Concreate, Inc. delivers concrete polishing and custom staining for both commercial and residential projects primarily in Virginia and Maryland (but also up and down the East Coast). We work hand in hand with with designers, architects, project managers, general contractors, tradesmen, and home owners alike from start to finish. We welcome the opportunity to serve your polished concrete needs in every way possible.

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An Overview of Concrete Defects and What You Can Do About Them

An Overview of Concrete Defects and What You Can Do About Them

Surface defects on an old concrete floor.

Surface defects can arise for several reasons, but a solution is usually available

Key Takeaways:

  • Concrete defects can have various underlying causes
  • These causes include old overlays, moisture, stains, and improper color application
  • Determining the cause can help develop a solution
  • Hiring a professional contractor to prepare the surface reduces potential problems

Defects can appear in concrete at any point in the surface’s lifetime. You could notice discoloration or other issues before or after polishing your concrete floors and developing a solution could prove challenging, depending on the underlying cause.

Moisture and humidity can commonly create concrete defects, although old overlays and improper color application can also be culprits. Determining the defect’s cause can help your contractor develop a solution when fixing the problem is possible.

Learning about common concrete defects is advisable so you aren’t caught off guard if they appear on your floors. Here’s a look at some surface defects you could encounter and what you can do to remove them.

Efflorescence on concrete floors

Perhaps the most common defect you’ll notice on your concrete floors are white spots called efflorescence. These spots are a mineral salt residue that is the byproduct of moisture leaving the concrete over time. Efflorescence is a natural occurrence, but its appearance can quickly hurt your concrete floor’s appearance. 

Efflorescence can appear for several reasons. First, it can occur when there’s no vapor barrier under your concrete slab, so the slab is sitting directly on the ground. Over time, moisture from the ground works its way up through the concrete, eventually appearing on the surface and leaving the mineral deposit behind. This problem typically arises in older concrete slabs that have been sitting in a building for a significant period. 

You can also end up with efflorescence if you polish or seal your concrete floor too quickly after pouring it. As concrete cures, it emits moisture and salts naturally as part of the hardening and drying process. If you polish your concrete floor before it has time to release this water, mineral deposits will come through the surface and leave a residue.

Finally, the environment in which your concrete floors cure can contribute to efflorescence. Concrete cures best in a climate-controlled space without variable weather and humidity. Environmental variability can contribute to efflorescence if the job site remains open between the curing and polishing processes.

Even if you end up with efflorescence deposits on your polished concrete floors, cleaning them with specialized products that remove mineral buildup is possible. If your surface has been sealed, however, you’ll have to remove the sealer before cleaning the surface because the efflorescence probably sits between the concrete’s surface and the sealer you applied.

Vinyl composition tile ghosting

Another issue you could experience during the polishing process is vinyl composition tile, or VCT, ghosting. The gist is that the previous floor that sat over the concrete can leave lines behind that affect the concrete’s appearance. 

VCT lines typically mirror the vinyl tiles that previously sat on the concrete. These lines are sometimes created by moisture from within or below the slab. They can also develop through treatments applied to the previous floor above the slab. 

Building owners commonly apply chemicals to a tile floor to clean it. These chemicals and the water used to rinse them seep through the seams and into the concrete slab. From there, efflorescence can occur, leaving salty residue behind.

The problem with VCT ghosting is that there’s no telling how deep the lines go until you start the grinding and polishing process. Sometimes, you can grind the marks out, and the final product will look as good as new. However, there’s a chance the faults were caused by vapor transmission starting under the slab so that the lines will run through the concrete. 

The floor remains polishable when the ghosting lines run through it, but you might have to apply some coloring to achieve a uniform look. Some building owners even appreciate the pattern the VCT ghosting leaves behind, but that will depend on numerous factors.

Other common surface defects

While efflorescence and VCT ghosting are two of the most common concrete defects you’ll encounter, other issues can appear. Developing a solution to these issues depends on their severity, as some will require significant work. Examples of surface defects include:

  • Discoloration: In some situations, polished concrete won’t have a uniform color. This discoloration occurs because the top of the concrete floor might be a different shade than the concrete a millimeter below the surface. A contractor can repair this problem by grinding deeper to achieve a uniform color, although that job will bring additional expenses.
  • Wavy surface: A wavy slab will give your polished concrete floor an uneven appearance. This issue is usually the result of an improperly installed, unlevel surface. However, it’s possible to grind the floor down to minimize the waves before polishing it.
  • Foreign material: Small items like leaves or garbage can get into the concrete before it’s cured and stay there for years. This debris might not be visible until after you grind, at which point you might notice a hole in the slab. Fortunately, this issue will usually present itself early in the process, and your contractor can patch the spot where the debris damaged the slab before polishing it.
  • Micro pitting: The grinding process can leave tiny pinholes that permit small particles to work their way out of the concrete. This issue is called micro pitting, and it reduces the floor’s reflective properties. Filling the holes with grout before polishing can make the surface smoother.
  • Uneven hydration: Uneven hydration occurs when moisture escapes through the slab’s surface. As this water escapes, items left on the surface can create hydration marks. This concrete could take months to dry in this scenario, too, extending your project considerably.

Concrete defects can appear under many circumstances and at any point in the concrete preparation process. Experienced contractors look for these defects throughout the job and offer repair options when needed.

Proper preparation of your concrete floor

The goal is to get your concrete floor looking as good as possible, and it all starts with removing defects during the preparation process. A skilled contractor will know what to look for when grinding and polishing the floor and can even provide tips on removing efflorescence from the floor’s surface after the fact.

Concreate can assist with every part of your concrete floor installation except pouring. Our team will remove concrete defects whenever possible and advise on how to best live with issues we can’t eliminate. Contact us or visit thisisconcrete.com for more insight.