Stone and Masonry
Stone and Masonry
A stone is defined as any individual piece of rock, which is any naturally occurring aggregate of minerals and mineraloids (a mineral–like substance that does not demonstrate crystallinity). Masonry is defined as the building human made structures with the use of mortar and stones such as granite, marble, limestone, and other similar materials. It is possible that ever since people first came to be builders, stone was used in constructing something: a fence, an oven in a hole or trench, or a shelf in a cave. The many cairns and stone hedges erected for religious or astronomical uses were the initial attempts at masonry. However, true masonry did not begin until the Egyptians built the pyramids. Previous to this, most stone structures were constructed by placing one stone upon, or next to, another, regardless of size or shape. It is possible that sometime during this era, someone coined the statement: “Leave no stone unturned.”
In constructing the pyramids, the stone was first hewn or carved into a certain shape and then placed into a preplanned position. Other great stone undertakings were walls, the wall of China being the largest. The Roman wall in England was 10 ft (3 m) thick at the base and up to 15 ft (4.6 m) in height in some places. Although it was filled with mud and pebbles, both faces were constructed with squared stones. It ran for over 70 mi (113 km). Surviving portions are about 6 ft (1.8 m) high.
It was during the Norman period that most old stone structures were erected in England. And many of the craftsmen were of Norman descent. Therefore, many of the architectural terms used in the English language are of French origin. Some of these are vault, buttress, niche, oriel, trefoil, fillet, and chamfer. French influence is also evident in the standardization of various building units, such as the course heights and in various moldings and carvings. Many of these were designed to fit the individual blocks of stone rather than create a regular repetitive pattern. The majority of the original stone buildings were cathedrals, churches, and castles. But as time went on, especially where stone was quite abundant, manor houses, farmhouses, and even barns began to be built of stone.
In America, especially in northern America, when settlers first came, many were tillers of the soil, or became such. The last glacier brought many stones to southern Canada and northern United States and deposited them on the land. The settlers then used them for fences and for barns and house foundations. Today stones are used to face many buildings.
In working with stone, one should know the various types of stone. There are three main types, given their name from the manner whereby they were formed. Igneous stone is formed when magma from below Earth’s crust comes to the surface and solidifies. The liquefied material from beneath the crust of the Earth spews forth from a volcano as lava. Basalt is the most common stone to be formed volcanically. It is composed mainly of silica, as is diabase and other primordial stone. Feldspar, which contains aluminum and calcium compounds, is the other common mineral spewed from a volcano.
Metamorphic stones are made from existing materials that have undergone change. As an example, when weathered on the surface, feldspar becomes clay, which can undergo tremendous pressure and become metamorphic slate. Granite is often taken for granted, but comes from quartz and feldspar, sometimes at molten temperatures. It can be either igneous or meta–morphic. Most metamorphic rocks have been crushed into their present state by errant stones upon it. Thus, limestone under pressure becomes marble. Quartzite is metamorphic quartz. Gneiss and schist are two other metamorphic rocks.
Sedimentary stones are formed from sediments on Earth’s surface. Such stones cover three–fourths of Earth’s crust, but account for less than 5% of Earth’s volume. Shale, sandstone, and limestone make up 99% of the sedimentary stone. Shale comes from clay deposits that were formed from feldspar. Sandstone comes from river carried erosion of other stones and minerals that build up at continents” edges. It can also be formed by erosion of igneous stone. Limestone is formed mainly from the buildup of exoskeletons of tiny sea animals drifting to shore. The shell material is mainly calcium carbonate. Limestone is often quarried for building stone, gravel, cement, or agricultural lime. Weathered stone supplies the minerals that plants and animals need for their existence.
The builder of a stone structure is more concerned with its chemical composition than its geological classification. There are three main categories for stone chemical content. Siliceous stone has as its main element, silica, or silicon dioxide (SiO2). Most stone from volcanoes is siliceous. This type of stone also includes compressed sediments of siliceous stone, like sandstone. Quartz is a very pure pressurized sandstone.
Argillaceous stone has as its main element alumina (AlO2). It, along with its compounds, comes from feldspar in the crust. When these meet up with the atmosphere, they change into clay-like compounds. Slate, a sort of petrified clay, is the most common to the mason. When clay combines with other stone in varying degrees, it can overlap into other types. If clay and sand mix, brownstone is formed. Brick is artificial argillaceous stone.
Calcareous stone is made up mostly of calcium carbonate (CaCO3), or lime. Lime comes from the bodies of sea creatures, whose skeletons have accumulated at the bottom of the seas. When lime is pressurized for millennia, it becomes marble. Marble is mainly a metamorphic rock. But, because it is still mainly lime after metamorphosis, it is calcareous in classification.
Certainly, there are many combinations of the above three classifications, but rocks are distinguished by the abundance of glassy (silceous), clayey (argillaceous), or limy (calcareous) material in them. It is the quantity of each basic compound found in rocks, along with the way they were formed and the presence of other minerals in smaller amounts, that give rocks their particular desirability by masons.
The strongest rock is trap, a very old igneous and siliceous primeval stone that can withstand over 67,000 lb/in2 (3,900 kg/cm2) pressure. Gabbro and basalt are similar. But, these rocks are very difficult to work, or quarry. They are not formed in layers and hence are very difficult to layer. Granite is somewhat manageable, and is used where great strength or resistance to weather are needed. But it is difficult to work with and therefore quite expensive. Other qualities of rock that make it more desirable for use in constructions are ease of quarrying, nearness to quarry, durability, resistance to absorbing water, and strength. However, stonemasons look mainly for shape (they desire stones more or less square), their proximity, and the price. The stone most often used by masons is sandstone or limestone.
Stone masonry always has stood for permanence. Anything properly made of stone outlasts the same thing made of any other material, even concrete with steel mesh imbedded. But one must be certain of one’s work. Depending on the size of the job, it can take weeks to repair a large mistake. Stone masonry differs entirely from brick or block masonry, where every layer must lie in a straight line, where there must be square and level units and mortar joints that are uniform. The main reasons for building with stone are its beauty, endurance, strength, and mass.
Stone walls can be constructed as dry walls or, if mortar is used, as wet walls. Dry walls are used mainly for fences or retaining walls. Dry walls are usually from 2 to 3 ft (0.6 to 0.9 m) thick. The base is usually a bed of sand around 5 in (12.1 cm) thick. At the beginning of the first layer of stones, one usually lays a stone, the bonding stone, which is faced relatively even. This helps keep the wall together. The bottom course should consist of alternating larger and smaller stones, all with the longest side along the outside surface. Such stones are placed on either side of the wall. Then, stones are put between the sides, filling in the center. The layers that are above the base layer are constructed such that stones connect two lower stones, and, if possible, are kept reasonably level. If spaces result, and stones do not seat firmly, gaps are filled by chinking, by driving narrow stones or chips in the spaces so that the wall is locked tight and weight is pressed inward to prevent collapsing.
A wet wall begins with a mortared bed. A trench is dug and filled with sand or gravel. This trench is, then, allowed to settle for a few days. An inch of mortar is then laid on the top of the slab. As above, a bonding stone is placed at the end. Other stones are added along the sides, leaving spaces for the mortar, which is poured as one moves along. The inside is filled with small stones, and mortar added. After laying but not filling in the next course, a broomstick is inserted in-between stones on the first tier to make weep holes, which should pass entirely through the wall. When the wall is finished, it should be raked with a piece of wood to compact the mortar.
Arch —Curved path or span across an opening, constructed of voussoirs (curved arch stones).
Bed —A stratified layer of stone in sedimentary rock, laid down by nature. A bed is also the term used to describe the horizontal layer of mortar, cement, sand, etc. on which the blocks or stone are laid. It is the base for the first layer.
Bevel —An instrument to determine that a layer of stone or brick does not change height over a distance. It also is the name for a splayed angle on a worked stone.
Block stone —A large stone block, roughly squared at the quarry.
Bonder —Any stone or brick that is so laid that it increases the strength of a wall, either in thickness or in length.
Brought to course —Where random walling is brought up to a level line, such as at the top of a wall or the bottom of a window.
Buttress —A strong stone pier built against a wall to give additional strength. (Flying buttresses extend quite far out from the wall.) A buttress must be bonded to the wall.
Chamfer —A flat splayed edge between two flat plain surfaces.
Chisel —A generic term for a certain type of cutting tool.
Cladding —Non–load bearing thin stone slabs or bricks used for facing a building.
Cock’s comb —A thin shaped steel plate with a serrated edge. It is used for finishing moldings and other shapes.
Corbel —A bracket of stone that projects from the face of a wall. It usually is used to give support to some feature above.
Course —A continuous layer of stone or brick of uniform height in a wall.
Diamond saw —A saw whose cutting edge has industrial diamonds inserted.
Dormer —A window that projects vertically from a sloping roof.
Dowel —A sort piece of metal (not iron) or slate fixed into a mortise or adjoining stones or tile to prevent movement.
Dressings —A generic term used to wart, chimneys, etc. made of freestone, on the elevation of a building.
Drum —A separate circular stone in a shaft or column.
Eave —The part of a roof or other structure that over–sails the wall face.
Entablature —In classical architecture, the upper part of an order. It comprises architrave, frieze, and cornice.
Fault —A natural fissure in a bed or stratum of stone at a quarry. Usual faults are somewhat vertical.
Fillet —A small member between moldings. It also is called a quirk.
Flagstone —Stone that is naturally stratified in slabs about two to three inches thick, used mainly for paving, copings, etc.
Float —A rectangular wooden hand trowel, used for smoothing surfaces.
Fluted stone —Stone worked with regular concave grooves, as found in columns.
Gauge —A tool used for marking parallel lines when setting out a piece of work.
Grain —A word used at times to describe the natural visible bedding planes in stone.
Most modern stone houses have stone faces only; the entire wall is usually not completely stone. The main reason is that stone is very expensive—with the inner part of the wall usually blocked by furniture, pictures, or other items. So only an outer facade of stone is added to the house. This facade has a depth of between 3 and 4 in (7.6 and 10.0 cm), and can be either field or quarried stone. One of the hardest stones that is relatively easy to work with is limestone. One of the hardest limestone is quarried in Valders, Wisconsin, which is about 30 mi (48 km) south of Green Bay. Here, the Valders glacier covered the area. But, when one digs beneath the glaciated land, an extra dense level of the Niagara ledge is found. Valders dolomite limestone ranges in color from a silvery white to a buff texture. It is one of the most enduring limestone in the United States.
Marble is another stone used by masons, and is found in almost every state. Depending on color, porosity, and strength, various marbles are used in various buildings, such as churches, museums, art galleries and the like. Again, due to expense, today the most common stone used in construction (primarily for facing) is limestone, although some marble can be found.
Grout —Mortar used for filling vertical joints (perpends).
Header —A stone that has its longest dimension built into the thickness of the wall to improve bonding and strength.
Hip —The inclined angle at which two sloping roofs meet. The converse of valley.
Hod —A device used for carrying mortar or other materials when climbing. It is placed on the shoulder.
Hydrated lime —Quicklime processed into an inert powdered lime ready for use.
Jamb —Vertical side of an archway, doorway or window.
Keystone —The central stone in an arch.
Ledger —A large flat stone covering an altar tomb or grave. Often forms part of a church floor.
Level —A tool for telling if horizontal surfaces are true and level.
Lintel —The block or stone that spans the top of an opening, such as a doorway or window. Sometimes called a head.
Molding —A projecting or recessed part, used to give shadows to a wall, arch, or other surfaces.
Mortar board —A board placed near the work. It holds the mortar, allowing the mason to pick it up with a trowel.
Mortise —A recess in a block cut to receive a dowel or tenon.
Mould —A shaped pattern used to set out the work. Called a template in carpentry.
Niche —A recess in a wall, usually prepared to receive a carved figure.
Oriel window —A window that projects from an upper story.
Pilaster —A flat pier attached to a wall, with a base and a capital.
Plinth —The projecting base of a wall or column, generally molded at the top.
Plumb rule —A straightedge about four or six feet long with a spirit level recessed in it. It is used to ensure vertical with when building a wall. (Along with the level, it is one of a mason’s most important tools.)
Pointing —Filling of mortar joints in masonry.
Quarry —Usually an opencast pit (but sometimes a mine) from which stone is extracted.
Rendering —A coating, usually of cement and sand, that covers rough stone.
Sill —Either the threshold stone under a doorway, if flush, that is not a step; or the stone across the base of a window opening.
Soffit —The underside of an arch, vault, cornice, lintel, or the like.
Square —A tool having a fixed right angle. It is used to set out work and keep angles truly square.
Straightedge —An unmarked ruler of any length that can be used to draw lines through two given points.
Throat —A name sometimes given to the small grove under a window sill or dripstone. Its purpose is to deflect water from the wall.
Transom —A structural part dividing a window horizontally.
Vein —A colored marking in limestone, marble, etc.
Weathered —Stones in buildings or other structures that have been exteriorly exposed to the elements for many years.
Bricks are artificially made argillaceous rock. Brick and cement or cinder block masonry are not quite as artistic as stone masonry, but are usually quicker and cheaper. Like stone masonry, a footing is laid, and tiers of block or brick are placed upon the footing. The way a brick is positioned in a wall is given a name. The long part of the brick is termed the stretcher, the short end, the header, and the flat face of the brick is the bed. A tier or layer of brick can be a stretcher course (if all faces showing are stretchers), a headed course (ends showing are heads), a sailor course (where bricks are upright, with beds showing), or soldier course (where bricks are upright, with stretchers showing). Bricks laid in stretcher position with headers abutting are termed rowlock stretchers, and with headers upright are termed rowlock headers. There are various patterns that are used in bricklaying. Strictly, in bricklaying, pattern refers to changes in arrangement or varied brick texture or color used in the face. But, the different methods of joining bricks with the mortar can also be termed patterns. There are five types of bonding. They are:
- Running bond—Consists of all stretchers, but each tier is moved over one half brick.
- Block or stack bond—Each tier is placed over the previous in exactly the same position.
- American bond—A variation of running bond, with a full course of headers every fifth, sixth, or seventh course.
- English bond—Alternates block bond tiers with header tiers.
- Flemish bond—Similar to English bond, but differs in that instead of alternating tiers, it alternates stretcher and header in the same tier.
Modern building codes require that masonry–bonded walls have no less that 4% headers in the wall surface. Headers bond the wall across its thickness. Metal ties are usually recommended for bonding an exterior wall. This allows for stretching and resistance to cracking.
The surface of the brick wall can vary—depending on how the joints are finished. There are about seven types of finished joints.
Concave is the most common. It keeps moisture out and the mortar is forced tightly between the brick and thus makes an excellent bond.
The V–joint is formed with a special jointer, a piece of wood or a trowel, and it stands out as a sharp line. V–joints direct water off.
The raked joint forms a deep recess, which does not keep water out, but produces a shading that accentuates the brick courses.
The weathered joint sheds the water better than any other. It is recessed at the top, and is level with the brick surface at the bottom of the joint.
The struck joint is the opposite of weathered—it is recessed at the bottom and slants towards the top.
The flush joint is the easiest of all to make. One simply uses the trowel to smooth the face. It is water resistant but not very strong since the mortar is not compacted.
The extruded joint, also called the weeping joint, is water resistant and is used mainly for garden walls or where a rustic appearance is desired. It is made by using an excess of mortar between tiers of brick. When a brick is put into place the excess mortar is then squeezed out, and left where it hangs over.
The type of stone, brick, or bonding to be used depends on the purpose and desire of the builder. But whatever type is chosen, stone and brick last the longest, besides being pleasant to the eye.