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Understanding the basics of concrete grinding, honing and polishing

If you are new to concrete grinding, honing and polishing and want to know more about it, this is the place to start.

It doesn’t matter if you are a homeowner or a contractor, if you want to understand the processes, the variables, and the differences between each category of a processed concrete floor, keep reading.

Ok, I got your attention, this will be worth the read if you’re interested in getting a grinding, honing or polishing job done on your property, whether you are a homeowner, architect, builder, concrete polisher or contractor who needs to know more about grinding, honing, and polishing concrete.

Even though the pandemic, the concrete grinding, honing and polishing industry has continued to grow steadily. Although various forms of concrete polishing and other concrete processing steps have been performed for many years, it has only been recently that architects, engineers, property owners, interior designers, and general contractors have taken increased notice to understand how to deliver modern low maintenance and durable floors.

With the Internet, we have access to information and knowledge, but we also need information and access to experts to have a good understanding of the technicalities and variables of the concrete grinding, honing and polishing processes relevant to your specific project.

The grinding, honing and polishing industry has many challenges that a contractor can face. What often happens is that some new contractors get enthusiastically into the industry and think that polishing concrete is simply choosing diamond disks and swapping them on and off the bottom of a concrete grinding machine.

In reality, the process of grinding, honing or polishing concrete is quite technical and when mixed with multiple variables beyond a contractor’s control, the outcome can be potentially disastrous if a contractor does not have the proper experience and know-how to overcome these issues.

There are also a number of variables within a contractor’s control that he or she also must learn to manage. This comes with experience, but why learn by experience only, we always encourage contractors to speak with the experts or experienced specialists ib their network. Joining a Facebook group or aligning with a good products company specializing in concrete grinding, honing and polishing is also a great idea as they often come from years of experience on the tools themselves and now are incentivised to help you and recommend their products.

From a business sense, we often see a common problem where a contractor goes in low with their price to win the job, who base their pricing on what other contractors are charging instead of basing their pricing on understanding all the associated conditions and making sure they cover expenses and make a profit.

We also see a lack of formal technical training for contractors and a significant lack of understanding by the customer in what concrete polishing actually is. An inexperienced contractor can ness up a floor and the customer can be hugely impacted.

If we are going to see the industry grow in the correct direction then contractors need to seek out the proper training and educate themselves on concrete processing as much as they can. They also need to be able to communicate with their customers effectively and be able to educate their customers on the differences between concrete grinding, honing and polishing means and how much it will cost. 

Concrete polishing and concrete processing

“Concrete polishing” is often used out of context because people don’t understand what the difference is between concrete grinding, honing or polishing.

We need to be more specific as some people use the term “concrete processing,” which describes a process that is also used in other industries like processing stone and metal.

Concrete processing is the act of changing an existing concrete surface by means of a mechanical process that involves cutting and/or refining the surface to the desired finish.

Polished concrete is one of many outcomes in what is the processing of the concrete surface by mechanical refinement through the use of multiple abrasives measured in grits.

Currently, the industry breaks down the process of concrete polishing into grinding and polishing while some simply use the word polishing for the entire process.

The process of polishing concrete consists of three consecutive categories:

  • Grinding
  • Honing
  • Polishing

Each of the grinding, honing and polishing categories are then broken down into multiple steps, consisting of consecutively finer grit abrasives. During this process, a densifier or hardener like FortiCol Colloidal Silica is applied that is absorbed into the concrete creating a chemical reaction that makes the concrete more dense and hard.

Not all processed concrete can be called polished concrete. For example, the grinding and honing category of steps results in a matte to a low, medium, or high sheen appearance and does not go through the polishing category of steps.

Defining the categories and steps

Ground concrete is the lowest category of steps of a processed concrete surface.

Any grit abrasive, if the abrasive medium is categorized in terms of grit, from approximately a 50-grit resin and below is considered a grinding step.

A ground concrete surface has a flat appearance with no or very slight reflection and may at times have a low sheen.

Honed concrete is the next category of steps above ground concrete in the processing system. 

Any grit abrasive from approximately a 100-grit resin to a 400-grit resin is considered a honing step.

A honed concrete surface has a matte appearance and/or slight clarity of reflection that has a low, medium or high sheen.

Polished concrete is the highest category of steps of processed concrete.

Any grit abrasive from approximately an 800-grit resin and above, typically to a 1,500 or 3,000 grit, is considered a polishing step.

A polished concrete surface has clarity of reflection like a mirror and has a glass-like finish.

The variables

The process of grinding, honing, and polishing concrete is more technical than most realize.

There are many pre-existing variables that can affect the end results of the process performed. Some of these variables are within the contractor’s control, such as the quality of your equipment and abrasives and the motion and speed at which you operate your equipment.

Others are beyond a contractor’s control, such as the levelness and flatness of the floor or the concrete mix design used.

Knowing how to contend with these variables is the difference between a craftsman who is detailed and results-oriented and a contractor who simply goes through the motions.

One of the main variables on a polishing job is the concrete itself.

Residential concrete is generally a low PSI concrete mix (2,500 psi and under) that has been hand troweled. Lower PSI concrete does not polish as well because the surface is not as dense and hand troweling leaves the surface with lots of highs and lows.

On the other hand, commercial concrete is a higher PSI concrete mix (3,500 psi and up) that is machine troweled in the open areas and hand troweled in the corners and tight areas.

Higher PSI concrete polishes better because it is denser and the surface does not have many highs and lows.

If you know a slab will be polished before it is poured, whether in a residential or commercial setting, suggest a polishing-friendly mix design and floor flatness rating to the general contractor or owner.

The customer will in turn get a better polishing result and possibly a lower cost to finish the floor.

Visual aspects processed concrete

There are three visual aspects of processed concrete:

  1. The degree to which the surface is cut
  2. The level of clarity of reflection of the cut surface, and
  3. Decorative enhancements

Contractors can cut the surface to any one of a number of degrees, including surface cream, fine aggregate, medium aggregate, or large aggregate.

These layers are a key element of processed concrete. The goal is to refine to and remain within the desired layer and make it as consistent as possible throughout. These layers often can vary in thickness through the surface of the slab.

Once the concrete has been ground to the desired layer, it needs to be refined to the desired level of reflection.

Honed concrete typically stops at 200- or 400-grit resin; a semi-polished surface typically stops at 400- or 800-grit resin; a highly polished surface typically stops at 1,500- or 3,000-grit resin.

Additional decorative enhancements may also be included in the process, including colouring with integral, acid-stained, and water-based or solvent-based stains and dyes; saw cut patterns; and engraving.

The grinding, honing and polishing processes

There is a difference between the clarity of reflection, sheen, shine, depth, uniformity, and colour of reflection.

To properly grind, hone and polish concrete and obtain the maximum “clarity of reflection” and “durability” the concrete surface will allow, a proper grit sequence must be used that allows for full refinement of the concrete surface with each grit abrasive before moving to the next progressively finer grit abrasive – even if the desired result is not a deep clarity of reflection.

To obtain a clean, crisp look of the concrete surface at a 200-, 400- and 800-grit resin, each grit must be performed and refined to its maximum potential.

Full refinement of the concrete surface extends beyond replacing the scratch pattern created by the previous grit abrasive with the next progressively finer grit abrasive.

Once the scratch pattern has been replaced from the previous grit, more refinement of the concrete can be achieved.

Not performing full refinement from one progressively finer grit to the next will not produce the best possible results, nor allow the floor to have its maximum durability and will cause the surface to prematurely wear.

It is heavily recommended that you not skip a grit in the processing sequence, and when transitioning from metal bonded abrasives to resin bonded abrasives the first resin bond grit abrasive used must be one grit lower than the last metal grit abrasive used.

In rare situations, you may be able to skip a grit or not drop back a grit, but it can never be used as a standard rule.

If you do attempt to skip a step in the polishing process, you should perform comparison testing in several areas of the slab to determine what type of quality you are giving up by skipping a grit or not dropping back a grit.

It will be up to the contractor to determine at what grit to start the process since he or she knows the goal to reach. The following example is an accepted grit sequence depending on the concrete surface given.

Start with a metal 50 or 70 grit, two or three segments per abrasive. Then, move up to a 100 or 120 grit with six segments per abrasive.

Switching from a two or three segment to a six-segment abrasive allows the concrete surface to be closed up and refined as quickly as possible to obtain the best clarity of reflection and durability.

The more surface area an abrasive has, the faster the surface of the concrete will be closed. There are situations where you may need to go higher in metal bond abrasives and situations where metal bond abrasives are not needed.

Now it’s time to move to the resin abrasives, remembering to drop back one grit. A typical sequence would be: 30/50,100/120, 200/220, 400, 800, 1,500/1,800 and 3,000/3,500.

All of the resin bonded diamonds are full-faced diamonds that close up the surface of the concrete quickly to obtain the best clarity of reflection and durability. Depending on your desired results, you may stop at any grit.

You will find that not all trade supply stores use the same grit designation. Some will use 70 instead of 50, 120 instead of 100, 220 instead of 200, etc. Also, there are some manufacturers that also offer a 600-grit resin and some that label their abrasives as 1, 2, 3, 4, etc.

It should be noted that some manufacturers produce hybrid abrasives where a combination of metal and resin is used.

The concrete always dictates at what grit a densifier would be applied, that is why we need an experienced hand and good knowledge of concrete grinding, honing and polishing processes.

There are five types of densifiers that are most commonly used – sodium, potassium, potassium/lithium blend, lithium and colloidal silica. Each manufacturer has specific directions for the application that should be followed.

Just because two contractors have the same grit sequence specified, the outcomes they achieve polishing on the same concrete can be drastically different.

Always remember that all the associated conditions and variables that are within the contractor’s control can be used through a good understanding, knowledge, skills and processes for the best results.

Variables within the contractor’s control

There are many variables a contractor must deal with on a polished concrete project.

An experienced concrete polishing contractor who knows how to deal with these variables will have success in his or her job.

The variables within the concrete polisher’s control:

Equipment

  • Weight, RPMs, the speed at which the machine is moving over the surface in a linear motion
  • Planetary movement – active or passive
  • The direction of planetary movement

Abrasives

  • Configuration of the diamonds’ face/tread
  • The saturation of diamond grit in the bonding
  • The hardness of diamond bonding
  • The point at which you switch abrasives

Densifiers

  • When you apply a densifier
  • What type of densifier you use

Physical grinding, honing and polishing

  • The degree to which the concrete surface is cut
  • The level of clarity of the cut surface
  • The refinement of the concrete from one grit to the next
  • How well the floor is cleaned between each grit abrasive

The variables NOT within the contractor’s control

The concrete surface

  • PSI
  • Imperfections that need to be removed
  • Surface flatness and levelness
  • Finish – hand troweled or mechanically trowel
  • Presence of coatings, glues or mastics

The concrete mix design

  • The types of admixtures used
  • Fibres and polymers used
  • Aggregate
  • Vibrated for air removal or not

This information will go a long way to help both property owners and contractors make the right decision with regards to the outcomes they want to achieve with their grinding, honing or polishing project.

Or, you are welcome to contact Barefoot Concrete, we will help you to achieve the result you want from your project.