Concrete Condition: The Hidden Factor in Polished Concrete Success

Polished concrete flooring is a popular choice. It looks sleek, lasts a long time, and doesn't need much maintenance. But there's something important that people often forget: the condition of the existing concrete you are starting with. Concrete takes a lot of abuse.  It can crack, it's prone to staining, and there are many different types of concrete and aggregates out there… All of these factors can affect the look of a finished, polished concrete floor and it can be a real hassle. 

We get it. It’s never fun to expect one thing only to have it turn out entirely different because of factors you were not fully aware of beforehand.  To help you, we created this article, which shares our 20 years of experience in the polished concrete game. 

In this article, we will discuss: 

• 2 Concrete Slab Problems that Will Show Through Your Concrete Polish
• How concrete slab condition impacts your finish options

2 Concrete Slab Problems that Will Show Through Your Concrete Polish

Polished concrete shows off the natural look of the stone underneath. It can be very aesthetically pleasing, but it also means that any imperfections in the concrete will be visible. 

You're not changing the slab out for something else, you are just grinding it down a little bit and then making it shiny. The condition of your slab is really important for how the finished floor will look. Here are some common slab problems that can affect the final result.

Problem 1: You Will See Patches, Cracks, and Repairs

It's important to be aware that any previous repairs to your concrete  affect the final look of your polished concrete floor. Patches are common, but they do create visual inconsistencies.

If you currently have cracks of any size in your concrete slab, you will need to repair those before the concrete is polished and sealed. This helps maintain the integrity of your floor, and by doing these things all at the same time you’ll ensure a more seamless aesthetic for your concrete flooring. 

Keep in mind however that regardless of how well these repairs are done, you will still have visual discrepancy. 

Some people feel that this variation adds depth and character to their flooring, but be aware the larger the cracks- the less desirable this character usually is. 

Before polishing your floors, take a good look at the current state of your slab. If there are major repairs that need to be done, it may make sense to pour a new slab altogether. 

Problem 2: Staining and Color Variations Are Visible

On a microscopic level, concrete is porous like a sponge. This means that spills will likely leave permanent marks on the concrete slab such as chemicals, oils or even water soak into the tiny holes in the surface and become trapped

Once these stains are present, polishing the concrete will actually make them more noticeable. 

Typically,  once a section of concrete flooring has been stained,  it is impossible to remove said stain. 

If you decide to go ahead and polish over them, understand that they will still be there and very visible once the polishing is complete. 

How Concrete Condition Impacts Finish Choices

The condition of the concrete slab also affects what kind of finish you can choose for your polished concrete floor. 

Think of it like choosing paint for your walls, a smooth creamy finish looks different than a matte finish. 

There are different types of polished concrete finishes. Each one gives a different look and shows different amounts of the "aggregate" (the little stones inside the concrete). The more you grind down the concrete, the more these stones show, and this can make any imperfections more obvious.

Cream Finish

A cream finish gives the smoothest and most even look you can get with polished concrete.

This finish is perfect for places that need to look very clean and aesthetically pleasing, like a restaurant floor where customers will see the flooring itself regularly.

Cream finishes only require a small amount of grinding, so the top layer of the concrete stays intact, preventing you from uncovering the actual aggregate within the concrete. This results in a very smooth, shiny surface.

Keep in mind that a cream finish doesn't magically erase imperfections.  Any cracks or stains will still be visible, as we mentioned above.

Furthermore, it’s important to note that you can't always achieve a cream finish, as this depends on how good the condition of your original concrete slab is.

Salt and Pepper Finish:

A salt and pepper finish gives the floor a bit of texture and shows some of the small stones in the concrete, adding subtle color variation. This finish requires more grinding than a cream finish to expose the fine aggregate, but it still maintains a relatively smooth surface. You'll see small stones that add visual interest without the pronounced texture of finishes that reveal larger aggregates. Keep in mind that, just like with a cream finish, any imperfections in the concrete slab will still be visible.

Medium Aggregate Exposure:

A medium aggregate exposure finish reveals larger stones in the concrete, creating a more textured, industrial look. This finish requires more grinding than a salt and pepper finish to expose the larger aggregate. The result is a surface with a bolder aesthetic, often favored for warehouses, garages, or spaces where a rugged look is desired.

Large Aggregate Exposure:

A large aggregate exposure finish involves the most extensive grinding process, revealing the largest stones embedded in the concrete slab. This creates a highly textured, rugged surface with a unique, almost three-dimensional appearance. Large aggregate exposure is ideal for high-traffic areas or spaces where slip resistance is crucial, such as warehouses, factories, or outdoor walkways. However, because this finish exposes the deepest layers of the concrete, any imperfections in the slab, including cracks, discoloration, or variations in the concrete mix, will be very prominent. It's essential to carefully assess the condition of your concrete slab before choosing this option.

 Additional Factors that Impact the look of Polished Concrete

Choosing the right aggregate exposure for your polished concrete is just the beginning. Hidden problems like "ghosting," "screed marks," and "helicopter marks" can lurk beneath the surface, impacting the final look with unexpected blemishes, uneven color, and inconsistent texture. These issues are often tied to the concrete slab's history and how it was originally installed.

Ghosting

Ghosting refers to faint outlines or discoloration caused by the remnants of old floor coverings, adhesives, or treatments. Imagine the shadow of old tiles mysteriously reappearing on your newly polished floor. Ghosting can create unevenness in color and sheen, making some areas look duller or darker than others.

Application Marks

Application Marks are essentially "scars" from the original concrete installation. Uneven troweling, blemishes, or variations in the concrete mix can become more noticeable after polishing. This can result in swirl marks, inconsistent texture, or noticeable differences in color across the floor.

Helicopter Marks

Helicopter marks are caused by the blades of the power trowel (also known as a "helicopter") used to smooth the concrete surface. These can appear as circular or swirling patterns.

Screed Marks

Screed marks are left by the “screed”, a tool used to level the concrete when it is first applied. These marks often appear as straight lines or ridges.

The finished product you will get from your polished concrete is the result of the slab you start with.  Depending on how your concrete was installed, you can expect all sorts of outcomes and it is important to set realistic expectations for outcomes going in.  

The Importance of Slab Condition for Polished Concrete

Polished concrete is an excellent choice for flooring. It looks good, lasts a long time, and is easy to take care of. But how it looks in the end depends a lot on the condition of the concrete slab underneath. 

Cracks, stains, and other imperfections can all affect how your polished concrete floor will look. It's vital to check the slab carefully before you start the project. Understanding how the condition of the slab and the type of finish you choose work together will help you get the result you want.

If you're thinking about polished concrete for your next floor, you should always take time to assess your slab and consult with a concrete professional. This ensures you get the best possible result with your current concrete slab conditions. 

To learn more about how much polished concrete costs, your next step is to read our article on the different things that affect the price of concrete polishing.