Repair, Replacement, and Maintenance
Chapter Introduction
This chapter covers all the repair, replacement, and maintenance work that a glazier must master for the Red Seal exam. These activities represent a significant portion of daily work and require in-depth knowledge of materials, techniques, and safety standards. You must understand not only how to perform this work, but also why it is necessary, how to diagnose failures, and how to prevent future problems.
Diagnosing Common Failures
Identifying Signs of Glazing Failure
Before any repair, you must be able to correctly identify the cause of the failure. The most common signs are:
Cracks: fracture lines in the glass, often caused by thermal shock, mechanical stress, or impact.
Fogging or condensation between panes: indicates a failure of the edge seal of an insulating glass unit (IGU).
Cloudiness or whitish deposit: a sign of chemical degradation of the glass or moisture infiltration.
Play in the frame: excessive movement of the glazing within its frame, indicating defective sealant or setting blocks.
Corrosion of fasteners: visible on metal fixings, often due to electrochemical incompatibility.
Diagnostic Methods
Diagnosis must be methodical. Follow these steps:
14.Visual inspection: examine the glazing from different angles and lighting conditions. Use a flashlight to detect micro-cracks.
15.Sound test: gently tap the glass surface. A dull sound may indicate sealant detachment or internal failure.
16.Moisture measurement: use a hygrometer to confirm the presence of moisture in an IGU.
17.Tolerance check: measure the gap between the glass and the frame using a feeler gauge. Typical tolerances are 3 to 6 mm for residential glazing and 6 to 12 mm for commercial glazing.
Common Causes of Failure
| Cause | Symptom | Solution |
|---|
| Thermal shock | Crack running from the edge toward the centre | Replace the glazing, check shading |
| Mechanical impact | Star-shaped crack or point impact | Replace the glazing |
| IGU seal failure | Internal fogging | Replace the complete unit |
| Dried-out putty | Water infiltration, play | Reseal |
| Differential expansion | Crack along the frame | Use appropriate setting blocks |
Glass Repair
Repairing Cracks and Chips
Small cracks and chips can sometimes be repaired without replacing the entire glazing, but this practice is limited. For the exam, you must know the repairability criteria:
Crack under 25 mm: repairable by resin injection.
Chip under 6 mm in diameter: repairable by injection.
Crack extending to the edge: not repairable, replacement required.
Crack over 300 mm: not repairable, replacement required.
The resin injection technique consists of:
28.Cleaning the area with an appropriate solvent.
29.Applying a surface adhesive to create a barrier.
30.Injecting the resin using a vacuum or pressure injector.
31.Allowing polymerization according to manufacturer specifications (generally 30 to 60 minutes under a UV lamp).
32.Polishing the surface to remove excess.
Repairing Putties and Sealants
Sealant replacement is a common operation. The essential steps are:
35.Removing the old sealant: use a putty knife, scraper, or rotary tool. Be careful not to damage the glass or frame.
36.Cleaning the surface: remove all traces of sealant, dust, or grease with an appropriate solvent (for example, acetone or a commercial degreaser).
37.Applying the new sealant: use a caulking gun for cartridges or a trowel for bulk sealants. Apply in a continuous bead, free of air bubbles.
38.Smoothing: use a smoothing tool or a moistened finger to create a clean, uniform surface.
39.Curing time: respect the curing time indicated by the manufacturer (often 24 to 72 hours).
Repairing Frames and Sashes
Wood, aluminum, or PVC frames may require repairs:
Wood: replacement of rotted sections, sanding, application of primer and paint. Use wood of the same species and treated.
Aluminum: straightening deformed profiles, replacing gaskets, touching up anodized finish.
PVC: welding cracks with a specific welding iron, replacing damaged profiles.
Glass Replacement
Standard Replacement Procedure
Replacing glazing follows a precise sequence. Here is the complete procedure:
48.Site assessment: measure the existing glazing, identify the glass type (tempered, laminated, insulating, etc.), and check the condition of the frame.
49.Work area preparation: set up a safety perimeter, protect adjacent surfaces with tarps.
50.Removing the old glazing:
Remove the stops or retaining profiles.
Cut the putty or sealant with a knife.
Remove the glazing with safety suction cups.
Place it on a flat, padded surface.
55.Frame preparation:
Clean the glazing pocket (rabbet).
Apply primer if necessary (wood).
Install setting blocks (usually neoprene or plastic).
59.Installing the new glazing:
Lift the glazing with suction cups.
Position it in the rabbet, respecting the perimeter clearances.
Install side blocks to keep the glazing centred.
63.Fastening and sealing:
Reinstall the stops or profiles.
Apply the putty or sealant.
Smooth and clean up excess.
67.Final inspection: check opening and closing (if a window), sealing, and overall appearance.
Calculating Replacement Dimensions
Dimension calculations are critical. For a single glazing in a rabbet:
Glass width = Rabbet width − (2 × perimeter clearance)
Glass height = Rabbet height − (2 × perimeter clearance)
The perimeter clearance depends on the glazing type and size:
| Glazing Dimension | Minimum Perimeter Clearance | Maximum Perimeter Clearance |
|---|
| ≤ 1 m² | 3 mm | 5 mm |
| 1 to 3 m² | 4 mm | 6 mm |
| > 3 m² | 6 mm | 10 mm |
For IGUs, add 2 mm to the perimeter clearance to compensate for internal expansion.
Replacing Insulating Glass Units (IGUs)
Replacing an IGU is more complex than replacing a single glazing:
77.Precise measurement: measure the total thickness of the IGU (usually 20 to 28 mm) and the exterior dimensions.
78.Checking the gas type: modern IGUs contain argon or krypton. Check the label or manufacturer specifications.
79.Ordering the replacement unit: specify the glass type (tempered, laminated, low-emissivity), pane thickness, spacer width, and gas type.
80.Installation: follow the standard procedure, but pay particular attention to setting blocks. IGUs must be supported along the full width of the bottom edge.
81.Sealing: use a sealant compatible with the spacer (butyl, polyurethane, silicone). Never use oil-based putty on an IGU, as it can degrade the seal.
Preventive Maintenance
Regular Maintenance Program
A preventive maintenance program extends the service life of glazing and reduces replacement costs. Recommended intervals are:
| Component | Inspection Frequency | Recommended Action |
|---|
| Exterior sealants | 2 times per year | Cleaning, touch-up if cracked |
| Gaskets | 1 time per year | Replacement if hardened or cracked |
| Hardware (hinges, locks) | 1 time per year | Lubrication, adjustment |
| Drains and vents | 2 times per year | Cleaning to ensure drainage |
| Glass (cracks, chips) | 1 time per year | Visual inspection, repair if necessary |
| IGU seals | 1 time per year | Seal integrity check |
Cleaning Glazing
Cleaning is an essential maintenance operation. Rules to know:
Use non-abrasive products (neutral pH) for coated glazing (low-emissivity glass).
Avoid razor blades on tempered or laminated glass, unless the dirt is stubborn and you use a new blade at a 30° angle.
For IGUs, never clean the edges with pressurized water, as this can damage the seal.
Use a professional-grade rubber squeegee to avoid streaks.
Checking Thermal Performance
Maintenance should include a check of the thermal performance of glazing. Typical values to know:
| Glazing Type | U-Value (W/m²·K) | Solar Heat Gain Coefficient (SHGC) |
|---|
| Single glazing | 5.8 | 0.85 |
| Double glazing (air) | 2.8 | 0.75 |
| Double glazing (argon) | 2.4 | 0.70 |
| Triple glazing (argon) | 1.8 | 0.60 |
| Double glazing with low-emissivity | 1.6 | 0.40 |
An increase in the U-value compared to original specifications indicates an IGU failure.
Applicable Standards and Codes
Canadian Electrical Code, Part I
Although a glazier does not work directly on electrical circuits, you must know the rules regarding safety distances when working near power lines. Rule 8-200 of the Canadian Electrical Code, Part I, stipulates that workers must maintain a minimum distance of 3 metres from any uninsulated power line. This rule applies when installing glazing at height or when using scaffolding.
CSA B149.1 (Natural Gas and Propane Installation Code)
This standard concerns gas installations, but it is relevant to the glazier because it specifies ventilation requirements. When replacing glazing in buildings with combustion appliances, you must ensure that natural ventilation is not compromised. The standard requires that ventilation openings not be obstructed by fixed glazing.
Safety Standards for Safety Glazing
The following standards are essential for replacement work:
CAN/CGSB-12.1: Safety glass for architecture — specifies requirements for tempered and laminated glass.
CAN/CGSB-12.3: Safety glass for doors and showers — requires tempered glass in hazardous areas.
CAN/CGSB-12.8: Insulating glass units — specifies performance and sealing requirements.
Fall Protection Safety Rules
Repair and replacement work often involves working at heights. Fall protection requirements are defined in the Canada Occupational Health and Safety Regulations (federal COHSR, Part II). Key points:
Use a safety harness with a lanyard of 1.8 m maximum if you are working more than 3 m above the ground.
Scaffolding must be erected according to manufacturer specifications and inspected before each use.
Aerial work platforms (boom lifts) must be used in accordance with the manufacturer's manual.
Specific Procedures
Replacing Glazing in a Door
Replacing door glazing presents particular challenges:
114.Removing the door: if possible, remove the door to work flat. This reduces the risk of breakage and facilitates access.
115.Glass protection: use vacuum suction cups to handle the glass safely.
116.Use of tempered glass: doors must use tempered or laminated glass according to building code requirements.
117.Installing stops: fasten the stops with screws or nails, being careful not to overtighten them to avoid stress on the glass.
Repairing Shower Glazing
Shower glazing is subject to particular stresses:
Use tempered glass of 6 mm minimum.
Edges must be polished or smoothed to prevent injury.
Hinges and supports must be stainless steel to resist corrosion.
Replacement must respect exact dimensions, as tolerances are tight (± 1 mm).
Replacing Roof Glazing (Skylights)
Skylights present specific risks:
126.Safe access: use scaffolding or an aerial lift, never a ladder alone.
127.Fall protection: install temporary guardrails around the opening.
128.Glass type: use laminated glass or polycarbonate to withstand hail impacts.
129.Sealing: apply a high-quality sealant (silicone or polyurethane) and check drainage.
Calculations and Measurements
Calculating Glazing Area
The area of a rectangular glazing is:
Area (m²) = Length (m) × Width (m)
For a triangular glazing:
Area (m²) = (Base × Height) / 2
For a trapezoidal glazing:
Area (m²) = ((Base1 + Base2) / 2) × Height
Calculating Wind Load
The wind load on glazing is calculated using the formula:
P = q × Cp × Ce
Where:
P = wind pressure (Pa)
q = dynamic wind pressure (Pa) — depends on wind speed and building height
Cp = pressure coefficient (depends on building shape and glazing position)
Ce = exposure coefficient (depends on topography and terrain roughness)
For the exam, you must know typical values:
| Wind Speed (km/h) | Dynamic Pressure (Pa) |
|---|
| 80 | 300 |
| 100 | 470 |
| 120 | 680 |
| 140 | 920 |
Calculating Thermal Expansion
Glass expands with heat. The coefficient of thermal expansion for glass is 9 × 10⁻⁶ /°C. Expansion is calculated by:
ΔL = α × L × ΔT
Where:
ΔL = change in length (mm)
α = coefficient of expansion (9 × 10⁻⁶ /°C)
L = initial length (mm)
ΔT = temperature change (°C)
Example: A glazing 2000 mm long undergoes a temperature change of 40 °C.
ΔL = 9 × 10⁻⁶ × 2000 × 40 = 0.72 mm
This expansion must be accommodated by the perimeter clearance.
Pitfalls to Avoid
160.Not measuring the glazing before ordering: always measure twice, at different locations, and use the smallest dimension.
161.Using sealant incompatible with the IGU: oil-based putties degrade butyl seals. Use only compatible products.
162.Forgetting setting blocks: without setting blocks, the glazing rests directly on the frame, creating stress points that can cause cracks.
163.Overtightening stops: overtightening creates stress on the glass. Tighten just enough to hold the glazing in place.
164.Ignoring safety requirements for tempered glass: in doors, showers, and hazardous areas, tempered glass is mandatory. Never replace it with annealed glass.
165.Working without fall protection: falls are the leading cause of accidents in the trade. Always use protective equipment.
166.Not checking material compatibility: some sealants do not adhere to certain frames (for example, silicone does not adhere to untreated PVC).
167.Forgetting to clean the glazing pocket: a dirty glazing pocket compromises sealant adhesion and sealing.
168.Cutting sealant with a knife too deeply: you risk damaging the frame or adjacent glazing.
169.Not respecting curing times: uncured sealant can deform and lose its sealing properties.
Summary
Diagnosis is the first step of any repair. Identify the cause before proposing a solution.
Cracks under 25 mm and chips under 6 mm can be repaired by resin injection. Beyond that, replacement is necessary.
Replacing glazing follows a standard procedure: assessment, removal, preparation, installation, sealing, inspection.
Perimeter clearances must be respected to accommodate thermal expansion and building movement.
IGUs require particular precautions: sealant compatibility, support along the full width, respect for gas type.
Preventive maintenance extends the service life of glazing and reduces costs.
Canadian standards (CAN/CGSB, Canadian Electrical Code, CSA B149.1) define safety and performance requirements.
Calculations for area, wind load, and expansion are essential for properly sizing glazing.
Safety is paramount: fall protection, safe glass handling, respecting distances from power lines.
Self-Assessment Questions
181.What is the correct procedure for replacing a failed IGU?
182.What are the repairability criteria for a crack in glazing?
183.How do you calculate the thermal expansion of a 2500 mm glazing subjected to a temperature change of 50 °C?
184.What are the recommended perimeter clearances for a 2.5 m² glazing?
185.What types of glass are mandatory in doors and showers according to CAN/CGSB standards?
186.What precautions should be taken when cleaning low-emissivity glass?
187.What minimum distance must you maintain from power lines according to the Canadian Electrical Code, Part I?
188.What are the signs of IGU failure and how do you diagnose them?
189.How do you choose the right sealant for an aluminum frame?
190.What are the steps of a preventive maintenance program for exterior glazing?
Answers: (1) Precise measurement, ordering a compatible unit, removing the old one, frame preparation, installation with setting blocks along the full width, sealing with compatible sealant. (2) Crack < 25 mm, chip < 6 mm, no crack extending to the edge, no crack > 300 mm. (3) ΔL = 9 × 10⁻⁶ × 2500 × 50 = 1.125 mm. (4) 4 to 6 mm. (5) Tempered or laminated glass. (6) Non-abrasive products, neutral pH, avoid razor blades. (7) 3 metres. (8) Internal fogging, cloudiness, moisture test. (9) Silicone or polyurethane sealant compatible with aluminum. (10) Semi-annual inspection of sealants, annual inspection of gaskets and hardware, cleaning of drains.
