Concrete float

What is a concrete float?

A concrete float is a finishing tool with a flat face that glides over fresh concrete. Used right after screeding, it knocks down high spots, fills low areas, embeds aggregate just below the surface, and brings up a thin layer of cement paste. This creates a uniform, slightly textured surface that is ready for edging, jointing, and final trowel work.

What floating does and why it matters

Floating is the bridge between rough placement and final finishing. Done at the right time, it:

• Levels minor imperfections left by screeding
• Consolidates the top layer and closes small voids
• Draws a workable paste to the surface for later finishing
• Leaves a texture that improves traction if you stop at the float stage (useful for exterior slabs)

Timing is critical. Start floating after bleed water has evaporated but before the surface gets too hard. Working concrete while bleed water is present can weaken the top layer and cause dusting or scaling later.

Where you will use a float

Homeowners and DIYers use floats for:

• Sidewalks and pathways
• Driveways and garage slabs
• Patios and shed pads
• Stairs and small landings
• Concrete countertops and benches
• Small repairs and patching

If you are placing a slab or casting a countertop, you will almost certainly use a float as part of the finishing sequence.

Types and variations

Hand floats

Hand floats are sized for close-up work. Common materials:

• Magnesium: Lightweight, popular for general finishing. Produces a medium-fine texture without sealing the surface.
• Aluminum: Similar to magnesium but slightly heavier. Durable and smooth.
• Wood: Leaves a rougher, more open texture that can help bond overlays or toppings. Good for exterior traction.
• Resin/composite: Durable and non-corroding; often used for plaster and some concrete tasks where a consistent, slightly open surface is desired.

Hand floats come in various sizes (often 12–20 inches long) and with square or rounded ends. Rounded ends reduce gouging; square ends reach tight corners.

Bull floats

A bull float is a large, wide float (commonly 36–48 inches) attached to one or more handle sections so you can reach across a slab from the edges. It is typically used immediately after screeding to quickly level and consolidate wide areas. Most bull floats are magnesium or aluminum and use a pitch-adjusting bracket so you can tilt the blade slightly on forward and backward passes to avoid digging in.

Darby

A darby is a long hand float, usually 24–48 inches, used where a bull float is impractical, such as small slabs or steps. It spans a wider area than a standard hand float and is useful for countertops and narrow placements.

Fresno (related tool)

A fresno looks like a long-handled steel trowel. It is used after the bull float to further smooth the surface. It is not a float, but you will often see it used in the same sequence.

Choosing the right float

Consider:

• Project size: For slabs and driveways, a bull float speeds up leveling; keep a hand float for edges and tight spots. For countertops or steps, a darby and hand float suffice.
• Material: Magnesium or aluminum for general-purpose floating; wood for a rougher, more open texture or when preparing a base for overlays; resin for durability and consistent texture.
• Blade shape and size: Rounded ends reduce edge marks; square ends work better in corners. Larger blades cover more area but can be harder to control.
• Handle comfort: For hand floats, a comfortable, offset handle reduces knuckle scraping. For bull floats, choose handle sections that lock securely and a bracket with easy pitch control.

How to use a concrete float (step by step)

1. Place and screed the concrete: Use a straight board or screed to strike off excess and get the surface roughly level.
2. Wait for bleed water to evaporate: The surface will darken and become less glossy. Do not add dry cement or water to speed this up.
3. Start floating:
   • Hand float: Hold the tool at a slight angle (5–10 degrees). Push and pull with overlapping passes, keeping steady pressure to avoid digging. Work from the edges inward.
   • Bull float: Set a light pitch so the leading edge is slightly raised. Push across the slab, then change the pitch for the return pull. Overlap each pass to blend the surface.
4. Check flatness: Use a straightedge or your screed to spot low areas. Float again to fill minor dips with paste.
5. Proceed to edging and jointing: Cut control joints with a groover and clean up perimeters with an edger while the concrete is still workable.
6. Finish as desired: For a broom finish, wait until the surface is ready and pull a broom for texture. For a smooth surface, proceed with steel troweling, but only when the concrete has set enough to support the trowel without tearing.

Safety tips:

• Wet concrete is caustic. Wear gloves, long sleeves, and waterproof boots.
• Be cautious with long bull-float handles near overhead lines.
• Keep work areas clear to avoid tripping over handle sections.

Care and maintenance

• Clean immediately after use before residue hardens. A stiff brush and water usually do the job.
• Avoid harsh acids on magnesium and aluminum. For stubborn buildup, soak briefly and scrub.
• Check edges for nicks. Dress lightly with a fine file to keep passes smooth.
• For steel tools (like fresnos), apply a thin coat of light oil before storage to reduce rust. Magnesium and aluminum do not rust but should still be stored dry.
• Store floats flat to prevent warping and avoid heavy items on top of them.

Common mistakes to avoid

• Floating too early: Working while bleed water is present traps water and weakens the surface.
• Overworking: Excess passes bring too much paste to the surface, leading to dusting or scaling.
• Pressing too hard: Digging with the leading edge leaves marks that are hard to remove.
• Not adjusting bull-float pitch: A flat blade can chatter or gouge; a slight pitch prevents edges from catching.
• Adding water to the surface: Sprinkling water to “revive” workability dilutes cement and causes weak spots.
• Skipping floating: Going straight from screeding to troweling can leave voids and uneven texture.

Related terms

• Screed: Tool or process for striking off excess concrete to level the surface.
• Darby: Long hand float for initial smoothing.
• Bull float: Large, long-handled float for wide areas.
• Fresno: Long-handled steel trowel used after floating.
• Edger and groover: Tools for rounding edges and cutting control joints.
• Trowel: Hand or power tool for final smoothing and densifying.
• Bleed water: Water that rises to the surface as concrete consolidates.

Practical examples

• Small patio slab: After screeding a 10×10 foot patio, use a bull float with a light pitch to smooth the entire surface. Switch to a hand float to blend along forms and around posts. Edge, cut joints, then broom for traction.
• Garage floor patch: Fill the repair area, screed flush with surrounding concrete, then hand float to level and close voids before troweling or brooming.
• Concrete countertop: After vibrating or tapping the form to release air, use a darby to level the top. Follow with a magnesium hand float to bring up paste, then proceed with steel troweling as the surface firms.

Learning to read the concrete—watching moisture, firmness, and how the paste responds—matters as much as the tool. With the right timing and a steady hand, a concrete float helps you achieve a flat, durable finish that looks good and lasts.