RANDOM RUBBLE MASONRY

Stone

The stone shall be of the type specified such as granite, trap, limestone, sand stone, quartzite, etc; 'and shall be obtained from the quarries, approved by the Engineer - in -Charge. Stone shall be hard, sound, durable and free from weathering decay and defects like cavities, cracks, flaws, sand holes, injurious veins, patches of loose or soft materials and other similar defects that may adversely affect its strength and appearance. As far as possible stones shall be of uniform colour, quality or texture. Generally stony shall not contain crypst crystalline silica or chart, mica and other deleterious materials like iron-oxide organic impurities etc. Stones with round surface shall not be used. The compressive strength of common types of stones shall be as per table I and the percentage of water absorption shall generally not exceed 5% for stones other than specified in table I. For laterite this percentage is 12%.

Size of stones

Normally stones used should be small enough to be lifted and placed by hand. Unless otherwise indicated, the length of stones for stone masonry shall not exceed three times the height and the breadth or base shall not be greater than three fourth the thickness of wall, or not less than 15cm. The height of stone may be up to 30cm. 

Random Rubble Masonry shall be uncoursed or brought to courses as specified. Uncoursed random rubble masonry shall be constructed with stones of sizes as referred and shapes picked up random from the stones brought from the approved quarry. tones having sharp comers or round surfaces shall, however, not be used. 

Random rubble masonry brought· to the course is similar to uncoursed random rubble masonry except that the courses arc roughly levelled at intervals varying from 30cm to 90cm in height according to the size of stones used.

Dressing

Each stone shall be hammer dressed on the face, the sides and the bed. Hammer dressing shall enable the stones to be laid close to neighbouring stones such that the bushing in the face shall not project more than 40mm on the exposed face and 10mm on the face to be plastered.

Laying

All stones shall be wetted before use. Each stone shall be placed close to the stones already laid so that the thickness of the mortar joints at the face is not more than 20mm. Face stones shall be arranged suitably to stagger the vertical joints and long vertical joints shall be avoided, Stones for hearting or interior filling shall be hammered down with wooden mallet into the position firmly bedded in mortar. Chips or sprawls of stones may be used for Filing of interstices between the adjacent stones in heartening and these shall not exceed 20% of the quantity of stone masonry. To form a bond between successive courses plum stones projecting vertically by about 15 to 20cm shall be firmly embedded in the heart erring at the interval of about one metre in every course. No hollow space shall be left anywhere in the masonry.