Coursed Rubble Masonry
Masonry is affected by the use of low grade materials that is in case of stone masonry, use of low grade stones, improperly cut stones, chipped off stones etc. The mortar mix should follow a specific standard for the proper bonding between the joints of Course Rubble Masonry. Therefore, specifications have to be given for the materials used, the laying technique, Bond or Through stones, Quoins and curing – for the ultimate strengthening of the final masonry work.
In our earlier articles, we studied different types of specifications, purpose of specifications, RCC specifications, Specifications for Brick Masonry in Cement Mortar. We will be discussing Specifications for Plain cement concrete in our next articles. In this article, we are going to discuss in detail all the necessary specifications that are to be given for the construction of Coursed Rubble Masonry.
Specifications for Coursed Rubble Stone (CRS) Masonry
Stone shall be hard, sound, free from decay and weathering. Stones with porous matter or with boulder skin shall be rejected. The size of stones shall not be less than 15cm in any direction.
Cement and sand for cement mortar or lime and surkhi for lime mortar shall be of standard specification.
Laying Technique specified
All the stones shall be thoroughly wetted before laying. Every course of stone shall be hammer dressed and laid truly horizontal and every vertical joint shall be truly vertical. Faces shall be accurately squared and each face joint shall be dressed at right angles. The face stones shall be laid in alternate headers and stretchers fashion. The masonry shall shall be carried up regularly and true to plumb. The thickness of joints shall not exceed 12mm.
Bond or through stones
The stones going through in the walls shall be well distributed by arranging them in a staggered fashion in successive courses. The intervals of through stones shall not be less than 1.5m in each course. For walls upto 60cm thickness, a through stone shall extend from one face of the wall to the other.
Laying of Quoins
Corner stones or quoins shall be dressed to correct angle. The short bed of the stone shall be at least equal to height. The quoins shall be laid with header and stretcher in alternate layers.
The work shall be protected from rain or sun while it is green. At the end of the day’s work, the top surface of the walls shall be kept flooded so that it acquires the required strength. The masonry shall be kept moist on all the faces for at least 7 days.