Adhesives, Underlayments, and Moisture Barriers

Adhesives, Underlayments, and Vapour Barriers

Chapter Introduction

This chapter covers the materials and techniques essential to substrate preparation and floor covering installation. Mastering adhesives, underlayments, and vapour barriers is crucial for the Red Seal exam, as these elements determine the durability, performance, and compliance of the installation. Failure in this area leads to costly problems: delamination, buckling, mould, or voided warranties. This chapter prepares you to identify, select, and apply these materials according to Canadian standards.

Adhesives: Classification and Selection

Role and Fundamental Requirements

A floor covering adhesive must create a permanent bond between the covering and the substrate, withstand mechanical stresses (shear, tension), and resist environmental conditions (moisture, temperature, chemicals). Selection is based on three factors: the type of covering, the type of substrate, and the service conditions (traffic, moisture, exposure).

Types of Adhesives and Their Applications

Adhesive Type	Compatible Coverings	Key Characteristics	Working Time (Open/Closed)
Water-based acrylic	Vinyl, linoleum, rubber	Low odour, water cleanup, flexible	10-30 min open / 5-15 min closed
Urethane (polyurethane)	Engineered wood, parquet, luxury vinyl tile (LVT)	Very high bond strength, moisture resistant, elastic	20-40 min open / 10-20 min closed
Epoxy	Vinyl, rubber, damp substrates	Extreme chemical resistance, waterproof, rigid	30-60 min open / 15-30 min closed
Neoprene (contact)	Rubber, linoleum, some vinyls	Applied to both surfaces, immediate bond	Dry contact (no open time)
Solvent-based mastic	Vinyl, carpet	High initial tack, strong odour, flammable	15-45 min open / 5-15 min closed
Carpet adhesive (acrylic or resin-based)	Carpet (tiles, rolls)	Trowel application, high coverage rate	10-20 min open / 5-10 min closed

Calculating Adhesive Quantity

The amount of adhesive required is calculated based on the area to be covered and the coverage rate specified by the manufacturer. The basic formula is:

Quantity (L) = Area (m²) ÷ Coverage Rate (m²/L)

Example: for a 45 m² area with an adhesive covering 6 m²/L, you need 45 ÷ 6 = 7.5 L. Add 10% for waste (spillage, touch-ups): 7.5 × 1.10 = 8.25 L. Round up to the next container size.

Application Techniques

Notched trowel: choose the notch size according to the adhesive type and covering. V-notches (1.5 mm to 3 mm) for thin vinyls; U-notches (3 mm to 6 mm) for thick coverings or porous substrates.

Open time: the period during which the adhesive remains tacky after application. Strictly follow the manufacturer's limits. Exceeding the open time makes the bond ineffective.

Press time: after installation, apply uniform pressure (minimum 45 kg roller) to ensure full contact between the covering and the adhesive.

Ambient temperature: maintain between 18 °C and 30 °C during application and curing. Water-based adhesives must not freeze.

Common Adhesive Pitfalls

Using an adhesive unsuitable for the substrate (e.g., acrylic adhesive on a damp substrate).

Ignoring the substrate moisture level (above 75% RH, use an epoxy adhesive or a vapour barrier).

Applying a layer too thick or too thin (follow the recommended trowel).

Not ventilating solvent-based adhesives (fire and toxicity risk).

Underlayments: Functions and Types

Role of Underlayments

Underlayments (or insulation underlayments) serve to:

Level minor substrate irregularities (up to 3 mm).

Dampen impact and footstep noise.

Provide thermal insulation.

Provide a stable surface for the covering.

Act as a moisture barrier (certain types).

Types of Underlayments

Type	Material	Typical Thickness	Primary Use	Moisture Resistance
Polyethylene foam	Cross-linked or non-cross-linked foam	2-6 mm	Under vinyl, LVT, floating parquet	Low to moderate
Cork	Natural agglomerated cork	2-5 mm	Under parquet, LVT, acoustics	Moderate (treated)
Felt	Compressed recycled fibres	3-6 mm	Under floating parquet, carpet	Low
Recycled rubber	Bonded rubber granules	3-8 mm	Under gym floors, high-traffic areas	High
High-density fibreboard (HDF)	Compressed wood fibres	6-12 mm	Under floating parquet (with integrated barrier)	High (with treatment)
Composite with integrated barrier	Foam + polyethylene film	3-5 mm	Under LVT, floating parquet	High (vapour barrier)

Selection Criteria

Acoustics: for multi-family buildings, the impact sound insulation index (ΔLw) must be ≥ 15 dB according to the National Building Code (NBC). Cork or rubber underlayments offer the best performance.

Leveling: an underlayment does not compensate for a substrate irregularity greater than 3 mm over 3 m. Use a self-leveling compound before installation.

Compatibility: check the covering manufacturer's recommendations. Some coverings (e.g., rigid-core vinyl) require specific underlayments.

Compression: the underlayment must not compress more than 10% under static load (furniture, partitions).

Underlayment Installation

39.Substrate preparation: sweep, vacuum, remove any dust, grease, or moisture.

40.Laying strips: roll out the underlayment perpendicular to the direction of the covering installation. Joints must be flush, without overlap.

41.Fastening: staple or glue the strips together (never to the substrate for floating floors). Use special underlayment tape for the joints.

42.Cutting: leave a 6 mm (1/4 in) expansion gap against the walls to allow for expansion.

43.Vapour barrier: if the underlayment does not have an integrated barrier, install a 6 mil (0.15 mm) polyethylene film under the underlayment, with a 200 mm overlap and a 50 mm rise up the walls.

Common Underlayment Pitfalls

Installing an underlayment on a damp substrate (mould, delamination).

Using an underlayment too thick for a thin covering (instability, indentation).

Forgetting the expansion gap against the walls (covering buckling).

Layering two underlayments (instability, voided warranty).

Vapour Barriers: Principles and Application

Definition and Role

A vapour barrier is a material with a water vapour permeance of less than 0.1 ng/(Pa·s·m²) (0.1 perm). It prevents moisture migration from the substrate (concrete slab) to the covering. Moisture can come from the water table, recent construction (uncured concrete), or ambient air.

Canadian Standards and Requirements

National Building Code (NBC): requires a vapour barrier under any resilient or wood floor covering installed on a concrete slab in contact with the ground or over a ventilated crawl space.

ASTM F1869: test method for measuring the water vapour emission rate of a concrete slab (calcium chloride test). The maximum allowable value is 3.0 kg/92.9 m²/24 h (3 lb/1000 ft²/24 h) for most coverings.

ASTM F2170: test method for measuring the internal relative humidity of concrete. The maximum allowable value is 75% RH for vinyl coverings, 80% RH for engineered wood coverings.

Types of Vapour Barriers

Type	Material	Thickness	Permeance	Use
Polyethylene film	HDPE or LDPE	6 mil (0.15 mm)	< 0.01 perm	Under slabs, under underlayments
Self-adhesive membrane	Modified bitumen + film	1-2 mm	< 0.01 perm	On slabs, repairs
Vapour barrier paint	Epoxy or urethane	0.2-0.5 mm	< 0.1 perm	On existing slabs
Liquid membrane	Polyurethane or acrylic	0.5-1 mm	< 0.1 perm	On slabs, wet areas

Installation Procedures

59.Moisture test: perform ASTM F1869 (emission) and F2170 (internal humidity) tests before any installation. Record the results in the job report.

60.Slab preparation: the slab must be clean, dry, free of cracks and laitance. Repair cracks with epoxy filler.

61.Polyethylene film installation:

Roll out the film over the slab, with a 200 mm (8 in) overlap at the joints.

Tape the overlaps with vapour barrier tape (membrane tape).

Run the film up 50 mm (2 in) on the walls.

Seal pipe penetrations and openings with caulking or a sleeve.

66.Liquid membrane installation: apply with a roller or trowel in one or two coats, according to the recommended thickness. Allow to dry completely (24-48 h) before installing the covering.

67.Verification: after drying, test the seal by pouring water on the membrane (no absorption should occur).

Calculations and Conversions

Permeance: 1 perm = 57.2 ng/(Pa·s·m²). A vapour barrier must have a permeance < 0.1 perm.

Emission rate: convert ASTM F1869 results: 3 lb/1000 ft²/24 h = 3.0 kg/92.9 m²/24 h. For a 50 m² area, the allowable rate is 50 ÷ 92.9 × 3.0 = 1.61 kg/24 h.

Internal relative humidity: ASTM F2170 probes must be inserted at 40% of the slab thickness (minimum 20 mm).

Common Vapour Barrier Pitfalls

Confusing a vapour barrier with an air barrier (a vapour barrier blocks vapour, not air).

Installing a vapour barrier on a damp slab (the vapour barrier traps moisture, causing delamination).

Using 2 mil (0.05 mm) polyethylene film instead of 6 mil (0.15 mm).

Not sealing the overlaps (vapour leaks).

Ignoring moisture tests (risk of voided warranty).

Applicable Standards and Codes

National Building Code (NBC) – Canada

Article 9.30.1.1: floor coverings must be installed on a dry, clean substrate.

Article 9.30.2.1: a vapour barrier must be installed under wood or resilient floor coverings installed on a concrete slab in contact with the ground.

Article 9.30.3.1: underlayments must comply with the covering manufacturer's specifications.

ASTM Standards (American Society for Testing and Materials)

ASTM F1869: test method for water vapour emission (calcium chloride test).

ASTM F2170: test method for internal relative humidity of concrete.

ASTM F710: standard practice for preparing concrete before installing resilient floor coverings.

CSA Standards (Canadian Standards Association)

CSA O118.1: standard for fibre and particle boards used as underlayments.

CSA A23.1: concrete and related materials (requirements for supporting slabs).

Safety Rules

Canadian Electrical Code, Part I (CE Code): when using power tools (sanders, mixers), maintain minimum distances from water sources and use ground fault circuit interrupter (GFCI) protected outlets.

Hazardous Products Regulations (WHMIS): adhesives and solvents must be handled with personal protective equipment (gloves, safety glasses, respirator). Consult safety data sheets (SDS).

Substrate Preparation Procedures

Initial Assessment

95.Visual inspection: look for cracks, holes, bumps, laitance, oil or grease stains.

96.Moisture test: perform ASTM F1869 and F2170 tests. Record the values and the date.

97.Adhesion test: apply a test adhesive to a small area and check the bond after drying.

98.Levelness test: use a 3 m straightedge and a level. Tolerances are ± 3 mm over 3 m for resilient coverings, ± 2 mm over 3 m for wood coverings.

Repairs and Leveling

Cracks: open the crack into a V-shape, clean, fill with epoxy filler or modified cement grout. Allow 24 h to dry.

Holes and bumps: fill with a leveling compound or repair filler. Sand after drying.

Laitance: remove by mechanical sanding or chemical stripping. Rinse thoroughly.

Self-leveling: apply a self-leveling compound (cementitious or gypsum-based) to correct irregularities from 3 to 25 mm. Follow the manufacturer's instructions for mixing (water, temperature, setting time).

Recommended Installation Sequence

105.Substrate preparation: cleaning, repairs, leveling.

106.Moisture test: perform and document.

107.Vapour barrier installation: film or membrane, as required.

108.Underlayment installation: if required, according to the covering type.

109.Adhesive application: choose the trowel, respect the open time.

110.Covering installation: follow the manufacturer's instructions.

111.Rolling and finishing: press roller, clean up residue.

Summary

Adhesives: choose according to the covering type, substrate, and moisture conditions. Respect the open time and recommended trowel. Calculate the quantity with 10% waste.

Underlayments: level, cushion, insulate. Never compensate for a substrate irregularity greater than 3 mm. Leave a 6 mm gap against the walls.

Vapour barriers: mandatory under resilient or wood coverings on concrete slabs. Permeance < 0.1 perm. ASTM F1869 (≤ 3.0 kg/92.9 m²/24 h) and ASTM F2170 (≤ 75% RH) tests.

Standards: NBC Articles 9.30.1.1, 9.30.2.1, 9.30.3.1; ASTM F710, F1869, F2170; CSA O118.1.

Safety: WHMIS for chemicals, GFCI for power tools.

Pitfalls to Avoid

119.Ignoring moisture tests: the Red Seal exam often includes questions on maximum allowable values. Memorize 3.0 kg/92.9 m²/24 h (ASTM F1869) and 75% RH (ASTM F2170).

120.Confusing a vapour barrier with an air barrier: a vapour barrier blocks water vapour, not air. Permeance is the key measurement.

121.Using a solvent-based adhesive on a damp substrate: water-based or epoxy adhesives are required. Solvents do not resist moisture.

122.Forgetting the expansion gap: 6 mm against the walls for all underlayments and floating coverings.

123.Neglecting underlayment/covering compatibility: some manufacturers void the warranty if the underlayment is not approved.

124.Misinterpreting units: conversions between perm and ng/(Pa·s·m²), or between lb/1000 ft² and kg/92.9 m², are classic traps. Always check the units.

125.Underestimating open time: an adhesive that is too dry or too fresh will not bond properly. Respect the manufacturer's limits.

126.Installing an underlayment on a substrate with laitance: laitance prevents adhesion. It must be removed mechanically.

127.Using polyethylene film that is too thin: 6 mil (0.15 mm) is the minimum. A 2 mil (0.05 mm) film is ineffective.

128.Not documenting test results: the exam may include questions on the documentation procedure. Always record the date, values, and test type.

Final Exam Tips

Memorize the limit values (3.0 kg/92.9 m²/24 h, 75% RH, 0.1 perm, 6 mil, 6 mm).

Familiarize yourself with the cited NBC articles (9.30.1.1, 9.30.2.1, 9.30.3.1).

Practice calculating adhesive quantities and unit conversions.

Review safety data sheets (SDS) for common products (adhesives, solvents, leveling compounds).

When in doubt on a question, apply the principle of safety and durability: the correct answer is the one that protects the covering and the health of the occupants.