Differential Movement

Differential movement in one form or another is the base cause of almost all foundation failures. What this means is that there is movement of the soil beneath your foundation but the movement is not even. There is more movement in some areas than in others. In some cases it can even be movement in one direction in some areas, and movement in the opposite direction in others.

If the movement were completely consistent throughout then there would not be a problem unless, of course, the movement were extreme. I mention this to illustrate why differential movement causes the damage.

To my knowledge I have never seen movement that was completely consistent across an entire foundation. But then how would you know? It would have to move a significant amount in order to even be measurable.

Workmanship and Materials

The soil may not have been compacted properly or organic material may have been mixed in with the fill dirt. Organic material tends to rot over time leaving voids.

While poor workmanship and inferior materials in the building of the foundation can contribute to the problem, it is still differential movement is the cause the problem. If the soil beneath the foundation were totally stable then it could not possibly move.

Causes of Differential Movement

So what are the possible causes? As mentioned above poor workmanship and materials can be potential causes. Soils with a high clay content like the soil we have in much of Texas is affected by moisture and/or the lack thereof more than any other factor.

As the moisture content of clay based soil increases it causes the total volume of the soil to also increase. As the soil becomes drier it shrinks. These two factors working together, or should I say working against each other are usually the root cause of movement.

You will find articles on this site that go into more detail on Expansive Soil and Moisture Content. They cover these topics in greater detail and can help you to understand what may be happening with your foundation.

You should educate yourself before you talk to a foundation repair salesperson. Knowing or not knowing what is causing your problem and how to fix it can mean the difference between getting exactly what you need for a fair price of getting ripped off.