Spalling is a concrete issue that often affects outdoor concrete surfaces. It is a term that describes a cracked surface that has delaminated from its substrate. You would see this as a flaking top layer, exposing a rough and brittle concrete slab. This is a common issue especially on patios, pool decks, driveways, and other outdoor concrete spaces. It is also one of the top issues that concrete repair experts deal with.
What Causes Spalling?
There are many reasons why concrete spalling occurs. The most common are:
- Freeze-Thaw Cycling – Concrete is a porous material. When water penetrates, it stays there until it actually dries out. However, when the slab is exposed to chilly weather, the water inside freezes and when water freezes, it expands. The expansion pushes the concrete around it, causing it to become brittle. When the frozen water thaws, it shrinks back again, leaving a void where it expanded before. This continuous cycle weakens the surface, where freeze-thaw often occurs, thus, causing spalling.
- Corroding Steel Bars – The steel reinforcement bars inside concrete slabs, when corroded or rusting, will expand up to 10 times its original size. This expansion puts pressure on the surrounding concrete, thus, causing spalling. It is important to note that there are factors that influence the level of spalling caused by corrosion, such as age, level of maintenance, the quality of concrete, the depth of the steel bars, and the local weather.
Concrete Repair Options for Spalling Issues
Resurfacing the concrete surface is a highly recommended solution to address spalling issues. The top layer that has spalled is first ground off to reveal a newer and stronger layer. This grinding process also makes it easier for the new material to adhere. An overlay or coating is then installed to create a new surface. Popular options include a stamped concrete overlay or a spray knockdown finish. The completed surface is then topped off with a concrete sealer. This will close the pores of the concrete, keeping moisture from penetrating.
If the main cause is a corroding steel bar underneath the slab, the contractor would need to assess the severity of the spalling issue to determine if it can still be repaired or if a replacement is needed. The corroded steels bars may also need to be removed and replaced with new ones before a new concrete mix can be poured.