Identifying Cracks vs. Fissures in Stone Countertops
A Guide for Stone Restoration Contractors – By Frederick M Hueston
Yellowing caulk in showers is a common issue that many restoration professionals encounter. Whether you’re inspecting a residential bathroom or troubleshooting a commercial spa facility, that once-bright caulk line turning yellow can raise questions from clients. Understanding why this happens—and which products perform best—can help you offer solutions that last.
Let’s break down the common types of caulk used in wet environments, why they yellow, and what you can do to prevent or correct it.
Understanding Fissures
Nearly all natural stone will have some degree of fissuring or veining. In simple terms, fissures and veins are naturally occurring, elongated openings formed during the stone’s geological creation. They result from mineral crystallization, environmental pressure, and other geological forces. These are sometimes called “hairline cracks,” but they are part of the stone’s natural character—not damage.
Micro-fissures are even smaller and are typically only visible under a microscope.
In general, fissures:
- Have minimal unevenness
- Show little to no chipping, separation, or movement
- Rarely cause fracturing
- May cause a slight break in reflection or show a small indentation
- Tend to have a slightly less glossy finish at the line
Measuring a fissure’s width in the field can be difficult and inaccurate without specialized equipment.
Understanding Cracks
Cracks, by contrast, are damage to the stone. They are usually the result of mishandling, impact, or inadequate structural support.
Typical indicators of cracks include:
- Noticeable unevenness along the break
- Chipping at the edges
- Clear separation that can be measured
- Visible movement when gentle pressure is applied
- Fracturing that may worsen over time
- Broken pieces of stone or distinct fragmentation
A crack compromises the strength of the stone and, if left unrepaired, can lead to larger structural problems.
Quick Field Tests to Tell the Difference
Here are two simple tests you can perform onsite:
- The Fingernail Test
Lightly run your fingernail across the line in question. If your fingernail catches, it is most likely a crack. Natural fissures and veins are typically smooth and should not catch a fingernail. - Crystal Path Test
Observe how the line interacts with the stone’s crystals.- If the line cuts directly through the crystals, it is most likely a crack.
- If the line winds around the crystals, it is more likely a natural fissure.
Final Note
Of course, there are always exceptions. If there’s any doubt—or if the homeowner is particularly concerned—it’s best to recommend a professional evaluation by an experienced stone inspector or restoration expert.
Knowing how to spot the difference not only helps you educate your clients but also positions you as a trusted professional who understands the finer details of natural stone behavior.
