A Crash Course on Concrete Grit Levels
Ever wonder how perfectly polished or matte concrete floors are created? Here’s the nitty gritty to help you choose the look you want.
- Grit level is determined by the amount of diamond in the abrasive used to polish a concrete floor
- Higher grit levels have more diamond and make the floors shinier
- Lower grit levels create a matte finish
- The finish you select depends on how you want your floor to look
Diamonds are the hardest substance on earth – nothing beats these little beauties for strength. It’s why heavy-duty industries, including construction, mining, and oil drilling, depend on them. Even the electrical device you’re reading this blog on wouldn’t exist without diamond-sliced silicon.
Diamonds are also vital components in some concrete industry services. These gems allow contractors to tailor the grit level of a floor to a nice matte finish, a pristine polish, or anywhere in between.
We spoke to technical expert Clif Rawlings on the finer points of diamond tooling for an episode of our This is Concrete podcast. It’s a great glimpse into how professionals do the job and educate their clients on the process and its pitfalls. Let’s examine every facet of a job that can make matte and gloss floors look like a million dollars.
The name’s Bond. Resin Bond.
You may be wincing at the thought of using something as precious as diamonds to grind concrete, but it’s justified. Concrete is a very tough material that requires something even tougher to tame it. The super-strong covalent bond that holds a diamond’s carbon atoms together is complex, so let’s summarize by saying it’s what makes them almost unbreakable.
The diamond-edged tools contractors use (also called grinding shoes) come in different shapes and sizes, from rectangular and round to single-, double-, or triple-segmented designs. These tools are used to remove whatever is currently on the floor’s surface, whether that’s carpet, tile mastic, old paint and epoxy, or just worn-out bare concrete.
The surface can then be smoothed off, buffed up, and prepped if necessary for staining or sealing. Diamonds aren’t limited to creating flush gloss floors – they can also expose the concrete’s aggregate for a rough, raw look that delivers some extra traction. It all depends on how gritty you want to get.
A carbon date with density
The grit levels of a concrete surface are determined by the density of diamonds in the abrasive, and the grit level you choose depends on how you want the finished surface to look. Generally speaking, the higher the grit level is, the shinier the floor becomes, and vice versa. Sheen and gloss increase with the number of abrasive passes, and your contractor will gradually increase the grit level in stages to fine-tune the effect.
There are four levels of finish for sheen and four for exposed aggregate (a more rugged but also more cost-effective look). These are classified as A to D for aggregate and 1 to 4 for sheen, with ratings set by the Concrete Polishing Council. Further classifications apply to each category, with varying gloss values ranging from 20–80 and aggregate cuts of varying depth.
Grit levels typically double as they increase, so you’ll see 50 jumps to 100, 100 to 200, 200 to 400, and so on. The only exception is 800 to 1500. That 1500 then doubles to 3000 for the most ultra-polished, almost mirror-like looks. A matte finish would be between 100-grit for next to no shine and 400-grit for what we’d call a “satin” finish. An 800-grit creates semi-gloss floors, and 1500 would be a gloss floor.
Exposed aggregate finishes cut into concrete to reveal what’s been mixed with it during blending. Like polishing, exposed aggregate can remove surface imperfections, but only if the grit cuts deeply enough. A “cream” aggregate finish (class A) is the shallowest and may not remove surface issues, while a class D large aggregate finish will cut as deeply as a quarter inch.
Practical and price considerations when selecting grit levels
The number of diamond-edged abrasions a surface can tolerate depends on the concrete’s quality. Concrete rendered too fragile by age, existing damage, or poor blending will only be strong enough for certain finishes. Only high-quality concrete can achieve the highest levels of shine.
The purpose of the space can also dictate grit level and finish. Would you install a super-reflective floor in a clothing store changing room? Nope! Matte or low-gloss floors can look softer and are ideal if you’re not looking for high levels of light reflectivity. They also hide foot traffic very well.
How much grip a floor has is a significant concern, and some people mistakenly think that the shinier a floor gets, the more dangerously slippery it becomes. Traction increases incrementally up to 800-grit, starts to plane off slightly at 1500, then decreases slightly at around 3000. All the grits are nonetheless still in line with requirements for high-traction floors set by OSHA and the Americans with Disabilities Act (ADA).
Next come the time and expense factors. The more abrasive passes necessary, the longer and more expensive the job. Abrasion can also uncover imperfections in the concrete as layers are ground away. These must be repaired as part of the process for the aesthetic of the finish. High grits may require concrete to be grouted first, which increases labor and material costs.
Lastly, there’s the wear and tear on the contractor’s tools. Diamonds are not always, in fact, forever. They’re most susceptible to friction-based heat and other damage where they come to a point. Since it’s the point that makes them useful for contractors, some large or particularly demanding jobs may require diamond segments to be replaced before work can continue.
Contact the experts on grit levels and gloss floors
At Concreate, we bring a high level of experience to grinding and polishing jobs – we do every concrete-based service except pouring. Through our podcast and knowledge base, we help professionals and the public to understand concrete better so they can make the right decisions for a safe and attractive finish. Visit our contact page to ask any concrete-related questions or discuss your project needs!