[1] These surveyors also surveyed and marked the boundary between
Maryland and Delaware.
MASON CITY, a city and the county-seat of Cerro Gordo county, Iowa,
U.S.A., on Lime Creek, in the northern part of the state. Pop. (1905,
state census), 8357 (929 foreign-born); (1910) 11,230. It is served by
the Chicago Milwaukee & St Paul, the Chicago & North-Western, the
Chicago Great Western, the Iowa Central and the St Paul & Des Moines
railways, and also by the Mason City & Clear Lake (electric) railway,
which connects Mason City with Clear Lake, a pleasure resort, 10 m. west
of the city. At Mason City is Memorial University (co-educational;
founded in 1900 by the National Encampment of the Sons of Veterans, and
opened in 1902), dedicated to the Grand Army of the Republic, the
special aim of which is to teach American history. The city is situated
in a good agricultural region, and there are valuable stone quarries in
the vicinity. The manufactures include lime, Portland cement, brick and
tile. Mason City was settled in 1853, laid out in 1855, incorporated as
a town in 1870 and chartered as a city in 1881.
MASONRY,[1] the art of building in stone. The earliest remains (apart
from the primitive work in rude stone--see STONE MONUMENTS; ARCHAEOLOGY,
&c.) are those of the ancient temples of India and Egypt. Many of these
early works were constructed of stones of huge size, and it still
remains a mystery how the ancients were able to quarry and raise to a
considerable height above the ground blocks seven or eight hundred tons
in weight. Many of the early buildings of the middle ages were entirely
constructed of masses of concrete, often faced with a species of rough
cast. The early masonry seems to have been for the most part worked with
the axe and not with the chisel. A very excellent example of the
contrast between the earlier and later Norman masonry may be seen in the
choir of Canterbury Cathedral. In those times the groining was
frequently filled in with a light tufa stone, said by some to have been
brought from Italy, but more probably from the Rhine. The Normans
imported a great quantity of stone from Caen, it being easily worked,
and particularly fit for carving. The freestones of England were also
much used; and in the first Pointed period, Purbeck and Bethersden
marbles were employed for column shafts, &c. The methods of working and
setting stone were much the same as at present, except that owing to
difficulties of conveyance the stones were used in much smaller sizes.
As time went on the art of masonry advanced till in England, in point of
execution, it at length rivalled that of any country.
_Tools._--The mason's tools may be grouped under five heads--hammers
and mallets, saws, chisels, setting-out and setting tools, and
hoisting appliances.
Hammers and Mallets.
There are several different kinds of iron hammers used by the stone
worker; the mash hammer has a short handle and heavy head for use with
chisels; the iron hammer, used in carving, in shape resembles a
carpenter's mallet but is smaller; the waller's hammer is used for
roughly shaping stones in rubble work; the spalling hammer for roughly
dressing stones in the quarry; the scabbling-hammer, for the same
purpose, has one end pointed for use on hard stone; the pick has a
long head pointed at both ends, weighs from 14 to 20 lb., and is used
for rough dressing and splitting; the axe has a double wedge-shaped
head and is used to bring stones to a fairly level face preparatory to
their being worked smooth; the patent axe, or patent hammer, is formed
with a number of plates with sharpened edges bolted together to form a
head; the mallet of hard wood is used for the finishing chisel work
and carving; and the dummy is of similar shape but smaller.
Saws.
A hand saw similar to that used by the carpenter is used for cutting
small soft stones. Larger blocks are cut with the two-handed saw
worked by two men. For the largest blocks the frame saw is used, and
is slung by a rope and pulleys fitted with balance weights to relieve
the operator of its weight. The blade is of plain steel, the cutting
action being supplied by sand with water as a lubricant constantly
applied.
Chisels.
There are perhaps even more varieties of chisels than of hammers. The
point and the punch have very small cutting edges, a quarter of an
inch or less in width. The former is used on the harder and the latter
on the softer varieties of stone after the rough hammer dressing. The
pitching tool has a wide thick edge and is used in rough dressing.
Jumpers are shafts of steel having a widened edge, and are used for
boring holes in hard stone. Chisels are made with edges from a
quarter-inch to one and a half inches wide; those that exceed this
width are termed boasters. The claw chisel has a number of teeth from
one-eighth to three-eighths wide, and is used on the surface of hard
stones after the point has been used. The drag is a semi-circular
steel plate, the straight edge having teeth cut on it. It is used to
level down the surfaces of soft stones. Cockscombs are used for the
same purpose on mouldings and are shaped to various curves. Wedges of
various sizes are used in splitting stones and are inserted either in
holes made with the jumper or in chases cut with the stone-pick.
Setting-out and Setting Tools.
The implements for setting out the work are similar to those used, by
the bricklayer and other tradesmen, comprising the rule, square, set
square, the bevel capable of being set to any required angle,
compasses, spirit level, plumb-rule and bob and mortar trowels. Gauges
and moulds are required in sinking moulds to the proper section.
[Illustration: FIG. 1.--(½ in. = 1 ft.) FIG. 2.--(1 in. = 1 ft.)]
Hoisting Appliances.
The _nippers_ (fig. 1), or _scissors_, as they are sometimes termed,
have two hooked arms fitting into notches in the opposite sides of the
block to be lifted. These arms are riveted together in the same way as
a pair of scissors, the upper ends having rings attached for the
insertion of a rope or chain which when pulled tight in the operation
of lifting causes the hooked ends to grip the stone. _Lewises_ (fig.
2.) are wedge-shaped pieces of steel which are fitted into a
dovetailed mortise in the stone to be hoisted. They are also used for
setting blocks too large to be set by hand, and are made in several
forms. These are the usual methods of securing the stone to the
hoisting rope or chain, the hoisting being effected by a pulley and
fall, by a crane, or by other means.
_Scaffolding._--For rubble walls single scaffolds, resting partly on
the walls, similar to those used for brickwork (q.v.), are employed;
for ashlar and other gauged stonework (see below) self-supporting
scaffolds are used with a second set of standards and ledgers erected
close to the wall, the whole standing entirely independent. The reason
for the use of this double scaffold is that otherwise holes for the
putlogs to rest in would have to be left in the wall, and obviously in
an ashlar stone wall it would be impossible properly to make these
good on the removal of the scaffold (see further SCAFFOLD).
_Seasoning Stone._--Stone freshly quarried is full of sap, and thus
admits of being easily worked. On being exposed to the air the sap
dries out, and the stone becomes much harder in consequence. For this
reason, and because carriage charges are lessened by the smaller bulk
of the worked stone as compared with the rough block, the stone for a
building is often specified to be quarry-worked. Vitruvius recommended
that stone should be quarried in summer when driest, and that it
should be seasoned by being allowed to lie two years before being
used, so as to allow the natural sap to evaporate. In the erection of
St Paul's Cathedral, Sir Christopher Wren required that the stone
after being quarried should be exposed for three years on the
sea-beach before its introduction into the building.
The regular and determined form of bricks makes it to a large extent a
matter of practice to enable a man to become a good bricklayer, but
beyond these a continual exercise of judgment is required of the
workman in stone, who has for the most part to deal with masses of all
forms and of all sizes.
_Setting Stones._--All beds and joints should be truly worked and
perfectly level. If the surface be convex it will give rise to wide
unsightly joints; if concave the weight thrown on the stone will rest
on the edges and probably cause them to "flush" or break off and
disfigure the work. Large stones are placed in position with the aid
of hoisting appliances and should be tried in position before being
finally set. Great care should be taken to avoid fracturing or
chipping the stone in the process of handling, as it is impossible to
make good such damage. All stratified stones--and this includes by far
the largest proportion of building stones--when set in a level
position should be laid on their natural bed, i.e. with their laminae
horizontal. The greatest strength of a stone is obtained when the
laminae lie at right angles to the pressure placed upon it. In the
case of arches these layers should be parallel with the centre line of
the voussoirs and at right angles to the face of the arch. For
cornices (except the corner-stones) and work of a like nature, the
stone is set with the laminae on edge and perpendicular to the face of
the work. With many stones it is easy to determine the bed by
moistening with water, when the laminae will become apparent. Some
stones, however, it is impossible to read in this way, and it is
therefore advisable to have them marked in the quarry. A horizontal
line in a quarry does not in all cases give the proper bed of the
stone, for since the deposits were made ages ago natural upheavals
have possibly occurred to alter the "lie" of the material.
For the shafts of columns especially it is necessary to have the
layers horizontally placed, and a stone should be selected from a
quarry with a bed of the required depth. An example of the omission of
this precaution is visible in the arcading of the Royal Courts of
Justice, London, where the small shafts of the front arcade in red
sandstone have been turned with the laminae in a vertical position,
with the result that nearly every shaft is flaking away or is cracked.
_Use of Mortar._--See BRICKWORK. Of whatever quality the stone may be
of which a wall is built, it should consist as much of stone and as
little of mortar as possible. Only fine mortar is admissible if we are
to obtain as thin joints as possible. The joints should be well raked
out and pointed in Portland cement mortar. This applies only to some
sandstones, as marbles and many limestones are stained by the use of
Portland cement. For these a special cement must be employed, composed
of plaster of Paris, lime, and marble or stone-dust.
_Bonding._--Bond (see BRICKWORK) is of not less importance in stone
walling than in brickwork. In ashlar-work the work is bonded
uniformly, the joints being kept perpendicularly one over the other;
but in rubble-work, instead of making the joints recur one over the
other in alternate courses they should be carefully made to lock, so
as to give the strength of two or three courses or layers between a
joint in one course and the joint that next occurs vertically above it
in another course. In the through or transverse bonding of a wall a
good proportion of header stones running about two-thirds of the
distance through the width of the wall should be provided to bind the
whole structure together. The use of through stones, i.e. stones
running through the whole thickness of the wall from front to back, is
not to be recommended. Such stones are liable to fracture and convey
damp to the internal face.
_Slip Joints._--As with brickwork so in masonry great care must be
exercised to prevent the different parts of a building settling
unequally. When two portions of a building differing considerably in
height come together, it is usual to employ a slip or housed joint
instead of bonding the walls into each other. This arrangement allows
the heavier work to settle to a greater extent than the low portion
without causing any defect in the stones.
_Footings._--The footings of stone walls should consist of large
stones of even thickness proportionate to their length; if possible
they should be the full breadth in one piece. Each course should be
well bedded and levelled.
_Walling._--There are broadly speaking two classes of stone walling:
rubble and ashlar. Rubble walls are built of stones more or less
irregular in shape and size and coarsely jointed. Ashlar walls are
constructed of carefully worked blocks of regular dimensions and set
with fine joints.
[Illustration: FIG. 3.--(¼ in. = 1 ft.)]
_Random Rubble_ (fig. 3) is the roughest form of stonework. It is
built with irregular pieces of stone usually less than 9 in. thick,
loosely packed without much regard to courses, the interstices between
the large stones being occupied by small ones, the remaining crevices
filled up with mortar. Bond stones or headers should be used
frequently in every course. This form of walling is much used in stone
districts for boundary walls and is often set dry without mortar. For
this work the mason uses no tool but the trowel to lay on the mortar,
the scabbling hammer to break off the most repulsive irregularities
from the stone, and the plumb-rule to keep his work perpendicular.
[Illustration: FIG. 4.--(¼ in. = 1 ft.)]
_Coursed Rubble_ (fig. 4) is levelled up in courses 12 or 18 in. deep,
the depth varying in different courses according to the sizes of the
stones. The stones are dressed by the workman before he begins
building, to obtain a fairly level bed and perpendicular face.
_Irregularly Coursed Squared Rubble_ is a development of uncoursed
random rubble, the stones in this case being squared with the hammer
and roughly faced up with the axe. The courses jump abruptly from one
level to another as the sizes of the blocks demand; the interstices
are filled in with small pieces of stone called "snecks."
For _Coursed Squared Rubble_ the stone is faced in a similar manner
and set in courses, the depth of each course being made up of one or
more stones.
In _Regular Coursed Rubble_ all the stones in one course are of the
same height.
_Block-in-course_ is the name applied to a form of stone walling that
has some of the characteristics of ashlar but the execution of which
is much rougher. The courses are usually less than 12 in. high. It is
much used by engineers for waterside and railway work where a good
appearance is desired.
The _Angles_ or _Quoins_ of rubble-work are always carefully and
precisely worked and serve as a gauge for the rest of the walling.
Frequently the quoins and jambs are executed in ashlar, which gives a
neat and finished appearance and adds strength to the work.
The name _Ashlar_ is given, without regard to the finish of the face
of the stone, to walling composed of stones carefully dressed, from 12
to 18 in. deep, the mortar joints being about an eighth of an inch or
less in thickness. No stone except the hardest should exceed in length
three times its depth when required to resist a heavy load and its
breadth should be from one and a half to three times its depth. The
hardest stone may have a length equal to four or perhaps five times
its depth and a width three times its depth. The face of ashlar-work
may be plain and level, or have rebated, chamfered, or moulded joints.
Backing to Stonework.
The great cost of this form of stonework renders the employment of a
backing of an inferior nature very general. This backing varies
according to the district in which the building operations are being
carried on, being rubble stonework in stone districts and brick or
concrete elsewhere, the whole being thoroughly tied together both
transversely and longitudinally with bondstones. In England a stone
much used for backing ashlar and Kentish rag rubble-work is a soft
sandstone called "hassock." In the districts where it is quarried it
is much cheaper than brickwork. (For brickbacking see BRICKWORK.)
Ashlar facing usually varies from 4 to 9 in. in thickness. The work
must not be all of one thickness, but should vary in order that
effective bond with the backing may be obtained. If the work is in
courses of uneven depth the narrow courses are made of the greater
thickness and the deep courses are narrow. It is sometimes necessary
to secure the stone facing back with iron ties, but this should be
avoided wherever possible, as they are liable to rust and split the
stonework. When it is necessary to use them they should be covered
with some protective coating. The use of a backing to a stone wall,
besides lessening the cost, gives a more equable temperature inside
the building and prevents the transmission of wet by capillary
attraction to the interior, which would take place if single stones
were used for the entire thickness.
All work of this description must be executed in Portland cement,
mortar of good strength, to avoid as much as possible the unequal
settlement of the deep courses of stone facing and the narrower
courses of the brick or rough stone backing. If the backing is of
brick it should never be less than 9 in. thick, and whether of stone
or brick it should be levelled up in courses of the same thickness as
the ashlar.
Walling.
There are many different sorts of walling, or modes of structure,
arising from the nature of the materials available in various
localities. That is perhaps of most frequent occurrence in which
either squared, broken, or round flints are used. This, when executed
with care, has a distinctly decorative appearance. To give stability
to the structure, lacing courses of tiles, bricks or dressed stones
are introduced, and brick or stone piers are built at intervals, thus
forming a flint panelled wall. The quoins, too, in this type of wall
are formed in dressed stone or brick work.
Uncoursed rubble built with irregular blocks of ragstone, an
unstratified rock quarried in Kent, is in great favour for facing the
external walls of churches and similar works (fig. 5).
[Illustration: FIG. 5.--(¼ in. = 1 ft.)]
_Pointing._--As with brickwork this is generally done when the work is
completed and before the scaffolding is removed. Suitable weather
should be chosen, for if the weather be either frosty or too hot the
pointing will suffer. The joints are raked out to a depth of half an
inch or more, well wetted, and then refilled with a fine mortar
composed specially to resist the action of the weather. This is
finished flat or compressed with a special tool to a shaped joint, the
usual forms of which are shown in fig. 6.
[Illustration: FIG. 6.--(¾ full size).]
_Stonewash._--To give a uniform appearance to the stonework and
preserve the finished face until a hardened skin has formed, it is
usual to coat the surface of exposed masonry with a protective
compound of ordinary limewhite with a little size mixed in it, or a
special mixture of stone-dust, lime, salt, whiting and size with a
little ochre to tone it down. After six months or more the work is
cleaned down with water and stiff bristle or wire brushes. Sometimes
muriatic acid much diluted with water is used.
_Technical Terms._--Of the following technical terms, many will be
found embodied in the drawing of a gable wall (fig. 7), which shows
the manner and position in which many different members are used.
_Apex Stone._--The topmost stone of a gable forming a finial for the
two sloping sides; it is sometimes termed a "saddle" (fig. 7).
[Illustration: FIG. 7.--(Scale--approximately ½ in. = 1 ft.)]
_Blocking Course,_ a heavy course of stone above a cornice to form a
parapet and weigh down the back of the cornice (fig. 8).
[Illustration: FIG. 8.--(½ in. = 1 ft.)]
_Bed._--The _bed_ surface upon which a stone is set or bedded should
be worked truly level in every part. Many workmen to form a neat thin
joint with a minimum amount of labour hollow the bed and thus when the
stone is set all weight is thrown upon the edges with the frequent
result that these are crushed.
_Coping._--The _coping_ or _capping_ stones are placed on the top of
walls not covered by a roof, spanning their entire width and throwing
off the rain and snow, thus keeping the interior of the wall dry. The
fewer the number of joints the better the security, and for this
reason it is well to form copings with as long stones as possible. To
throw water off clear, and prevent it from running down the face of
the wall, the coping should project an inch or two on each side and
have a throat worked on the under-side of the projections (fig. 7).
_Cornice,_ a projecting course of moulded stone crowning a structure,
forming a cap or finish and serving to throw any wet clear of the
walls. A deep drip should always be worked in the upper members of a
cornice to prevent the rain trickling down and disfiguring the face of
the moulding and the wall below (fig. 8).
_Corbel,_ a stone built into a wall and projecting to form a
cantilever, supporting a load beyond the face of the wall. It is
frequently richly ornamented by carving (fig. 7).
_Skew Corbel,_ a stone placed at the base of the sloping side of a
gable wall to resist any sliding tendency of the sloping coping.
Stones placed for a similar purpose at intervals along the sloping
side, tailing into the wall, are termed "kneelers" and have the
section of the coping worked upon them (fig. 7).
_Corbel Table,_ a lino of small corbels placed at short distances
apart supporting a parapet or arcade. This forms an ornamental feature
which was much employed in early Gothic times. It probably originates
from the machicolations of ancient fortresses.
_Dressings,_ the finished stones of window and door jambs and quoins.
For example, a "brick building with stone dressings" would have brick
walls with stone door and window jambs, heads and sills, and perhaps
also stone quoins (fig. 7).
_Diaper,_ a square pattern formed on the face of the stonework by
means of stones of different colours and varieties or by patterns
carved on the surface (fig. 7).
_Finial,_ a finishing ornament applied usually to a gable end (fig.
7).
_Gablet,_ small gable-shaped carved panels frequently used in Gothic
stonework for apex stones, and in spires, &c.
_Gargoyle,_ a detail, not often met with in modern work, which
consists of a waterspout projecting so as to throw the rain-water from
the gutters clear of the walls. In early work it was often carved into
grotesque shapes of animal and other forms.
_Galleting._--The joints of rubble are sometimes enriched by having
small pebbles or chips of flint pressed into the mortar whilst green.
The joints are then said to be "galleted."
_Jamb._--Window and door jambs should always be of dressed stone, both
on account of the extra strength thus gained and in order to give a
finish to the work. The stones are laid alternately as stretchers and
headers; the former are called outbands, the latter inbands (fig. 7).
_Label Moulding,_ a projecting course of stone running round an arch.
When not very large it is sometimes cut on the voussoirs, but is
usually made a separate course of stone. Often, and especially in the
case of door openings, a small sinking is worked on the top surface of
the moulding to form a gutter which leads to the sides any water that
trickles down the face of the wall.
_Lacing Stone._--This is placed as a voussoir in brick arches of wide
span, and serves to bond or lace several courses together (see
BRICKWORK).
_Lacing Course,_ a course of dressed stone, bricks or tiles, run at
intervals in a wall of rubble or flint masonry to impart strength and
tie the whole together (fig. 7).
_Long and Short Work,_ a typical Saxon method of arranging quoin
stones, flat slabs and long narrow vertical stones being placed
alternately. Earls Barton church in Northamptonshire is an example of
their use in old work. In modern work long and short work, sometimes
termed "block and start," is little used (fig. 7).
_Parapet,_ a fence wall at the top of a wall at the eaves of the roof.
The gutter lies behind, and waterways are formed through the parapet
wall for the escape of the rain-water.
_Plinth,_ a projecting base to a wall serving to give an appearance of
stability to the work.
_Quoin,_ the angle at the junction of two walls. Quoins are often
executed in dressed stone (fig. 7).
_Rag-bolt,_ the end of an iron bolt when required to be let into stone
is roughed or ragged. A dovetailed mortise is prepared in the stone
and the ragged end of the bolt placed in this, and the mortise filled
in with molten lead or sand and sulphur (fig. 9).
[Illustration: FIG. 9.--(1 in. = 1 ft.)]
_Sill,_ the stone which forms a finish to the wall at the bottom of an
opening. Sills should always be weathered, slightly in the case of
door sills, more sharply for windows, and throated on the under side
to throw off the wet. The weathering is not carried through the whole
length of the sill, but a stool is left on at each end to form a
square end for building in (fig. 7).
_String Courses,_ horizontal bands of stone, either projecting beyond
or flush with the face of the wall and often moulded or carved. They
are frequently continuations of the sills or head lines of windows
(figs. 5 and 7).
_Scontion._--In a thick wall the dressed stones forming the inside
angles of the jamb of a window or door opening are termed scontions.
_Spalls,_ small pieces chipped off whilst working a stone.
_Templates,_ slabs of hard stone set in a wall to take the ends of a
beam or girder so as to distribute the load over a larger area of the
wall.
_Tympanum,_ the triangular filling of masonry in a pediment between
the cornices, or between the horizontal head of a window or door and
the under-side of the relieving arch above it. It is often panelled or
enriched with carved ornament (fig. 7).
_Throat,_ a groove worked on the under-side of projecting external
members to intercept rain-water and cause it to drop off the member
clear of the work beneath (fig. 8).
_Weathering._--The surface of an exposed stone is weathered when it is
worked to a slope so as to throw off the water. Cornices, copings,
sills and string courses should all be so weathered.
_Voussoirs,_ the wedge-shaped blocks of which an arch is built up.
_Methods of finishing Face of Stones._--The _self face_ or _quarry
face_ is the natural surface formed when the stone is detached from
the mass in the quarry or when a stone is split.
_Saw-face,_ the surface formed by sawing.
_Hammer-dressed, Rock-faced, or Pitch-faced._--This face is used for
ashlar-work, usually with a chisel-draughted margin around each block.
It gives a very massive and solid appearance to the lower storeys of
masonry buildings, and is formed with little labour, and is therefore
the cheapest face to adopt for ashlar-work (fig. 7).
_Broached and Pointed Work._--This face is also generally used with a
chisel-draughted margin. The stone as left from the scabbling hammer
at the quarry has its rocky face worked down to an approximate level
by the point. In broached work the grooves made by the tool are
continuous, often running obliquely across the face of the block. In
pointed work the lines are not continuous; the surface is rough or
fine pointed according as the point is used over every inch or
half-inch of the stone. The point is used more upon hard stones than
soft ones (fig. 7).
_Tooth-chiselled Work._--The cheapest method of dressing soft stones
is by the toothed chisel which gives a surface very much like the
pointed work of hard stones.
_Droved Work._--This surface is obtained with a chisel about two and a
half inches wide, no attempt being made to keep the cuts in continuous
lines.
_Tooled Work_ is somewhat similar to droved work and is done with a
flat chisel, the edge of which is about four inches wide, care being
taken to make the cuts in continuous lines across the width of the
stone.
_Combed or Dragged Work._--For soft stones the steel comb or drag is
often employed to remove all irregularities from the face and thus
form a fine surface. These tools are specially useful for moulded
work, as they are formed to fit a variety of curves.
_Rubbed Work._--For this finish the surface of the stone is previously
brought with the chisel to a level and approximately smooth face, and
then the surface is rubbed until it is quite smooth with a piece of
grit stone aided by fine sand and water as a lubricant. Marbles are
polished by being rubbed with gritstone, then with pumice, and lastly
with emery powder.
Besides these, the most usual methods of finishing the faces of
stonework, there are several kinds of surface formed with hammers or
axes of various descriptions. These types of hammers are more used on
the continent of Europe and in America perhaps than in England, but
they deserve notice here.
The _toothed axe_ has its edges divided into teeth, fine or coarse
according to the work to be done. It is used to reduce the face of
limestones and sandstones to a condition ready for the chisel. The
_bush hammer_ has a heavy square-shaped double-faced head, upon which
are cut projecting pyramidal points. It is used to form a surface full
of little holes, and with it the face of sand and limestones may be
brought to a somewhat ornamental finish. The _patent hammer_ is used
on granite and other hard rocks, which have been first dressed to a
medium surface with the point. The fineness of the result is
determined by the number of blades in the hammer, and the work is said
to be "six," "eight" or "ten-cut" work according to the number of
blades inserted or bolted in the hammer head. The _crandall_ has an
iron handle slotted at one end with a hole 3/8 in. wide and 3 in.
long. In this slot are fixed by a key ten or eleven double-headed
points of ¼ in. square steel about 9 in. long. It is used for
finishing sandstone and soft stones after the surface has been
levelled down with the axe or chisel. It gives a fine pebbly sparkling
appearance.
There are several methods of finishing stone which involve a great
deal of labour and are therefore expensive to work, but which result
in imparting a very stiff and unnatural appearance to the masonry.
_Vermiculated Work._--This is formed by carving a number of curling
worm-like lines over the face of the block, sinking in between the
worms to a depth of a fourth of an inch. The surface of the strings is
worked smooth, and the sinkings are pock-marked with a pointed tool
(fig. 7).
_Furrowed Work._--In this face the stone is cut with a chisel into a
number of small parallel grooves or furrows (fig. 7).
_Reticulated Face_ is a finish somewhat similar to vermiculated work,
but the divisions are more nearly squares.
_Face Joints of Ashlar._--The face joints of ashlar stonework are
often sunk or rebated to form what are termed rusticated joints;
sometimes the angles of each block are moulded or chamfered to give
relief to the surface or to show a massive effect (fig. 7).
_Joints in Stonework._--The joints between one block of stone and
another are formed in many ways by cramps, dowels and joggles of
various descriptions.
[Illustration: FIG. 10.--(1 in. = 1 ft.)]
Cramps.
The stones of copings, cornices and works of a similar nature, are
often tied together with metal cramps to check any tendency for the
stones to separate under the force of the wind (figs. 10 and 11).
Cramps are made of iron (plain or galvanized), copper or gun-metal, of
varying sections and lengths to suit the work. A typical cramp would
be about 9 in. long, 1 or 1½ in. wide, and from ¼ to ½ in. thick, and
turned down about 1½ in. at each end. A dovetailed mortise is formed
at a suitable point in each of the stones to be joined and connected
by a chase. The cramp is placed in this channel with its turned-down
ends in the mortises, and it is then fixed with molten lead, sulphur
and sand, or Portland cement. Lead shrinks on cooling, and if used at
all should be well caulked when cold. Double dovetailed slate cramps
bedded in Portland cement are occasionally used (fig. 11).
[Illustration: FIG. 11.--(¾ in. = 1 ft.)]
Dowels.
Dowels are used for connecting stones where the use of cramps would be
impracticable, as in the joints of window mullions, the shafts of
small columns, and in similar works (figs. 7, 8 and 20). Dowels for
bed and side joints may be used. They are of slate, metal, or
sometimes of hard wood.
[Illustration: FIG. 12.--(½ in. = 1 ft.)]
Joggles.
There are many ways of making a joggle joint. The joggle may be worked
on one of the stones so as to fit into a groove in the adjoining
stone, or grooves may be cut in both the stones and an independent
joggle of slate, pebbles, or Portland cement fitted, the joggle being
really a kind of dowel. The pebble joggle joint is formed with the aid
of pebbles as small dowels fitted into mortises in the jointing faces
of two stones and set with Portland cement; but joggles of slate have
generally taken the place of pebbles. Portland cement joggles are
formed by pouring cement grout into a vertical or oblique mortise
formed by cutting a groove in each of the joining surfaces of the
stones. What is known as a he-and-she joggle, worked on the edges of
the stones themselves, is shown in fig. 13.
[Illustration: FIG. 13.--(½ in. = 1 ft.)]
Plugs or dowels of lead are formed by pouring molten lead through a
channel into dovetailed mortises in each stone (figs. 14 and 15). When
cold the metal is caulked to compress it tightly into the holes.
[Illustration: FIG. 14.--(¾ in. = 1 ft.)]
[Illustration: FIG. 15.--(1 in. = 1 ft.)]
The saddle joint is used for cornices, and is formed when a portion of
the stone next the joint is left raised so as to guide rain-water away
from the joint (fig. 8).
Two forms of rebated joints for stone copings and roofs are common. In
one form (shown in fig. 7) the stones forming the coping are thicker
at their lower and rebated edge than at the top plain edge, giving a
stepped surface. The other form has a level surface and the stone is
of the same thickness throughout and worked to a rebate on top and
bottom edges. In laying stone roofs the joints are usually lapped over
with an upper slab of stone.
_Joints in Spires._--Four forms of jointing for the battering
stonework of spires are shown in fig. 16. A is a plain horizontal
joint. B is a similar joint formed at right angles to the face of the
work. This is the most economical form of joint, the stone being cut
with its sides square with each other; but if the mortar in the joint
decay moisture is allowed to penetrate. With these forms dowelling is
frequently necessary for greater stability. The joints C and D are
more elaborate and much more expensive on account of the extra labour
involved in working and fitting.
[Illustration: FIG. 16.--(½ in. = 1 ft.)]
Where a concentrated weight is carried by piers or columns the bed
joints are in many cases formed without the use of mortar, a thin
sheet of milled lead being placed between the blocks of stone to fill
up any slight inequalities.
_Moulded Work._--The working of mouldings in stone is an important
part of the mason's craft, and forms a costly item in the erection of
a stone structure. Much skill and care is required to retain the
arrises sharp and the curved members of accurate and proportionate
outline. As in the case of wood mouldings, machinery now plays an
important part in the preparation of stone moulded work. The process
of working a stone by hand labour is as follows: The profile of the
moulding is marked on to a zinc template on opposite ends of the stone
to be worked; a short portion, an inch or two in length termed a
"draught," is at each end worked to the required section. The
remaining portion is then proceeded with, the craftsman continually
checking the accuracy of his work with a straight-edge and zinc
templates. A stone to be moulded by machinery is fixed to a moving
table placed under a shaped tool which is fixed in an immovable
portion of the machine, and is so adjusted as to cut or chip off a
small layer of stone. Each time the stone passes under the cutter it
is automatically moved a trifle nearer, and thus it gradually reduces
the stone until the required shape is attained.
[Illustration: FIG. 17.--(1 in. = 1 ft.)]
_Iron in Stonework._--The use of iron dowels or cramps in stonework,
unless entirely and permanently protected from oxidation is attended
by the gravest risks; for upon the expansion of the iron by rusting
the stone may split, and perhaps bring about a more or less serious
failure in that portion of the building. A case in point is that of
the church of St Mary-le-Strand, London, where the ashlar facing was
secured to the backing with iron cramps; these were inefficiently
protected from damp, with the result that many of the blocks have been
split in consequence of rusting. John Smeaton in his Eddystone
Lighthouse used dowels of Purbeck marble.
[Illustration: FIG. 18.--(½ in. = 1 ft.)]
_Stone Arches._--Stone arches are very frequently used both in stone
and brick buildings. (For general definitions and terms see
BRICKWORK.) They may be built in a great variety of styles, either
flat, segmental, circular, elliptical or pointed. Each block or
voussoir should be cut to fit exactly in its appointed place, the
joints being made as fine as possible. The joints should radiate from
the centre from which the soffit or intrados is struck, or in the case
of an elliptical arch they should be at right angles to a tangent
drawn to the intrados at that point. The extrados or back of the arch
is usually concentric with the intrados, but is sometimes made thicker
in one portion than in another; thus the arch may be deeper at the
crown than at the sides, or at the sides than in the centre. In some
cases two or more voussoirs are of one stone, having a false joint cut
in the centre; this is economical, and in some cases adds to the
stability of the arch. Generally the arch is divided into an uneven
number of voussoirs so as to give a keystone, the voussoirs being laid
from each side of the keystone and fitting exactly in the centre of
the arch. The keystone is not a necessity, arches being frequently
formed with an even number of voussoirs; some architects hold that the
danger of the voussoirs cracking is thereby lessened. Where lintels
are used in a stone wall over openings of small span it is usual to
build a relieving arch above to take the superincumbent weight of
masonry; or the same purpose may be effected in walls of ashlar by a
flat relieving or "save" arch, formed in the next course of three
stones above the lintel, the tapering keystone resting between the two
side stones which are tailed well into the wall.
In very many cases it is desired to form square heads to openings of
greater span than it is convenient to obtain lintels for in one piece,
and some form of flat arch must therefore be adopted. The voussoirs
are connected by joggles worked on their joints, as in fig. 17. The
weight of the superimposed wall is taken by a lintel with relieving
arch above at the back of the arch.
Arches built to an elliptical form when used for large spans (if of
flat curve they should bridge over 8 ft. or 10 ft.) are liable if
heavily loaded to fail by the voussoirs at the centre being forced
down, or else to burst up at the haunches. With arches of this
description there is a large amount of outward thrust, and abutments
of ample strength must be placed to receive the springers.
_Stone Tracery._--The designs of Gothic and other tracery stonework
are almost infinite, and there are many methods, ingenious and
otherwise, of setting out such work. Nearly all diagrams of
construction are planned on the principle of geometrical
intersections. In the example illustrated in fig. 18 the method of
setting out and finishing the design is very clearly shown, together
with the best positions for the joints of the various parts. The
jointing is a matter which must be carefully considered in order to
avoid any waste of stone and labour. It will be observed that the
right-hand side of the elevation shows the method of setting out the
tracery by the centre lines of the various intersecting branches, the
other half giving the completed design with the cusping drawn in and
the positions of joints. All the upper construction of windows and
doors and of aisle arches should be protected from superincumbent
pressure by strong relieving arches above the labels, as shown in the
figure, which should be worked with the ordinary masonry, and so set
that the weight above should avoid pressure on the fair work, which
would be liable to flush or otherwise destroy the joints of the
tracery.
_Carving._--Stone carving is a craft quite apart from the work of the
ordinary stonemason, and like carving in wood needs an artistic
feeling and special training. Carving-stone should be of fine grain
and sufficiently soft to admit of easy working. The Bath stones in
England and the Caen stone of France are largely used for internal
work, but if for the exterior they should be treated with some
chemical preservative. Carving is frequently done after the stone is
built into position, the face being left rough--"boasted"--and
projecting sufficiently for the intended design.
See E. Viollet-le-Duc, _Dictionnaire raisonné de l'architecture
française_; W. R. Purchase, _Practical Masonry_; J. O. Baker, _A
Treatise on Masonry Construction_; C. F. Mitchell, _Brickwork and
Masonry_; W. Diack, _The Art of Masonry in Britain_. (J. Bt.)