Broom Finishing

Written for Canada. Plans are metric, but many crews and suppliers work in feet and inches, so this site gives both: millimetres and metres, with feet and inches beside them. Codes are the National Building Code of Canada 2020 (NBC 2020) Part 9 as your province adopts it. A number marked Confirm has not been checked against every province, so check it with your own authority before you act on it.

Reviewed by a working tradesman with 17+ years in the field.

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A broom finish gives exterior concrete a slip-resistant texture. It depends on timing and a steady stroke.

The big idea

A broom finish gives exterior concrete a textured, slip-resistant surface. It is the usual finish for sidewalks, driveways, patios and steps. It suits exterior work because a steel trowel leaves a surface that is slippery when wet, and steel troweling air-entrained concrete can cause serious durability problems.

The result depends on timing and a steady stroke.

Timing

• Broom after the floating operation. Every other finishing step has to wait until the concrete has stopped bleeding (NRMCA CIP 14).
• Too early and the broom tears the surface. Too late and the texture is shallow.
• Test a small area first, in a spot that will be easy to touch up. There is no fixed clock time, because the mix and the weather decide.

Brooms and texture

• Soft fibre broom: a medium to fine texture, for patios and walks.
• Stiff broom: a coarser texture. An ACI paving specification allows a steel or fibre broom.
• Push broom: long, straight passes.
• Depth: specifications call for corrugations about 1.5 to 3 mm (1/16 to 1/8 in) deep for medium to coarse textures. A parking-structure guide says deep broom finishes are not recommended.
• Use the same type of broom across the whole job, so the texture looks consistent.

Technique and direction

1. Edge and joint first Edge and tool or cut joints before the broom goes on, as the CIP 14 sequence lists. Edging gives durable rounded edges and stops the edge tearing.
2. Test a strip Broom a small area and look at the texture and the surface.
3. Pull across the traffic route Pull the broom in straight, even strokes, across the main traffic route. Broom all of a panel in the same direction.
4. Keep the pressure steady Overlap slightly, lift the broom cleanly at the end of each stroke, and do not stop in the middle of a stroke.
5. Do not overwork One clean pass is usually enough. Going over it again tears and smears the surface.

For a sidewalk, that means across the walking direction. For a driveway, across the main line of travel. On steps, across the tread. On the drawings, follow any slope and drainage direction first.

Curing

• Start curing as soon as finishing is complete, with curing compound, poly or wet burlap.
• Cure for at least 7 days for exterior flatwork, and keep the concrete above 10°C (50°F), according to the cement-industry flatwork guide.
• Keep de-icing salt off through the first winter.
• Foot and vehicle traffic: follow your supplier and the engineer. I did not find a verified minimum in the sources, so confirm it.

Common mistakes

• Brooming too early or too late
• Uneven pressure
• Chatter marks from stopping mid-stroke
• Wrong direction
• Overworking the surface
• Switching broom types between panels