Spalling or Flaking in Natural Stone: an Indicator of Sub-florescence

Spalling or Flaking in natural stone is generally an indicator of sub-florescence, a condition in which mineral salts are carried into the stone by moisture and accumulate beneath the stone’s surface, creating stress within the pores of the stone. This condition can be particularly damaging if the stone experiences freeze-thaw cycles, since the moisture and salts will freeze and expand, building up even more pressure within the stone.

Spalling

Generally speaking, spalling sometimes incorrectly called “spaulding” or “spalding” is the result of water entering brick, concrete, or natural stone. It forces the surface to peel, pop out, or flake off. It’s also known as flaking, especially in limestone. Spalling happens in concrete because of moisture in the concrete. Moisture, and often salt, too push outward from the inside in basements especially. Spalling can eventually cause crumbling and destruction of a structure.

What Causes Spalling?

Spalling usually occurs for one of three reasons, or sometimes a combination of these reasons.

Salt

Salt, particularly the sodium chloride that’s used on frozen roads in many northern states, can result in oxidation or rusting of reinforcing steel when it’s repeatedly introduced to a surface or building.

Concrete Hardening Process

But spalling is more likely to occur due to the curing process or the way the concrete hardened.

Mixing Carbon Dioxide with Alkalis

Carbon dioxide in the air and alkalis in the concrete mix can also interact and force cracking that admits water.

Salts Can Come from Many Sources

Salts can come from many sources. They may be inherent in the stone itself. They can come from the presence of de-icing salts or polluted rain water, from improper cleaning methods, from the setting bed, and even from the soil beneath the setting bed if the installation has not been properly insulated. Lab testing may be required to determine the source of the salts, which can also indicate the source of the moisture if it is not readily apparent.

Steps to Extract Salts

Once the specifics are known, steps must then be taken to extract the salts from the stone. This allows the stone to dry completely. Then, protect it from additional moisture. A major mistake that is often made even by some professionals is to apply a sealer before the sub-florescence is completely resolved. Applying a sealer prematurely will not solve the sub-florescence and will actually block the escape of moisture, making things even worse.

Spalling is a Serious Issue

If spalling progresses too far, the stone will wind up needing to be replaced, so it is best to address the problem as early as possible, by contacting a stone restoration expert to evaluate the stone. They can help determine the source of both the moisture and the salts and offer practical solutions specific to your situation to resolve the problem and help prevent its re-occurrence.

Dealing with Sub-florescence

Dealing with sub-florescence is really not an easy task and it may take some time to achieve complete resolution, so it is important to contact your stone restoration expert as soon as the condition is noticed. Be aware that efflorescence (a white haze or powdery residue on the surface of the stone) can be a precursor to sub-florescence, and an early warning sign. If you think your stone is showing signs of either condition, don’t hesitate to contact your stone restoration technician. Acting before the damage becomes severe can help you avoid having to replace rather than restore your stone.

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Sources

marblerestore.com/tips-and-articles/why-is-my-natural-stone-flaking/#:~:text=Flaking%20(also%20called%20spalling)%20in,the%20pores%20of%20the%20stone.&text=They%20may%20be%20inherent%20in%20the%20stone%20itself

www.thebalance.com/what-is-spalling-1798631