Limestone Use in Wet Areas

By Frederick M. Hueston

Over the past 30 years I have inspected hundreds if not thousands of shower installation that have use limestone.  The amount of deterioration I have observed in nearly all these installations ranged from staining to complete disintegration of the stone. Most will attempt to blame the installation method, but I can assure you these issues occur in installations that are installed within industry guidelines.

In a nutshell I would not recommend using limestone in wet areas. The following is why I would not recommend it

1. Limestone is a sedimentary stone. It naturally contains minerals such as iron. When iron is exposed to continued wetting the iron will begin to oxidize causing a large stain. At first the stain may appear light brown but over time it will darken and continue to oxidize to a deep brown to reddish stain. Removing the iron from the stone is nearly impossible since it is part of the mineral makeup of the stone.
2. Limestone, even when sealed is typically very porous. Water will enter the pores of the stone and react with the setting bed. The setting bed contains salts which become dissolved in the water. The water carries the salts into the pores of the stone. When the stone dries, the salts recrystallize causing pressure in the pores resulting in the stone blowing out(spalling).
3. Limestone is an organic sedimentary rock that forms from the accumulation of shell, coral, algal, and fecal debris. It is formed by sediment settling to the bottom of a water basin. The main mineral is calcium carbonate. Calcium carbonate can be soluble in water. This is yet another reason to avoid using limestone in a wet environment. Since it often contains organic matter, this too is soluble in water.
4. Steam showers are even a bigger concern with limestone installation due to the fact the vapors produced by the steam can enter very tiny pores that liquid water cannot. The steam than condense in the pores causing the stone to deteriorate.
5. The Natural Stone Institute, who is the leading trade association in the industry, recommends that only class A & B stones be used in interior wet areas. Limestone fall into a C class at best, Many fall into the D classification. For more info on this classification system go to The Natural Stone Institutes website at https://www.naturalstoneinstitute.org/

One may question the fact that limestone is used on building exteriors with no issues. This is true but there is a big difference. The average shower produces on average of over 8000 inches of water per year. To put this in perspective the rainiest area of earth is in China which has 321 inches of rain a year.. The average shower has over 26 times that amount. That’s a lot of water.

I have been in the stone business for over 35 years and have numerous colleges who agree that using limestone in a shower is not recommended.