Photograph of a cracked and heaved concrete slab that had control joints Frost Heave / Expansive Soil Damage to Concrete
How to Identify & Evaluate Frost Heave/Expansive Soil Cracks in Concrete

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What are frost heaves or frost heaving damage to foundations & slabs?

This article describes How to Identify, Diagnose, & Evaluate Frost Heave/Expansive Soil Cracks in Poured Concrete Slabs & floors or in Building Foundations.

This article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Guide to Diagnosing & Fixing Frost Heaves or Expansive Soil Cracks in Poured Concrete Slabs

Photograph of a cracked concrete slab from frost damage

Frost heaves or expansive soils damage to building floor slabs can range from minor to extensive in buildings depending on soil and weather conditions, site preparation, and slab construction details, as we elaborate here.

The photograph above shows a rather straight crack across a garage slab near the garage entry door. What is happening here and why is this particular crack straight if it's a frost or soil heave crack?

In freezing climates building foundations include a footing which extends below the frost line. This is true for both the occupied space as well as garages.

When a concrete slab is poured either abutting the top of such a foundation, or poured extending over the edges of such a foundation, there is risk of cracking across the concrete at the interior edge of the buried footing.

The combination of water under a garage floor (watch out for driveways and sites that slope towards the garage or home) and freezing can cause the portion of the slab which rests directly on the soil to move up and down during freeze/thaw cycles.

Since a garage is often colder near the garage entry door than in other areas, there is extra risk of these cracks occurring there, but they can occur anywhere.

When there is freezing and heaving of a slab, particularly one which omitted reinforcing steel, or did not extend the steel over the footing, these garage floor slab cracks may appear during freeze/thaw cycles.

Similar floor slab damage might occur in areas of expansive clay soils if the proper moisture level is not maintained.

Photograph of a cracked concrete slab from frost damage

Basement floor heave patterns - frozen floor drains: Basement floors can be frost heaved in other patterns in buildings which are unheated or which lose heat.

We have found basement floor slabs broken and heaved above buried drain lines which ran below the basement floor of a home which remained unheated during freezing weather. A clogged drain sitting full of liquid combined with prolonged freezing weather was the culprit in most of these cases.

The heaved concrete was raised following exactly the path of the frozen (and burst) buried, clogged drain line. This problem can be epidemic in older homes which were constructed using a downspout drain line extending below the basement slab.

How To Evaluate the Risk of Frost Cracking to a Building Foundation or Floor Slab

Sketch of the effects of frost on footings, foundations, slabs (C) Carson Dunlop AssociatesWe don't know of an actual "foundation freeze test" that you can perform to predict foundation damage if the heat is left off completely in a building. Such tests would creating freezing conditions and would risk building damage.

But there are some things you can check to predict the chances that a building foundation wall or floor slab will be damaged by horizontal frost pressure on the foundation walls or by vertical frost pressure under a slab.


a sub topic
of WINTERIZE A BUILDING, we discuss this question and we offer these things to check:

Watch out: other factors can still cause slab or foundation damage due to frost.


Continue reading at FREEZING & WATER DAMAGED SLABS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



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Publisher - Daniel Friedman