Sanding concrete

Concrete Sanding and Polishing in 6 Easy Steps

Concrete polishing is a method of making concrete smooth and with a pleasant finish in a similar way that wood is sanded. Whereas with wood, you use sandpaper, with concrete polishing you use special diamond-segmented abrasives. As with wood, you use gradually finer abrasives to give a smooth, glossy, mirror-like finish.

Concrete can be polished using either a wet or dry method. Wet polishing extends the life of the abrasives but is messier than dry polishing and requires more time to clean up. Dry polishing is probably the more common method and is more environmentally kind because the dust created is collected in a dust containment system similar to a large vacuum cleaner.

Polished concrete is often used in shops and business premises, but also in private homes, because it is easy to maintain, requiring only mopping with water and a cleaning product.

The 6 Steps to Sand and Polish Concrete

The Tools and Equipment Needed

  • Concrete sander, polisher or grinder
  • Abrasive tools / Discs
  • Chemical concrete hardener (Densifier)
  • Concrete sealant or stain guard

1. Inspect and Evaluate before Polishing the Concrete Surface

First of all, you will want to find out how hard or soft the concrete actually is. This will determine which kind of equipment you will have to use. It also affects the time it will take to sand down the concrete surface. You can find this out by testing different types of abrasives, sandpapers or diamond pads, or you can test it more accurately by using a Mohs Hardness Pick Set (source). Workinng on a softer concrete surface generally consumes less abrasive tools and takes less time. It may require more attention, though, to limit the amount of material you are removing.

If the surface is already porous or has cracks and marks, you should repair it with a concrete crack filler or an epoxy -based filling material. Once these repairs are dried, you should continue with the next preparation step: cleaning the surface.

If the surface is not too stained, you can do this by using water and household detergent. For more stubborn stain, you may choose Hydrogen Peroxide, TSP or Ammonia. However, make sure that you do not mix different chemicals together as it might lead to unintended reactions, hurt the surface or even be dangerous for you.

2. Choosing a Concrete Sander for the Project and Getting the Equipment

Concrete polishing requires a specialised concrete grinding tool (source). Some look similar to an industrial floor polisher in that it has a base with rotating disc underneath and two handles used for control. Other concrete sanders are hand held and look similar to an angle grinder. Whereas a floor polisher uses a polishing disc, an angle grinder uses a cutting disc, concrete polishers use special diamond tipped grinding discs.

Concrete grinders of all types are available for hire at some DIY shops and hardware stores. However, you can consider purchasing one if you have a large area of or several concrete surfaces that need polishing.
Concrete sanders are available as models for dry sanding or wet polishing. The latter are usually equipped with a water hose connector that provides a constant flow of water during the wet concrete sanding. Good dry polishers, on the other hand, allow you to attach a vacuum which reduces the dust production significantly. Check our reviews to find the best concrete polisher for your needs.

Apart from the concrete polisher, you will need to have the following equipment at hand to perform the concrete polishing: abrasive tools, chemical concrete hardener (Densifier), concrete sealant or stain guard.

3. Preparing the Room and Yourself for Sanding Concrete

Sanding concrete is a messy endeavour. If you go for wet sanding, you will not produce dust but a liquid consisting of water mixed with cement dust that will become solid when it dries. Therefore, you will want to use plastics to protect objects around your work area. Spilled concrete/water liquid should be wiped away quickly before it hardens.

When dry-grinding concrete, protective clothing should always be used. Depending on the type of concrete grinder you will have to be aware of the amount of dust produced (if you are doing dry sanding). Some concrete grinders have a built-in dust collection system and these tend to work very well, but there is always a small amount of dust released into the air. Obviously if you are using a grinder without a dust collection system, the dust generated will be far more.

You should wear an approved dust mask and goggles as a minimum requirement. Ear protectors can be worn if required and also a paper dust suit can be worn to protect your clothing. Make sure your footwear has sufficient grip and you are not at risk of slipping.

4. Using the Concrete Grinder to Sand and Polish the Countertop, Floor, Wall or Pathway

Sanding concrete

You will need to select the coarseness of grinding discs that you are going to use. Only select metal bonded diamond discs as non-diamond discs will not be hard enough to grind down your concrete.
When you first start grinding, if there are marks or stains that remain after the initial cleaning stage, use a 40-grit grinding disc to remove these. Read the concrete grinder instructions how to attach the discs safely to the grinder. Once any stains are removed, move on to an 80-grit grinding disc. Cover the whole concrete area working from corner to corner.

Note that the grinding disc numbers indicate the discs coarseness. Lower numbers are more coarse, than higher numbers which are finer and should be used later. You will need to progress gradually changing discs to higher and finer discs. Depending on the hardness of your concrete, this may take some time but as a general guideline, 40-grit discs can then be followed by 80-grit, 150-grit, 200-grit and then finally 400-grit discs for a polished glass like finish.

When you change grinding discs, ensure you have passed over the entire working area first. With each change of disc, the idea is to polish away all the scratches left from the previous disc. Do this by crossing over previous scratch lines in a perpendicular direction.

For a detailed guidance on the sanding process, read our “HowTo” article.

5. Applying Liquid Chemical Hardener

A Densifier will facilitate a strong and durable finish of your concrete surface. You can apply it at any stage of the polishing process in accordance with the hardness of the concrete. As a rule of thumb, you can apply the densifier on a surface with low or medium hardness after the rough sanding (e.g. 80 grit). For harder surfaces, an application after the fine sanding (e.g. with 200er grit) will be sufficient.

The hardener is usually applied with a sprayer but there are also other methods you can choose from. Let it dry before you continue sanding or polishing. Refer to the instructions on the can or bottle for a precise guidance for your densifier.

This treatment will increase the hardness and durability of the concrete. Although some people make argue that it is not necessary in all cases, it is recommended at least for older concrete objects and those that tend to become porous.

6. Completing the Polishing

To get a polished surface, use 3000-grit discs for the final polishing which will help you achieve high-gloss appearance.

You will have to work over the entire workpiece to create a uniform look. Afterwards, vacuum the area to remove any dust before applying a stain guard or sealant.

This final coat of concrete sealer will protect the countertop, floor or pathway from stain and wear. It also prevents potential damage of the cement composite when chemicals or liquids are spilled.

How to Get Started Now

To start your project soon, get your tools and equipment ready. If you do not already have a concrete sander, make sure you check out our reviews of the best concrete sanders. Otherwise, you will want to get the discs that you need for your project – you can easily find concrete sanding and polishing discs on Amazon.