Can concrete be sanded smooth?

Concrete is one of the most versatile and commonly used construction materials. It is durable, affordable, and can be formed into any shape. However, concrete has a rough, grainy texture after it has cured. This texture is not ideal for every application. Sometimes a smooth, even finish is desired for concrete surfaces. So can concrete be sanded smooth?

The Short Answer

Yes, concrete can be sanded smooth. However, there are some important factors to consider when sanding concrete to achieve the desired smooth finish.

How to Sand Concrete

Sanding is a process of working the surface of cured concrete with abrasive materials to wear down any roughness or uneven spots. The main tools used are:

• Handheld sanders – Either manual or powered using electricity or compressed air.
• Floor sanding machines – Larger powered rotary sanders used for smoothing and leveling large horizontal surfaces.
• Sandpaper – Sheets of gritty abrasive paper used for smoothing smaller areas by hand.

The basic process involves:

1. Letting the concrete fully cure – Concrete needs 28 days to reach full strength. Sanding too early risks damaging the surface.
2. Choosing the right abrasive – Start with a coarser grit sandpaper or disc to level out unevenness, then switch to finer grits for smoothing.
3. Sanding in multiple passes – Apply even pressure and work in different directions to get a consistent finish.
4. Cleaning and drying the surface – Remove all dust and debris when finished to prepare for sealing/polishing.

Factors That Affect Results

Several variables impact how smooth sanded concrete ultimately turns out:

Age of Concrete

– New concrete less than 28 days old is prone to gouging and creating furrows if sanded too vigorously.

Base Texture

– Rough surfaces with exposed large aggregate take more work to level and smooth out.

Type of Abrasive

– The grit size determines cutting speed and smoothness. Larger grits cut faster, smaller grits make smoother finishes.

Skill Level

– An experienced concrete finisher will get better results than a DIYer or novice.

Sealing and Polishing

– Applying concrete sealers and/or polishers after sanding enhances the smoothness.

Ideal Concrete Surfaces for Sanding

Sanding works best on concrete surfaces that are:

• At least 4 weeks old – Ensures concrete has fully cured and hardened.
• Free of large aggregate – Exposed rocks and stones prevent achieving a smooth finish.
• Indoors – Outdoor concrete tends to have rougher finishes that require heavy grinding rather than sanding.
• Lightly textured – Surfaces with a basic medium broom or float finish provide the right starting point.

Tips for Sanding Concrete

Follow these tips to get the best results when sanding concrete:

• Wear proper safety gear – Mask, goggles, ear protection, gloves, etc.
• Work wet whenever possible – Water prevents creating harmful silica dust.
• Begin sanding at the corners – Start where two surfaces meet to prevent rounding edges.
• Use sanding blocks for small areas – Helps ensure an even, consistent finish.
• Change sandpaper frequently – Old sandpaper doesn’t cut well and produces poor results.
• Apply concrete sealer after final sanding – Enhances smoothness and protects the surface.

Power Sanding vs Hand Sanding

Power sanders allow sanding large surfaces faster, while hand sanding gives greater control for precision work.

Power Sanding Advantages

• Covers more area faster.
• Creates a more even overall finish.
• Different attachments suit various needs.
• Less physical exertion required.

Hand Sanding Advantages

• Better suited for confined spaces.
• Allows getting into corners and edges.
• Gives more control and precision.
• Gets into hard to reach areas.

What Grit Sandpaper for Concrete?

The ideal sandpaper grit range for concrete is:

• Rough Leveling – 16 to 30 grit
• Smoothing – 60 to 100 grit
• Polishing – 120 to 220 grit

Always start with a more coarse grit to remove bigger imperfections, then work up to finer grits for polishing.

How Smooth Can Concrete be Sanded?

With the proper techniques and tools, concrete can be sanded to a remarkably smooth finish, comparable to many other flooring types.

Typical maximum smoothness levels attainable by sanding include:

• Fine Grit Sanding – 400 grit, smooth to the touch
• Polishing – 800 to 1500 grit, glossy sheen
• High Gloss – Up to 3000 grit, mirrored finish

Always follow sanding with sealing and polishing for best results.

Power Sanding Equipment

Some common power sanding machines and tools used for concrete include:

Tool	Description
Walk-behind floor sander	Larger rotary drum sander for smoothing horizontal surfaces like floors.
Handheld orbital sander	Compact powered disc sander good for vertical applications.
Belt sander	Uses continuous abrasive belt for rapid stock removal from large areas.
Angle grinder	Grinding discs can smooth and shape edges and hard to reach spots.
Burnisher	Rotary machine polishes concrete to a high sheen.

Hand Sanding Tools

Hand sanding concrete requires little equipment, primarily:

• Sandpaper sheets – Aluminum oxide or silicon carbide abrasive papers.
• Sanding blocks – Helps apply consistent even pressure.
• Handscrapers – Removes localized high points and imperfections.
• Wood floats – For smoothing surfaces between sanding.

Plus safety gear – gloves, knee pads, protective eyewear, dust masks, etc.

Concrete Surface Prep

Proper preparation is key before sanding concrete:

1. Clean surface – Remove all dirt, oil, debris, etc.
2. Fill any holes or voids – Use patching compound to fill gaps and smooth.
3. Allow concrete to fully cure – Wait at least 4 weeks after pouring.
4. Seal surface – Waterproof concrete to limit dust and surface damage.

Risks of Sanding Concrete

Potential hazards to be aware of when sanding concrete include:

• Silica dust – Concrete particles pose respiratory health risks without proper ventilation.
• Eye injuries – Sanding debris can damage unprotected eyes.
• Hearing loss – Power sanding equipment produces high noise levels.
• Hand-arm vibration – Extended power tool use creates vibration injuries.

Always wear safety gear and follow good practices to mitigate these hazards when sanding concrete.

Cost to Sand Concrete

Hiring a professional concrete crew costs $2-$6 per square foot on average to sand and polish a concrete floor. DIY sanding has much lower upfront costs but requires owning/renting equipment.

Some cost factors include:

• Labor rates for installers
• Concrete surface area
• Condition of existing floor
• Location accessibility
• Level of smoothness desired
• Cost of concrete sanding supplies

Does Sanding Concrete Remove Sealer?

Yes, sanding down to the bare concrete will completely remove any previously applied sealer or coating.

However, it is possible to do minor smoothing or “screening” of sealed concrete without penetrating through to the bare concrete below. This requires using very fine grit sandpaper and light pressure.

Any exposed concrete will need resealing after sanding.

How to Smooth Concrete After Sanding

Steps for smoothing and finishing concrete after sanding include:

1. Wipe away all dust with slightly damp towels.
2. Apply concrete sealer and let fully dry.
3. Finish with increasingly finer grit sandpapers.
4. Apply final sealer coat for protection.
5. Optional – Apply concrete polishing compounds.

Conclusion

Sanding is an effective method to smooth and polish the surface of cured concrete. With the right tools, techniques, and preparation, concrete can be sanded to a very smooth finish suitable for many flooring applications.

Paying attention to factors like the concrete’s age, base texture, and using proper grit sandpapers allows achieving professional quality results. Power sanding quickly smoothes large areas, while hand sanding allows precise control on smaller projects.

Following up sanding with quality sealing and polishing compounds enhances the smoothness while protecting the concrete surface. With some labor and patience, sanding can transform rough poured concrete into a super smooth floor.