What Is Spalling And What Causes It?

What is the Difference Between Cement and Concrete?

Many people use the words, “cement” and “concrete” interchangeably, but, they are not the same.

Cement is one of the ingredients within concrete.

What is Portland Cement Made Of

  • Clay
  • Limestone
  • Gypsum
  • Water

What Is Concrete Made Of?

  • Portland Cement
  • Aggregate (rocks and sand)
  • Water

 

Portland cement is the most common type of cement.  It is used around the world for concrete, mortar, stucco and concrete grouts.

Concrete Is Porous

Due to its ingredients, concrete is a very porous material. It has a hard surface, but, as the cement dries, small capillaries form that are smaller than a hair’s width.  You cannot see them, but, you can get an idea of how porous your concrete is by pouring a gallon of water onto your flat slab of concrete.  Wait an hour and see how much water remains.

This is why spalling occurs.

Water or Moisture

Spalling (also known as scaling or pitting) typically occurs when water or moisture seeps into the porous capillaries of the concrete.  The water then freezes and thaws, creating internal pressure on the top, solidified layer.

When the internal pressure becomes too great, the frozen water erupts toward the surface, creating a chip, or pit in the concrete surface.  This damages the top surface, but, can also damage the slab, itself.

Spalling Can Damage the Concrete’s Strength

Spalling can also occur due to chemical changes, such as the corrosion of the steel reinforcement bars, commonly known as rebar.  Rebar is used to reinforce the strength of the concrete. It is installed

When water or moisture seeps into a concrete slab; the steel rebar rods can begin to rust.  This chemical change can affect both the structural strength, as well as the visual appearance of the concrete, as the rust rises to the top of the slab.

Lightly spalled concrete is an unsightly cosmetic issue; however, if left untreated, damage can occur to the rebar inside the concrete, leaving the slab structurally unsound.

Chemicals – Salt, De-Icer and Fertilizers

Salt is one of concrete’s biggest enemies.  In cyclical, (winter/summer) climates such as in the north, and the midwest, spalling (pitting, chipping) is exacerbated further when salt or deicing chemicals are used on the concrete surface.  Even after cleaning the surface, due to the porous nature of concrete, some salt will still be present near the surface of the slab.

Oil

Oil, too, seeps into the concrete.  Some oil will still remain below the surface, within the capillaries of the concrete, in unprotected, unsealed concrete, even after oil spills are cleaned off the surface of the slab with a good degreaser.

This can affect the ability of a refinishing product to properly adhere to the slab.  It can also affect the visual color of the slab after refinishing or sealing it.

Chemical Changes

All chemical changes (including water and moisture) within any existing concrete slab can affect the final visual appearance after application of a concrete epoxy, acid stain or sealant product.

 

Powerwashing and sealing of concrete surfaces is the best method to protect the concrete from top-down damage and surface spalling.

If you would like a concrete contractor quotation to create a beautiful stamped concrete patio like this in your backyard, please give us a call or fill out our contact form to schedule a convenient time.

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