Module 6 - Stone Work: Construction & Materials - Iii (Rar - 302) Section B: Building Construction Technology
Module 6 - Stone Work: Construction & Materials - Iii (Rar - 302) Section B: Building Construction Technology
Module 6 - Stone Work: Construction & Materials - Iii (Rar - 302) Section B: Building Construction Technology
DEFINITION :
The craft of shaping rock into accurate
geometric shapes, mostly simple but
some are considerably complex and
then arranging the resulting stones,
often together with mortar.
Masonry means construction of
buildings using building blocks like
stone, bricks, concrete blocks etc.
Masonry is used for the construction
of foundation, plinth, walls and
columns.
Mortar is the building material for the
building blocks.
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HISTORY
Stonemasonry is one of the earliest trades in civilization's
history. During the time of the Neolithic revolution and
domestication of animals, people learned how to use fire
to create quicklime, plasters, and mortars. They used these
to fashion homes for themselves with mud, straw, or
stone, and masonry was born.
Gateway of India
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CLASSIFICATION OF ROCKS
A) MACHINE DRESSING
B) HAND DRESSING
C) QUARRY DRESSING
D) ELABORATE DRESSING
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DRESSING OF STONES – MACHINE DRESSING
This consists of a circular steel blade, one size being 1.5 in diameter and 6 mm thick.
Some 240 diamonds are secured in small U-shaped sockets round the edge of the blade.
The slab of stone is clamped on to a moving table which is caused to travel towards the
blade at a uniform rate; at the same time the blade rotates at a speed which varies from
500 to 600 revs, per min.
The cutting rate of the machine depends upon its power and the hardness of the stone.
Thus, a 15 kw machine will cut from 645 to 1000 cm2 of Portland stone per minute.
Whilst this rate is considerably faster than that of the frame saw, the circular saw can only
deal effectively with stones which are less than 1 m thick.
Only limestones or soft sandstones should be cut by means of the diamond saw, hard
sandstones cause an excessive wearing action on the sockets and blade.
This has a 50 mm wide continuous rim of carborundum which is dovetailed round the
periphery of the steel blade.
Its cutting rate is half that of the diamond saw. It is preferred to the diamond saw on
account of the more accurate work which it produces, and it is therefore very suitable for
the jointing (forming the ends) of cornices and similar stones which have been moulded.
Cuts as fine as 6 mm are obtainable.
Water is supplied during the cutting operation in order to cool the blade of each of the
above two circular saws. Some circular saws have two blades.
Another type consists of a blade which traverses the fixed stone as it rotates, and it is
therefore particularly useful for cutting long stones.
The above operations are usually all that are necessary for the cutting and dressing of
stones for walling, but it is sometimes required to have the surface of each stone which
will be exposed when fixed, rubbed so as to remove the machine marks.
This is accomplished on a machine called a rubbing bed.
This consists of a steel circular table, about 3 in diameter, which rotates.
The stone is placed on the bed, clamped from above, and as the table rotates, the
abrasive action of carborundum, sand and water eliminates the machine marks.
A large block of stone is split into smaller units as shown at B, in Fig. Straight lines are
marked on three of the faces along which a narrow groove is chiselled by means of the
punch (6, in Fig.) or wide chisel called a nicker.
Shallow holes at 150 to 225 mm centres are formed along the groove, a steel bar is
placed under the stone in the same plane as the groove, steel wedges or gads or wedges
and feathers are placed in the holes, and the wedges are gradually and uniformly
hammered in until the stone splits.
Large blocks of hard sandstone are divided at the quarry as described but the work is
expedited by using a pneumatic drill to form 100 to 150 mm deep holes to receive the
wedges.
SNAPPING
This is adopted for splitting hard stones which are about 150 mm thick. In splitting a block
of stone, a groove is formed on all four sides and in the same plane.
The pitching tool (1, in Fig.) is held vertically and struck smartly as it is moved along the
groove on each face. A piece of waste stone is placed under the block and a few blows of
a heavy hammer on the latter (which is protected by a piece of wood) will be sufficient to
snap the stone.
Alternatively, a continuous nick is formed across the top and both sides, the block is
turned over on to a small stone and split with a smart blow from a heavy hammer.
Bath or similar stone is best divided into units by sawing immediately after it has been
quarried, as it then contains moisture (quarry sap) which renders it comparatively soft.
A true face is worked on the stone as follows and as shown at D, in Fig. The marginal draft E is first
formed by the mason using a drafting chisel (22, in Fig.) and wood mallet (24) or electric hammer and
chisel to remove the superfluous stone to a level slightly below that of the deepest hollow on the
rough face.
The draft must be level as tested by a straight-edge, although an experienced mason can dispense
with this. A similar parallel draft is formed at F in the same plane as E in order that the face shall be "
out of winding or twist. " This is tested by placing straight-edges on the drafts and sighting through as
indicated by broken lines at J.
Drafts G and H are then formed and the whole of the superfluous stone between them removed by
means of the pitching tool (1), punch (6) or point (9). After continuous furrows have been formed
across the face with the point or punch, the ridges may be removed by the chisel claw (20) and
mallet; the chisel is worked parallel to the furrows, the teeth preventing the formation of holes.
Diagonal drafts (K), in addition to the marginal drafts, are necessary for working a true face on a large
stone. The adjacent surfaces may be dressed in a similar manner, the square (26) being used to
ensure that the adjacent surfaces are square and also for marking any necessary lines.
The terms plain work or plain face are applied to the labour on a stone to form a true face. Half plain
work describes a similar but rougher dressing, such as is only necessary for beds and joints.
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DRESSING OF STONES – HAND DRESSING
SURFACE FINISHES
The finishes which may be given to the face (exposed surface) of a stone are many and
varied, but those applied to the beds (upper and lower surfaces), joints (ends) and back
of the stone are more limited, as the essential requirements are reasonably smooth and
square surfaces.
The finish varies with the stone and the class of work for which it is required.
Thus, for rubble work of the random rubble, uncoursed class (see in Fig.), very little
labour is expended, whereas certain other finishes are both elaborate and costly. Stone
which is roughly shaped and dressed is known as quarry-dressed.
HAMMER-DRESSED
Also known as hammer-faced, quarry-faced, quarry-pitched and rustic-faced, its appearance somewhat
resembles that shown at L, in Fig. The face is roughly shaped by means of the mash hammer (27, in Fig.)
used to remove the larger raised portions of stone and shape it. The blocks are sometimes squared, the
beds and joints being dressed back some 75 or 100 mm from the face. This is done by using the square
to mark the boundaries and working the pitching tool along them. This enables the stones to be fitted
more closely together to give reasonably uniform thick joints.
STRAIGHT-CUT
This is applied to the faces of small blocks of stone used for squared rubble and regular coursed rubble.
The larger blocks are split at right angles to the natural bed into smaller blocks and it is this split surface
which provides the face, the slightly uneven texture being very effective. These small blocks are quickly
squared by applying the mash hammer along the edges, followed by the punch.
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DRESSING OF STONES – ELABORATE DRESSING
The following are some of the finishes which are worked by hand on squared stones: Boasted, punched, picked, tooled,
furrowed, rock-faced, scabbled, combed, vermiculated and reticulated.
DRAGGED OR COMBED
This finish is given to soft limestones, such as Bath stone, by the application of drags (23). These drags are second steel
plates (about 2.5 mm thick) having serrated edges, and graded into “coarse”, “second” and “fine”, according to the
number of teeth per 25 mm. After the surface of the stone has been brought to the required level means of the dummy
(the head of which is made of zinc or pewter and is shown at 25) soft stone chisel (19), the coarse drag is dragged
backwards and forwards in different ions across the surface until the tool marks have been eliminated; this is followed
by the second drag and finally by the fine drag until all scratches have disappeared.
A few of the many tools used by the mason have been referred pages and illustrated in Fig.
Chisels are struck cither with the mallet (24) - which is made of hardwood such as beech
or hickory - or the hammer.
The striking ends of mallet-headed chisels are broader (see 5, 9 and 13 than those which
are hammer-headed (e.g., 1 and 6) to prevent damaging the mallet.
Cutting tools which have to withstand heavy impacts are usually made entirely of cast
steel, others used for the dressing of soft stones may have wood handles (19) and these are
struck with the dummy (25) which has a zinc or pewter head.
a) Random Rubble
Uncoursed.
Built to courses.
b) Squared Rubble
Uncoursed.
Built to courses.
Regular coursed.
c) Miscellaneous
Polygonal walling.
Flint walling.
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Lake District masonry.
RANDOM RUBBLE
The stones are those which have been quarry dressed. Unlike bricks, the stones are be
exercised in arranging that they shall adequately distribute the pressure over the maximum
area and in the avoidance of long continuous vertical joints.
The bond should be sound both transversely (across the thickness of the wall) and
longitudinally. Transverse bond is obtained by the liberal use of headers (or bonders) and
throughs.
Headers are stones which reach beyond the middle of the wall from each face to overlap in
the centre (sometimes called dog's bond). Through stones or throughs extend the full
thickness of the wall (as shown in the figure).
Satisfactory stability may reasonably be assured if one-quarter of the face consists of headers
(approximately two per square metre), in addition to one—eighth Of the face area of
throughs (one per square metre).
The footings should consist of concrete (see section CC at A, in figure) or, in the case of
garden walls, large flat-bedded stones twice the thickness of the wall in width (as in elevation
at A, in figure).
This is the roughest and cheapest form of stone walling and consists of stones which are usually
quarried near, if not on, the building site. The face appearance varies considerably on account of the
great difference in the sizes and shapes of material used.
The “waller” takes the stone, more or less at random, from the heap and builds them in to form the
strongest bond, any inconvenient corners or excrescences being knocked off the stones if such will
assist in this operation. The larger stones are flat-bedded and packed or wedged up with small pieces
of stone or spalls; the intervening spaces are then filled in with the smaller stones, no attempt being
made to form vertical joints.
The joints are well filled and flushed with mortar; these are sometimes of considerable width on face,
being as much as 50 mm or more in places. A reduction in the quantity of mortar results if small pieces
of stone are driven into the mortar at the face joints; are these splinters may also be used to wedge up
the stones; such joints are said to be galleted.
The larger stones are selected for the quoins and jambs to give increased strength and, incidentally, to
improve the appearance.
Boundary walls constructed of this class are usually given a slight batter on both faces, as shown, to
give additional stability.
It is common to build dwarf walls, such as garden or field boundary walls or fences, of common rubble
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RANDOM RUBBLE
This walling is similar to the above, excepting that the work is roughly levelled up to form
courses varying from 300 to 450 mm thick. These courses usually coincide with the varying
heights of the quoin and jamb stones.
In the construction of the wall, the quoins are built first, the line is stretched level with the
tops of the quoin stones, and the intervening walling is brought up to this level.
One of the courses is shown numbered in the order in which the stones would be bedded.
The stones are set in mortar and at every course the work is well flushed with mortar and
pressed into the internal joints.
This forms a stronger wall than the uncoursed type (long continuous vertical joints being
more readily avoided), although the somewhat regular horizontal joints at the courses
detract from its appearance.
Provided the site and stone are satisfactory, one course of through stones at E (equal to
twice the thickness of the wall) is a sufficient foundation for boundary walls, otherwise a
double course (E and F) would be required as shown in the section.
The stone used is generally one which is found in quarries In thin beds, or in
thicker beds of laminated stone which can be easily split into smaller units.
Little labour is necessary to form comparatively straight bed and side joints: the
stones are usually squared and brought to a hammer dressed or straight-cut
finish although they may be given either tooled or dragged surface finishes.
Figure shows a gable wall (i.e., an end wall which is continued up to and
sometimes above the roof line and the upper portion of which conforms with the
shape of the roof) of a building which may be constructed in any one of the three
types of squared rubble.
A portion of the wall is drawn to a larger scale in Figure 1 and details of three
varieties arc shown. The stones forming the window may be given a smoother
finish than that of the general walling so as to form a contrast.
This is often known as Square-Snecked Rubble. The stones are available in various
sizes and are arranged on face in several irregular patterns.
A very effective appearance results if the walling comprises a series of combined
units consisting of four stones, i.e., a large stone called a riser or jumper
(generally a bonder or through stone), two thinner stones known as levellers and
a small stone called a sneck or check
The snecks are characteristic of this class of wall (hence the name) and their
object is to prevent the occurrence of long continuous vertical joints.
As shown on plan, the side joints of the face stones arc only dressed square for
about 75 mm from the face which is usually only quarry-dressed (sec p. 38).
Another form of snecked rubble is shown at F, Fig. 1.
The stones are similar to those used for snecked rubble, but, like
the random rubble built to courses class, the work is levelled up to
courses of varying depth.
The squared face stones may be arranged as shown at B, in random
rubble, or each course may consist of quoins, jamb stones, bonders
and throughs of the same height, with smaller stones built in
between them up to the height of these larger stones, to complete
the course.
This latter arrangement is sometimes known as Coursed Header
Work and is shown at G, Fig. 1.
The walling is constructed in a manner which is unique and much skill is demanded of the
wallers. As shown in the sections, the wall in effect consist of three portions, i.e., inner and
outer faces with an intermediate c' hearting." Particular attention is drawn to the through
stones which are tilted downwards towards the external face.
This is known as " watershot," and the amount of watershot is 50 to 64 mm per 300 mm
thickness of wall. Thus if the watershot is 50 mm, the back edge of the bed in a 600 mm
thick wall will be about 100 mm above the corresponding front edge. The remaining face
stones are given a similar watershot.
The top bed of stone window. and door heads and the bottom bed of window sills are
watershot. The damp proof course consists of two courses of slates in cement mortar. The
quoins are of limestone or slate, the characteristic colour and rich texture of the stone give
a delightful appearance to this class of work.
Solid walls vary in thickness from 525 to 750 mm. Alternatively, a 320 mm thick cavity wall
having a 160 mm slate outer leaf, 70 mm and 90 mm concrete brick inner leaf can be
made.
In this type ashlar masonry, each stone is cut to uniform size and shape with
all sides rectangular, so that the stone gives perfectly horizontal and vertical
joints with adjoining stone. This type of ashlar masonry is very costly.
In this type of masonry, the face work is provided with rough tooled or
hammer dresses stones and backing of the wall may be made in rubble
masonry or brick masonry. This is combinati on of ashlar masonry
and rubble/Brick masonry.
The following are some of various joints which are used in masonry:
FIGURE 2
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MASORY JOINTS
RUSTICATED JOINTS
Plinths, lower storeys of buildings, and quoins are
sometimes emphasized by the use of blocks of stone
which have their margins or edges sunk below the
general face. The term “rusticated” is applied to such
masonry. That at L and M (in figure 2) shows a channelled
or rectangular joint and is often adopted (at ‘B’ in figure
3). Note that the sinking is on the lower stone; if the bed
joint was at the bottom of the channel, water would
lodge on the bottom and perhaps penetrate into the
mortar joint. The Vee-Joint at N and O (in figure 2) is
formed when stones having chamfered edges arc placed
in position. A more elaborate form of vee-joint is shown
at P and O (in figure 2), and is known as a vee and
channelled joint.
SADDLE JOINTS
A saddle joint is shown at A, C, Q and M in figure 3. It is
formed by rounding off the stone from the top bed to the
weathering at each end; this prevents rain from lodging
on top of the joint. The saddle is rendered inconspicuous
by bevelling it backwards from the front edge as shown.
FIGURE 3
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MASORY JOINTS
JOGGLES, DOWELS AND CRAMPS
In order to prevent movement and displacement of certain stones the ordinary mortar
joints between them have to be supplemented and strengthened by various means.
additional strength is obtained by the employment of joggles, dowels and cramps.
JOGGLED JOINT
The mortar joggled joint is adopted for the end joints of ashlar, especially when the
blocks have a small bed, and for cornice stones. The grooves down which the grout
formed by the means of a hammer and punch.
DOWELLED JOINT
Stones which are liable to become displaced are prevented from doing so by the
introduction of dowels at the joints (see G in fig 2). Dowels are either of slate or
gunmetal (an alloy of copper and tin) which are from 25 to 50 mm square in section
and two or three times the thickness in length. They are set in cement mortar. A
horizontal dowel in an end joint is usually run in with grout (through a vertical hole
prepared for the purpose) after it has been inserted and the adjacent stone fixed. (see
R in fig. 2)
CRAMPED JOINTS
The joints between stones which are liable to be pulled apart in the direction of their
length are reinforced with either metal or slate cramps.
Details of a metal cramped joint are shown at M, Fig. 2. The cramp is a piece of non-
corrosive metal such as gunmetal, which is from 25 to 50 mm, 6 to 13 mm thick and
225 to 450 mm with long ends which are turned down from 20 to 40 mm. The cramp
must be fitted in tightly, after which it is and covered with either cement or asphalt. A
slate cramped or keyed joint, consisting of a double dovetailed piece of slate set in
cement, is shown at S, Fig. 2.
FIGURE 2
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MORTAR JOINTING
The thickness of the mortar joints varies considerably, thus for ashlar the joints may be as fine as mm whereas those in random
rubble work may exceed 50 mm width on face. Certain of the joints used for brickwork, are also suitable for stonework, e.g. flush
joints are used for ashlar and the keyed or vee-joint may be adopted for thicker joints. The mason joint is also used for wide
joints.
This may be of the three forms shown at U, V and W, Fig. 2. The two former are sometimes used for rubble work, and that at W
is frequently adopted for pointing. These projecting joints should be of cement mortar if the character of the stone will permit it.
As mentioned, the beds of ashlar blocks should be square with the face. hand-dressed, there is a tendency for the mason to
work hollow beds when very fine ashlar joints are required. This may cause the edges to spall off when the stone is fixed owing
to the pressure not being distributed over the whole area of the bed but concentrated at the edges. A portion of a hollow bed is
shown at X, Fig. 2, where the bed surface of the upper stone only is concave. The shaded triangular portion is likely to be
splintered off, especially if joint is not completely filled with mortar. There is little likelihood of the beds being worked hollow
when the stone is sawn by machinery.
The mortar specified for jointing masonry depends a good deal upon the character of the stone. Mortar joints for ashlar should
be as inconspicuous as possible, and it is often necessary to experiment with various composition of mortar until the desired
colour (which should conform with that of the stone) is obtained.
That used for walling built of sandstone is sometimes composed of 1-part Portland cement and 4 parts sand, and occasionally a
little lime is added.
The mortar recommended for certain limestones, e.g. Portland stone, consists of 1-part Portland cement, 2 1/2 parts lime putty
(well slaked mixed with water to a consistency of a paste) and 3 1/2 parts stone dust (powder obtained by the crushing of waste
pieces of the limestone). Neat cement should never be used for grouting Portland stone blocks, as this may cause staining of the
face of the work; only liquid mortar of the above composition should be used this purpose.
Rubble walling (especially if of sandstone) should be built with cement mortar composed of 1 part of cement to 4 parts sand, as
the strength of the work depends very largely upon that of the mortar.
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LIFTING APPLIANCES
Blocks of dressed stone which are too large to be lifted
by hand are raised by means of a crane or other hoisting
apparatus and lowered gently into the correct position
in the wall. Various appliances, such as Chain Dogs and
Lewises, are used for this purpose as shown in the
figure.
CHAIN DOGS
Dogs in various sizes are made of steel and shaped
as shown at C. The stone to be lifted has a hole
(about 20 mm deep) punched in the centre of each
end and hooked from 75 to 100 mm down.
A steel chain shown is passed through the ring of
each dog and is hooked on to the chain from the
crane (as shown at D) and the points of the dog are
placed in the holes of the stone. When the chain
from the crane is wound up taut, the dogs bite into
the stone, which is hoisted and lowered to the
required position.
Chain dogs grip the stone very securely and are
particularly suited for lifting heavy stones and long
stones with narrow beds.