Concrete Cracks and Expansive Soils – Unavoidable Movement
Date Published: August 26, 2019
A close examination of anything in a house will reveal small details that often go overlooked. At Scott Home Inspection, we specialize in taking time to look for these details. Oftentimes, minor details from many different areas of a house can produce a much clearer picture of larger developing conditions.
For example, superficial drywall cracking around a door jamb may not mean very much on its own, but can be a small piece of evidence of structural movement when placed alongside other evidence found in a house.
Similarly, cracks found in concrete installations around a house may not be evidence of improper installation or a larger problem, but may just be caused by normal expansive soil movement.
What are expansive soils?
Every major population center in Colorado is located at least partially on expansive soils. Expansive soils contain clay which expands when it comes into contact with moisture. The expansive soils in a given area dictate which types of structures are permissible and how they are to be built. This is part of the reason that some developments are built with basements and others are built with crawlspaces.
For decades, developments were designed and houses were built with very little consideration for grading and drainage, after all, most of the Front Range of Colorado is a high desert climate with very little annual precipitation. The overall grading in a neighborhood built through the ’50s may appear “flat” for instance.
Over time it became abundantly clear that even with the relatively small amount of 15 inches of annual rainfall in Colorado, this water must be very carefully controlled to reduce the stress of the expanding soils on concrete systems around a house, including the concrete foundation.
What can expansive soils actually do?
As home inspectors in Colorado, we expect to see cracks in nearly every concrete surface on most of the houses that we inspect. You just need to know where to look and pay attention to the very minor details. Exterior concrete surfaces like a driveway, walkway, and patio are designed to accommodate some movement and cracking. Concrete does two things, it cures and then cracks.
This is the reason that there are “lines” throughout concrete installations. These are “control joints” and “expansion joints.” As the clay soils hold water and expand, you will begin to see cracks in concrete ranging from barely noticeable hairline cracks all the way to significant heaving damage, which would require replacement.
An example of expansion joints and hairline cracks.
Minor hairline cracks that develop at the control joints are common and simply mean that the concrete is working as designed. The control joints are there to accommodate minor movement. These types of minor cracks can be found in concrete that is less than six months old. That isn’t an installation error but can be part of the concrete curing process.
Recommendation: Keep an eye on it, but don’t lose sleep over it. We find minor cracking even in new concrete and at new construction properties, and it can take as long as five years for the soils around a house to settle down and remain static, and that is with proper grading and drainage maintenance along the way.
It is also very common to find minor cracking that has developed outside of control joints or at the transitions between two concrete systems, like from a walkway to the front porch. Depending on the size and location of the cracks, a recommendation to seal these cracks may be in order to prevent water from penetrating below the concrete surfaces and contributing to further movement.
Exterior concrete cracks can be sealed with an “Elastomeric Sealant” which is a fancy word for flexible. These types of sealants can be found at just about every hardware store in town and applied with a caulk gun.
A concrete crack in a driveway has been sealed. However, the sealant is older and needs to be reapplied.
But what if I am finding cracks in my garage floor or even my basement floor?
Related to the soils underneath, concrete in the garage and basement floors are the same as anywhere else and subject to the same kinds of movement. In most construction, the “load” of the house is borne on the foundation walls and not on the poured concrete floors. More modern construction from the last few decades won’t even have the interior framing in a basement resting on the concrete floor.
The “floating wall” in a basement has become the standard. This is a small gap placed between the bottom of a basement framed wall and the concrete floor. This is required because we expect the concrete floor in a basement to move upwards. Because of that, a gap is left at the bottom of the wall to accommodate this movement.
You might never even see it since a finished wall with drywall and baseboard will cover the floating section of the wall. Similarly, ducts for forced-air systems and drain lines may have expansion fittings that prevent damage to these systems over time as the floor moves.
Will non-structural concrete ever need to be repaired?
While the movement of non-structural concrete is to be expected, there are conditions that can develop that demand correction. These more significant conditions develop when concrete cracks and then separates, heaves, or drops. These conditions can result in drainage issues where water is pressed back toward the house as a result of a negative pitch in the concrete pad.
Cracking on or around stairs is a common occurrence. Occasionally this can create a trip hazard that would likely need to be repaired.
Cracked and heaved concrete can also lead to trip hazards, where sections of concrete have offset from one another. Corrections for these types of conditions can range from simple sealing efforts to prevent further moisture penetration, “sheering” the concrete to remove trip hazards, to alternative remedies like mudjacking. Mudjacking is the process of injecting materials under concrete to lift it back to its proper position and has become a popular repair method in Colorado.
Sometimes, we come across concrete systems that just can’t be salvaged. Concrete that has cracked and heaved so much that the only appropriate remediation of the condition is replacement.
Home inspectors can be hesitant to make this recommendation as cracking and movement is so common in Colorado and replacement of concrete can be very expensive. However, like many building materials, concrete will need to be replaced eventually as it ages, moves, and cracks.
Here is a great example of concrete sheering. This is a common fix for a concrete pad that has heaved upwards and created a trip hazard.
How do I keep my concrete in good condition?
The key to maintaining your concrete and preventing the more serious conditions from developing lies in your grading and drainage around the house. At Scott Home Inspection we have written extensively on the subject of moisture control.
Monitoring minor hairline cracks and sealing cracks that have begun to separate should be part of every homeowner’s regular house maintenance. If it’s a more serious condition that you inherited from the previous homeowner, an evaluation by a qualified concrete contractor may be in order to get the issue addressed.
In Colorado, it’s likely that all concrete will move, but if you are diligent in the war against water intrusion, you can expect to maintain the upper hand on the concrete that you have.
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