How To Sand A Concrete Patio Smoothly

Sanding a concrete patio is a great way to improve its appearance and make it safer by smoothing out rough surfaces and rounding off sharp edges. It is also a vital step in preparing concrete for further treatment, such as applying paint or sealant. The process involves using tools like orbital sanders and concrete grinders to smoothen and refine the concrete surface, creating a polished look. Before sanding, it is important to inspect the concrete for flaws and protect the surrounding area from dust. After sanding, cleaning and applying a sealant are crucial steps to maintain the patio's integrity and enhance its smoothness.

Sanding concrete: the why and the how

Concrete is a popular building material for homes due to its low cost and high durability. However, sometimes it needs to be sanded to achieve a smoother appearance, remove stains, and refresh old surfaces. Sanding concrete can also prepare surfaces for sealants and repairs, as well as increase visual appeal.

How to Sand Concrete:

Before you begin sanding concrete, it is important to make a few considerations, such as whether you will leave the concrete exposed, if you will sand the entire floor or just specific areas, and what sort of finish you want to give the floor. Additionally, you should inspect the surface and remove any wood or metal objects, such as embedded nails, and fix any cracks or holes. It is also important to wear protective gear, such as a dust mask, safety glasses, and hearing protection.

When sanding concrete, you can choose between wet sanding and dry sanding. Wet sanding creates less dust and reduces wear on pads, but it takes longer. On the other hand, dry sanding is faster but creates more dust. If you choose to dry sand, consider using sanders with built-in vacuums to reduce dust.

There are several types of concrete sanders available, including handheld orbital sanders, angle grinders, belt sanders, and floor sanders (also called drum sanders or walk-behind sanders). The type of sander you choose will depend on the size of the job. For example, a handheld orbital sander is suitable for countertops or smaller areas, while a floor sander is more appropriate for driveways, patios, and other large areas.

The sandpaper you choose will depend on the amount of sanding that needs to be done. For basic stripping and sanding, use sandpaper with a grit between 40-60. To remove minor imperfections, use 80-120 grit sandpaper. For a smooth finish, use superfine sandpaper with a grit of 200 or higher.

When sanding, always start from the corners and move towards the center of the floor. Work in small sections and use even, steady pressure to prevent divots or swirls. Make follow-up passes as needed to smooth out uneven areas and repeat with increasingly fine sandpaper until you achieve the desired smoothness.

After sanding, it is important to clean the area and remove all dust from the surface. Then, apply a concrete sealant to protect the surface and maintain its appearance. Concrete floors should be resealed once a year.

Sanding Concrete Patios:

When it comes to sanding a concrete patio, you have a few options. You can rent a concrete grinder to even out the surface and then paint or cover it with something else. Alternatively, you can fill in the cracks with adhesive or concrete caulking and then apply polymeric sand to fill in the gaps between pavers. Polymeric sand is a blend of sand and special additives that resist weed growth, rain washout, and insect penetration better than regular sand. However, it is more expensive and requires more time and attention to detail.

The right tools for the job

Before you begin sanding your concrete patio, it's important to select the right tools for the job. The tools you'll need will depend on the size of the job, the condition of the concrete, and the outcome you're expecting.

Hand Sanding

If you're working with a small area, you may be able to sand the concrete by hand. This method is time-consuming but doesn't require any special machinery. To hand-sand concrete, you'll need 80- to 100-grit sandpaper and a sandpaper block or a block of wood that's easy to hold. Wet the sandpaper and the concrete, then use moderate pressure to rub the sandpaper across the concrete in long, smooth strokes. Work in small sections, completing each before moving on to the next.

Orbital Sanders

Orbital sanders are handheld power tools with an elliptically rotating sanding face that can move in any direction. They are a good choice for larger projects that require more pressure or power than hand sanding. When using an orbital sander, use even pressure at all times to prevent swirls, divots, and over-sanding in some areas. Choose sandpaper with a grit of 80 to 220, depending on how much surface you want to remove.

Angle Grinders

Angle grinders are handheld power tools with circular grinding blades. They don't use sandpaper but instead have a hard disc that quickly removes a lot of concrete in a single pass. Angle grinders can be tricky to use and may result in inconsistent results for inexperienced users. Always wear eye and ear protection and a respirator when using an angle grinder. Choose a grinder with a speed of at least 10,000 RPM and an abrasive disc for grinding concrete.

Floor Sanders

Floor sanders, also called floor concrete grinders or walk-behind sanders, are large, powerful machines that use diamond abrasive discs to sand concrete surfaces. They are suitable for large areas and can cover a lot of ground quickly. However, they are not suitable for novices, as they are powerful and require an experienced operator. Choose the right grit sandpaper for the concrete and the results you want, and load it into the machine. Stand behind the sander and push evenly on both handles while walking slowly across the floor from one side to the other.

Belt Sanders

Belt sanders are powerful handheld tools that are best for sanding large areas or concrete that needs deeper sanding. They typically require 120- to 180-grit sandpaper loaded onto the sanding drum in a loop shape. Maintain a firm grip on the belt sander and move it evenly across the surface of the concrete without using too much downward pressure. Belt sanders can be loud and create a lot of dust, so always use eye and ear protection when operating one.

Diamond Sandpaper

When sanding concrete, it's important to use the correct type of sandpaper. Diamond sandpaper is designed specifically for sanding hard surfaces like concrete and will last much longer than regular sandpaper. It's more expensive than regular sandpaper, but it will save you time and effort in the long run.

Power Tools

If you don't have the necessary power tools for the job, you can rent them from most hardware stores or home improvement centres. Before you go, do some research to determine what type of tool you need and what size sandpaper or grinding discs to purchase.

Safety Gear

It's important to wear the appropriate safety gear when sanding concrete to protect yourself from injury and exposure to concrete dust. This includes long sleeves, pants, waterproof gloves, safety goggles, a face mask or respirator, and ear protection.

Preparing the concrete surface

Inspect and Repair

Begin by thoroughly inspecting the concrete surface for any damage or imperfections. Look for cracks, holes, or bumps that need to be addressed. If you find any cracks or holes, use a concrete repair patch or a suitable concrete repair material to fix them. Make sure that the cracks are not a sign of structural damage, especially if you're working on a concrete foundation.

Remove Debris and Clean

Once the repairs are complete, it's time to remove any remaining debris from the surface. Sweep the area with a broom to get rid of loose dust and dirt. Then, clean the surface with dish soap and water. For smaller areas, use a cleaning brush and a squeegee to remove stubborn particles. If you're working on a large outdoor area, such as a driveway or patio, use a pressure washer to ensure a thorough cleaning.

Protect Surrounding Areas

Cover any large furniture or anchored pieces with drop cloths or tarps to protect them from dust and debris during the sanding process. If you're working indoors, apply plastic sheeting in the doorway and close HVAC vents to prevent dust from escaping into other areas of the house.

Wear Appropriate Safety Gear

Sanding concrete can generate harmful dust and debris, so it's important to wear the proper safety gear. At a minimum, wear a dust mask or respirator to prevent inhaling concrete dust and safety glasses to protect your eyes. If you're using a belt sander, consider using hearing protection as well, as they can be quite loud.

Allow New Concrete to Cure

If you're working with newly poured concrete, make sure it has adequately cured and dried before sanding. Fresh concrete can develop bumps or sharp edges during the curing process, so it's important to wait until it has fully set.

Choose the Right Sandpaper

Select the appropriate sandpaper grit for your project. Coarse grits, such as 40- to 60-grit, are suitable for basic stripping and sanding. Fine grits, like 80- to 120-grit, are ideal for smooth finishes and sanding down minor imperfections. For the smoothest finishes, opt for superfine grits of 200- to 400-grit or higher.

Additionally, choose diamond-grit sanding discs or sandpaper designed for hard surfaces, not wood surfaces. Regular sandpaper is not strong enough for sanding concrete.

By following these steps, you'll ensure that your concrete patio is properly prepared for sanding, leading to a better final result and a more durable finish.

Sanding techniques for different finishes

The sanding technique you use will depend on the finish you want to achieve. Here are some common concrete finishes and the sanding techniques required for each:

Polished Finish

The polished finish is one of the easiest looks to achieve. This finish only requires a quick, light sand to remove any imperfections and create a glossy finish. Start with a coarse grit (around 30-60) to remove bumps and stains, then move to a very fine grit (200-400) for the final polish.

Stained Finish

If you want to add a stain to your concrete for a pop of colour, you'll first need to give the surface a quick sand to scuff the top layer. This will create a porous surface that will absorb the stain more effectively. As with the polished finish, a quick sand with a coarse grit followed by a finer grit is all that's needed.

Epoxy Finish

For an epoxy finish, you'll also need to scuff sand the surface of the concrete to remove any paint or gloss and create a porous surface for the epoxy to bond with. Sand with a coarse grit, then a finer grit to ensure the surface is ready for the epoxy.

Salt and Pepper Finish

For a salt and pepper finish, you'll need to use a moderate sanding technique to remove the top layer of concrete and expose the fine aggregates beneath. Start with a coarse grit to remove the top layer, then move to a finer grit to refine the finish. This technique will create a subtly textured, speckled appearance.

Exposed Aggregate Finish

The exposed aggregate finish requires more extensive sanding to remove a significant layer of the surface (around 1/4 inch) and expose the larger aggregates, such as pebbles or coloured glass. This technique requires more powerful sanding tools and a more aggressive approach to ensure evenness and depth across the entire area.

Step-by-step guide to sanding concrete

Step 1: Prepare the Concrete

Before you start sanding, fill in any cracks or holes in the concrete. Use a crack filler that matches the colour of your concrete, and smooth it with a trowel. Remove any dust or debris from the hole so that the filler can properly bond with the concrete. Dampen the area before adding the filler and allow it to cure for 24-48 hours.

Step 2: Select the Correct Tool

The tool you use will depend on the size of your project. For small projects like crack repairs, use handheld diamond sandpaper or polishing pads. For small indoor projects like bathroom floors or countertops, use a handheld concrete sander or orbital sander. For larger, more intensive projects like garage floors, use a belt sander. For large outdoor spaces like patios or driveways, use a floor concrete grinder or walk-behind grinder.

Step 3: Prepare the Work Area

If you're sanding indoors, remove all objects from the room or cover them with plastic drop cloths to protect them from dust and debris. For large areas, divide the space into separate zones and work on each zone one by one.

Step 4: Put on Protective Gear

The dust from sanding concrete contains harmful silica particles, so it's important to wear protective gear. Put on goggles and a dust mask to protect your eyes and lungs, and keep a shop vac on hand to remove residual dust.

Step 5: Begin Sanding

Start with a coarse sanding pad (30-60 grit) and sand in long strokes with uniform pressure. You can sand wet or dry, but wet sanding is safer as it reduces the amount of dust. After the first round of sanding, clean the surface of dust or debris with a vacuum or sponge. Continue sanding with increasingly finer grits, cleaning the surface between rounds. Finish with a high-grit sandpaper (200-400 grit) for a super-smooth finish.

Step 6: Clean the Area

After sanding, vacuum or brush away any remaining dust or debris. Then, rinse the area with soapy water and allow it to dry completely, which may take up to two days. Properly dispose of any leftover mix or waste.

Step 7: Apply a Finish

Once the area is dry, apply a finish or sealant to protect the concrete from wear and tear and guard against spills and stains. Open the windows for ventilation and follow the instructions on your product. Typically, you'll use a paintbrush for corners and edges and a roller for the rest of the surface. Allow 1-2 days for the finish to dry completely.

Frequently asked questions