Common Problems with Natural Stone Floors and Their Causes

Natural stone is an extremely durable flooring surface, and is far more resistant to water and wear than just about any material other than porcelain tile. What happens if it gets wet, I mean really wet? Can a natural stone floor become damaged due to flooding? What about slab leaks?

Let’s take a look at some common problems with natural stone floors and some common causes.

Discolored

Description:

Staining either on the surface, or through the body of a stone tile.

Causes:

1. Ground Water

Water that migrates upward from the ground may transport minerals from the ground and the substrate. These minerals may the end up as deposits on top of, or in the body of stone flooring. This type of staining may appear as dark spots in a light colored tile, (common in Carrara marbles), or rust colored stains in the body, or in veining and at grout joints. Sub-subterranean moisture staining is usually very difficult to remove.

2. Spills or Cleaning Products

Certain types of natural stone, especially those containing high concentrations of calcite minerals such as limestone and marble, are easily affected by chemicals. Contact with some chemicals may stain or etch natural stone.

3. Water Intrusion

Water intrusion may cause leaching of compounds from the substrate that can either react with calcite minerals, or transport minerals from the substrate.

Hollow

Description:

Tile sounds hollow when tapped on.

Causes:

There are several reasons why a flooring tile may sound hollow when tapped on:

1. Installation

• Tile was not installed with sufficient mortar coverage. This may result in voids, or air pockets that sound hollow when tapped on.

• Tile was not “back buttered,” meaning, mortar was not applied to the back of tile as well as the substrate. This may result in mortar pulling away from the back of tile when the mortar cures, causing voids underneath the tile.
• Tile floor was installed without expansion joints.
  • If the substrate is concrete, the concrete may shrink over time as it cures. Because the tile assembly is a facade, installed as a unit over the substrate, substrate shrinkage will cause the tile assembly to bind. If no expansion joints were installed, pressure will be placed upon the grout. The grout will absorb some pressure, but if pressure exceeds the compressive strength of the grout, it may become crushed and fail. If the mortar bond is not sufficient to keep tiles bonded to the substrate, tiles may de-bond, causing voids underneath tiles. In some cases, the grout may fail over a large enough area for tiles to “tent,” meaning that several tiles de-bond from the substrate at once, forming a ridge of tiles. This usually happens in the center of an expanse, or at a place where shear forces cause the tile to bind, such as at a corner between two expanses or at a narrow spot near the center of a large expanse.
  • If tile was installed over a wood substrate, it may be susceptible to all of the substrate movement issues described above, in addition to movement common to wood substrates, such as moisture and temperature related expansion and contraction.
  • Tiles that are installed next to wood moldings, cabinetry or framing, may be subjected to compression forces from the expansion of those wood components. Compression forces may be amplified by adjacent wood components swelling due to moisture intrusion. In ancient times, wood wedges were placed in fissures or small grooves cut into large stones. These wood wedges were then soaked with water, causing an expansion force strong enough to split stone into blocks. Installing flooring tiles against wood components without room for expansion will almost always result in hollow or cracked tiles.
• Tile was installed over contaminants, such as paint overspray or concrete a curing agent.
• Thin-set mortar was used past its pot life.

2. Moisture Intrusion

• Slab leaks, especially hot water slab leaks can cause a slab to expand. This expansion can cause tiles to de-bond from the substrate; if the slab moves while the tile facade stays in place, the mortar bond will shear.
• Any moisture that finds its way into a wood subfloor, either through the grout joints or through exposed sub-floor underneath cabinets, through carpeting, or underneath the crawl space, may cause wood to expand. This may result in the flooring assembly de-bonding from the subfloor.

Spalling

Description:

Spalling can be identified as flaking of stone surface, or deterioration in veining of stone.

Cause:

Caused by salts that are transported into the stone by moisture migration. These salts can deposit and build up within cracks, fissures and veins in the stone body. Recrystallization of the salts will cause them to grow and expand, thus resulting in damage to the stone.