A kind of repair mortar for geotechnical building was prepared with lime and metakaolin as major materials. Two kinds of water-repellent admixtures (tung oil and calcium stearate) were used to improve the water resistance of the mortars. Different properties of the mortars were evaluated， such as strength, the process of reaction, water absorption, softening coefficient and shrinkage. Phase and microstructure analysis of the mortars were carried out through XRD and SEM. The results show that tung oil and calcium stearate can improve water resistance of the mortars significantly. Water absorption of the mortars with tung oil or calcium stearate can be below 2.5%.Tung oil and calcium stearate hinder the pozzolanic reaction of metakaolin, which as a result decrease the mortars’ strength. But 28 d compressive strength of the mortars are all above 5 MPa. Also, tung oil and calcium stearate can regulate the growth of products and affect the micromorphology and structure of mortars. Tung oil make the particle size smaller and the structure more compact, while calcium stearate leads to a looser structure. Considering both the mortar strength and water resistance, the optimum dosage of tung oil and calcium stearate was 5% and 1.5% respectively.