Lime stabilization has been a trusted solution for improving expansive clay soils for more than 70 years, particularly in Texas. Yet, despite its widespread success, several misconceptions persist—namely that lime leaches out, isn’t permanent, or loses effectiveness over time. In reality, when lime is properly applied at the designed quantity, it creates a durable, long-term foundation that continues to gain strength over time. Let’s set the record straight on these common myths.
Misconception #1: Lime Leaches Out of the Soil
One of the most common concerns is that lime washes away or leaches out over time. However, this is not true when lime is designed in accordance with the test procedure and is correctly applied to expansive clay soils. Here’s why:
Once lime is mixed into a clay soil, pozzolanic reactions occur, permanently altering the soil structure. These reactions are irreversible, involving chemically binding the lime with silica, alumina, and water within the soil, making it impossible for the lime to leach out.
Studies and decades of field performance have proven that lime-stabilized subgrades remain intact for the lifespan of a roadway or structure. The only time lime may leach is if it’s applied incorrectly—for instance, using it on sandy soils with a low plasticity index (PI), where lime stabilization is not recommended in the first place. Proper application on the right soil type ensures leaching is virtually impossible.
Misconception #2: Lime Stabilization Is Not Permanent
Another misconception is that lime stabilization is only a temporary fix. In reality, lime permanently transforms clay soils. The key to this durability lies in maintaining the correct pH levels. Note: the silica and alumina in the clay soil are not soluble at pH levels below 10, and therefore can’t form pozzolonic reactions.
When lime is applied, it raises the pH to 12.4, initiating stabilization. Studies show that once stabilized, the pH value remains above 10, creating ongoing chemical reactions. Those pozzolanic reactions continue over time, ensuring the soil continues to gain strength rather than degrade.
This long-term chemical reaction is what separates stabilization from mere modification. Soil modification makes the soil more workable, but stabilization ensures it continues to gain strength indefinitely.
Misconception #3: Lime Loses Its Effectiveness Over Time
Some believe that lime-treated soil gradually loses its strength. However, when lime is used correctly, the opposite is true. The chemical reaction between lime, silica, alumina, and water creates cementitious compounds that strengthen over time.
As long as the initial lime demand is met(see our Lime Series Test blog for details), the soil will remain stabilized indefinitely. Roads and foundations built on lime-stabilized subgrades continue to perform for decades without a loss of integrity.
Why Do Some Believe Lime Leeches or Fails Over Time?
Misapplications or improper design can lead to issues that fuel these misconceptions. Here are a few reasons why lime might appear to “fail”:
- Insufficient Lime Application: If not enough lime is used to reach a pH of 12.4, the soil may be modified but not fully stabilized.
- pH Drops Below 10: If the applied lime isn’t sufficient to maintain pH levels, stabilization won’t occur.
- Overmixing the Soil: If lime is mixed deeper than the target depth, it can reduce the pH level of the soil, and therefore prevent the chemical reaction needed for stabilization.
The Bottom Line: Lime Stabilization Is Proven and Permanent
When properly designed and constructed, lime stabilization is one of the most durable and cost-effective methods for strengthening expansive clay soils. It does not leach, it is permanent, and it actually improves over time thanks to ongoing pozzolanic reactions. With over seven decades of proven performance, lime remains the number one choice for stabilization of expansive soils in Texas and beyond.
By understanding the science behind lime and ensuring proper application, engineers and contractors can rely on it to create stronger, more resilient foundations—for today and for decades to come.
