Sealants, Gaskets, and Weatherproofing

Sealants, Joints, and Weatherproofing

Chapter Introduction

This chapter covers the full range of weatherproofing and joint sealing systems that a journeyman glazier must master for the Red Seal exam. The performance of a glazed façade depends as much on the quality of the glass as on the continuity of its weathertight envelope. You must understand failure mechanisms, material properties, and installation procedures that comply with Canadian standards.

1. Roles and Functions of Weatherproofing Systems

1.1 Primary Functions

A weatherproofing system performs four distinct functions:

1.2 Distinction: Mastic vs. Caulking vs. Sealant

In Canada, these terms are often confused, but technically:

Golden rule: for structural glazing and movement joints, use a sealant; for static fill joints, a caulking may suffice.

2. Sealant Classification

2.1 Main Chemical Families

2.2 Silicones: Acetoxy vs. Neutral

Acetoxy silicone (acetic acid-based) releases a vinegar odour during curing. It is ideal for glass and ceramic, but corrodes ferrous metals, copper, and zinc. It must never be used on concrete, masonry, or alkaline substrates.

Neutral silicone (oxime- or alcohol-based) does not attack metals and is suitable for almost all substrates. For structural glazing, use exclusively a neutral silicone certified for structural application.

2.3 Selection Criteria

To choose a sealant, evaluate:

3. Joint Design

3.1 Calculating Joint Width

The minimum width of an expansion joint is calculated using the formula:

W = (ΔT × L × α) / (M × 100)

Where:

Practical example: A 1500 mm glass panel, with ΔT = 60 °C, α = 9 × 10⁻⁶ /°C (glass), and a sealant with 25% movement:

W = (60 × 1500 × 9 × 10⁻⁶) / 0.25 = 3.24 mm

The practical minimum width is 6 mm to allow proper application. If the calculation gives less than 6 mm, use 6 mm.

3.2 Width-to-Depth Ratio

The aspect ratio of the joint is critical:

Rule of thumb: the sealant depth must never exceed half the width for an expansion joint. Beyond that, the sealant cannot deform properly and is subjected to excessive stress.

3.3 Backer Rod

The backer rod (polyethylene foam) serves three functions:

Types of backer rods:

Backer rod diameter: must be 25% larger than the joint width for a snug fit.

4. Surface Preparation

4.1 Fundamental Requirements

Surface preparation is responsible for 80% of sealant failures. The three requirements are:

4.2 Cleaning Procedures

Double-cloth method: apply the solvent with a clean cloth, then wipe with a second clean, dry cloth before the solvent evaporates. Never rub back and forth (cross-contamination).

4.3 Primers

Primer improves adhesion on difficult substrates:

Adhesion test: after applying the primer, allow 24 hours to dry, then perform a pull-off test. Failure must be cohesive (tear within the sealant) and not adhesive (separation from the substrate).

5. Sealant Application

5.1 Application Conditions

Dew point: the substrate temperature must be at least 3 °C above the dew point to prevent condensation.

5.2 Application Techniques

Cartridge gun:

Tooling:

5.3 Glazing Joints

For glazing, the sealant plays a structural or non-structural role:

Application rule: for structural glazing, apply the sealant on both faces (double bead) and ensure complete contact with both the glass and the frame.

6. Gaskets and Weatherproofing Profiles

6.1 Types of Gaskets

Gaskets (preformed seals) are classified by their installation method:

6.2 Gasket Materials

Canadian recommendation: for exterior applications, use EPDM or silicone. PVC degrades rapidly under UV and becomes brittle at low temperatures.

6.3 Gasket Installation

Compression gasket:

Slide-in gasket:

Compression requirement: the gasket must be compressed 15 to 25% of its original thickness. Insufficient compression causes leaks; excessive compression causes creep and loss of seal.

7. Setting Blocks

7.1 Functions of Setting Blocks

Setting blocks provide:

7.2 Types and Dimensions

Positioning rules:

7.3 Hardness Requirements

Caution: never use wood, metal, or non-compliant hard plastic blocks. They create stress concentration points that can fracture the glass.

8. Applicable Canadian Standards

8.1 Main Reference Standards

8.2 National Building Code of Canada (NBC)

The National Building Code of Canada (NBC) imposes specific requirements:

Key NBC requirement: glazing systems must be designed to drain water that enters the cavity (drainage and ventilation). A non-drained glazing system is non-compliant.

8.3 Energy Performance Standards

Air sealing requirements are defined in:

9. Common Failures and Diagnostics

9.1 Failure Modes

9.2 Field Diagnostics

On-site adhesion test:

Hardness test: use a Shore A durometer. Hardness higher than specification indicates a sealant that is too old or poorly formulated.

9.3 Repair vs. Replacement

10. Health and Safety

10.1 Chemical Hazards

WHMIS requirement: all products must have a Safety Data Sheet (SDS) accessible on site. Wear the specified personal protective equipment (PPE).

10.2 Physical Hazards

11. Testing Procedures and Quality Control

11.1 Pre-Application Testing

11.2 In-Process Control

11.3 Post-Application Testing

Summary

Pitfalls to Avoid

This chapter covers the essential knowledge for the "Sealants, Joints, and Weatherproofing" section of the Red Seal exam. Review the cited CGSB and ASTM standards, and practice joint width calculations until they become automatic.