Carpet Installation (Stretch-in and Glue-down)

Chapter Introduction

Carpet installation represents a major portion of the work of a Floorcovering Installer. This chapter covers the two main methods: stretch-in installation with underlay and tackless strips, and glue-down installation using full spread or double glue-down methods. You must master substrate preparation principles, quantity calculations, seaming techniques, and applicable Canadian standards. This chapter is structured according to Red Seal requirements and emphasizes the skills assessed on the exam.

Section 1: Substrate Preparation and Job Site Assessment

1.1 Substrate (Underfloor) Requirements

Before any installation, the substrate must be inspected and prepared. The minimum requirements are:

Dryness: relative humidity of concrete ≤ 75% (measured with a pin-type or non-destructive moisture meter). For concrete, moisture must be ≤ 4.5% (carbide method) or ≤ 3.0% (hygrometer method).

Flatness: tolerance of 3 mm under a 3 m straightedge (1/8 in under 10 ft). Any greater irregularity must be corrected with a self-leveling compound.

Cleanliness: free of dust, grease, oil, peeling paint, or adhesive residue.

Soundness: the substrate must be structurally sound, without active cracks or areas of delamination.

Table 1: Substrate Tolerances by Installation Type

Installation Type	Max Flatness (3 m straightedge)	Max Concrete Moisture	Minimum Temperature
Stretch-in	3 mm	4.5% (carbide)	15 °C
Glue-down	3 mm	3.0% (hygrometer)	18 °C
Double glue-down	2 mm	3.0% (hygrometer)	18 °C

1.2 Concrete Preparation

Concrete must be cured (28 days minimum) before installing glue-down carpet. Laitance must be removed by grinding or shot blasting. Shrinkage cracks must be repaired with a flexible polyurethane or epoxy filler. Expansion joints must be respected and never covered with carpet without an appropriate transition joint.

1.3 Wood Preparation

Plywood subfloors must have a minimum thickness of 19 mm (3/4 in) for stretch-in installation and 15 mm (5/8 in) for glue-down installation. Panels must be fastened with screws or nails every 15 cm along supports. Gaps between panels must be ≤ 3 mm. Any squeaking areas must be corrected before installation.

Section 2: Stretch-in Installation

2.1 General Principles

Stretch-in installation involves securing the carpet to tackless strips using a knee kicker and a power stretcher. The carpet is held under constant tension, which prevents ripples and extends the product's service life.

Required conditions:

Underlay (cushion) 6 to 12 mm thick, with a minimum density of 2.2 kg/m³.

Wooden tackless strips with pins angled at 60°, spaced 5 to 8 mm from the wall.

Room temperature ≥ 15 °C and relative humidity between 30% and 60%.

2.2 Installing Tackless Strips

Strips are nailed or screwed to the floor, pins facing the wall, at a distance of 5 to 8 mm from the wall (the thickness of the carpet). Pin spacing must be 10 to 12 mm. At doorways and thresholds, strips must be cut at a 45° angle to facilitate passage.

Calculating Strip Length:

For a rectangular room with dimensions L × W, the total length of strips required is:

L_strips = 2 × (L + W) + 10% waste

Example: room 4 m × 5 m → L_strips = 2 × (4 + 5) = 18 m + 1.8 m = 19.8 m.

2.3 Installing the Underlay

The underlay is rolled out perpendicular to the carpet direction. Sheets are laid edge to edge, without overlapping, and fastened with a stapler every 15 cm along the seams. Underlay seams must never coincide with carpet seams. The underlay must be cut 5 mm from the wall to allow for strip installation.

2.4 Cutting and Installing the Carpet

35.Measuring: add 10 to 15 cm of surplus on each dimension (allowance for wall returns).

36.Cutting: use a hook knife with a new blade. Cut on a flat surface, with the carpet face side up.

37.Positioning: roll out the carpet and allow it to acclimate for 24 hours at the job site temperature.

38.Initial tension: use the knee kicker to hook the carpet onto the strips, starting at the center of a wall.

39.Final tension: use the power stretcher to eliminate all ripples. Work from the center toward the walls, with a tension of 10 to 15 kg (measured with a tension gauge).

40.Wall fastening: tuck the carpet into the space between the strip and the wall using a carpet chisel, then trim the excess to 3 mm above the floor.

2.5 Seams and Welds

Stretch-in carpet seams are made by seaming with hot melt tape and a seaming iron.

Procedure:

44.Align the two pieces with a 5 cm overlap.

45.Cut through both layers simultaneously with a double-blade cutter to achieve a perfect seam.

46.Remove the scraps, place the hot melt tape under the seam.

47.Heat the tape with the seaming iron at 350 °C (surface temperature) until the adhesive melts.

48.Press the two pieces together and allow to cool for 30 minutes.

Table 2: Hot Melt Tape Width by Carpet Type

Carpet Type	Tape Width	Iron Temperature
Loop pile	15 cm	350 °C
Cut pile	15 cm	350 °C
High density	20 cm	380 °C

2.6 Finishes and Thresholds

Doorways are covered with transition strips in aluminum or brass. Installation is done with screws or adhesive. Stairs require a specific technique: each step is stretched individually, with a stair nosing fastened with staples or screws.

Section 3: Glue-down Installation

3.1 Types of Glue-down Installation

There are three variations of glue-down installation:

57.Full spread: adhesive is applied over the entire substrate surface.

58.Double glue-down: an underlay is first bonded to the substrate, then the carpet is bonded to the underlay.

59.Perimeter bonding: adhesive is applied only at the edges (used for PVC-backed carpets).

3.2 Adhesive Selection

The adhesive must be compatible with:

The carpet type (bitumen, PVC, or polyurethane backing).

The substrate type (concrete, wood, metal).

Moisture and temperature conditions.

Table 3: Adhesive Types and Applications

Adhesive Type	Base	Open Time	Use
Acrylic	Water	15-20 min	PVC-backed carpet
Polyurethane	Solvent	30-45 min	Bitumen-backed carpet
Epoxy	Two-component	60-90 min	Wet areas
Hot melt	Thermofusible	5-10 min	Quick repairs

3.3 Applying Adhesive

68.Mixing: follow the manufacturer's specified ratios. Incorrect mixing reduces adhesion by 50%.

69.Application: use a notched trowel with the recommended notch size (typically A1, A2, or B1 depending on adhesive type).

70.Open time: the period during which the adhesive remains tacky. If the adhesive forms a dry film (skin), it must be removed and reapplied.

71.Carpet installation: roll the carpet into the fresh adhesive, then press it with a 45 kg (100 lb) roller to ensure full contact.

Calculating Adhesive Quantity:

For a room with area S (m²), with a manufacturer-specified consumption rate C (kg/m²):

Q_adhesive = S × C × 1.10 (10% waste)

Example: S = 50 m², C = 0.45 kg/m² → Q = 50 × 0.45 × 1.10 = 24.75 kg.

3.4 Double Glue-down Installation

Double glue-down is used for cushion-backed carpets or to improve comfort and acoustic insulation.

Procedure:

79.Bond the underlay (6 mm polyurethane foam) to the substrate with an acrylic adhesive.

80.Allow to dry for 24 hours.

81.Apply the installation adhesive to the underlay (consumption of 0.30 to 0.40 kg/m²).

82.Install the carpet and press with a roller.

Advantages of double glue-down:

Better acoustic absorption (Δ of 5 to 10 dB).

Superior walking comfort.

Reduced risk of rippling.

3.5 Seams in Glue-down Installation

Seams in glue-down installation are made by hot welding for PVC-backed carpets or by seaming for textile carpets.

Hot welding:

90.Rout the seam with a V-shaped router bit, 3 to 5 mm deep.

91.Clean the groove with a vacuum.

92.Insert the welding rod with a hot air gun at 350-400 °C.

93.After cooling (15 minutes), trim the excess with a multi-blade knife.

Table 4: Hot Welding Parameters

Parameter	Recommended Value
Air temperature	350-400 °C
Feed speed	1.5-2.0 m/min
Routing depth	3-5 mm
Cooling time	15 min

Section 4: Calculations and Quantities

4.1 Calculating Carpet Area

For a rectangular room with length L and width W:

S = L × W

For an L-shaped room, divide into rectangles and add the areas.

Waste:

Stretch-in installation: 5 to 10% depending on configuration.

Glue-down installation: 3 to 5%.

Rooms with patterns: 15 to 20% for pattern matching.

Calculating the Number of Widths:

If the roll width is W (typically 3.66 m or 4.00 m) and the room width is l:

N_widths = ⌈l / W⌉ (round up to the next whole number)

The total length required is:

L_total = N_widths × (L + 10 cm surplus)

4.2 Calculating Linear Metres for Stairs

For a straight staircase with n steps, each step having a tread depth p and riser height h:

Length per step = p + h + 5 cm (return under the nosing)

Total length = n × (p + h + 5 cm)

4.3 Complete Calculation Example

Problem: Install stretch-in carpet in a room measuring 6.00 m × 4.50 m. The roll width is 3.66 m. Calculate the total area to order with 10% waste.

Solution:

118.Room area: S = 6.00 × 4.50 = 27.00 m².

119.Number of widths: N = ⌈4.50 / 3.66⌉ = ⌈1.23⌉ = 2 widths.

120.Length per width: L_width = 6.00 + 0.10 = 6.10 m.

121.Total length: L_total = 2 × 6.10 = 12.20 m.

122.Total area: S_total = 12.20 × 3.66 = 44.65 m².

123.With 10% waste: S_order = 44.65 × 1.10 = 49.12 m².

Answer: Order 49.12 m² (or 12.20 linear metres × 3.66 m wide).

Section 5: Canadian Standards and Codes

5.1 National Building Code (NBC)

The National Building Code of Canada (NBC) 2020, Part 9 (housing) and Part 3 (large buildings), specifies fire resistance and flame spread requirements for floor coverings. Carpets must have a flame spread rating ≤ 300 (Class A) according to CAN/ULC-S102 (tunnel test).

5.2 CSA Standards

CSA A82: Concrete and masonry materials (requirements for concrete substrates).

CSA O121: Plywood (requirements for wood subfloors).

CSA Z116: Occupational safety (requirements for job sites).

5.3 Canadian Electrical Code

The Canadian Electrical Code, Part I (C22.1-21) applies when installing carpet over radiant floor heating. Rule 8-200 requires that heating cables be installed at a minimum distance of 50 mm from mechanical fasteners (staples, nails) of the carpet. The floor surface temperature must not exceed 28 °C under the carpet.

5.4 Installation Standards

ASTM F710: Preparing concrete before installation of floor coverings.

ASTM F1869: Concrete moisture emission test (calcium chloride method).

ASTM F2170: Concrete relative humidity test (in-situ probes).

Table 5: Moisture Limits by Test Method

Method	Maximum Limit
ASTM F1869 (calcium chloride)	3.0 kg/100 m²/24 h
ASTM F2170 (relative humidity)	75% RH
Carbide method (CM)	4.5%

Section 6: Tools and Equipment

6.1 Stretch-in Installation Tools

Knee kicker: for initial tension.

Power stretcher: for final tension, with 3 m extension tubes.

Carpet chisel: for tucking carpet into spaces.

Hook knife: with curved or straight blades.

Seaming iron: adjustable temperature 300-400 °C.

Wall trimmer: for trimming excess along walls.

6.2 Glue-down Installation Tools

Notched trowel: notch sizes A1 (1.5 mm), A2 (2 mm), B1 (3 mm).

Roller: 45 kg for carpet, 68 kg for vinyl.

Router: for grooving seams before welding.

Hot air gun: adjustable temperature 200-600 °C.

Multi-blade knife: for trimming excess welding rod.

6.3 Measuring Equipment

Moisture meter: pin-type (wood) or non-destructive (concrete).

3 m straightedge: for checking flatness.

Tension gauge: for measuring carpet tension (10-15 kg).

Infrared thermometer: for checking substrate temperature.

Section 7: Occupational Health and Safety

7.1 Specific Hazards

Cuts: hook knives are extremely sharp. Always cut away from your body and wear cut-resistant gloves.

Inhalation of fumes: solvent-based adhesives emit VOCs (volatile organic compounds). Use a cartridge respirator (Type A) and ventilate the work area.

Noise: concrete shot blasting produces noise of 110-120 dB. Wear hearing protection (earplugs + earmuffs).

Posture: working on knees and bent over causes MSIs (musculoskeletal injuries). Use knee pads and take breaks.

7.2 Safety Rules

WHMIS (Workplace Hazardous Materials Information System): read the safety data sheets (SDS) before using any product.

Lockout/tagout: when working on electrical equipment.

Scaffolding: inspect before use, respect maximum load.

Section 8: Quality Control and Inspection

8.1 Pre-installation Checkpoints

175.Substrate: flatness, moisture, cleanliness.

176.Acclimation: carpet must be stored in the room for 24 h at 18-25 °C.

177.Pile direction: all widths must have the pile oriented in the same direction (toward the main window).

178.Patterns: pattern alignment within ± 2 mm.

8.2 Post-installation Checkpoints

180.Tension: no visible ripples, no wrinkles.

181.Seams: invisible, without gaps or overlaps.

182.Adhesion: pull test (carpet must not lift).

183.Finishes: clean edges, properly secured thresholds.

8.3 Common Defects and Corrections

Table 6: Defects, Causes, and Corrections

Defect	Probable Cause	Correction
Ripples	Insufficient tension	Re-stretch with power stretcher
Visible seam	Unclean cut	Recut and re-weld
Delamination	Inappropriate adhesive or exceeded open time	Remove and re-bond
Adhesive stains	Excess adhesive	Clean with appropriate solvent

Section 9: Pitfalls to Avoid

189.Neglecting concrete moisture: moisture > 3% (ASTM F2170) causes adhesive failure and alkali staining. Always measure before installing.

190.Forgetting adhesive open time: if the adhesive has skinned over, the carpet will not bond. Follow manufacturer's instructions.

191.Confusing roll widths: carpet rolls are 3.66 m or 4.00 m wide. Verify before calculating the number of widths.

192.Ignoring pile direction: carpet installed with widths in opposite directions shows shading variations.

193.Using a seaming iron that is too hot: temperature > 400 °C burns the hot melt tape and weakens the seam.

194.Not checking flatness: irregularity > 3 mm under a 3 m straightedge causes permanent wrinkles in glue-down installation.

195.Forgetting expansion joints: carpet must be cut at expansion joints and a transition profile installed.

196.Underestimating waste: for patterns, allow 15-20% waste. A calculation error results in insufficient material.

197.Working in a room that is too cold: below 15 °C, adhesive does not cure properly.

198.Not wearing PPE: knife cuts are the leading cause of injury among floorcovering installers.

Section 10: Exam Tips

201.Memorize key values: concrete moisture (3% / 4.5%), flatness (3 mm/3 m), minimum temperature (15 °C / 18 °C), roll widths (3.66 m / 4.00 m).

202.Master the calculations: area, number of widths, adhesive quantity. Calculation questions represent approximately 15% of the exam.

203.Know the standards by name: NBC, CSA, ASTM, Canadian Electrical Code, Part I.

204.Understand the differences between stretch-in and glue-down installation: substrate conditions, tools, seaming techniques.

205.Review defects and corrections: troubleshooting questions are common.

206.Read questions twice: Red Seal exams contain wording traps (e.g., "except", "not", "always").

207.Use the metric system: all answers must be in SI units (m, mm, kg, °C).

Summary

Stretch-in installation uses tackless strips and a power stretcher; it requires underlay and tension of 10-15 kg.

Glue-down installation uses adhesive applied with a notched trowel; open time is critical.

Double glue-down improves comfort and acoustic insulation.

The substrate must be dry (≤ 3% ASTM F2170), flat (≤ 3 mm/3 m), and clean.

Quantity calculations include waste (5-10% stretch-in, 3-5% glue-down, 15-20% with patterns).

Applicable Canadian standards are the NBC, CSA standards, ASTM, and the Canadian Electrical Code, Part I (Rule 8-200 for heated floors).

Seams are made by hot melt seaming (stretch-in) or hot welding (glue-down).

Safety requires PPE (cut-resistant gloves, respirator, hearing protection) and WHMIS compliance.

Common defects (ripples, delamination, visible seams) have identifiable causes and specific corrections.

Pitfalls to Avoid

Pitfall	Consequence	Prevention
Installing on damp concrete	Delamination, mould	Measure moisture (ASTM F2170)
Exceeding open time	Zero adhesion	Work in sections of 10 m²
Ignoring pile direction	Shading variation	Verify before cutting
Calculating without waste	Material shortage	Add 10% minimum
Using the wrong adhesive	Premature delamination	Verify compatibility
Cutting with a dull blade	Frayed edges	Change blades frequently
Not acclimating the carpet	Shrinkage after installation	Store for 24 h at 18-25 °C
Forgetting expansion joints	Deformation	Cut at expansion joints
Working below 15 °C	Adhesive not curing	Heat the room before installation
Neglecting flatness	Permanent wrinkles	Level with self-leveling compound

This chapter covers all the skills assessed for stretch-in and glue-down carpet installation in the Red Seal exam. Review the tables, redo the calculations, and practice troubleshooting questions. Good luck with your preparation!

Carpet Installation (Stretch-in and Glue-down)