Flashing, Dampproofing, and Waterproofing

Chapter Introduction

This chapter covers the techniques, materials, and principles related to flashing, dampproofing, and waterproofing in the bricklaying trade. For the Red Seal exam, you must master the fundamental distinction between these three concepts, applicable Canadian standards, installation methods, and quantity calculations. This chapter is structured to prepare you directly for exam questions, with an emphasis on common pitfalls and practical applications.

1. Definitions and Fundamental Distinctions

1.1 Flashing

Flashing is a thin barrier, typically metallic or composite, installed in a masonry wall to divert water to the exterior or toward drainage openings (drips). It does not make the wall watertight; it manages the flow of water that has already penetrated.

Primary function: Intercept water and redirect it out of the structure.

Typical locations: Above openings (windows, doors), at the base of walls, at wall-roof intersections, at parapets, and above through-wall flashing.

1.2 Dampproofing

Dampproofing aims to prevent the passage of moisture in the form of water vapor or capillary action through masonry. It does not resist hydrostatic pressure.

Typical materials: Bituminous coatings, integral water-repellent cements, silanes/siloxanes (surface water repellents).

Application: On below-grade faces of foundation walls, on walls exposed to weather.

1.3 Waterproofing

Waterproofing is a complete system that prevents the passage of water under hydrostatic pressure. It is required for below-grade structures, reservoirs, swimming pools, etc.

Typical materials: Multi-layer bituminous membranes, liquid-applied membranes (polyurea, polyurethane), bentonite, EPDM rubber membranes.

Key requirement: Must be continuous, without interruption, and capable of resisting water pressure.

1.4 Comparison Table

Characteristic	Flashing	Dampproofing	Waterproofing
Purpose	Manage infiltrated water	Prevent moisture	Prevent water under pressure
Hydrostatic pressure	Not applicable	No	Yes
Typical application	Above-grade walls	Foundations, below-grade walls	Basements, reservoirs
Materials	Metal, PVC, rubber	Bitumen, water-repellent cement	Multi-layer membranes, bentonite
Continuity required	At break points	Over entire surface	Absolute, without flaws

2. Flashing Materials: Properties and Selection

2.1 Common Metals

Material	Minimum Thickness (Gauge)	Advantages	Disadvantages
Copper	0.46 mm (28 ga)	Longevity, aesthetics	High cost, galvanic corrosion with steel
Galvanized steel	0.46 mm (28 ga)	Economical, strong	Corrosion in acidic or saline environments
Aluminum	0.61 mm (24 ga)	Lightweight, corrosion-resistant	Must not contact fresh mortar (alkaline reaction)
Stainless steel	0.38 mm (26 ga)	Excellent corrosion resistance	High cost
Lead	1.32 mm (4 lb/ft²)	Malleable, durable	Toxicity, cost, creep under load

2.2 Non-Metallic Materials

PVC (polyvinyl chloride): Flexible, chemical-resistant, but degrades in UV. Must be protected from direct sunlight exposure.

EPDM (ethylene-propylene-diene monomer rubber): Excellent elasticity, resists UV and ozone. Used for parapet flashing and movement joints.

Self-adhesive membranes (bituminous): Easy to install, adhere to the substrate, used for base flashing and sills.

2.3 Selection Criteria

29.Electrochemical compatibility: Avoid direct contact between dissimilar metals (e.g., copper and galvanized steel) to prevent galvanic corrosion. Use isolators or compatible materials.

30.Corrosion resistance: In coastal or industrial environments, prioritize stainless steel or copper.

31.Durability: Flashing must have a service life at least equal to that of the surrounding masonry.

32.Malleability: The material must be formable on site to conform to required shapes.

3. Flashing Installation Principles

3.1 General Rules

Minimum slope: All flashing must have a slope of at least 15° (or 25 mm per 300 mm) toward the exterior to ensure water drainage.

Lap: Joints between flashing sections must have a minimum lap of 75 mm (3 inches), with sealing if required.

Drip edge: The exterior edge of the flashing must have a drip edge (water drop) to prevent water from following the flashing back toward the interior.

Fastening: Flashing must be securely fastened to resist wind and thermal movement, but must allow for some expansion.

3.2 Flashing Above Openings

41.Install the flashing on the lintel or support, with a slope toward the exterior.

42.The flashing must extend 25 mm (1 inch) beyond each side of the opening.

43.Embed the ends into the mortar joints of the adjacent walls (embedment of at least 40 mm).

44.Install the drip edge at the exterior edge, projecting 10 to 15 mm from the wall plane.

45.Lay the brick or stone over top, leaving a 10 mm gap between the flashing and the brick to allow for drainage.

3.3 Base Flashing (At Grade Level)

Install the flashing at a minimum of 150 mm above finished grade.

The flashing must extend up 200 mm along the interior wall (against the foundation wall).

Use an "L-shaped" or "Z-shaped" flashing to direct water to the exterior.

Provide weep holes at a maximum spacing of 600 mm (24 inches), placed immediately above the flashing.

3.4 Parapet Flashing

The flashing must cover the top of the parapet and extend down both sides.

Use a two-piece flashing: a horizontal piece (coping) and a vertical piece (counter-flashing).

The lap between the two pieces must be at least 100 mm.

Seal all joints with a compatible sealant.

3.5 Cavity Wall Flashing

Install the flashing within the cavity, at the base of the wall and above openings.

The flashing must span the cavity and exit through the exterior veneer.

Slope the flashing toward the exterior at an angle of at least 15°.

Provide drips to prevent water from traveling back up by capillary action.

4. Dampproofing: Methods and Materials

4.1 Types of Dampproofing

Type	Application	Typical Thickness	Use
Bituminous coating	Brush, roller, spray	1.5 to 3 mm	Foundations, below-grade walls
Water-repellent cement	Trowel or spray	3 to 6 mm	Retaining walls, reservoirs
Surface water repellents (silanes/siloxanes)	Spray	Penetration 5-10 mm	Exposed walls, facades
Liquid-applied membranes (acrylic)	Roller, spray	0.5 to 1 mm	Repair, irregular surfaces

4.2 Application on Foundations

66.Surface preparation: Clean the surface, remove debris, laitance, and sharp edges. Surfaces should be damp but not saturated.

67.Crack repair: Cracks larger than 1.5 mm must be repaired before applying the dampproofing.

68.Application: Apply the coating in two cross coats (the second perpendicular to the first) for a total minimum thickness of 3 mm.

69.Protection: Protect the dampproofing from mechanical damage during backfilling (protection boards, geotextile).

4.3 Surface Water Repellents

Principle: Silanes and siloxanes penetrate the pores of the masonry and react with moisture to form a hydrophobic barrier.

Application: On a dry surface, in one or two coats, by low-pressure spraying.

Caution: Do not apply during rain or when the temperature is below 5 °C.

Verification: Water should bead on the treated surface. A simple test involves spraying water and observing the formation of droplets.

5. Waterproofing: Systems and Requirements

5.1 Common Waterproofing Systems

System	Material	Thickness	Application
Multi-layer bituminous membrane	Bituminous felt + hot bitumen	4-6 mm	Foundations, roofs
Liquid-applied membrane (polyurea)	Sprayed polyurea	1-2 mm	Complex structures, repairs
Bentonite	Sodium bentonite panels	6-10 mm	Foundations, below-grade walls
EPDM	Synthetic rubber	1.5-2 mm	Reservoirs, roofs

5.2 Waterproofing Requirements

Absolute continuity: No interruptions, no unsealed joints.

Hydrostatic pressure resistance: The system must be tested to resist the anticipated water pressure (calculated based on water height and soil conditions).

Mechanical protection: A protective layer (rigid boards, geotextile) is mandatory to prevent punctures during backfilling.

Drainage: A drainage system (drainage stone, French drains) must be installed to reduce hydrostatic pressure on the wall.

5.3 Hydrostatic Pressure Calculation

The hydrostatic pressure (P) exerted by water on a wall is calculated as follows:

P = ρ × g × h

Where:

ρ (rho) = density of water = 1000 kg/m³

g = gravitational acceleration = 9.81 m/s²

h = height of water (m)

Example: For a water height of 3 m:

P = 1000 × 9.81 × 3 = 29,430 Pa ≈ 29.4 kPa

This pressure must be less than the resistance of the chosen waterproofing system.

6. Applicable Canadian Standards

6.1 National Building Code (NBC)

The National Building Code of Canada (NBC) is the primary reference. Relevant sections include:

Article 9.20.5.1: Requirements for flashing in masonry walls.

Article 9.20.6.1: Dampproofing of foundation walls.

Article 9.20.7.1: Waterproofing of foundation walls.

Article 9.20.8.1: Drainage of foundation walls.

6.2 CSA Standards

CSA A371: "Mortar and Masonry for Construction" — covers requirements for flashing and masonry accessories.

CSA A123: Series of standards on bituminous membranes and waterproofing materials.

CSA S478: "Durability of Buildings" — provides guidelines on material selection for durability.

6.3 Canadian Electrical Code (Cross-Reference)

Although not directly related to masonry, the Canadian Electrical Code, Part I (CE Code) (C22.1) may apply when installing metal flashing near electrical components. Rule 8-200 addresses the bonding requirements for non-electrical metal elements, including large-area metal flashing. Consult this rule if the flashing is in contact with conductive parts.

7. Quantity Calculations

7.1 Flashing Calculation

To calculate the quantity of flashing required:

Quantity (m) = Perimeter of openings + Length of walls + 10% waste

Example: A building with:

8 windows measuring 1.2 m × 1.5 m

2 doors measuring 1.0 m × 2.1 m

Building perimeter: 40 m (base flashing)

Calculation:

Opening flashing: 8 × (2 × 1.2 + 2 × 1.5) + 2 × (2 × 1.0 + 2 × 2.1) = 8 × 5.4 + 2 × 6.2 = 43.2 + 12.4 = 55.6 m

Base flashing: 40 m

Total: 55.6 + 40 = 95.6 m

With 10% waste: 95.6 × 1.10 = 105.2 m

7.2 Dampproofing Calculation

Area to be treated (m²) = Perimeter × Below-grade height

Example: Foundation measuring 20 m × 10 m, below-grade height of 2.5 m:

Perimeter = 2 × (20 + 10) = 60 m

Area = 60 × 2.5 = 150 m²

With 15% waste (overlaps, wastage): 150 × 1.15 = 172.5 m²

7.3 Material Coverage Rates

Material	Typical Coverage
Bituminous coating (2 coats)	1 L / m² per coat
Water-repellent cement	3-4 kg / m² per coat
Surface water repellent (silane)	0.2-0.3 L / m²
Self-adhesive membrane	1 m² / m² (10% waste)

8. Detailed Installation Procedures

8.1 Base Flashing Installation

133.Preparation: Clean the foundation wall surface and mark the level line at 150 mm above finished grade.

134.Flashing placement: Unroll the flashing along the wall, fastening it with nails or large-head screws (spaced at 400 mm maximum).

135.Lapping: Overlap joints by a minimum of 75 mm, sealed with a compatible sealant.

136.Upstand: Fold the flashing up 200 mm against the interior wall.

137.Drip edge: Form a drip edge at the exterior edge using flashing pliers.

138.Weep holes: Install wick cords or PVC tubes every 600 mm, above the flashing.

139.Masonry: Lay the first course of brick, ensuring the weep holes remain clear.

8.2 Flashing Installation Above a Window

141.Support: Install the lintel (steel, precast concrete) with a 15° slope toward the exterior.

142.Flashing placement: Lay the flashing on the lintel, extending 25 mm beyond each side.

143.Embedment: Insert the ends into the mortar joints of the adjacent walls (40 mm depth).

144.Drip edge: Form the drip edge at the exterior edge, projecting 10-15 mm.

145.Counter-flashing: Install a counter-flashing above the window, fastened to the frame.

146.Masonry: Lay the brick above, leaving a 10 mm gap between the flashing and the brick.

8.3 Multi-Layer Waterproofing System Application

148.Preparation: Clean the surface, repair cracks, round off corners (minimum 25 mm radius).

149.Primer: Apply a bituminous primer to the dry surface.

150.First layer: Install the first membrane (bituminous felt), bonding it with hot bitumen.

151.Second layer: Install the second membrane in a staggered pattern (50% offset), with a 100 mm lap at joints.

152.Sealing: Seal all edges and joints with hot bitumen.

153.Protection: Install a protective layer (rigid extruded polystyrene boards or geotextile) before backfilling.

9. Quality Control and Inspections

9.1 Inspection Points

Slope: Verify the minimum 15° slope on all flashing.

Laps: Verify minimum 75 mm laps at joints.

Drip edge: Ensure the drip edge is continuous and projects 10-15 mm.

Weep holes: Verify maximum 600 mm spacing and that they are clear.

Continuity: For waterproofing, verify the absence of any interruptions.

9.2 Common Tests

Spray test: Spray water on the surface for 15 minutes and check for any infiltration.

Beading test: For surface water repellents, verify that water beads and runs off.

Visual inspection: Look for bubbles, blisters, delamination, or cracks in membranes.

10. Pitfalls to Avoid

168.Confusing dampproofing and waterproofing: Dampproofing does not resist hydrostatic pressure. Never use it for a deeply buried structure.

169.Forgetting the slope: Horizontal flashing without a slope retains water and causes infiltration. The 15° slope is mandatory.

170.Insufficient laps: A lap of less than 75 mm at flashing joints is a common cause of leaks.

171.Galvanic contact: Putting copper in direct contact with galvanized steel or aluminum causes accelerated corrosion.

172.Aluminum and fresh mortar: Aluminum reacts with the alkalis in fresh mortar. Protect it or use another material.

173.Blocked weep holes: Weep holes must be clear after the masonry is laid. A mortar joint blocking them defeats their purpose.

174.Applying dampproofing to a dirty surface: Adhesion is compromised. The surface must be clean and free of laitance.

175.Ignoring CSA A371 standards: This standard contains specific requirements for flashing and accessories. Do not rely solely on common practices.

176.Forgetting mechanical protection: A waterproofing membrane without protection will be punctured during backfilling.

177.Calculating quantities without waste: Always allow 10-15% for cuts, laps, and wastage.

11. Exam Tips

Memorize key values: 15° slope, 75 mm laps, 600 mm weep hole spacing, 200 mm upstand for base flashing.

Understand the differences: Flashing (water management), dampproofing (moisture), waterproofing (hydrostatic pressure). This distinction comes up frequently.

Know your materials: Properties and incompatibilities of metals (copper vs. galvanized steel, aluminum vs. mortar).

Review the standards: NBC Articles 9.20.5 to 9.20.8 and CSA A371.

Practice the calculations: Flashing quantities, dampproofing area, hydrostatic pressure.

Read questions carefully: Exam questions often use precise terminology. "Dampproofing" and "waterproofing" are not interchangeable.

Summary

Flashing is a barrier that manages water already infiltrated into the masonry. It must have a 15° slope toward the exterior, 75 mm laps, and be equipped with a drip edge.

Dampproofing protects against moisture (capillary action, vapor) without resisting hydrostatic pressure. It is applied in two cross coats on foundations.

Waterproofing resists hydrostatic pressure and requires absolute continuity, mechanical protection, and a drainage system.

Flashing materials must be electrochemically compatible. Avoid copper-galvanized steel contact and aluminum-fresh mortar contact.

Weep holes are essential for drainage and must be spaced at a maximum of 600 mm.

Canadian standards (NBC Articles 9.20.5 to 9.20.8, CSA A371) define minimum requirements.

Quantity calculations must include 10-15% waste.

Hydrostatic pressure is calculated using the formula P = ρ × g × h (in Pa or kPa).

Pitfalls to Avoid

Pitfall	Consequence	Solution
Confusing dampproofing and waterproofing	Infiltration under pressure	Identify hydrostatic pressure before choosing
Flashing without slope	Stagnant water, infiltration	Minimum 15° slope
Lap < 75 mm	Leaks at joints	Respect minimum lap
Copper + galvanized steel	Galvanic corrosion	Isolate metals or choose compatible materials
Aluminum + fresh mortar	Corrosion of aluminum	Protect aluminum or use another metal
Blocked weep holes	Water trapped in cavity	Verify clearance after installation
Membrane without protection	Puncture during backfilling	Install a protective layer
Application on dirty surface	Delamination of dampproofing	Clean and prepare the surface
Ignoring material waste	Shortage of materials on site	Add 10-15% to calculations
Not consulting standards	Non-compliance with code	Review NBC 9.20.5 to 9.20.8 and CSA A371

This chapter prepares you for Red Seal exam questions on flashing, dampproofing, and waterproofing. Review the numerical values, conceptual distinctions, and Canadian standards. Good luck with your preparation.

Flashing, Dampproofing, and Waterproofing