Munj fibres (Saccharum munja) and jute are the fibres commonly used in lime construction. There is a difference between munj and jute. Munj is made with dry grass found in wetlands, the same one that they use to make a charpoy, and jute is the one that they make jute bags with.
Munj fibres are used in the plaster mixes after finely chopping them. It gives tensile strength, gives a firm grip to the plaster to hold it together tightly. These fibres prevent cracking, even if it cracks (which is the inherent nature of lime to crack and self-heal), the cracks will be connected by these strands preventing deeper cracks.
Jute rope is placed in horizontal and vertical planes between a thicker layer of floor to make a grid or strips of fibres. After the brickbat is laid, we lay a layer of lime-surkhi above that. Then strips of jute are laid in a grid-like pattern and again covered with a layer of lime-surkhi. This natural way is a simple way of lime reinforcement and works fantastically well. They use and steel and cement concrete we use jute and lime surkhi.