paving is a system with multiple layers and the strength of each layer is reflected on the entire pavement. Two kinds of materials are used as the base layer, and the materials are divided into ordinary traditional granular materials and recycled materials such as foundry sand. This paper presents the results of laboratory tests in the laboratory and discusses the effect of each of the materials and foundry sand and its effect as a stabilizer on the strength of the substrate and as a stabilizer. Also, a comparison is made between the changes that occur in the base layer Cast sand treated and compared with untreated. A mixture of foundry sand with graded natural aggregate according to certain sizes is used as a stabilizer in proportions (5, 10 and 15) %. The treated and untreated base layer is compared in terms of strength. The base layer material is a traditional base material taken from the Nabaie quarry. Samples are made of three replicates of each possible group. Samples were prepared and subjected to a compressive strength CBR test. The obtained results indicate an increase in the resistance of the base material when using FS at a rate of (5%) with a treatment period of 4 days, while a ratio of 10% gave the highest resistance in a treatment period of 14 days, and these ratios gave more resistance than the untreated samples without the additive.