How do you smooth concrete after grinding?

Grinding concrete is a common process used to remove layers of concrete in order to prepare the surface for new flooring or coatings. It leaves the concrete rough and uneven after removal. However, most flooring materials require the concrete to be as smooth as possible for proper installation. This means the concrete will need to be smoothed and leveled after grinding before any new flooring can be installed.

There are a few different methods that can be used to smooth and level concrete after grinding. The most common methods include power troweling, burnishing, and overlaying. Choosing the right method will depend on the look you want to achieve, your budget, and how smooth the concrete needs to be. With the proper method and some hard work, you can turn heavily textured concrete into a smooth, uniform surface.

Why Grind Concrete in the First Place?

Before getting into the smoothing methods, it helps to understand why grinding is done. There are a few key reasons concrete may need to be ground before new flooring is installed:

Removing old or contaminated surfaces – Grinding is an ideal way to remove old paint, oils, grease, and adhesives from concrete. It removes the top layer(s) where these contaminants have soaked in over time.
Removing uneven surfaces – Concrete can become uneven due to conditions like freeze and thaw cycles, installation issues, foundation movement, etc. Grinding levels out minor pits, bumps, and cracks in slabs.
Scarifying for better adhesion – Grinding roughens the slick surface of concrete, giving new coatings, adhesives and cementitious materials something to bond to.

Aesthetics – Grinding gives concrete a more uniform appearance by removing minor imperfections and opening the pores. This provides an excellent base for stained, polished, or decorative concrete applications.

In most cases where new flooring is being installed, grinding is primarily used to remove contamination and level the surface. The roughened texture left behind provides the perfect base for applying smoothing and leveling materials.

Power Troweling

Power troweling involves working a smoothing compound into the concrete surface with a power trowel (a tool similar to a floor buffer). Troweling fills in small holes and depressions in the concrete, creating a smooth finish.

Here is a step-by-step overview of power troweling:

Clean the surface – Eliminate any dirt, dust, debris, oil etc. from the concrete with a detergent wash and rinse.
Apply a concrete grinding aid – These liquid compounds help reduce friction and wear on the trowels.

Mix the smoothing compound – Portland cement-based patching compounds designed for smoothing are ideal.
Spread compound over the surface – Work the material into the concrete with a trowel to fill all holes and depressions.
Let it sit for 15-30 minutes – Allow the material time to absorb into the concrete.

Power trowel the surface – Move the rotating trowel over the concrete to smooth and level.
Repeat as needed – Allow each application of smoothing compound to dry before adding more.
Apply a final pass with water – This provides maximum smoothness.

With power troweling, the concrete surface can usually be made smooth enough for most floor coverings after 1-3 passes. It just takes some elbow grease!

When to Use Power Troweling

Here are the ideal situations for using power troweling:

Minor imperfections – Small pits, grooves, and birdbaths left from grinding.

Foot traffic areas – Smooth finish for garages, walkways, patios, etc.
Minimal leveling – When the slab is mostly level and just needs smoothing.
Budget option – Power troweling is more affordable than other methods.

Power troweling works best on concrete that is in relatively good shape and just needs some minor smoothing and leveling. It can be done by a DIYer with some concrete experience.

Disadvantages of Power Troweling

Very labor intensive – Requires hard physical troweling work to smooth large areas.
Not ideal for heavy leveling – Only fills minors dips; will not fix major slab depressions.

Requires skill – It takes some practice to master the circular troweling technique.
Long cure time – Cannot be coated for several days until compound fully cures.

Power troweling provides a cost-effective way to smooth concrete, but it has limitations. Other methods may be better for extensive leveling or fast turnaround projects.

Burnishing

Burnishing uses a weighted floor buffer with an abrasive pad to literally “polish” the concrete surface. The friction heat from the rotating pad makes the top layer of concrete more dense.

Here is the typical process:

Deep clean the concrete – Remove all dirt, debris, stains, etc. with degreasers and scrubbing.

Run the buffer over the surface – Do an initial pass with a mild abrasive pad.
Change to a finer grit pad -Typically you would start with 50, then switch to an 80 or 120 grit.
Keep buffing until smooth – Make several passes with each pad, moving up to a finer pad each time.

Apply concrete sealer – A guard against moisture and staining.

Burnishing produces an extremely smooth surface and hardens the existing concrete slab. No additional materials are needed like with power troweling.

Benefits of Burnishing

Here are some benefits that make burnishing a great solution:

Very smooth finish – Mirror-like gloss with no remaining rough spots.
Hardens surface – Makes concrete up to 25% stronger.
Fast process – Quickly smooth and polish, usually within a day.

No odor or fumes – Environmentally-friendly with no chemicals.
Enhances color – Makes any integral concrete color much more vibrant.

Burnishing turns rough concrete into a smooth, durable surface ready for any application. It eliminates the need for extra smoothing materials.

Potential Drawbacks

Does not level – Simply polishes the existing surface without filling low spots.
Requires equipment – You need a heavy-duty floor buffer and abrasive pads.
Lots of grinding – It takes many passes to fully smooth and polish the slab.

Minimal thickness removal – Only removes a thin layer so stains may remain visible.

If major slab leveling is needed, burnishing alone is not the best option. Power troweling or overlaying may work better.

Applying an Overlay

Overlaying means pouring or placing a layer of fresh concrete, cement, or other material over the floor. This resurfaces the concrete for a completely smooth and level finish.

Here are some popular overlay options:

Traditional concrete resurfacing – Afresh layer of concrete that can be colored, stained, or stamped.
Latex cement overlays – Cement mix with latex polymers added to create a dense topping.

Epoxy overlays – Applying epoxy and aggregate creates a durable, seamless surface.
Self-leveling compounds – Pour high-flowing materials that settle into a smooth, flat layer.

Applying a Concrete Overlay

Here is a basic step-by-step process for applying a concrete overlay:

Prep the concrete – Clean and profile the surface for maximum bonding.
Install bond coat – Coat the concrete to increase overlay adhesion.
Pour or place overlay material – Spread evenly and work the layer to desired thickness.

Screed and trowel – Smooth it flat, filling all depressions.
Let cure – Allow proper curing time according to product instructions.
Seal surface – Apply protective sealer to resist stains, moisture, etc.

Skim coating, micro-topping, and similar methods follow the same basic steps. An overlay provides the smoothest possible surface.

Benefits of Overlays

Smooth, flat, and level finish – Fixes even the roughest concrete.
Hides imperfections – Covers blemishes, stains, cracks, spalls, etc.

Enhances appearance – Variety of color and finish options.
Corrects slab issues – Can be used on badly deteriorated concrete.
Long lifespan – Durable overlays last for decades with proper care.

When done properly, overlays create an entirely renewed concrete surface ideal for demanding applications. It’s the best solution for extensive smoothing and leveling.

Potential Challenges

More expensive – Overlay materials and labor increase costs versus other methods.
Extensive process – Proper slab prep is crucial and installation is labor-intensive.

Bond failure risks – Installation errors or poor prep can cause delamination.
Specific equipment needed – Requires mixers, pumps, etc. for installation.
Long curing – Most overlays take days to fully cure before use.

While an ideal solution in many cases, concrete overlays also come with increased costs and installation considerations.

Comparing Concrete Smoothing Methods

Method	Smoothness	Leveling Ability	Cost	Cure Time
Power Troweling	Moderate	Minimal	Low	Days
Burnishing	High	None	Moderate	Hours-Days
Overlays	Very high	High	High	Days

As you can see, each method has pros and cons. Power troweling provides basic smoothing at a low cost. Burnishing quickly polishes smooth with no leveling ability. Overlays offer the best finish but have higher installation requirements.

The right choice depends on your specific project, budget, and needs. Many times, a combination of methods yields the best results.

Tips for Maximizing Smoothness

Here are some useful tips to help achieve the smoothest finish possible, regardless of the method used:

Start with the right concrete – Opt for high-quality mixes with the best aggregate available.
Minimize trowel marks – Careful finishing when pouring new slabs prevents unevenness.

Repair concrete properly – Fill cracks and spalls with appropriate materials before smoothing.
Allow proper curing times – This prevents weak surfaces and grinding later.
Hire experienced contractors – They have the right techniques and tools.

Grind thoroughly – Removing enough existing concrete is vital for smooth overlays.
Follow manufacturer instructions – Don’t cut corners on things like cure times, mix ratios, etc.

Paying attention to details and using proper methods will help you achieve the best outcome, with smoother concrete after grinding.

Professional Tips for Maximum Smoothness

For the absolute smoothest finish, experienced concrete professionals recommend:

Use pan floats for finishing fresh concrete – This creates an ideal surface texture to build on.
Apply a steel trowel finish – Troweling seals pores and burnishes the top layer.

Double trowel the surface – Troweling again after the first pass smooths tiny imperfections.
Consider specific smoothness enhancing techniques:
- Apply a shake-on hardener while troweling.
- Burnish fresh concrete immediately after floating.
- Use plastic trowel blades instead of steel.

Taking these extra steps ensures the smoothest possible finish right out of the gate. This minimizes work needed after grinding.

Achieving Ultra-Smooth Finishes

For critical applications that demand perfectly smooth concrete with no imperfections, consider these options:

Polishable Overlays

Special polymer-modified overlays can be ground and polished after curing to achieve an ultra-smooth, glossy finish. These include:

Polymer cementitious overlays

Epoxy terrazzo
Methyl methacrylate (MMA)

Micro-Toppings

Fluid-applied thin resurfacers can produce a smooth finish under 5 mils thick. These include:

Magnesium phosphate cement micro-toppings
Calcium aluminate cement
Gypsum-based micro-toppings

Hybrid Floor Systems

Multi-layer flooring systems combine self-leveling underlayment with polishable overlays. This provides maximum smoothness and durability.

Synethetic Materials

Seamless materials like epoxy, polyaspartic, polyurea can also create glass-like finishes when applied properly.

Conclusion

Grinding concrete is just the first step in creating a smooth floor. While it levels the overall slab, additional smoothing is usually needed after grinding to achieve a surface finish appropriate for flooring installation or other applications.

Methods like power troweling, burnishing, and overlays each offer different benefits in terms of smoothness, leveling ability, cost and project time. Selecting the right method, or combination of methods, for your specific project is key to achieving the best outcome. Patience and proper techniques also go a long way toward maximizing smoothness.

With the right approach and methods, you can turn heavily textured, uneven concrete into a smoothly polished surface ready for a beautiful new flooring application.