Red Seal Lather (ISM) key terms

A deliberate groove or gap formed in a gypsum board or plaster surface that forces shrinkage and structural movement to crack at that planned line rather than randomly across the finished field.

A continuous break through the entire wall or ceiling assembly, including framing and finish, that allows separate building sections to move independently without transferring stress into the finished surface.

Deflection, shrinkage, or settlement of structural members under load or moisture change that must be anticipated and isolated so brittle finishes such as plaster and joint compound do not crack.

The maximum allowable bending of a floor or ceiling assembly under load, commonly stated as a fraction of span, used to confirm the framing is stiff enough to support brittle ceiling finishes.

A light-gauge steel hat- or C-shaped section fastened across framing or masonry to create a straight, level plane for attaching gypsum board, lath, or ceiling panels.

A flexible galvanized steel channel installed perpendicular to framing and attached at one flange only, isolating the finished board from the structure to reduce airborne sound transmission.

Wood or metal strips run across framing members to provide a continuous fastening surface, correct alignment, or a cavity for wiring and insulation behind the finished surface.

A secondary ceiling hung below the structure on hangers, consisting of a metal grid of main runners and cross tees that supports lay-in acoustic panels or gypsum board.

The primary load-carrying grid member of a suspended ceiling, hung from the structure at regular intervals and supporting the cross tees and panels.

A secondary grid member in a suspended ceiling that spans between main runners and forms the panel openings at the specified module size.

Galvanized wire used to suspend ceiling grid or framing from the structure above, sized and spaced per the ceiling layout and required load capacity.

A thin piece of material placed behind furring, strapping, or framing to bring a surface into plane before the finish is applied.

A panel of gypsum core faced with paper or glass mat, manufactured in standard thicknesses and types for walls, ceilings, and sheathing applications.

A gypsum board with additives in the core that improve fire resistance, manufactured to a specific fire-rated assembly listing and required in rated partitions and ceilings.

Gypsum board with a water-repellent core and water-resistant facing, used as a substrate in bathrooms and other damp areas where regular board would deteriorate.

A rigid sheet of cement and aggregate used as a substrate for tile in wet areas, unaffected by moisture and suitable where gypsum-based board is not permitted.

A fire-rated partition enclosing a vertical shaft such as an elevator or mechanical chase, typically framed with steel studs and clad in one or more layers of gypsum board.

The period, in hours or minutes, that an assembly resists fire as tested and listed, determining the board type, layers, and fastening required for that assembly.

A listed material or system installed to seal openings and penetrations through a rated wall or floor so the fire-resistance rating is not compromised.

A light-gauge cold-formed steel framing member, usually C-shaped, used in non-load-bearing partitions and furring, installed with the web facing the direction shown on the drawings.

The horizontal light-gauge steel member, shaped like a U, that caps the top and bottom of a steel stud partition and receives the stud ends.

A ready-mixed or dry powder material used to embed tape and fill joints, corners, and fastener heads, applied in successive coats and sanded to a smooth finish.

Paper or glass-mesh strip embedded in joint compound over board joints and inside corners to reinforce the joint and prevent cracking.

A defined standard describing how completely joints, fasteners, and imperfections are treated, from fire-taped only through to a fully skimmed surface ready for glossy paint.

A thin application of joint compound or plaster spread over a broad area to smooth the surface, hide texture, or prepare it for a high-quality paint finish.

A low-permeance membrane installed on the warm side of insulation to limit moisture diffusion into the assembly and reduce the risk of condensation within it.

A continuous system of materials that resists air leakage through the building envelope, including joints, penetrations, and transitions between assemblies.

A measure of how readily water vapour passes through a material of a given thickness, used to compare membranes and decide where a vapour retarder belongs in the assembly.

Material installed in cavities or on surfaces to slow heat flow, supplied as batts, loose fill, or rigid board and installed to the thickness and coverage stated on the drawings.

A base material that provides a mechanical key for plaster, such as metal diamond mesh, gypsum lath, or a gypsum board base coat.

The first coat of plaster applied over lath, scored to create a key that helps the following coat bond to it.

The second coat of three-coat plaster, applied over the scratch coat to build thickness and provide a straight, true surface for the finish coat.

The final, visible plaster or stucco layer applied over the base coats to give the required texture, colour, and appearance.

A portland-cement-based exterior plaster applied over lath or a prepared substrate, typically in multiple coats with reinforcing mesh at joints and corners.

A perforated metal accessory fixed at the base of a stucco wall that establishes the thickness of the coat and allows moisture to drain out of the assembly.

A thin plaster system applied over a special gypsum base board, producing a hard, monolithic surface in one or two coats rather than the traditional three.

A cementitious material applied wet to a substrate, hardening into a continuous interior or exterior surface that can be textured or smoothed.

A single-number rating of how well an assembly blocks airborne sound, used to compare partition designs and confirm compliance with the specified acoustic requirement.

A detailed drawing prepared by the contractor showing how a specific assembly will be built, used to confirm dimensions, materials, and coordination before installation.

A drawing that views the ceiling from above as if mirrored, showing grid layout, panel sizes, lighting, and other ceiling-mounted items for coordination.

The written portion of the contract documents that states the materials, standards, and workmanship required for each part of the work.

The legally adopted set of regulations governing construction, including fire separations, means of egress, and the assemblies permitted in each location.

A document supplied with a hazardous product describing its hazards, safe handling, required protective equipment, and first-aid measures.

Fine crystalline silica dust released when cutting or sanding concrete, cement board, or plaster, which can cause serious lung disease if inhaled.

The clothing and gear worn to reduce exposure to workplace hazards, such as eye protection, hearing protection, gloves, and respiratory protection.

A system of guards, harnesses, or platforms required when working at height to prevent or arrest a fall.

A temporary elevated platform and its supporting structure used to reach work areas above floor level, which must be erected and inspected as required.

The process of measuring and listing the quantities of each material required from the drawings, used to order stock and plan installation.

A percentage added to the calculated material quantity to allow for offcuts, breakage, and pattern loss when ordering stock.

The safe lifting of boards, panels, and framing to upper floors by crane, hoist, or manual means, planned to protect workers and prevent damage to materials.

Checking and adjusting a measuring or levelling instrument against a known reference so readings are accurate before layout begins.

An instrument that projects a level or plumb reference line or plane, used to set heights, align tracks, and check the plane of ceilings and walls.

The marking and setting out of positions, heights, and grid lines on the structure before installation, based on the drawings and a common reference datum.