Bleach and Stone: sometimes they mix. Sometimes they don't.

The Science of Bleach and Stone

By Frederick M. Hueston – SR-Manual.com

Bleach, or sodium hypochlorite, is a powerful oxidizing agent. It works wonders for disinfecting and removing organic stains, but stone surfaces can react unpredictably to it. 

Here's Why

  1. Porosity: Natural stone like marble, travertine, and limestone is porous. Bleach can seep into the pores, causing discoloration or even etching. Even dense stones like granite aren’t immune if the surface isn’t sealed properly.
  2. Chemical Reactions: Stones containing calcite (like marble and limestone) are particularly vulnerable. Bleach can break down the calcite, leading to dull spots, surface damage, or worse—irreversible etching.
  3. Sealant Interference: Bleach can degrade stone sealers over time, leaving the surface more exposed to stains and damage.
  4. Rust Formation: Some stones contain natural iron deposits. Bleach can oxidize these, leading to rust stains that are challenging to remove.

When Bleach Might Be a Friend

There are scenarios where bleach can be cautiously used on stone surfaces:

  • Mold and Mildew Removal: For mold or mildew growth in grout lines or porous stones, a diluted bleach solution (no more than 1 part bleach to 10 parts water) can be effective. Make sure to rinse thoroughly and neutralize the area.
  • Exterior Stone: Bleach is less risky on exterior stone surfaces where etching or discoloration may be less noticeable. However, even outdoors, it should be used sparingly and rinsed thoroughly.

When Bleach is a Foe

There are plenty of situations where bleach should be avoided entirely:
  • Polished Surfaces: Polished marble, travertine, and limestone can dull or etch under bleach’s chemical attack.
  • Sealed Stone: Bleach can weaken or strip sealants, leaving the stone vulnerable.
  • Unknown Stone Composition: If you’re unsure of the stone type, it’s best to avoid bleach altogether. Better safe than sorry!

What to Tell Your Customers

Educating your customers is just as important as the restoration work itself. Here’s what you should emphasize:

  1. “Bleach is Not a Magic Solution”: Explain that while bleach might kill mold or bacteria, it can also damage their stone surfaces. Suggest alternatives like hydrogen peroxide or professional-grade stone cleaners.
  2. “When in Doubt, Call a Pro”: Remind customers that improper use of bleach can lead to costly repairs. Encourage them to consult with you or another stone restoration professional before trying any DIY fixes.
  3. “Maintenance Matters”: Stress the importance of regular cleaning with pH-neutral stone cleaners and maintaining sealants to prevent the need for aggressive cleaning methods like bleach.
  4. “Spot Test First”: If they insist on using bleach, advise them to test a small, inconspicuous area first.

Safer Alternatives to Bleach

For professionals and customers alike, there are safer, stone-friendly alternatives to bleach:
  • Hydrogen Peroxide: Great for organic stains and safe for most stones when used properly.
  • Ammonia-Free Cleaners: Ideal for regular maintenance without compromising the stone’s finish.
  • Steam Cleaning: A chemical-free option that’s highly effective for grout and certain types of stone.

Wrapping Up

Bleach can be both a friend and a foe in the world of stone restoration. While it has its place in specific, controlled situations, the risks often outweigh the benefits. As a professional, understanding these nuances and educating your customers will not only protect their stone surfaces but also reinforce your reputation as an expert in the field. When it comes to bleach and stone, the golden rule is simple: Proceed with caution—or better yet, choose a safer alternative.

author avatar
Fred Hueston
Frederick M. Hueston is an internationally recognized stone and tile consultant, historic property preservation expert, and failure investigator. Fred is a highly accomplished and well-respected scientist, with a diverse educational background and extensive expertise in the stone and tile industry. Born and raised in a family immersed in the stone and tile business, Fred developed an early passion for the field, which ultimately shaped his career and accomplishments.