What type of mortar is typically used for interior and restoration applications?

Type O mortar is specifically formulated for interior and restoration applications due to its lower compressive strength, making it suitable for use in non-loadbearing walls and for repair work. This type of mortar is composed of one part cement, two parts lime, and nine parts sand, which allows for better workability and flexibility. Its softer nature means it can accommodate movements and settling in structures without cracking, which is important in restoration work where preservation of existing materials is critical. Additionally, Type O is not typically used in exterior applications or where higher strength is required, which is why it is ideal for specific interior projects.