WBCHSE HS Vocational Construction key terms

The mass of a material divided by its total volume including the voids inside it, expressed in kg per cubic metre. Used to judge the weight and porosity of aggregates, bricks and timber.

The fraction of a material's volume occupied by open or closed pores. Higher porosity usually means more water absorption, lower strength and poorer resistance to frost in bricks and stones.

The amount of water a material takes in when soaked, expressed as a percentage of its dry mass. It indicates durability and suitability of bricks, tiles and stones for exposed work.

A whitish powdery deposit of soluble salts that appears on the surface of masonry when water evaporates from it. It is unsightly and shows that dampness and salt-bearing materials are present.

The distribution of particle sizes in a sample of sand, gravel or crushed stone. Well-graded aggregate packs densely, needs less cement paste and gives stronger, more workable concrete.

A single number obtained by adding the cumulative percentages retained on a standard set of sieves and dividing by 100. It compares the coarseness of different sand samples.

The increase in the volume of moist sand caused by films of water pushing the grains apart. It matters because batching sand by volume when damp leads to short measurement of sand in mortar or concrete.

How easily fresh concrete or mortar can be mixed, placed, compacted and finished without segregation. It is commonly assessed by the slump test on site.

The mass of water divided by the mass of cement in a concrete mix. Lowering it raises strength and durability but reduces workability, so it is the key control on concrete quality.

A site test in which fresh concrete is placed in a standard cone, the cone is lifted, and the drop of the concrete is measured. It gives a quick indication of workability and consistency.

A laboratory test in which standard cubes are cured and crushed in a compression machine at 7 and 28 days. The crushing stress shows whether the concrete has reached its specified grade strength.

Keeping concrete or mortar moist and at a suitable temperature after placing so that cement hydration continues. Proper curing for the specified period develops strength, reduces shrinkage cracks and improves durability.

A concrete or mortar mix stated as fixed proportions of cement, fine aggregate and coarse aggregate, such as 1:2:4. It is used for ordinary small works where strength is not tested by design.

The stated proportion of cement or lime to sand in a mortar, such as 1:6. Richer mixes give stronger, less permeable joints; leaner mixes are cheaper but weaker.

The thickness of concrete between the outer surface of the steel bar and the nearest concrete face. Adequate cover protects steel from corrosion and fire and ensures bond with concrete.

The length of bar embedment needed to transfer the force in a reinforcing bar safely into the surrounding concrete without the bar pulling out. It depends on bar diameter, grade and concrete strength.

The overlapping length provided where two reinforcing bars are joined end to end so force passes from one bar to the other. It is specified as a multiple of bar diameter for each concrete grade.

The temporary moulds of timber, plywood or steel that hold fresh concrete in shape until it hardens. Formwork must be strong, rigid, tight against grout loss and easy to strike.

A brick masonry bond made of alternating courses of stretchers and headers. It is strong and has no continuous vertical joints through the wall, though it needs more facing bricks.

A brick bond in which each course contains alternating headers and stretchers. It gives a neat appearance on both faces of a half-brick wall but is weaker than English bond.

A brick cut lengthwise into two equal halves, used at the end of a header course or beside a quoin to break the vertical joint. It helps bond the corner and keep the courses true.

The external corner of a wall, usually built with specially chosen or shaped bricks to give strength and a clean edge. Quoins are set out first and act as guides for the rest of the wall.

A small weight hung on a string to give a true vertical line. It is used to check that walls, columns and formwork are vertical and not leaning.

A tool with sealed glass vials containing liquid and an air bubble, used to check whether a surface is horizontal or vertical. The bubble centres between the marks when the surface is true.

A nylon or cotton line stretched between two pins or nails along the face of a wall. It keeps successive courses at a constant height and line during brick or block laying.

A rigid right-angled tool used to check and set out 90-degree corners in masonry, carpentry and tiling. It is also used to test whether cut ends are square.

A woodworking tool with a fixed blade set at 90 degrees to a stock, used to mark and test square ends and right angles on timber. The stock is held against the reference face.

A joint in which a projecting tongue (tenon) on one member fits into a matching rectangular hole (mortise) in another. It resists pulling apart and is common in door frames and furniture.

A carpentry joint made by removing half the thickness from each of two overlapping members so that their faces finish flush. It is used in framing and is often pinned or glued.

Controlled drying of timber to reduce its moisture content before use. Properly seasoned wood is lighter, stronger, more stable and less likely to shrink, warp or decay in service.

The fixed ratio between a distance on a drawing and the real distance it represents, such as 1:100. It lets a drawing show a building or component at a convenient size on paper.

A drawing showing a building or object as seen from above, cut at a stated level, with walls, openings and fittings in their true relative positions. It is the main drawing used for setting out and estimating.

A drawing showing the external face of a building or one side of an object, without perspective, giving heights and levels. Elevations show doors, windows, finishes and roof lines.

A drawing that shows a building or object as if cut by an imaginary vertical plane, revealing internal construction such as floor levels, foundations and roof structure. Cut surfaces are hatched.

A table listing each type of reinforcing bar with its mark, diameter, shape, length, number and total weight. It guides cutting and bending at site and supports steel quantity estimation.

A plumbing fitting that holds a water seal to stop sewer gases entering a building while allowing waste water to pass. Every fixture except some direct-outlet ones needs a trap.

A pipe connected to the drainage system that admits air and releases gases above roof level, protecting trap seals from siphonage. It keeps the system at atmospheric pressure.

An access point in a drainage run, with a removable cover, where pipes can be inspected, rodded and cleaned. It is placed at changes of direction, junctions and intervals along the drain.

A continuous impervious layer built into a wall near ground level to stop moisture rising by capillary action. It is usually bituminous felt, polythene or a cement-rich mortar layer.

Connecting exposed metal parts of an electrical installation to the general mass of earth through a low-resistance path. It makes protective devices operate and limits shock risk during a fault.

An automatic switch in a distribution board that trips and breaks the circuit when current exceeds its rating or a short circuit occurs. It can be reset after the fault is cleared.

A protective device that trips when it detects a small imbalance between live and neutral currents, indicating leakage to earth. It gives added protection against electric shock.

An estimating method in which the total length of walls is measured along their centre lines and multiplied by width and depth. It is quick for long walls of the same thickness but needs care at junctions.

An estimating method in which walls running in one direction are measured as long walls and cross walls as short walls, adjusting lengths at junctions. It suits buildings with walls of differing thickness.

A summary sheet that lists each item of work with its quantity, unit rate and amount, then totals the cost. It is prepared from the detailed measurement sheet and supports the tender or estimate.

A provisional sum included in an estimate to cover unforeseen items or price changes during construction. It is usually a small percentage of the estimated cost and is spent only with approval.

A priced document listing measured items of work with descriptions, quantities and rates, forming part of a contract. Contractors price each item and the total becomes the tendered amount.

The longest sequence of dependent activities through a project network, which fixes the shortest possible project duration. Any delay on it delays completion unless the plan is changed.

A bar chart that shows project activities against a calendar, with bars giving start, duration and finish. It is simple to read and useful for progress monitoring and resource planning.

The amount of time an activity can be delayed without delaying the project finish or the next activity. Activities on the critical path have zero float.

A hard hat worn on site to protect the head from falling objects and knocks. It must be worn in designated areas, fit correctly and be replaced after a heavy impact or when damaged.

Items worn by a worker to reduce risk of injury, such as helmet, safety shoes, goggles, gloves, ear protection and high-visibility clothing. It is the last line of defence after hazards are controlled.

A temporary working platform with supports, standards, ledgers and boards that lets workers reach heights safely. It must be stable, tied to the structure, and fitted with guard rails and toe boards.

The process of identifying an opportunity, arranging resources and taking calculated risk to start and run a business. In construction it commonly means setting up as a contractor or specialist firm.

The money a business needs for day-to-day running, calculated as current assets minus current liabilities. Contractors need enough of it to pay wages and materials before payments are received.

A formal offer by a contractor to carry out specified work at stated rates within a stated time and conditions. It is prepared from tender documents and submitted before the closing date.