NCCER Glazier cheat sheet

Glass is a supercooled liquid/amorphous solid: no crystalline lattice, so it fails by brittle fracture with no yield point; design assumes elastic behavior up to rupture.

Safety glazing is required in hazardous locations: within 24 in (610 mm) of a door edge, glass under 18 in (457 mm) above the floor, and glazing in bathrooms, stairways, and walkways where a 3 in (76 mm) sphere can contact it.

Fall-protection threshold under OSHA: 4 ft (1.2 m) in general industry, 6 ft (1.8 m) in construction; guardrails top rail 42 in +/- 3 in (1.07 m), midrail at half height.

Ladder angle rule: 4:1 ratio (1 ft out per 4 ft up), extending 3 ft (0.9 m) above the landing; secure top and bottom before climbing with glass.

Glass weight formula: weight (lb) = area (ft2) x thickness (in) x 13.0 for typical soda-lime glass; 1/4 in glass weighs about 3.25 lb/ft2 (16 kg/m2).

Lifting limit: two-person manual carry is generally capped near 96 lb (43 kg) of glass per person; above that use vacuum lifters, slings, or mechanical equipment.

PPE for glazing: cut-resistant gloves (ANSI/ISEA 105 level A4 or higher for handling cut glass), safety glasses with side shields, and Kevlar or leather sleeves when carrying lites.

Waste glass goes in a rigid, labeled container; never in a trash bag or open bin, and never compacted by hand - cuts from shards are the leading glazier injury.

Annealed glass: cooled slowly, surface compression about 0 to low levels; breaks into large sharp shards, so it cannot be used where safety glazing is required.

Heat-strengthened glass: surface compression around 3,500-7,500 psi; breaks into larger pieces than tempered, used where thermal stress resistance is needed but not safety rating.

Tempered glass: surface compression 10,000 psi or greater; breaks into small dice-like fragments, must be cut and drilled before tempering, and cannot be edge-worked after.

Laminated glass: two or more lites bonded with PVB or SGP interlayer; remains in the opening after breakage, and the interlayer thickness (e.g., 0.030, 0.060 in) sets the safety and security rating.

Insulated glass unit (IGU): sealed cavity between lites; the perimeter seal (polyisobutylene primary plus polysulfide or silicone secondary) keeps out moisture, and desiccant keeps the air space dry.

Low-E coatings: soft-coat (sputtered) is applied to a surface inside the IGU and is fragile; hard-coat (pyrolytic) is durable and can be exposed. Surface 2 faces the air space from the exterior side.

Visible light transmittance (VLT) and solar heat gain coefficient (SHGC) trade off: lower SHGC reduces cooling load but usually lowers VLT; U-factor measures heat flow, lower is better.

Spandrel glass is opaque and often heat-treated; it must be tempered or heat-strengthened when thermal stress from the shadow line or backpans could crack annealed glass.

Storefront systems are typically 1-3/4 in x 4-1/2 in (44 x 114 mm) nominal tube members, designed for a maximum height around 10 ft (3 m); above that, use curtain wall.

Curtain wall is a non-load-bearing envelope hung from the structure, carrying only its own weight and wind load; storefront carries limited loads and is not a structural frame.

Deflection limit for glazing frames under wind load is commonly L/175 for spans up to 13 ft 6 in, and L/240 + 1/4 in for longer spans, to avoid glass edge contact.

Glass bite (edge engagement) is typically 1/2 in to 3/4 in (13-19 mm) in a wet-glazed storefront; insufficient bite causes edge loading and breakage.

Setting blocks are placed at the quarter points (each about 1/4 of the lite width from the edge), not at the corners, to support weight while allowing thermal expansion.

Edge clearance: glass edges must not touch metal; keep at least 1/8 in (3 mm) clearance and use EPDM or neoprene glazing gaskets to isolate the glass from the frame.

Thermal movement: aluminum expands about 1.3 x 10^-5 per degree F, roughly twice that of glass; allow for differential movement at mullion splices and at the head.

Anchor spacing for storefront mullions is set by the manufacturer, commonly 24 in (610 mm) on center maximum, with anchors placed within 12 in of jamb ends.

Dry glazing uses a compression gasket (EPDM) pressed into the frame; wet glazing uses sealant or glazing tape, and the two are not interchangeable on the same joint.

Install setting blocks before the lite: block thickness equals glass thickness, length at least 4 in (100 mm), and durometer 85-90 Shore A to carry the weight without flattening.

Glazing tape (closed-cell PVC or butyl) must be compressed 25-30 percent of its thickness to seal; under-compression is the most common cause of water leaks.

Head and sill joints are the leak paths: use a continuous bead at the sill, but leave weeps open at the head and sill to drain the glazing channel.

For a butt-glazed vertical joint, structural silicone sealant is used; its bite depth is computed from the design wind load, typically at least 1/4 in (6 mm) and never less than the joint width.

When setting a lite, tilt it in from the bottom first, seat it on the setting blocks, then rotate into the head; never drop it into the frame or rest it on the sill.

Vacuum lifter capacity must exceed the lite weight by a safety factor of 2 or more; verify pad seal and gauge reading before lifting, and never lift over workers.

Tolerance check after installation: glass edges plumb within 1/8 in per 10 ft, and adjacent lites aligned within 1/16 in (1.5 mm) at the joint.

Sealant joint design: width must be at least 1/4 in (6 mm) and depth at least 1/4 in; the depth-to-width ratio should be 1:1 up to 1/2 in wide, then 1:2 for wider joints.

Backer rod (closed-cell polyethylene) sets sealant depth and prevents three-sided adhesion; sealant must bond only to the two faces, never to the back of the joint.

Joint movement capability: silicone sealants handle +/- 50 percent movement, polyurethane +/- 25 percent, acrylic +/- 12.5 percent; match the sealant to the calculated joint movement.

Structural silicone glazing requires a primer and a bond-breaker tape; the sealant bonds to glass and frame but must not bond to the backer, or the joint tears.

Tooling the sealant within the working time (usually 10-20 minutes) forces it against the substrates and produces a concave profile that sheds water.

Cure time: silicone sealant skins in about 10-30 minutes and cures at roughly 1/8 in (3 mm) per 24 hours; do not water-test or clean until fully cured.

Weep holes and drainage: a drained-and-vented system needs weeps at the sill at spacing set by the manufacturer (commonly 12-24 in), kept clear of sealant and debris.

Cleaning new glazing: use a neutral pH cleaner and a squeegee; avoid abrasive pads and hydrofluoric-acid-based cleaners that etch glass or attack anodized frames.

Air barrier continuity: sealant joints, gaskets, and flashing must form a continuous line; a single unsealed penetration defeats the assembly's air and water control.

Flashing at the sill: install a sill pan or flashing with end dams and a back dam, lapped shingle-style so water drains outward, never trapped behind the frame.

Water test standard: AAMA 501.2 field water test sprays at 5 gal/hr per nozzle for 5 minutes minimum; failure shows as water at the interior face.

Compatibility check: sealant must be compatible with the glazing gasket, setting blocks, and any protective tape; test a sample because incompatible plasticizers cause gasket hardening.

Fire-rated glazing: fire-protective glazing blocks smoke and flame but not radiant heat; fire-resistive glazing also limits temperature rise and is required in some rated walls.

Final punch: verify sealant beads are continuous, tooled, and cured, weeps are open, and glass is labeled with the safety-glazing mark before sign-off.

Before cutting, inspect glass for scratches and edge chips; a chip at the edge propagates into a crack under thermal or wind stress and is a reject.

Score-and-break cutting applies only to annealed glass; tempered and laminated glass must be ordered cut to size and cannot be field-cut.

Cutting fluid (light oil or kerosene) is applied along the score line to let the crack run cleanly; a dry score produces a ragged break.

Glass storage: keep lites on an A-frame rack at 5-10 degrees from vertical, never flat or leaning, with the bottom edge on a soft pad.

When moving glass in wind, keep the lite vertical and edge-on to the wind; a flat lite acts as a sail and can be blown out of control.

Emergency response for a cut: apply direct pressure, elevate if possible, and get medical help; do not remove embedded glass shards from a wound.

Dropped glass is never reused or rehung; inspect for invisible edge damage, and quarantine the lite for disposal.

Borosilicate glass has a low coefficient of expansion and resists thermal shock; used in fire-rated glazing and laboratory applications, not typical architectural lites.

Wired glass is no longer accepted as safety glazing in most jurisdictions because the wire does not hold fragments together on impact.

Acrylic and polycarbonate are plastics, not glass; polycarbonate resists impact far better but scratches easily and has a higher expansion rate.

Solar control: spectrally selective coatings reduce SHGC while keeping VLT high; a ratio of VLT to SHGC above 1.0 is the common target for daylighting.

Tinted glass reduces both VLT and SHGC; body-tinted gray or bronze absorbs heat, raising thermal stress and requiring heat-treated glass in some exposures.

Reflective coatings reduce SHGC and VLT sharply and can cause glare complaints; check the reflected angle against neighboring buildings.

Glass strength is not permanent: surface damage, edge flaws, and sustained loads reduce capacity; design uses a safety factor, commonly 2.5 for wind load.

Head and jamb details must allow for live load and wind deflection of the structure, typically 1/4 in to 1/2 in of movement at the head, sealed with a slip joint.

Mullion splice joints are located at floor lines and designed to slip, not to transfer moment; splices are sealed with a gasket or sealant and allow thermal movement.

Curtain wall systems are either stick-built (assembled on site) or unitized (factory-assembled panels); unitized systems are faster and more weather-tight but need crane access.

Expansion joints in aluminum framing are spaced per the manufacturer, commonly every 20-24 ft (6-7 m) to accommodate thermal movement.

Corner and jamb conditions need a continuous sealant or gasket line; a gap at a corner is the most common source of air infiltration.

Shop drawings must show glass bite, setting block location, weeps, and sealant joints; field changes without revised drawings void the warranty.

Measure the opening in at least three places (top, middle, bottom) and use the smallest dimension; out-of-square openings need a template or shimmed frame.

Glass size for a wet-glazed opening equals the opening size minus the required edge clearance and glass bite on each side; never order to the opening size.

Check diagonal measurements of the opening: equal diagonals mean square; a difference signals a racked frame that will load the glass edge.

Verify sill level with a level or laser; a sloped sill causes uneven setting-block load and can crack the lite.

Record field dimensions on a signed field-measure sheet and reconcile with the shop drawing before ordering; field changes are the leading cause of remakes.

Surface preparation: clean substrates with a solvent recommended by the sealant maker and wipe dry with a clean, lint-free cloth; two-cloth method removes residue.

Masking tape protects adjacent surfaces and gives a clean joint line; remove it while the sealant is still wet, before it skins.

Apply sealant with a positive pressure gun and push the bead ahead of the nozzle; pulling the bead traps air and leaves voids.

Do not apply sealant in rain, on wet surfaces, or below the manufacturer's minimum temperature (often 40 F / 4 C); cold surfaces prevent adhesion.

Adhesion test: pull a cured sample bead and check for cohesive failure (sealant tears) rather than adhesive failure (clean release from the substrate).

Structural silicone joints need a compatibility test with the glazing components and a primer where the manufacturer requires it.

The rainscreen principle: keep the outer face open to drain and vent, and place the air/water barrier behind it so pressure equalizes and water drains out.

Pressure-equalized glazing channels use baffled weeps and an internal baffle so wind pressure does not drive water past the gasket.

Water flows down and inward under capillary action; a joint narrower than about 1/32 in (0.8 mm) can draw water against gravity, so maintain a drainage gap.

Gaskets must be continuous and compressed; a spliced gasket needs a corner vulcanized or a sealant-filled joint to stay watertight.

Flashing laps: upper flashing laps over lower, side flashing laps over the sill pan, and the sill pan laps over the building wrap.

After installation, perform a hose test at the sill and jambs before interior finishes go in; catching leaks early avoids costly rework.

A glass cutter scores the surface with a small wheel; the score is a controlled flaw, and the break follows it when pressure is applied.

Running pliers apply bending force at the score line to propagate the crack; tapping the score from below also helps the break run.

A suction cup or vacuum lifter is rated by capacity and must be inspected for seal damage; a slipping cup drops the lite.

Setting blocks are neoprene or EPDM, sized to the glass thickness; wood blocks are never used because they absorb water and crush.

A caulking gun with a nozzle cut at 45 degrees gives a bead sized to the joint; a nozzle cut too small forces excessive pressure and strings the sealant.

Torque wrench for structural connections: follow the manufacturer's torque value; over-torquing crushes gaskets and strips threads.

Safety glazing is marked permanently with the manufacturer's name and the standard (e.g., ANSI Z97.1 or 16 CFR 1201); unmarked glazing in a hazardous location fails inspection.

ASTM C1036 covers flat glass quality (types, kinds, and quality levels); ASTM C1048 covers heat-treated glass; ASTM C1172 covers laminated glass.

AAMA 501 covers test methods for exterior walls; AAMA 2605 covers high-performance organic coatings on aluminum.

LEED and energy code compliance use U-factor, SHGC, and VLT from the manufacturer's certified performance data, not field estimates.

Warranty documents must list the sealant, gasket, and glass types installed; substitutions without written approval void coverage.

A cracked lite is replaced, not repaired; sealant or tape over a crack is not an acceptable repair for safety glazing.

When replacing an IGU, replace the whole unit; a failed seal shows as fogging or a milky film from desiccant saturation.

Check the cause before replacement: a repeat break at the same location points to edge loading, frame deflection, or thermal stress, not bad glass.

Remove old sealant fully with a plastic scraper; metal tools scratch the frame and anodized finish, and residue prevents new sealant adhesion.

After replacement, re-test the joint with a water test and confirm weeps are clear and gaskets are seated.

Wind load on glass is calculated from the design pressure (psf) and the lite's short-side span; the glass thickness is selected from the manufacturer's or ASTM E1300 chart.

ASTM E1300 gives the load resistance of glass based on type, thickness, area, aspect ratio, and load duration; a 1-minute wind load uses a different factor than a sustained load.

Thermal stress cracking occurs when the center of the lite is hotter than the edge; heat-treated glass resists higher thermal stress than annealed.

Shadow lines from adjacent buildings or overhangs create a temperature differential across the lite; deep shadows increase thermal stress.

Interior shading devices and dark backpans raise glass temperature; spandrel glass in these conditions must be heat-treated.

U-factor is the overall heat transfer (Btu/hr-ft2-F); lower values mean better insulation, and the frame and spacer dominate IGU performance.

Sequence: frame installation and anchoring, then flashing and weather barrier, then glass, then gaskets and sealant, then final cleaning and punch list.

Do not glaze before the frame is plumb and anchored; glass installed into a moving frame will crack or leak.

Coordinate glazing with the dry-in schedule; glass installed before the roof is dry can be damaged by water and debris.

Protect installed glass with a protective film or board where traffic passes; remove film within the manufacturer's stated time or adhesive bakes on.

Inspect delivered glass before signing the delivery receipt; note chips, scratches, and label damage on the paperwork.

Check every lite for the safety glazing mark, correct thickness, and correct type against the shop drawings.

Verify sealant beads are continuous, tooled, and free of voids; run a finger or a tool along the bead to feel gaps.

Confirm weeps are open and drainage paths are clear; sealant blocking a weep traps water and causes leaks.

Check glass edges are not in contact with metal and setting blocks are in place; a missing block means the lite is edge-loaded.

Document deficiencies with photos and a written punch list, and get the installer's sign-off before releasing retainage.

Doors: glazing in a swinging door, and glazing within 24 in of the door edge, must be safety glazing if the bottom edge is under 60 in above the floor.

Windows: glazing with a bottom edge under 18 in above the floor and more than 9 ft2 in area must be safety glazing in a hazardous location.

Stairways and ramps: glazing within 36 in of the walking surface, or within 60 in horizontally of the stair tread, is a hazardous location.

Bathrooms: glazing in a tub or shower enclosure, and within 60 in of the water's edge, must be safety glazing.

Glass in walls next to a walking surface must resist human impact; check the local code because the IBC and IRC thresholds differ slightly.

IGU cavity width is commonly 1/4 in to 3/4 in (6-19 mm); wider cavities improve U-factor up to a point, then convection reduces the benefit.

Argon fill improves U-factor over air; krypton is better but more expensive and used in narrow cavities.

Warm-edge spacers (stainless steel or non-metal) reduce condensation at the glass edge compared with aluminum box spacers.

Primary seal (polyisobutylene) blocks moisture vapor; secondary seal (polysulfide, silicone, or hot-melt butyl) provides structural strength.

A failed IGU shows fogging, a milky edge, or condensation between lites; the unit must be replaced, not resealed in the field.

Never carry glass by the edges with bare hands; use cut-resistant gloves and carry with the lite vertical and balanced.

Two-person carry: one at each end, lifting together, with the lite kept vertical and the bottom edge clear of the ground.

A-frame racks must be anchored or chocked; a tipped rack of glass is a fatal hazard.

Keep the storage area clear of traffic and marked; glass leaning against a wall can slide out at the base.

Inspect slings and vacuum pads before each lift; a damaged sling or pad is removed from service, not taped or patched.

Silicone: best weather resistance and movement capability, used for structural and weatherseal joints; not paintable.

Polyurethane: strong adhesion and abrasion resistance, used in traffic areas and expansion joints; limited movement capability and not UV-stable in some formulations.

Acrylic latex: paintable and low cost, used for interior joints; poor movement capability and not for exterior weatherseal.

Butyl: excellent moisture vapor resistance, used as a tape or primary seal in IGUs; poor UV and movement performance.

Structural silicone sealant must be tested for compatibility with the glazing components and applied with a primer where required.

Storefront systems rely on a continuous gasket and sealant line plus weeps at the sill; the head is not the primary drain path.

Sill flashing must have end dams and a slope to the exterior; a flat sill traps water and rusts the frame.

The glazing pocket must drain: keep the weep path clear of setting blocks and sealant.

Head joints are sealed but not rigid; allow for movement with a slip joint or gasket rather than a solid sealant bridge.

Field water testing at the sill and jamb confirms the system before interior finishes are installed.

Score the glass once, firmly, from edge to edge; a double score or a light score produces a poor break.

Apply cutting oil to the score and tap the underside along the score to start the crack.

Break the glass over a straight edge with even pressure; do not bend the lite beyond the break line.

Edge work: seamed edges reduce handling cuts, and polished or ground edges are required where the edge is exposed or load-bearing.

Holes and notches must be drilled before tempering; tempered glass cannot be drilled or cut after heat treatment.

Curtain wall carries wind load to the structure through anchors at each floor; the mullions span floor to floor and deflect under wind.

Mullion deflection is limited to L/175 or 3/4 in, whichever is less, to keep glass edges from contacting the frame.

Dead load of the glass is carried by setting blocks and transferred to the frame, not by the sealant or gaskets.

Interstory drift is accommodated by slip joints and gaskets; a rigid connection between floors cracks glass during an earthquake or wind sway.

Thermal movement of aluminum mullions is absorbed at splices and at the head; a fixed head with no slip joint buckles the frame.

Glass type, thickness, and safety mark match the approved shop drawings.

Setting blocks are present, correctly sized, and located at the quarter points.

Glass bite is within the manufacturer's range and the edge clearance is maintained.

Sealant beads are continuous, tooled, and cured; no voids or gaps at corners.

Weeps are open and drainage paths are clear; water test passes at the sill and jambs.

Sealant plasticizers can migrate into EPDM gaskets and cause hardening or shrinkage; verify compatibility with a sample test.

Bituminous and asphaltic materials are incompatible with some sealants and can stain or soften them.

Solvent cleaning must match the substrate: use the sealant manufacturer's recommended cleaner, and avoid solvents that attack the frame finish.

Protective films on glass must be removed within the manufacturer's time limit; sunlight bakes the adhesive and leaves residue.

Dissimilar metals in contact (aluminum and steel) need isolation to prevent galvanic corrosion at anchors.

U-factor is the overall heat transfer coefficient; lower values mean better insulation, and the frame and spacer dominate IGU performance.

SHGC is the fraction of solar heat admitted; lower SHGC reduces cooling load, and values range from about 0.2 to 0.7.

VLT is the fraction of visible light transmitted; a good daylighting target keeps VLT high while SHGC stays low.

Energy codes set maximum U-factor and SHGC by climate zone; check the local code because values differ by jurisdiction.

Certified performance data comes from the manufacturer's tested values, not field estimates.

Field-measure sheets must be signed and dated by the person who measured the opening.

Changes to glass size or type require a written change order before fabrication; verbal changes are not binding.

Shop drawings show glass bite, setting blocks, weeps, and sealant joints; field changes without revised drawings void the warranty.

Report delivery damage on the receipt before signing; undocumented damage is charged to the installer.

Coordinate with the general contractor on the dry-in schedule before glazing begins.

Edge chips and shells concentrate stress and can propagate into a crack; reject lites with edge damage in safety glazing.

Scratches on the surface reduce strength and visibility; deep scratches in the viewing area are a reject.

Bubbles, seeds, and stones are glass defects; small seeds are allowed within the quality level, and large stones are a reject.

Distortion from heat treatment (roller wave) is checked against the standard; excessive distortion is visible as waviness in reflected light.

Coating defects (pinholes, scratches) in Low-E coatings are inspected before installation; damaged coatings cannot be repaired in the field.

Caulking gun nozzle is cut at 45 degrees and sized to the joint; a nozzle cut too small forces excessive pressure and strings the sealant.

Tooling tool (plastic or wood) shapes the bead and forces sealant against the substrates; a dry finger leaves a rough bead.

Masking tape protects adjacent surfaces and gives a clean joint line; remove it while the sealant is still wet.

Backer rod is closed-cell polyethylene, sized about 25 percent larger than the joint width to hold position.

Bond-breaker tape prevents three-sided adhesion in structural joints and is applied before the sealant.

16 CFR 1201 is the federal safety glazing standard for doors and windows in residential and commercial buildings.

ANSI Z97.1 is the voluntary safety glazing standard with Class A and Class B impact ratings.

Safety glazing must be permanently marked with the manufacturer's name and the standard; unmarked glazing fails inspection.

Tempered and laminated glass are both acceptable safety glazing; wired glass is generally not accepted.

Local codes may adopt different editions; check the jurisdiction's adopted code before specifying.