How do I prepare a subfloor for vinyl or carpet?

Find out everything you need to know to prepare your subfloor for vinyl or carpet flooring!

00:06 Materials and tools required
00:11 PREPARING A CONCRETE SUBFLOOR
00:15 Moisture measurement
00:41 Checking surface for conformity and unevenness
00:56 Rectifying irregularities and cleaning up
01:02 Installing adhesive tape around the perimeter of the room
01:07 Preparing, applying and drying undercoat primer
01:17 Preparing, applying and drying self-levelling compound
01:26 Check surface for unevenness
01:31 Remove irregularities and clean up
01:34 Preparing, applying and drying finishing cement
01:43 Removal of irregularities and cleaning
01:48 PREPARING A PLYWOOD SUBFLOOR
01:52 Checking surface for conformity and unevenness
02:10 Use of self-levelling compound
02:20 Removal of final irregularities and clean-up

Store our underlayment primer, self-levelling and self-levelling patching compounds

Materials and tools required

This list covers the essential materials needed to prepare the subfloor, but you may need to adapt some items to suit the specifics of your project (subfloor type, humidity, general floor condition, etc.).

Subfloor materials

• Exterior-grade plywood

• Wood screws or floor screws (11/4” long or longer, depending on subfloor thickness)

Levelling materials

Self-levelling patching compound (if subfloor has significant irregularities).

Reliefs must be levelled and depressions filled with a suitable cementitious compound so that the subfloor does not show a difference in level greater than 4.7 mm over a 3 m (3/16 in. over 10 ft.) stretch. If this is the case, apply a self-levelling compound to smooth the surface.

Tools for subfloor preparation

• Hammer and nails or screwdriver

• Circular saw

• Spirit level or long ruler

• Trowel

• Bucket

• Mixer

• Vacuum cleaner or broom

• Sponges

• Sander
  

Preparing a concrete subfloor

Moisture measurement

For a fresh concrete subfloor, allow at least 30 days drying time before performing a reliable moisture test.

Concrete drying times vary according to thickness, quality and ventilation conditions.

All concrete floors must meet moisture and alkalinity standards before any coating is installed.

Acceptable moisture levels vary according to the type of flooring and ventilation conditions.

It is recommended to measure the actual moisture content of the slab before installation, using tools such as :

• In-situ relative humidity probes (ASTM F2170) that measure at 40% of the total depth of the slab, or at 20% using two probes (top and bottom).
• Non-destructive moisture meters based on the electrical impedance of concrete.
• The calcium chloride moisture test (ASTM F1869) measures the rate of water vapor escaping from the concrete surface over a 24-hour period.
  

Compliance check and surface unevenness

Check that the floor surface is solid, clean and dry, with a maximum unevenness of 1/8” (3 mm) over a distance of 10 ft (3 m). If this is the case, apply a self-levelling compound to rectify the surface.

Deformations must not exceed 3/64” (1.1 mm). To check surface flatness, use a 10' (3 m) metal straightedge.

The surface is considered level if the maximum progressive deviation does not exceed 1/4” (6 mm) in 90% of the samples checked.

Rectifying irregularities and cleaning

The subfloor surface must be smooth: rectify slight irregularities and remove roughness with a scraper or sander.

Remove dust and residues with a vacuum cleaner or broom.

Install adhesive tape around the perimeter of the roomInstall adhesive tape around the perimeter of the room to avoid direct contact between the products and the wall.

Preparing, applying and drying undercoat primer

Mix the underlay primer according to the manufacturer's instructions.

Then apply the underlayment primer with a roller to the concrete surface and allow to dry according to the manufacturer's instructions.

Check surface for unevenness

Once the self-levelling compound has dried, check that your surface is level.

Removing irregularities and cleaning

Make sure you remove any unevenness to ensure a smooth surface.

Remove residues and dust with a vacuum cleaner or broom.

Preparing, applying and drying finishing cement

Mix finishing cement according to manufacturer's recommendations.

Using a trowel, apply the finishing cement evenly over the surface to be covered.

Allow to dry according to manufacturer's instructions.

Remove irregularities and clean up

If necessary, scrape, sand or sand down small irregularities and remove dust and residues with a broom or vacuum cleaner.

Now you're ready to install your floor.

Preparing a plywood subfloor

Checking conformity and surface unevenness

Make sure that the floor surface is solid, clean and dry, with a gradient not exceeding 3/16” (4.7 mm) over a distance of 10 ft (3 m). If this is the case, apply a self-levelling compound to rectify the surface. Deformations must not exceed 3/64” (1.1 mm).

To check surface flatness, use a 10' (3 m) metal straightedge. The surface is considered level if the maximum progressive deviation does not exceed 1/4” (6 mm) in 90% of the samples checked.

If your subfloor is not level, level it.

Subfloor leveling is essential to ensure a flat, even surface, prevent moisture and unevenness, improve safety and comfort, reduce costs and facilitate maintenance.

Using a self-levelling compound

If your plywood is cracked, be sure to smooth the surface by applying a cement-based undercoat finish.

Depending on the condition of the plywood, one or two coats may be necessary.

Start by covering joints and screws with a first coat, then apply a second coat over the entire surface for a uniform finish.

This step ensures that screw-head holes and cracks will be invisible once the flooring is installed.

Removing final irregularities and cleaning

The subfloor surface must be free of all defects.

Use a sander or scraper to correct small irregularities and joints.

Sand bumps and joints so that the maximum deflection does not exceed 3/64” (1.1 mm), then remove dust with a broom or vacuum cleaner.