Pouring concrete is only half the job. The finishing process determines how the surface looks, how well it drains, how resistant it is to wear, and in many cases how long it lasts.
Professional concrete finishers are not simply smoothing wet concrete. They are carefully controlling the surface while the concrete moves through several stages of setting.
Understanding when to perform each finishing operation is just as important as knowing how to do it.
Step 1: Place the Concrete
Concrete should be placed as close as possible to its final location.
Dragging concrete long distances with rakes can cause the coarse aggregate to separate from the cement paste, a problem known as segregation.
When placing concrete:
- Spread it evenly throughout the forms.
- Avoid large piles whenever possible.
- Make sure concrete gets underneath and around reinforcing steel.
- Consolidate concrete along forms and around embedded objects.
- Do not excessively vibrate the concrete.
Concrete should generally be placed slightly higher than the finished surface so there is enough material to screed it accurately.
Step 2: Screed the Concrete
Screeding establishes the basic elevation of the slab.
A straight board, aluminum screed, or powered vibrating screed is moved across the forms while excess concrete is pushed forward.
The screed should ride firmly on the forms or grade rails.
When hand screeding, finishers typically use a sawing motion while slowly advancing across the slab.
The goal is to:
- Cut down high spots.
- Fill low spots.
- Establish the correct slope.
- Produce a reasonably flat surface.
Low spots should be filled with concrete—not simply cement paste.
On patios and exterior slabs, maintaining proper drainage is particularly important. Even a beautifully finished patio can become a problem if water collects against the house.
Step 3: Bull Float
Immediately after screeding, the slab is normally bull floated.
A bull float performs several important functions.
It:
- Removes screed lines.
- Pushes larger aggregate slightly below the surface.
- Helps fill small depressions.
- Levels minor imperfections.
The float should generally be kept fairly flat.
Tilting the leading edge too aggressively can dig into the surface and move too much paste.
The concrete should normally only require a few passes. Excessive floating can bring additional cement paste and water to the surface.
Step 4: Wait for Bleed Water
This is one of the most important stages of concrete finishing.
After placement, some water inside the concrete naturally migrates toward the surface. This is called bleed water.
It may look like a thin film or small puddles.
Do not finish this water back into the concrete.
Doing so can increase the water-cement ratio at the surface and create a weak layer that is more susceptible to:
- Dusting
- Scaling
- Delamination
- Surface deterioration
Professional finishers learn to recognize when the bleed water has evaporated and the concrete has stiffened enough for additional finishing.
Waiting is often harder than finishing.
Step 5: Edge the Slab
An edger is run along the forms to create a rounded edge.
Sharp concrete corners are fragile and tend to chip. A properly edged slab creates a stronger and more attractive perimeter.
Finishers usually insert the edger between the form and concrete and move it back and forth until the edge is smooth.
The tool should not be tilted excessively because doing so can leave deep tool marks.
Edges can be touched up again later in the finishing process.
Step 6: Cut Control Joints
Concrete shrinks as it dries.
Because of this, some cracking is almost inevitable.
Control joints create intentional weak points where the slab is encouraged to crack in a controlled, relatively straight line.
Joints can be created with:
- Groovers while the concrete is plastic.
- Saw cuts after the slab has hardened enough to support the saw.
A common rule is that joint depth should be approximately one-quarter of the slab thickness.
For example, a 4-inch slab generally needs joints around 1 inch deep.
Joint spacing, slab geometry, reinforcement, weather, and subgrade conditions all influence cracking.
Step 7: Float the Surface
Once the concrete has stiffened enough, the surface may be floated again.
Hand floats, magnesium floats, wood floats, and power floats can all be used depending on the type of work.
Floating:
- Removes small imperfections.
- Helps embed aggregate.
- Consolidates the surface.
- Prepares the slab for its final texture.
Magnesium floats are common for exterior flatwork because they smooth the concrete without closing the surface as tightly as a steel trowel.
Step 8: Trowel if Appropriate
Steel trowels create a denser, smoother surface.
This type of finish is commonly used on:
- Garage floors
- Shop floors
- Interior slabs
- Warehouse floors
Exterior concrete normally should not be finished to an extremely slick steel-troweled surface because it can become slippery when wet.
Repeated troweling also closes the surface.
Professional finishers wait until the concrete is sufficiently hard before troweling.
If a finisher kneels on the slab and sinks deeply into it, the concrete is usually still too wet.
As the concrete firms up, progressively flatter trowel angles and additional passes can create an extremely smooth finish.
Step 9: Apply the Final Texture
Exterior concrete is commonly broom finished.
A concrete broom is dragged across the surface after floating or light troweling.
Timing greatly affects the appearance.
Broom too early and the grooves may be excessively deep and rough.
Broom too late and the broom may barely texture the concrete.
A good broom finish provides both traction and a clean, uniform appearance.
Common decorative variations include:
- Light broom
- Heavy broom
- Picture-frame borders
- Swirl finishes
- Salt finishes
- Exposed aggregate
- Stamped concrete
Step 10: Cure the Concrete
Finishing does not end when the tools are put away.
Concrete needs moisture to complete the chemical reaction that gives it strength.
That reaction is called hydration.
Concrete that dries too quickly can develop:
- Surface cracking
- Reduced strength
- Dusting
- Curling
- Poor durability
Common curing methods include:
- Spray-on curing compounds
- Wet coverings
- Plastic sheeting
- Continuous water curing
Protecting the concrete during the first several days can significantly improve the final product.
Good Concrete Finishing Is Mostly About Timing
There is no timer that tells a finisher exactly when to perform each operation.
Temperature, wind, humidity, sunlight, concrete temperature, mix design, slab thickness, and subgrade conditions can all affect setting time.
That is why experienced finishers constantly watch the slab.
Finishing concrete like a professional comes from understanding the material rather than simply trying to make the surface smooth.