Glass Types and Materials

Types of Glass and Materials

Chapter Introduction

This chapter forms the foundation of your glazing practice. Before cutting, handling, or installing glass, you must know precisely the nature of the material you have in your hands. The Red Seal exam requires in-depth knowledge of glass types, their mechanical, thermal, and optical properties, as well as related materials used for installation. This chapter covers all the mandatory content for the exam, organized logically to facilitate memorization and practical application.

Classification of Basic Glasses

Annealed Glass

Annealed glass is the standard flat glass produced by the float process. It is cooled slowly and uniformly after formation, which eliminates internal stresses. It is the base material from which all other processed glasses are manufactured.

Key Properties:

Uses: Annealed glass is used in interior applications, furniture, picture frames, and as a substrate for tempering or laminating. It is never used in doors, showers, or safety applications without additional treatment.

Major Limitation: When it breaks, it forms large, sharp, and dangerous shards. Its resistance to thermal shock is limited to approximately 40°C difference between the center and the edge.

Tempered Glass

Tempered glass is annealed glass that has undergone a thermal tempering treatment. It is heated to approximately 650°C and then rapidly cooled by air jets. This process creates compression on the surface and tension in the interior.

Properties After Tempering:

Golden Rules for the Glazier:

On-Site Identification: Use a polariscope or observe the tong marks. When in doubt, check for the manufacturer's certificate of conformity.

Laminated Glass

Laminated glass consists of two or more sheets of glass (annealed, tempered, or heat-strengthened) bonded together by an interlayer of polyvinyl butyral (PVB), ionomer (SentryGlas), or resin.

Interlayer Characteristics:

Breakage Behavior: If the glass breaks, the fragments adhere to the interlayer. The glazing remains in place, preventing injuries from falling glass and delaying intrusion.

Typical Applications:

Performance Calculation: For a 6 mm + 6 mm laminated glazing with a 0.76 mm interlayer, the total thickness is 12.76 mm. The equivalent strength is approximately that of a monolithic glass of the same total thickness, but with a radically different breakage behavior.

Heat-Strengthened Glass

Heat-strengthened glass is thermally treated like tempered glass, but with a slower cooling process. It achieves approximately 2 times the strength of annealed glass (80-100 MPa).

Differences from Tempered Glass:

Specialty and Performance Glasses

Low-Emissivity Glass (Low-E)

Low-E glass has a microscopic coating (metal oxide) that reduces the thermal emissivity of the surface. This coating reflects infrared radiation while allowing visible light to pass through.

Two Types of Coatings:

Installation Rules: The Low-E coating must be oriented toward the interior of the sealed unit (surface 2 or 3 depending on configuration). Never expose the magnetron coating to open air — it is fragile and deteriorates quickly.

Reflective Glass (Solar Control Glass)

Reflective glass has a metallic or metal oxide coating that reflects a portion of solar radiation. It reduces glare and thermal load.

Performance Indicators:

Calculation Example: A unit with reflective glass at 35% VLT transmits 35% of incident visible light. Standard clear glazing transmits approximately 80-88%.

Body-Tinted Glass

Tinted glass contains metal oxides incorporated during manufacturing. Common colors: bronze, grey, green, blue.

Properties:

Acoustic Control Glass

Acoustic glass uses special PVB interlayers and asymmetric thicknesses to optimize sound insulation.

Principle: Using two panes of different thicknesses (e.g., 6 mm + 8 mm) avoids resonance at the same frequency. The PVB interlayer acts as a damper.

Sound Transmission Class (STC) / Weighted Sound Reduction Index (Rw): Expressed in decibels (dB). A standard 4/12/4 glazing offers approximately 30 dB. An acoustic glazing 6/16/6 with acoustic PVB can achieve 38-40 dB.

Safety Glass and Wired Glass

Wired glass contains an embedded metal mesh. It is used in fire-resistance and vandal-resistance applications.

Important Limitations:

Insulating Glass Units (IGUs)

Construction of an IGU

An insulating glass unit (double or triple glazing) consists of two or three sheets of glass separated by spacers and hermetically sealed.

Components:

Standard Designation: An IGU 6/12/6 means: 6 mm glass, 12 mm space, 6 mm glass. A triple IGU 6/12/6/12/6: three 6 mm panes with two 12 mm spaces.

Thermal Performance

The U-value (thermal transmittance coefficient) measures the amount of heat transmitted through the glazing. The lower the U-value, the better the insulation.

Condensation Factor (interior surface temperature): The lower the U-value, the higher the interior surface temperature, reducing the risk of condensation.

Thermal Load Calculation

Thermal stress in glazing is caused by the temperature difference between the center (exposed to sun) and the edge (shaded by the frame).

Simplified Formula:

ΔT = (α × I × A) / (h × P)

Where:

Rule of Thumb: For tinted or reflective glass, the temperature difference between the center and the edge must not exceed the thermal resistance of the glass. Annealed glass withstands approximately 40°C difference; tempered glass withstands 250°C.

Installation Materials and Accessories

Sealants and Caulking

Types of Sealants:

Compatibility Rule: Acetic silicone (which releases acetic acid) must never be used in contact with polysulfide or polyurethane — it causes their degradation. Use neutral silicone.

Setting Blocks

Setting blocks support the weight of the glazing and maintain spacing within the frame.

Requirements:

Calculating the Number of Blocks: For glazing wider than 1.5 m, use at least 3 support blocks. For glazing wider than 2.5 m, use 4 blocks.

Profiles and Frames

Framing Materials:

Thermal Expansion: Aluminum expands 2.4 mm per 10 m for a 100°C variation. PVC expands 5.5 mm for the same variation. Expansion joints must be planned accordingly.

Applicable Canadian Standards

CAN/CGSB-12.1 — Safety Glass

This standard defines the requirements for safety glass used in doors, showers, low windows, and similar applications.

Key Requirements:

CAN/CGSB-12.2 — Flat Glass

This standard covers flat annealed glass, its dimensions, tolerances, and permissible defects.

Thickness Tolerances:

CAN/CGSB-12.3 — Tempered Glass

This standard specifies requirements for flat tempered glass, including fragmentation and strength tests.

National Building Code of Canada (NBC)

The NBC references the CAN/CGSB standards for glazing safety requirements. Relevant sections include:

Mandatory Marking: All safety glass must be permanently marked with the manufacturer's name and the standard of conformity (e.g., "CAN/CGSB-12.1"). This marking must be visible after installation.

Installation Procedures and Best Practices

Receiving and Storing Glass

Receiving Procedure:

Storage:

Handling and Lifting

Safety Rules:

Weight Calculation: Weight (kg) = Area (m²) × Thickness (mm) × 2.5

Example: A 1.5 m × 2.0 m panel of 10 mm glass weighs:

1.5 × 2.0 × 10 × 2.5 = 75 kg

Installation in a Frame

Standard Procedure:

Minimum Clearance in Frame: 3 mm per side to allow for thermal expansion. For large panels (over 2 m²), allow 5-6 mm per side.

Defect Identification and Quality Control

Manufacturing Defects

Permissible Defects per CAN/CGSB-12.2:

Installation Defects

On-Site Testing

Polarization Test: Use a polariscope to verify if glass is tempered. Tempered glass shows colored stress patterns; annealed glass shows no pattern.

Sound Test: Tap the glass lightly. Tempered glass produces a sharper, more metallic sound than annealed glass. This test is indicative but not conclusive.

Practical Calculations for the Glazier

Calculating Allowable Deflection

The maximum deflection of glazing under wind load is limited to L/175, where L is the smallest panel dimension.

Example: For a 1200 mm × 1500 mm panel, the maximum deflection is:

1200 / 175 = 6.9 mm

Calculating Wind Resistance

The design wind pressure is determined according to the NBC (Appendix C). For a standard building, the pressure can be calculated as:

P = q × Ce × Cg × Cp

Where:

Rule of Thumb: For most residential applications, the design wind pressure is 0.5 to 1.0 kPa. For high-rise buildings, it can reach 3-5 kPa.

Calculating Minimum Thickness

For simple glazing supported on 4 sides, the minimum thickness can be estimated:

t = (P × A) / (σ × k)

Where:

Example: Panel 1.2 m × 1.5 m, wind pressure 1.0 kPa, annealed glass:

t = (1.0 × 1.8) / (17 × 0.4) = 0.26 m = 260 mm

This result indicates that single annealed glass is not suitable — you must use tempered glass or increase the number of supports. In practice, manufacturer tables or calculation software are used.

Pitfalls to Avoid

Summary

Self-Assessment Questions

This chapter covers all the knowledge required for the "Types of Glass and Materials" section of the Red Seal exam. Review the Canadian standards, basic calculations, and installation procedures. Mastery of these concepts will enable you to answer exam questions correctly and apply these principles in your daily practice.