Between screeding a slab flat and troweling it smooth sits the most misunderstood step in concrete finishing: floating. A concrete float — whether a 4-foot bull float on a long pole or a hand-sized magnesium float — does three jobs no other tool does: it pushes coarse aggregate just below the surface, cuts down high spots and fills lows the screed missed, and opens the surface texture so bleed water can rise and evaporate. Get floating right and every later step gets easier; skip it or mistime it and no amount of troweling rescues the slab. Here’s the full picture: bull floats vs mag floats, materials, timing, and stroke-by-stroke technique.
Float vs Trowel: The Distinction That Matters
Floats and steel trowels look adjacent in the toolbox and do opposite things. A float (magnesium, aluminum, wood, or resin) has a relatively soft, slightly textured interaction with fresh concrete — it levels and opens the surface, leaving a gritty, porous texture that lets bleed water escape. A steel trowel closes the surface, densifying the paste into a hard skin. The sequence is always float first, steel later, because closing the surface while bleed water is still coming up traps that water under a sealed skin — the root cause of scaling and delamination. Floating happens minutes after screeding; troweling happens an hour or more later, after bleed water is gone. Everything about the steel stage — tools, timing tests, burnishing — lives in our concrete trowel guide; this article stays on the float side of that line.
The Bull Float: First Tool on the Slab
The bull float is a wide, flat blade — typically 42 to 48 inches long and 8 inches deep — on a set of push-button or threaded extension poles reaching 12 to 18 feet. It runs immediately after screeding, while the concrete is still plastic and wet-sheened. Its jobs: knock down screed ridges, fill voids and “bug holes,” and embed the coarse aggregate so a layer of mortar paste sits at the surface for later finishing.
- Magnesium bull floats ($90–$200) are the default for modern air-entrained mixes: light, stiff, and they slide over sticky concrete without tearing.
- Wood bull floats ($60–$120) drag more and open the surface aggressively — useful on low-slump or non-air mixes and where a coarse open texture is wanted.
- Aluminum and composite versions split the difference; aluminum can react and streak on some mixes, so mag remains the safe buy.
- Channel floats and check rods are stiffer variants pros use to cut highs on big floors — beyond DIY need.
Bull Float Technique
- Go on immediately. The window opens the moment a section is screeded — don’t wait for the whole pour to be struck off; float behind the screed in sections.
- Angle the leading edge up. Tilt the blade a few degrees away from the direction of travel — pole down slightly on the push, pole up on the pull — so the edge rides over the surface instead of digging in. Rocker-style adjustable heads do this automatically; with a fixed head, it’s all wrist.
- Two directions, minimal passes. Run passes perpendicular to the screed direction first, overlapping each pass by half a blade, then one set of passes at 90 degrees if the surface needs it. One or two passes total — the bull float is a leveling tool, not a finishing tool.
- Stop before you polish. Overworking pumps excess paste and water to the top, weakening the wear surface. When the surface is uniformly flat, wet-sheened, and lightly textured, you’re done. Now everyone waits for bleed water.
The Magnesium Hand Float
The mag float — 12 to 20 inches long, $15–$40 — is the hand-scale version, and it works both ends of the process:
- Early: floating edges, corners, and the perimeter strip the bull float can’t reach, and working down around forms right after screeding.
- Later, the “second floating”: after bleed water evaporates and the slab takes a footprint of about 1/4 inch, a hand-float pass re-levels the wobbles that settlement and evaporation left, cuts off surface lumps, and re-opens the texture just before the first steel pass. On broom-finish exterior work, this mag pass often is the final finish under the broom — many pros go screed → bull float → wait → mag float → broom, with no steel at all. That’s exactly the right sequence for driveways and walks in freeze climates, as covered in our broom finish concrete guide.
Technique: hold the float flat with the leading edge barely raised and work sweeping arcs with moderate pressure — enough to move paste, not enough to dig. Keep a margin trowel in your pocket to cut concrete away from forms, and follow edge floating with an edger tool for a compacted, rounded slab edge.
Wood and Resin Hand Floats
Wood floats ($10–$25) drag and tear on air-entrained concrete, which is most exterior ready-mix today — but their aggressive opening action still earns them a place on stiff mixes, repair mortars, and anywhere maximum surface roughness is wanted for a bonded overlay. Laminated resin/canvas floats behave like long-lasting wood. If you buy one hand float, buy magnesium; add wood only when a job calls for it.
Which Float When: Quick Reference
| Situation | Tool | Timing |
|---|---|---|
| Any slab wider than ~4 ft | Bull float (mag) | Immediately after screeding |
| Edges, forms, small pads | Mag hand float | Immediately after screeding |
| Re-level before steel/broom | Mag hand float or fresno-width mag | After bleed water; ~1/4-in footprint |
| Stiff, non-air mix; overlay prep | Wood float | Same windows as mag |
| Slabs 500+ sq ft | Power trowel with float pan/blades | Replaces second floating at scale |
Reading the Slab: Timing Signals
- Bull float window: now. It closes within minutes as bleed water starts rising; floating through standing bleed water works water back into the surface and weakens it.
- Second float window: bleed sheen fully gone, footprint ~1/4 inch with no water pumping into the print. Hot wind can bring this in 30 minutes; cool damp weather can stretch it past 3 hours.
- Danger sign — crusting: in hot, windy weather the top can dry while the slab below stays soft. If the surface skins early, mist with an evaporation retarder (not free water) and float gently. Getting the mix right for the weather is half of finishing; slump and admixture choices are covered in our concrete mix guide.
Common Floating Mistakes
- Waiting too long to bull float. Screed the section, float the section — not screed everything, then float.
- Digging the blade edge. Flat-bladed gouges take multiple later passes to erase; keep the leading edge up.
- Overfloating. More than two or three total passes brings fat paste and water to the top and invites crazing and dusting.
- Floating standing bleed water back in. Wait it out — never blot with dry cement either.
- Wood float on air-entrained mix. It tears the creamy surface; use magnesium.
- Skipping the second floating. The bull-floated surface always settles slightly unevenly; the mag pass is where flatness is actually won on small pours.
- No plan past floating. Decide the final finish — broom, steel, or exposed — before the pour, because it dictates every downstream timing decision on your concrete slab.
Buying Guide: A Sensible DIY Kit
For a patio, walkway, or garage-pad scale pour: a 48-inch magnesium bull float with three 6-foot handle sections and a rocker bracket (~$130–$200 all-in), one 16-inch mag hand float (~$25), a margin trowel (~$12), and an edger (~$12). Add a groover for control joints and, if you’re steel-finishing, the trowels from the companion guide. Rinse magnesium tools before paste sets — cured concrete bonds to mag ferociously — and store bull float poles straight; a bent pole makes flat floating nearly impossible.
FAQ
Do I really need a bull float for a small pad?
Under about 4 feet wide, no — you can reach everything with a mag hand float from the sides. Wider than your reach from both edges, yes: screed marks left unfloated telegraph through every later step.
What does floating actually do that screeding doesn’t?
Screeding strikes the concrete to grade but leaves aggregate at the surface and ridges between passes. Floating pushes stone down, brings paste up, heals the ridges, and creates the mortar layer that finishing tools work.
Magnesium vs aluminum float — does it matter?
Mag is lighter, slides better on sticky air-entrained mixes, and doesn’t streak. Aluminum is cheaper and fine on many mixes, but mag is the professional default for good reason.
Can floating fix a bad screed job?
Minor ridges and lows, yes — that’s its job. Actual grade errors (a slab draining the wrong way), no. Flatness comes from forms and screeding; floats refine, they don’t re-grade.
