Terms & Tools: Masonry
aggregate
Mineral components (sand, stone, shell) added to mortar, plaster, or concrete. Aggregates are the strength reinforcement to mixture and it decreases shrinkage. The choice of aggregate for a mortar is directly related to particle size distribution, or the range of small to large and proportions thereof.
alluvium
Clay, silt, or gravel carried and deposited by a river or other running water. Typically made up of fine particles of silt and clay and larger particles of sand and gravel.
antefixae
Vertical blocks of masonry used at the termination of roof tiles at the eave.
arris
The sharp edge created by the meeting of two surfaces, as in the corner or edge of a brick.
attapulgite
A magnesium aluminum silicate clay of very fine particle size. Has needle-shaped crystals. Also known as palygorskite or Fuller's Earth, it occurs naturally near Attapulgus, Georgia.
belt course
A wood or masonry band, either projecting or flush with the face of the building. Generally coincides with the masonry pockets of floors higher than the first. Walls usually reduce at belt course where the structural beams are inset; can be both decorative and structural.
calcium carbonate (CaCO3)
Chemical compound commonly known as limestone, one of the steps in the lime cycle. Burned at a {{specific temperature}} for {{a set amount of time}} it will create quicklme (CaO), and slaked with water it will create hydrated lime [Ca(OH)2]
calcium chloride (CaCl2)
A salt created by reacting calcium carbonate (limestone) with hydrochloric acid (muriatic acid) commonly used as a de-icing salt because of its deliquescent nature, which allows it to keep water in a liquid state.
calcium oxidide (CaO)
Chemical compound commonly known as quicklime or lump lime; one of the steps in the lime cycle. The compound is created when calcium carbonate (CaCO3) is calcined. Calcining causes CO2 to separate from the calcium carbonate compound, leaving CaO.
carbonation
When the lime (calcium hydroxide) in mortar or plaster is changed into a carbonate. Occurs when lime reacts with carbon dioxide from the air, releasing water through evaporation and forms calcium carbonate.
cementitious bond
In lime plastering or pointing, it is the intimate bonding of calcium hydroxide and water that is achieved through pressure. Failure to get sound cementitious bond between layers of plaster or mortar leads to delamination or two separate unconnected lifts.
chamfer
A bevel, made by cutting off the edge of a corner (arris) of wood, masonry or other material.
Chimney Lining Cone
This simple jobsite-built cone allows the deteriorated mortar on the inside of historic chimneys to be replaced rapidly. The cone is pulled up through the chimney flue with a rope on a wheelwell suspended from scaffolding above as thinned lime mortar is poured down onto it from above. In this way recessed mortar joints are pointed and the interior face of the chimney is parged in lime mortar, allowing the reuse of historic chimneys that might otherwise have been considered fire hazards due to mortar loss. Unlike popular modern ceramic and portland cement relining methods, this lime mortar treatment is compatible with porous historic brickwork. The soft rubber flippers on the bottom of the cone allow the cone to accommodate variability in the interior of the chimney, whether from irregular surfaces or from the flue narrowing as it rises. The cone has proven successful in relining both straight flues and those that curve as they rise out of the firebox and up through the smoke shelf. It takes about half a day to make a site-specific cone and reline the chimney. This method allows unstable chimneys that would otherwise be torn down and relaid to remain, saving both historic fabric and weeks worth of labor. If the rubber flippers are trimmed back, then they can also line the inside of chimney flue with a layer of lime mortar.
coping
In wood: a process for joining pieces of wood with intricate profiles, such as cornice moldings. These joints are called "coped joints." In masonry: The masonry course that caps a wall. Masonry units usually have a sloping top in order to shed water.
course
A row of bricks running horizontally.
delamination
A mode of failure where bonded layers of a material separate. Both manmade and natural materials can delaminate. Wood, plaster, paint and even stone can delaminate. Stone delamination, similar to exfoliation, occurs along the natural bedding planes. This kind of deterioration can occur when layers of a stone are laid skyward instead of horizontally, when expansion and contraction occur due to trapped moisture in the stone, by the expansion of rusting metal embedded in the stone, or by weathering caused by harsh conditions.
deliquescent
The property of becoming liquid on exposure to air or having the ability to pick up moisture up from the air, commonly attributed to salts that continue to remain wet and move through masonry walls in the wet state as the crystals continue to grow in size.
double-ended striker
A masonry tool, used to press mortar into a joint during the pointing process.
dutchman
A patch fashioned of the same material or other compatible material as a damaged or incomplete piece shaped to fit seamlessly in a void or damaged area of the existing piece. For example, a brick dutchman is set into a piece of damaged brick. A wood repair in which a piece of wood is of an existing piece of wood
efflorescence
Chalky residue deposited on the surface of masonry. After moisture in masonry is drawn to the surface by capillary action and the water has evaporated, concentrated powdery compounds such as salts or calcite are left on the surface. Often caused by chemical reactions of masonry components with chlorine in municipal water or acidic/basic cleaning solutions, all of which create salts which then deposit onto the surface.
exfoliation
A kind of masonry failure in which the stone separates in flakes or scales, usually due to salts or ice chrystals forming in a shallow planes just behind face. See delamination.
fire skin
The outer surface of a brick heated more thoroughly and expected to weather better over time.
flute
Shallow grooves running vertically along a surface, most commonly a column or pilaster.
frost-jacking
The cumulative displacement of or in objects caused by frost action, the freezing and thawing of moisture in a material.
galleting
Pieces of stone chips set into pointing at a fairly regular interval. Believed to be a decorative feature but in some cases applied to facilitate stucco application.
glauconitic
Glauconite is a greenish mineral of silicate hydrate. Often found in sand or aggregate deposits. Its softness can create problems: when a joint is slicked glauconite breaks down and acts as a pigment, causing joints to become a spotty green.
grapevine joint
Term originated in mid-late 18th century. This joint tool is ridden along arris of brick, making an indentation into the joint.
grout
A thin mortar, with small aggregate particles. Sometimes dispensed into mortar joints with a grout gun.
harling
An ancient technique where the render is thinned with water to a soupy consistency, scooped up on a curved trowel and thrown against the masonry with considerable force to create a cratered surface.
hawk
Also known as a mortarboard. A square board with a handle underneath; used by masons and plasterers to carry mortar or plaster.
hydraulic
Describes a material that sets in or under water. Once water is added it will harden on its own, like portland cement or hydraulic lime.
jack arch
A structural element in masonry that spans over an opening in the masonry, providing support. Alternate names are "flat arch" and "straight arch."
Jahn
Proprietary masonry compound made to imitate most kinds of masonry.
jamb
The side member running vertically in an arch, doorway, or window. What a door is hinged to and what a sash window rides up and down in.
lift
An individual pass of mortar application into a masonry joint. Pointing a joint usually takes three lifts, the last being the pointing mortar. Modern term for one layer application of mortar in a joint. Often mentioned in conjuntion with a common construction edict "put in the next lift after its thumb print hard," but basically this recommendation is a recipe for disaster.
lintel
The structural member that spans an opening, generally doors or windows. In masonry buildings, lintels would have traditionally been wood or stone, but today in masonry buildings they are always steel or steel-reinforced concrete.
Moxon tool
Replica of an 18th century jointing tool designed based on drawings in Moxon's Mechanick Exercises or the Doctrine of Handy-Works. The curved shape and rolling action used to create the line down the center of a joint creates a puffiness and fullness to the joint that is traditionally seen in Georgian joinery and cannot be achieved with any tool that is pushed or dragged.
newel post
The base structural post for a staircase. The center pillar for a spiral staircase.
pilaster
A flattened column, attached to the wall.
pointing
A tooled finishing treatment applied to the mortar joints between brick or stone.
Pointing Guide
Simple pointing rig made out of angle iron, flat steel, and a few thumbscrews allows one mason to quickly set up his own straightedge to guide the curved pointing tool based on Joseph Moxon's drawings. Traditionally, a straightedge of up to 12' was used to create the illusion of uniformity and straightness in Georgian brickwork.
portland cement
A generic term referring to modern hydraulic mortar, i.e. a mortar that when mixed with water will cure or harden. These are cements created by a multi-stage process that involves firing limes and clays until they are centered, or overcooked, to the point of rock-hardness. The clinkers that are created from this process are ground into fine powder. When water is added, a hydraulic set occurs. Because this is a manufactured process, the properties of a portland cement can be manipulated by changing the variables in the temperatures in which it is fired, the firing time, materials, etc.
poultice
Absorbent, porous material soaked in a liquid that onto a surface to draw out salts or stains. When placed onto a surface the liquid is absorbed in, then porous material draws the liquid back out.
proud
Describes an feature or element that is raised, not flush with the surface.
quartz silica
Silica, or silicon dioxide, is most commonly found in the form of quartz. A very hard mineral known for its resistance to weathering is the most common as aggregate in mortar because it it ubiquitous in the environment.
queen closer
A brick split in half lengthwise.
relieve
To remove, carve wood.
render
A type of stucco exclusively applied to masonry walls.
repointing
The process of refilling a masonry joint with mortar after being cleaned and dressed properly. Mortar between bricks gradually erodes away from the face over time, and eventually repointing is required.
striking
Packing mortar into joints between masonry. When working with lime mortar, the use of pressure in packing the mortar into the joint instead of slicking the joint creates a strong cementitious bond.
watertable
A horizontal shelf with skyward facing joints that steps out on the base of the building. Helps to shed water away from base of building. Generally coincides with the masonry pockets of the first floor joists on the interior. Traditionally this also coincides with the narrowing of the foundation width from a foundation thickness to a wall thickness.
wythe
The horizontal interior-to-exterior number of rows of bricks in a wall. For example, an 18" thick foundation wall would be four thicknesses of approximately 4" bricks with mortar between each. In contrast, the vertical rows of bricks are called courses.