Lime mortar is a substance used to bind together brick or stone. It can also be used to fill gaps in masonry. Lime mortar has been used since earliest times and variations are known from all over the world.
Make lime putty. Lime putty is a preparation of calcium hydroxide, or lime. Start with some lime chalk or small pieces of limestone. Blend these with water to create hydrated lime. Heat the hydrated lime at a temperature of about 1650 degrees Fahrenheit until it turns into a thick paste. Once this consistency is reached, put the lime putty aside to set. Setting normally takes several months. The end product should resemble any other common putty in texture and hardness.
Obtain a quantity of sand or other aggregate. Aggregate is the agent that is added to the lime putty to make the actual mortar. Sand is the most common, but other materials, like gravel, can be used. Sometimes hair was also added to the mix to help bind it together. Mix up the mortar according to the formula of 1 part lime putty to 3 parts aggregate. Powdered brick and volcanic materials can be added to the mixture to try to create something similar to Portland cement. Portland cement is hydraulic, meaning it can set under water. Common lime mortar is non-hydraulic.
Lay the mortar by spreading it on top of and in between blocks of masonry. This can be bricks, stones, or concrete blocks. Mortar takes time to dry. As it dries, the calcium hydroxide reacts with the air to produce calcium carbonate. Calcium carbonate is actually the same as limestone, the substance from which the lime putty was originally made. The material created is thus a hard bond or joint between the pieces of masonry. The longer the lime mortar takes to dry, the stronger it will be.
To obtain a faster drying mortar, use hydrated lime in your mixture. This means heating the calcium hydroxide together with whatever impurities were found in the original lime chalk. Usually this means bits of clay. Hydraulic lime reacts with water to form crystal. These crystals create a partial hardening effect that will be speed the overall setting of the lime mortar.