Concrete
Concrete flatwork finishing sequence field guide
Screed, bull float, wait out the bleed water, then float, trowel, and cure, on the timing that decides whether the surface holds up or dusts off.
Direct answer
Finishing concrete is a timed sequence, not a single step: screed, bull float, wait for the bleed water to leave, then float, trowel, and cure. The biggest mistake in flatwork is finishing too early. Work the surface while bleed water sits on it and you seal it in, which dusts, scales, and delaminates. Timing makes the floor.
Key takeaways
- Concrete finishing order is place, screed, bull float, wait for bleed water to leave, edge and joint, float, trowel, then cure, per ACI 302.
- Never finish over bleed water; floating or troweling while water sits on top seals a weak skin that dusts, scales, and delaminates.
- Start floating when a footprint or thumbprint leaves about a 1/4 in mark and no water wells up around it.
- Do not hard steel-trowel exterior air-entrained concrete; it traps the entrained air and delaminates the surface, so float and broom instead.
- Start curing the moment the finish is done; a finish left to dry comes up weak and crazed regardless of troweling quality.
Finishing concrete, and the timing that makes or breaks the surface
Finishing concrete is a sequence, and the sequence is timed by the bleed water, not by the clock on the wall. You place, you screed to grade, you bull float, and then you wait. Everything after the wait, the floating and the troweling and the broom, has a window that opens when the bleed water leaves and the surface takes weight, and closes when the slab gets too hard to work. Hit the windows and you get a sound floor. Miss them and no amount of effort fixes it.
The single biggest mistake in the trade is finishing too early. A finisher floats or trowels while bleed water is still on the surface, works that water back down into the top, and seals a thin, soft, high water-to-cement layer right where the wear and the weather hit. That skin dusts under traffic, scales off in freeze-thaw, and in the worst case delaminates in sheets. It looks perfect the day you leave. It fails six months later, after the check cleared.
So the craft is patience with judgment. The good finisher is not the one who works the slab the hardest. It is the one who reads the surface, knows which mix is under the float, and waits for the right moment on every pass. Timing makes the floor. Effort spent at the wrong moment is what wrecks it.
What is the order of operations for finishing concrete?
The order is place, screed, bull float or darby, wait for the bleed water, then edge and joint, float, trowel one or more passes, and cure. ACI 302, the guide for concrete floor and slab construction, lays out this sequence, and the part crews skip is the wait in the middle. Bull floating happens right after strikeoff and before bleed water shows. Then nothing touches the surface until the bleed water is gone.
Not every slab runs the whole list. An exterior walk gets screeded, bull floated, edged and jointed, floated, and broomed, with no steel troweling at all. An interior warehouse floor gets the full sequence through several trowel passes to a hard, dense finish. The finish schedule on the drawings tells you how far down the list to go, and the mix tells you how fast the windows open and close.
The table below is the sequence and the window for each step. Read it as the shape of the day, not a stopwatch, because the real timing comes off the surface in front of you.
| Step | What it does | When |
|---|---|---|
| Place and screed | Brings concrete to grade and rough level | As placed, ahead of the finishers |
| Bull float or darby | Knocks down ridges, embeds aggregate | Right after screed, before bleed water |
| Wait | Lets bleed water rise and leave | Until the water sheen is gone |
| Edge and joint | Tools edges, cuts or tools joints | After bleed water, or saw later |
| Float | Opens surface, brings up cream, levels | When the surface bears weight, about 1/4 in footprint |
| Trowel, one or more passes | Closes and densifies the surface | After floating, each pass later and steeper |
| Cure | Holds moisture for strength gain | Start as soon as the finish is done |
Screeding and strikeoff: bringing the surface to grade
Screeding, also called strikeoff, brings the fresh concrete to grade and gives the finishers a flat starting plane. It is the first cut at flatness, and the flatness of the finished floor starts here, not at the trowel. You cannot trowel a wavy screed flat. The high and low spots you leave in the strikeoff are the high and low spots the floor keeps.
Three tools do the work. A wet screed, a straightedge run by hand on wet pads or off the forms, is the cheapest and the most operator-dependent, and it commonly lands a floor around the FF 25, FL 20 range. A vibratory screed rides a vibrating blade across the surface, consolidating the concrete and bringing the cream up as it strikes off, better on flatness and consolidation than a hand screed. A laser screed, the self-propelled machine guided by a laser plane, holds grade far tighter and routinely doubles the flatness numbers a hand screed gets, which is why the flat warehouse floors are placed with one.
Strike off slightly high and let the bull float bring it down, rather than chasing low spots later by throwing concrete back on a setting surface. Patching a low spot after the bleed has started is how you build in a debonded patch that pops later. Get the grade in the strikeoff.
When do you bull float concrete?
Bull float right after the screed and before any bleed water shows on the surface. That is the window, and it is short on a hot pour. The bull float, a wide blade on a long handle, and the darby, its shorter hand-held cousin, knock down the ridges the screed left, fill the small voids, and push the coarse aggregate down so the surface is paste-rich and workable. Done in time, it sets up every pass that follows.
Use a magnesium float on air-entrained and most exterior concrete. Magnesium and aluminum smooth the surface and open the pores so bleed water and air can still escape, while a wood float pulls more paste and texture up. The rule that matters: do the bull floating before the bleed water arrives, because once water is on the surface, floating it works the water back in and you are sealing the skin you were trying to prepare.
Do not overwork it. One or two passes to flatten and embed, then stop and get off the slab. A finisher who keeps floating brings up too much fines and water, overworks the surface, and starts the same premature-sealing problem from a different direction. Bull float, then wait. The waiting is the next step, and it is the one that decides the floor.
Why do you wait for the bleed water to leave?
You wait because finishing over bleed water seals the water into the surface and ruins it. After the bull float, the concrete bleeds: water rises to the top as the solids settle. While that water sits there, you do nothing to the surface. Float or trowel it then and your tools push the bleed water and the entrapped air back down, trapping them under a densified skin. You get a weak, high water-to-cement layer that dusts, scales, crazes, and can delaminate. This is the failure that finishes more slabs than any other.
So the rule is blunt: never finish over bleed water. Wait until the water sheen has left the surface or been removed before any floating or troweling. The bleed has to finish bleeding and the surface water has to go, by evaporation on a normal day, or pulled off with a hose or a squeegee if it pools. Then you start.
The low-bleed mix flips the trap. A mix heavy in fly ash, slag, or silica fume, or a low water-to-cement mix, barely bleeds at all, so a finisher waiting for a water sheen that is never coming holds the crew on a surface that is drying and cracking underneath the wait. On those mixes you watch the set, not the sheen, and you protect the surface from drying instead of waiting on bleed. The evaporation-rate guide covers reading that surface and protecting it. Two opposite traps, same rule underneath: match the finishing to what the surface is actually doing.
When do you start finishing concrete?
Start floating when the bleed water is gone and the surface bears weight without sinking, which the footprint or thumbprint test tells you in seconds. Step on the slab. When your foot leaves a clean print about 1/4 in deep and no water wells up around it, the surface is ready for the first float. Press a thumb in: an indent around 1/4 in that holds its shape says the same thing. Too soft and the print sinks deep and water comes up, wait. Too hard and you cannot get a print, you are late.
The window is not a fixed number of hours. It depends on the mix, the temperature, the wind, and the slab. A normal interior pour might be ready to float in a couple of hours and ready to trowel a while after. A hot, dry, windy day can pull that window in hard and stack the steps on top of each other, which is exactly when crews get caught. The evaporation-rate guide covers why heat and wind shrink the window and how to read it.
Read the surface, not the clock. The clock is a planning tool. The print test is the decision. On a big pour the finishers chase the set across the slab, starting where it set first, because the slab does not set all at once and the window opens corner by corner.
Edging and jointing during finishing
Edging and jointing happen in the finishing sequence, after the bleed water leaves and around the floating passes. Edging runs an edger along the forms to round and compact the slab edge, so it does not chip and so the panel has a clean tooled border. You edge exterior flatwork, walks, and drives as part of the finish. On interior floors poured to a wall or a form, the edge gets tooled or left per the finish schedule.
Joints are cut or tooled to steer the shrinkage crack, and you can do it two ways. You can hand-tool a groove with a jointer during finishing, common on walks and residential flatwork, cutting the joint while the concrete is still workable. Or you saw the joints later, once the slab has set enough to cut clean and before it cracks on its own, which is how slabs on grade and industrial floors are usually jointed. Either way the joint has to reach about a quarter of the slab depth to control the crack.
The timing of a tooled joint rides with the floating. The timing of a sawcut is its own window, hours after finishing, and it is the one that gets missed when the saw crew is not staged. The control-joint guide covers spacing, depth, and the sawcut window in full. Here the point is only that jointing is part of finishing the slab, planned before the pour, not improvised after.
Floating: opening the surface and bringing up the cream
Floating opens the surface, brings the cream up, and levels the slab into a uniform, slightly textured plane ready for whatever finish follows. It is the first working pass after the wait. Run flat across the surface, the float embeds any remaining aggregate, fills and cuts the small highs and lows, and works a layer of fine paste, the cream, up to the top where the trowel can later close it.
By hand it is a bull float again on a big slab, or a hand float and a fresno, a long-handled float used to reach across a slab from the edge. By machine it is a power float, a walk-behind or ride-on trowel running float pans or float blades laid flat. The pan is a flat steel disk that floats a wide path and flattens fast, and on flat-floor work the ride-on with pans is the production tool of choice. Float when the surface bears the weight, which on a power float means the machine and the operator leave only a shallow mark and the top does not stick and tear.
A float finish, left as floated, is a legitimate final finish: matte, slightly rough, and more slip-resistant than steel. Many exterior slabs are floated and then broomed with no troweling at all. Where a hard, dense floor is specified, the floating is the setup pass that makes the troweling work. Float first, always. Trowel a surface that was not floated flat and you just polish the waves.
Troweling: closing and densifying the surface
Troweling closes and densifies the surface, working the floated cream into a tight, smooth, hard skin. Where the float opens the surface, the trowel shuts it. The steel blade, pitched and dragged across the set surface, compacts the paste, drives out the last of the surface voids, and brings the floor to the density and sheen the finish schedule calls for.
It is a multi-pass job, and each pass comes later and at a steeper blade angle than the last. The first trowel pass runs nearly flat as the surface is just hard enough, the blades barely pitched. As the slab hardens, you raise the pitch and increase the speed, pass after pass, each one tighter and harder than the one before, until the surface reaches a hard-troweled, burnished sheen on the floors that call for it. By hand it is a steel trowel or a long-handled fresno. By machine it is a walk-behind or ride-on power trowel with finish blades or combination blades, pitched up as the floor hardens.
The failure at this stage is over-troweling, called burning the floor. Trowel too hard, too long, or too late and the friction and the pressure pull the surface dark and blotchy, a marbled, near-black discoloration that does not come out. It comes from forcing a surface that is too stiff, or from overworking it chasing a sheen. Know how hard the floor is supposed to go, hit it, and stop. More passes past the spec do not buy a better floor. They burn it.
The finish types
The finish type is set by where the slab lives and what walks or rolls on it, and it decides how far down the sequence you go. An exterior walk wants traction and never wants a hard steel finish. A warehouse floor wants a hard, dense, flat surface. The finish schedule on the drawings governs, but the common types fall into a short list.
A broom finish is the standard for exterior flatwork: float the surface, then drag a broom across it to leave fine parallel ridges for slip resistance. A float finish is left as floated, matte and lightly textured, common on utility slabs. A hard-troweled finish is the dense, smooth, interior and warehouse floor, taken through multiple steel passes. Exposed aggregate washes or seeds the surface to reveal the stone for a rough, slip-resistant, decorative finish. Stamped concrete presses a pattern into the floated surface before it sets. A burnished or polished finish takes the hard trowel further, or grinds and polishes the cured slab, for a dense, reflective floor.
The broom finish has its own timing. Broom after the surface has set enough to hold the marks without them closing back up, but while it is soft enough for the bristles to cut clean lines. On a slab with slope, broom perpendicular to the slope, or toward the drain, so the texture does not pond water. Broom direction is a real decision, not a cosmetic one, on anything that has to drain.
| Finish | Where it lives | How far down the sequence |
|---|---|---|
| Broom | Exterior walks, drives, ramps | Float, then broom; no steel trowel |
| Float | Utility slabs, slabs to receive a topping | Stop at the float pass |
| Hard-troweled | Interior, warehouse, industrial floors | Float, then multiple steel trowel passes |
| Exposed aggregate | Decorative exterior flatwork | Wash or seed; no hard trowel |
| Stamped | Decorative patios and walks | Stamp the floated surface before set |
| Burnished / polished | Dense interior, retail, showrooms | Hard trowel further, or grind and polish cured |
Can you trowel exterior concrete?
You can trowel exterior concrete, but you should not hard steel-trowel exterior air-entrained concrete, and almost all exterior flatwork is air-entrained for freeze-thaw durability. This is the rule that catches crews who finish interior floors and bring the same habit outside. Hard troweling an air-entrained slab densifies and seals the top, traps the entrained air just under the closed surface, and sets up delamination and blistering, the surface peeling or popping off in patches.
The mechanism is the same premature-sealing failure. Steel troweling closes the surface, the air and any remaining bleed water cannot get out, they collect in a plane right under the skin, and that plane debonds. The American Society of Concrete Contractors position is plain on this: if a spec calls for a hard-troweled finish on air-entrained concrete, the risk of delamination and blistering rides with the specifier, not the finisher. So for exterior air-entrained flatwork, finish with the bull float and the broom. Float it, broom it, cure it, and leave the steel trowel in the truck.
Interior floors are a different case. Interior concrete is usually not air-entrained, and that is exactly why it can be hard-troweled to a dense, smooth finish without the delamination risk. The line is the air, not the trowel. If the slab has entrained air and lives outside, the broom is the finish. If it is interior and not air-entrained, the steel can go on.
Power floats and trowels: walk-behind, ride-on, pans and blades
Power floats and trowels are the production tools on anything bigger than a sidewalk, and they come as walk-behind and ride-on machines. A walk-behind power trowel, a single rotor the operator steers from behind, suits smaller slabs, edges, and tight areas. A ride-on, two counter-rotating rotors with the operator seated, covers ground fast and is the tool for big flat floors. Many crews float the first pass with a walk-behind even when a ride-on does the finishing, to get into the surface early.
The attachment changes the job. Float pans, flat steel disks clamped over the blades, float a wide path and flatten the surface fast in the early passes. Combination blades float when run flat and finish when pitched up, so the same blade carries the floor from floating into troweling without a change. Finish blades, narrow and always slightly pitched, are the last passes, raised steeper as the floor hardens to close and burnish it.
The machine has a timing of its own: the slab has to bear the machine. Put a ride-on on too soon and it sinks, gouges, and tears the surface. The walk-on test is the gate. When an operator leaves a footprint around 1/8 to 1/4 in and the top does not stick to the boots, the surface will carry a power float. Some crews run plastic finish blades on the last passes to spread the load and cut the risk of burning the floor.
What causes blisters and delamination?
Blisters and delamination both come from sealing the surface before the slab is done bleeding and releasing air. A blister is a small, hollow bump, dime to palm sized, that forms when bleed water or entrapped air rises and gets trapped under a surface the finisher closed too early. Delamination is the same failure spread wide: a thin top layer, often 1/8 to 1/4 in, debonds from the concrete under it over a broad area and sounds hollow when you drag a chain or tap it.
The cause is premature finishing, the same root as dusting and scaling. The finisher floats or trowels and densifies the surface while the concrete underneath is still bleeding and releasing air. The water and air cannot escape through the sealed top, so they collect in a plane right under the skin, and that plane has no bond. It holds until traffic, freeze-thaw, or a forklift wheel breaks it, and then it pops. Air-entrained concrete that gets hard-troweled is the classic setup, because the entrained air has nowhere to go.
Prevention is the bleed-water rule and a light early hand. Do not close the surface until the bleeding and the air release are done. Bull float, then wait. Use a magnesium float that opens the surface rather than sealing it early. Delay the hard finishing as long as the set allows. And do not hard steel-trowel air-entrained concrete at all. The cure for a blister is on the front end, in the timing, because once it has delaminated it is a repair, not a touch-up.
Cure the moment the finish is done
Curing starts the moment the finish is done, and a perfect finish with no cure is a wasted finish. As soon as the last pass is off the surface, the concrete needs its moisture held in so the cement keeps hydrating and the surface gains the strength and abrasion resistance the finish was meant to deliver. Leave a fresh-finished slab to dry in the sun and wind and the top comes up weak and crazed no matter how clean the troweling was.
The methods are a curing compound sprayed on right after finishing, wet curing with burlap, cotton mats, or ponding, or covering with plastic sheet or curing blankets. ACI 308 covers the methods and the durations. On a broomed exterior slab the curing compound goes on as soon as the broom is done. On a hard-troweled floor you cure after the final pass, watching that the cure method does not mar the finish you just closed. Either way the gap between finishing and curing is where slabs get hurt, because that is the window when the new surface dries fastest.
This is the handoff the evaporation-rate guide tracks from the other side. The plastic-stage protection, the fogging and the windbreaks, carries the surface to finishing. The curing carries the set concrete through the days after. A slab needs both, in order. The finish is the middle of the story, not the end.
Flatness and the finish
Flatness is built by the screed and the floating, and it is measured as FF and FL numbers under ASTM E1155, the floor flatness and levelness test. FF, the flatness number, controls the short bumps you feel every couple of feet. FL, the levelness number, controls the overall slope across the floor. Higher numbers are flatter and more level. A hand-screeded floor commonly lands around FF 25, FL 20, while a laser screed routinely doubles the flatness, which is why specified flat floors are placed with one.
Technique drives the number. The flatness is set in the strikeoff and protected through the floating, so chasing flatness at the trowel is too late, the trowel follows the surface it is given. On a high-FF floor the crew restraightens between passes, running a highway straightedge, a long bar dragged across the surface, to cut the highs and fill the lows while the concrete still moves. The restraightening pass is what separates a flat floor from an average one, and it happens during finishing, not after.
Measure flatness within about 72 hours of placement, because the slab curls and changes after that and the reading drifts. The control-joint guide covers how curling at the joints shows up as a flatness defect a wheel feels at speed. For a floor with a real FF and FL spec, the screed choice, the restraightening, and the crew size are all decided around hitting the number, not discovered at the test.
Weather and the finishing window
Weather sets the size of the finishing window, and the hot day is the one that hurts. Heat, sun, low humidity, and wind drive water off the surface fast, which pulls the set forward, shrinks every window, and stacks the steps on top of each other. The bleed water leaves sooner, or never shows on a low-bleed mix, and the crew that planned for a normal day gets caught finishing a surface that is already drying and tearing. The evaporation-rate guide covers reading the rate and protecting the surface, and on a hot pour you stage that protection before the truck.
Cold stretches the window the other way. Below about 50°F the set slows hard, the bleed takes longer, and the finishers wait, sometimes for hours, for a surface that is not ready. The trap in the cold is finishing too early out of impatience, sealing in bleed that has not finished rising. Cold-weather work also means protecting the slab from freezing and never finishing on frozen subgrade, which is a separate fight from the finishing itself.
Rain is the simple one and the brutal one. Rain on a fresh, unfinished surface dilutes the paste, raises the surface water-to-cement ratio, and wrecks the finish. Keep plastic and squeegees on site, cover the slab if a cell comes through before it sets, and never trowel rainwater into the surface. A slab caught by a downpour at the wrong moment is often a tear-out, not a repair.
Field example: a warehouse floor and an exterior walk
Walk two slabs poured the same week. One is a 6 in interior warehouse floor, not air-entrained, with a hard-troweled, high-flatness spec. The other is an exterior entry walk, air-entrained for freeze-thaw, with a broom finish. Same crew, same finishing principles, two different paths down the sequence.
The warehouse floor goes the full distance. Laser screed to hold the flatness, bull float before bleed, wait out the bleed water, float with pans on the ride-on, restraighten with a highway straightedge, then three to four steel trowel passes, each later and steeper, to a hard burnished surface, then cure. The window is read off the footprint test and the floor is chased corner by corner as it sets. The flatness spec drives the screed choice and the restraightening.
The entry walk stops short on purpose. Wet screed to grade, bull float with a magnesium float before bleed, wait, edge and hand-tool the joints, float, then broom perpendicular to the slope, and cure with compound right behind the broom. No steel trowel, because the concrete is air-entrained and hard troweling it would delaminate the surface outside through the first winter. Same rule under both: bull float, wait out the bleed, finish to the schedule, cure right away. The schedule and the air content decided everything else.
| Step | Interior warehouse floor | Exterior entry walk |
|---|---|---|
| Air-entrained | No | Yes |
| Screed | Laser screed for flatness | Wet screed to grade |
| Float | Power float, pans on a ride-on | Magnesium bull float |
| Restraighten | Highway straightedge between passes | Not required |
| Trowel | 3 to 4 steel passes, hard finish | None |
| Surface finish | Hard-troweled, burnished | Broom, perpendicular to slope |
| Cure | After the final pass | Compound right behind the broom |
What to document
Let the surface dust or pop a year out and the argument lands on finishing timing every time, which is why the record has to capture when each pass ran against the bleed and the set. The record shows the sequence was run right, the bleed was respected, the finish matched the schedule, and the cure started on time. Write it at the pour, against the surface, not from memory.
Capture the pour and area, the mix and whether it bleeds normally or low, the screed method, the time the bleed water left, the set test result and when finishing started, the finish type and how many trowel passes, whether the slab was air-entrained and how it was finished accordingly, the curing method and start time, and the flatness numbers if the floor was measured. If the finishing window was tight from heat or weather, log that and what was done. The next person reading it, the inspector or the owner, wants to see that the timing was honest.
| Field to record | Why it matters |
|---|---|
| Pour, area, and date | Ties the finish to the placement |
| Mix and bleed behavior | Low-bleed mixes change the wait and the risk |
| Screed method | Sets the flatness the finish starts from |
| Time bleed water left | The gate for floating; finishing before it fails |
| Set test and finish start | Shows finishing began at the right set, not early |
| Finish type and trowel passes | Ties the surface to the finish schedule |
| Air-entrained and how finished | No hard trowel on exterior air-entrained |
| Cure method and start time | A finish with no cure comes up weak |
| FF and FL if measured | The flatness result against the spec |
Common mistakes
- Finishing over bleed water, sealing in a weak skin that dusts, scales, and delaminates.
- Hard steel-troweling exterior air-entrained concrete, which traps the air and delaminates the surface.
- Over-troweling and burning the floor dark and blotchy by working it too hard, too long, or too late.
- Leaving the slab with no cure after finishing, so the surface comes up weak and crazed.
- Sprinkling water or dry cement on the surface to make it finish, raising the skin water-to-cement ratio.
- Waiting for a water sheen on a low-bleed mix while the surface dries and tears underneath the wait.
- Tooling or sawing the joints too late, after the slab has already cracked on its own.
- Bull floating after the bleed water shows instead of before, working the water back into the surface.
- Chasing flatness at the trowel instead of building it in the screed and the floating.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The project specification and the finish schedule govern the finish, full stop. Everything below is the framework those documents sit on, and where the contract is more specific or stricter, it wins.
ACI 302, the guide for concrete floor and slab construction, is the main reference for the finishing sequence: screeding, bull floating before bleed, the bleed-water wait, floating, troweling, and the practices that cause or prevent dusting, scaling, blistering, and delamination. ACI 117 carries the tolerances for concrete construction, the framework behind the flatness and levelness limits a floor is held to. ACI 301 is the specification for structural concrete, often referenced for the floor finish requirements. For parking lots and site paving, ACI 330 is the guide, where surface drainage and a broom finish matter more than a hard-troweled flatness. The exact document numbers and contents shift between editions, so confirm the edition the project adopted before citing a provision.
On the test-method side, ASTM E1155 is the test for FF floor flatness and FL levelness numbers, the way a specified flat floor is measured and accepted. ACI 308 governs curing, the stage that follows finishing. The American Society of Concrete Contractors position statements address finishing practice directly, including the warning against hard-troweling air-entrained concrete. Name the standard that controls the point, and let the project specification override any rule of thumb when it is stricter.
Units, terms, and conversions
Finishing carries its own vocabulary, and the same surface can read differently across a spec, a finish schedule, and the crew talking on the slab. The key conversions are few. Flatness rides on FF and FL numbers, unitless and higher-is-flatter. Joint and cut depths run in inches in the US and millimeters in metric, where a 6 in slab is about 150 mm and a 1/4 in cut is about 6 mm. Set windows are in hours, and they shrink with heat and stretch with cold rather than holding a fixed value.
The terms below are the ones that get mixed up, mostly the float-versus-trowel distinction and the names for the failures. Keep them straight, because calling for the wrong tool or the wrong pass at the wrong set is how the surface gets hurt.
- Bleed water
- Water that rises to the surface as solids settle; no finishing happens while it is present
- Bull float / darby
- Wide float run right after screed to flatten and embed aggregate before bleed water
- Float
- Opens and levels the surface, bringing the cream up; magnesium opens, wood pulls paste
- Trowel
- Closes and densifies the set surface; a steel blade pitched steeper each pass
- Broom finish
- Slip-resistant texture dragged into the floated surface, run perpendicular to slope
- Burnish / burn
- Burnish is a hard polished trowel finish; burning is over-troweling that darkens the surface
- Delamination
- A thin top layer debonding over a wide area from finishing over bleed water or air
- Set window
- The span when the surface is firm enough to work but not too hard, read by the footprint test
FAQ
When do you start finishing concrete?
Start floating once the bleed water has left the surface and a footprint or thumbprint leaves about a 1/4 in mark with no water welling up. Too soft and the print sinks deep with water, so wait. Too hard and you cannot print it, so you are late. Read the surface, not the clock.
What is the difference between floating and troweling?
Floating opens and levels the surface, embedding aggregate and bringing the fine paste, the cream, up to the top. Troweling comes after and closes that surface, densifying it into a hard, smooth skin with a pitched steel blade. Float first to flatten, trowel after to densify. Many exterior slabs are floated and broomed with no troweling.
Can you trowel exterior concrete?
You can trowel exterior concrete, but do not hard steel-trowel exterior air-entrained concrete, which most exterior flatwork is. Hard troweling seals the surface and traps the entrained air below it, causing delamination and blistering through freeze-thaw. Finish exterior air-entrained slabs with the bull float and the broom, not the steel trowel.
Why does concrete dust or scale?
Concrete dusts or scales mostly from finishing over bleed water. Working the surface while bleed water sits on it pushes that water back into the top, leaving a weak, high water-to-cement skin that powders under traffic or flakes off in freeze-thaw. Wait for the bleed water to leave before finishing, then cure the slab.
How long do you wait before troweling concrete?
There is no fixed number of hours. You wait until the bleed water is gone and the surface bears the trowel without tearing, which on an interior floor can be a few hours and longer in cold. Heat shortens it hard. Use the footprint test, around 1/4 in, not a clock, to call it.
What is the thumbprint test for concrete?
The thumbprint test reads the set by pressing a thumb into the surface. An indent around 1/4 in that holds its shape means the surface is firm enough to start floating. If the thumb sinks deep and water rises, it is too early. If you cannot leave a mark, the finishing window has passed.
Should you broom finish or trowel an exterior slab?
Broom finish an exterior slab, do not hard trowel it. Exterior flatwork is air-entrained for freeze-thaw, and hard troweling air-entrained concrete traps the air and delaminates the surface. A broom finish also adds the slip resistance a steel-troweled surface loses. Float the slab, broom it perpendicular to the slope, and cure it.
What causes concrete to blister or delaminate?
Blisters and delamination come from closing the surface before the slab finishes bleeding and releasing air. The trapped water and air collect in a plane under the sealed skin, which debonds and later pops. Do not finish over bleed water, do not hard-trowel air-entrained concrete, and use a magnesium float that keeps the surface open.
When do you start curing concrete after finishing?
Start curing the moment the finish is done, with no gap. Spray a curing compound right behind the broom or after the final trowel pass, or cover with wet burlap, plastic, or curing blankets per ACI 308. The window between finishing and curing is when the new surface dries fastest and comes up weak if left bare.
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Codes cited in this guide
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