Rubble masonry

Rubble masonry is a masonry made of natural stones that have an irregular shape, with two approximately parallel surfaces (beds). Natural stones suitable for masonry include limestone, sandstone, shell rock, tuff, granite, as well as cobblestone for the construction of foundations for buildings up to two stories high. Used in construction, rubble stones usually weigh up to 30 kg. Larger stones are pre-split into smaller ones. This process is called skirting. Simultaneously with the plinth, sharp corners of stones are chopped off, the so-called pinning of stones is made, adjusting their shape to a parallelepiped. For plinting stones, a rectangular sledgehammer weighing about 5 kg is used, and for processing stones – a hammer-cam weighing 2.3 kg, with which sharp corners are cleaved (Fig. 1). With the same hammer, rubble stone is upset and split during laying. In addition to the tools shown in fig. 1, the same tools are used in rubble masonry as in brick.

Fig. 1. Tools for rubble masonry.
a – metal rammer; b – hammer-cam.

With rubble laying, it is difficult to achieve such a thorough dressing as with brick laying, since the stones do not have the correct shape and are not the same in size. Therefore, the selection and arrangement of stones in verst rows and in the back of the masonry is done to ensure dressing in such a way that when erecting walls, stones can be laid alternately: either with the long side – with spoons, then with the short side – with a jab. Consequently, in each row of masonry, butt and spoon stones are successively alternated both in versts and in zabutka. In adjacent rows, spoon stones are laid above the butt stones, and bonded stones above the spoon ones. In this way, the dressing of the seams of rubble masonry is provided, which is similar to the chain dressing when laying from bricks. Also, stones are laid out in rows at intersections and in the corners of walls (Fig. 2).

Fig. 2. Bandaging rubble stone masonry.
a – walls; b – crossing walls; в – corners.

When laying, stones are selected and adjusted so as to create, if possible, the same height of a row of masonry within the range from 20 to 25 cm and horizontal seams. At the same time, 2-3 thin stones can be laid in one row of masonry, and some large stones can be included in 2 adjacent rows of masonry. Rubble masonry is performed “under the shoulder blade”, “under the bracket” and “under the bay” (Fig. 3).

Fig. 3. Types of rubble masonry.
a – “under the shoulder blade”; b – under the “bracket”; c – in the formwork; g – surprise.
1 – milestone stones; 2 – solution; 3 – base laid with rubble; 4 – bed stones of the first row.

Laying under the “shoulder blade” is performed in horizontal rows 25 cm thick with the selection and pinning of stones, cleaving (filling) of voids and bandaging the seams. The first bottom row is laid on a prepared base dry from large bedded stones facing down with the bed. In order for the stones to fit snugly to the base, they are upset with a rammer. Then the voids between them are filled with small stones or crushed stone and filled with a liquid solution (with a cone draft of 13-15 cm) until all the voids between the stones are filled. The crushed stone is also compacted by tamping. Further, the laying is carried out in order, observing the dressing, on a plastic solution. The mobility of the masonry mortar should correspond to the immersion of the reference cone by 4-6 cm.

The masonry process is carried out in the following order. Each subsequent row begins with stacking versts. Before the construction of the inner and outer versts at corners, intersections and every 4-5 m on straight sections of the wall, lighthouse stones are laid on a solution. On the lighthouse stones on both sides of the masonry, they pull the moorings, along which, in the process of laying, they check the horizontal row and the straightness of the front surface of the foundations and walls. Stones for verst rows, selected in height, are first laid out dry in order to find the most stable position in the masonry. Then the stone is lifted, a layer of mortar 3-4 cm thick is laid and the stone is finally installed, settling it with a hammer. Having laid down the versts, they begin to fill the zabutka.

The mortar for backing, as for verst rows, is fed with a shovel and spread with an excess so that when laying stones it is squeezed into the vertical seams between the stones. Zaboutka can be made from stones of any size and shape with a tight fit (without swinging) on ​​the bed and with the observance of dressing, alternating pokes with spoons. For a tighter fit, the stones are upset with a rammer or hammer. It is necessary to ensure that the stones do not come into contact with each other without mortar, as this significantly reduces the strength of the masonry. After laying the zabutka, the masonry is cleaved, settling crushed stone and small stones into the solution with weak blows of a hammer. The surface of the laid row of masonry is leveled by adding mortar only to the recesses between the stones. The next rows of masonry are performed in the same sequence.

Masonry “under the bracket” is used in the construction of walls and pillars. This masonry is a kind of “shoulder blade” masonry, and it is made of stones of the same height, selected using a template.

Masonry with a pinned front surface is also a type of masonry “under the shoulder blade”. When performing this masonry, irregularities on the front surface of the stones laid in the outer or inner verst are pre-dug in. With a pin on the front surface, pillars and basement walls are usually laid out.

Laying in the formwork by the “under the blade” method is performed to obtain a smooth surface of both sides of the wall with low-pitched and uneven rubble stone. In this case, the selection of more bedded stones for verst rows and corners need not be done.

Laying “under the bay” is made of torn rubble or cobblestone without the selection of stones and laying out verst rows. Laying “under the bay” is made in the formwork, which is installed in the trenches after the end of earthworks. If the soil is dense, then with a trench depth of up to 1.25 m, it is possible to lay the masonry without formwork with the walls of the trench. The first layer of rubble stone with a height of 20-25 cm is laid on a dry base without mortar, a spar with walls and compacted by tamping. Then fill in all the gaps between the stones with fine stone and rubble. The laid layer is poured with a liquid solution so that all voids are filled. The subsequent laying is carried out in the same way in horizontal rows 20-25 cm high, filling each row of masonry with mortar.

Due to its low strength, rubble masonry “under the bay” is allowed only for foundations of buildings up to 10 m high and only when building on non-subsiding soils.

Masonry with the use of vibration compaction has a strength 25-40% higher than the strength of masonry, made by the “under the blade” method. The stones are laid in the following sequence: 1st row – dry, the voids between the stones are filled with gravel, and then the mortar is spread with a layer of 40-60 cm and the masonry is compacted until the solution ceases to penetrate into the masonry. Then the next row of stone is laid on the solution using the “under the scapula” method, covered with a solution and compacted again. Such masonry is done in a formwork or a bulge with trench walls in dense soils..

Cyclopean masonry is used when you need to create a decorative surface. To do this, rubble masonry is performed in the “under the scapula” method, and specially selected stones are used for the front surface of the masonry, placing them in vertical rows so as to create a pattern of seams between them.

Fig. 4. Cyclopean masonry.

These seams are also made convex (2-4 cm wide) and embroidered. Sometimes, roughly hewn stones are used to lay the corners, laying them in a bandage with the wall masonry. Cyclopean cladding of ordinary rubble masonry with bed stones after the construction of the masonry is also used.