Take steps to protect home from excessive concrete cracks
Q. Some of the newer houses in my area have experienced cracks in the concrete. The soil in our area has a lot of expansive clay in it. When I build my house, what should we do to avoid excessive cracks?
A. I am glad, as are most builders, to hear you say "excessive cracks" in the houses. Anytime concrete is poured and sets up, there will be some cracks no matter how carefully it is done. This is just the nature of concrete and its curing process over time. It can take many months for concrete to cure to its full strength.
During the first two years after construction is when most of the typical cracks occur. This often happens at sharp inside corners, such as window openings. These cracks are easy to find and repair in most cases. Another common location for cracks is along long expanses, such as basement floors and slabs. These are more difficult to repair and completely seal.
Visit the homes of some of your future neighbors who have expressed concerns about cracks in their houses. Hopefully you can have your builder accompany you. An experienced builder should be to determine if the cracks are truly excessive and what might be the possible causes.
There are many possible causes of cracks in the concrete in houses. Most often, people assume cracks are due to settling of the ground and the resultant movement of the foundation of a house. Actually, many cracks are caused by over stressed support lumber, insect damage, concrete and lumber slippage, or just poor installation techniques.
The soil itself can have a significant impact upon the amount of cracking in a new house. Expansive clay is actually one of the worst types of soil when it comes to cracks. To tell if you have expansive clay, look at a mud puddle after it has dried. If you see a matrix of cracks in it, it probably has a good percentage of expansive clay.
Expansive clay soil can support a lot of weight, but its problem is it also shrinks vertically as much as 15 percent as it dries. Looser soils do not shrink as much, but they can shift under the extreme weight of a house.
With expansive clay soil, consider installing a water injection system if your area experiences periods of heavy rainfall and drought. This type of system uses perforated drain pipe buried deep around the perimeter of the foundation. This is connected to a riser pipe up to the ground surface. During very dry periods, trickle water down the riser to keep the clay soil moist.
When the foundation is poured, install steel rebar (reinforcing rod) in the foundation walls and in the slab or floor for additional strength and stability. There will still be some fine cracks as the concrete cures, but most of the serious cracks should be eliminated.
Try to keep the structural lumber covered and dry before it is used. When supporting lumber gets wet, it expands considerably. If it is installed in this damp condition and then dries and shrinks later, what once was a tight fit will now be loose. This can unevenly load the concrete and cause cracks in it and in the walls.
• Ms. Builder's column appears Sundays in Homes Plus. Send questions to Ms. Builder, c/o Daily Herald, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit dulley.com/msbuilder.
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