4 Steps to Help Your Exterior Limestone Walls Stand the Test of Time

How do you care for limestone exterior walls? Learn about our 4-step process for cleaning & sealing limestone walls to preserve beauty & value.

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History of Limestone’s Use and Properties

From the Egyptian pyramids to the Empire State Building, limestone remains one of the most popular building materials in the world — across cultures and across the centuries.

  • This sedimentary rock, made of at least 50% calcium carbonate, has formed over millions of years, in warm, clear marine waters from the shells and skeletal remains of ancient sea creatures.
  • Because it comes in a variety of textures and colors, limestone is a versatile material that has proven very helpful for a wide range of uses, including roofing, cement, agriculture, smelting, and mining.
  • Limestone adds beauty and character to modern and classic buildings alike and is commonly cut into blocks or slabs for use in construction and architecture.

But it’s also important to give your exterior limestone walls the TLC they need to retain their strength, appearance, and value into the future. Caring for limestone is a four-step process involving professional limestone cleaner and sealer.

Challenges to Caring for Exterior Limestone Walls

RGA Global Headquarters, located in Chesterfield, Missouri just outside of St. Louis, recently had an issue with its limestone exterior.

Although the walls were only 2 years old, they were already showing signs of degradation, including mold and dark streaks from dirt and moisture. Why is limestone so vulnerable to this kind of damage? How does limestone maintenance and refinishing differ from other traditional forms of stone refinishing?

Because it’s a porous rock, limestone deteriorates when exposed to acid and other pollutants commonly found in urban environments. When left untreated, this can lead to significant damage including cracked masonry, spalling, and loss of structural integrity.

In the case of RGA, a limestone sealer was never initially used.

Proactive Care for Your Exterior Limestone Walls

After a series of tests and discussing some options with a supplier, Mid America Specialty Services came up with a solution to clean and seal RGA’s 25,000 square feet of exterior limestone.

The solution involved a 4-step limestone cleaning and sealing process.

#1: Mask off surrounding area

Before cleaning the limestone, the surrounding area was masked off so that no unintended surfaces would be hit with overspray.

#2: Clean exterior limestone with pump sprayer

Mid America Specialty Services began by cleaning the building with a limestone cleaner.

  • The initial application was applied with a 4-gallon back pack pump sprayer.
  • This particular limestone cleaner is mild, which offers many benefits:
    • It avoids killing surrounding foliage
    • It won’t etch glass or metal
    • It continues to treat the mold for up to 2 weeks after application
  • A dwell time allows the stone to absorb the product.
  • The stone was agitated with natural fiber brushes to get into the pores.
  • Finally, the stone was rinsed with low-pressure power washers at 1600 psi.

As with any cleaning process, it was important to follow the manufacturer’s directions as it can differ depending on the surface or the product used.

#3: Dry limestone thoroughly

The limestone surface must dry thoroughly.

Mid America’s service pros returned after a few days because some portions of the wall did not get direct sunlight and took longer to dry.

#4: Protect exterior limestone with sealer

Finally, the limestone was impregnated with a protective sealer.

  • Limestone is a very porous stone that traps a lot of dirt and moisture.
  • Mid America used a limestone sealer to stop water penetration from causing the mold.
  • Two applications of the treatment were used. The solution was allowed to dry between applications.
  • Most of the treatment was applied with a pump sprayer.
  • Hard-to-reach walls were rolled on.

With proper cleaning and sealing, your limestone exterior walls will remain in excellent condition, enhancing the aesthetic and economic value of your building for years to come.

To learn more, contact the limestone experts at Mid America Specialty Services.

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