The structural mortars used in the construction of stone houses during the 13th to 17th centuries in Riga are examined, and their chemical composition, hygroscopic properties, porosity, etc., are tabulated along with the analytical methods of investigation. These houses were primarily of the three following architectural styles: 13th-14th century Pomansky style; 14th-16th century Gothic style; and 17th century manor and barrack style. Local dolomitic and imported magnesium limes were used for the houses of the 13th-16th centuries. In the 17th century, calcium lime, gypsum, and gypsum-lime cementing materials were included. The lime in all cases was hydraulic. The quality of structural mortars improved with time and the average lime-sand ratio varied from 1:3.1 in the 13th-14th centuries to 1:1.9 in the 15th-16th centuries and to 1:1.1 in the 17th century. -- AATA