Your May Home Inspection Primer



Dear Renata;


We had a pretty cool start to the month of May here in Northern California. And this week we have warmed up quickly. This reminds us that fast changes in temperature can stress out building materials that have to expand and contract, like concrete. So, it's time for a short article about what cracks in your concrete really mean. 

Plus, test yourself with our Spot-the-Problem Puzzler




My Concrete is Cracked. Am I in Trouble?  



We get questions about concrete on a consistent basis, because

if you have concrete as a building material, you will eventually find some cracks in it. Homeowners fret about those cracks, especially in new homes where any crack is seen as a flaw.   


Concrete Cracks Not Always a Problem


Concrete is a wonderful building material, flexible in application, and strong when cured (dried in place), especially when fortified with steel reinforcing bars (rebar). However, because it is a mix of pulverized rock and sand glued together with water, it has a tendency to crack as it dries. And, over time external stresses will also cause cracking.


What sort of cracks are cosmetic, and not a threat to the structure?


Fine cracks are a common occurrence when concrete dries, so you have to examine them 

over time to find out whether the crack is something you can live with, or if it signals a need for remedial work. Here are typical types of cracks you may have: 


Plastic Shrinkage

A classic plastic shrinkage crack


When the concrete is still in its plastic state (before hardening), it is full of water. As the slab loses moisture while curing it gets a bit smaller. As the concrete shrinks, the slab could crack in order to relieve tension. Shrinkage cracks are common and can occur as early as a few hours after the slab has been poured and finished. Usually they are not a threat to the structure.




In hot weather a concrete slab will expand as it heats up and pushes against any object in its path, such as a brick wall or an adjacent slab of concrete. If that object cannot flex, the resulting force might cause cracking.

You can see how temperature changes put stress on concrete.



Cracking can also result from ground movement due to freeze/thaw cycles, or by growing tree roots. During freezes, the ground can lift several inches, then settle again when it thaws. If the slab cannot rise and fall evenly, it will crack. Tree roots can also cause concrete to heave, if slowly over time.


Settling (also called Subsidence)


When the ground under the concrete settles, cracks could form if the settling is uneven. It can occur if the soil under the concrete gets saturated and soft, and the weight of the concrete compacts the soil. 




Settling can also be caused the other way, if too much weight is placed on the concrete. Concrete is strong once cured, but still has weight limits. 


Premature Drying


If the top of the concrete slab dries too quickly, crazing cracks can form. These are very fine surface cracks that resemble spider webs or shattered glass. Crazing cracks can be unsightly, but are not a structural problem.


Crusting can occur when you stamp a pattern on concrete that has dried too quickly. Stamping literally shakes loose pieces of the concrete around the stamping pattern. This is also a cosmetic flaw, not a structural threat.


When are cracks in concrete a threat?


If the cracks widen past about an eighth of an inch, issues may develop: Water can regularly seep into the wall or slab. This can lead to two problems:

  • If water reaches the rebar, the steel can rust. Rusting expands the steel, which further cracks the concrete. Too much rusting and cracking can weaken the area around the cracks. This is not always a threat to the structure, however. It depends on where the rusting and cracking is occurring. Remove the source of water to fix the issue.
  • If water is in the crack when a freeze occurs, water turning into ice expands and puts pressure on the sides of the crack. Over time this could weaken the area around the crack.

We are great home inspectors , but we assess the condition of your concrete as it stands today. Assessing whether a harmless-looking crack could lead to problems needs your occasional inspection over time. If the condition of the crack never degrades further, you may simply have a cosmetic "flaw" that thousands of other homeowners  share  with you!


Agent Partners:

Let us know if you need more information like this to help you manage client expectations about future concrete maintenance needs in a house they are considering. 


Would you like a personalized flyer
on this topic to send to clients?

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What issue did our NBI inspector see when he crawled under a house and spotted this plumbing arrangement?


Your answer is below... 



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Your Spot the Problem Answer:


Annotated version of May 2014 Spot the problem.

This drain line is an "S" trap design rather than a "P" trap. P-traps are designed to hold water in the curve to block sewer gases from coming up your sink and shower/tub drains.This particular method of installation is not approved under building code standards because the water flowing down the main pipe to the right can lower the pressure in the S-trap and suck out the trapped water, because it isn't vented properly. This allows the sewer gases free access up through the drain into your bathroom. 



Thank you for taking the time to read our monthly newsletter. We hope you found it useful. If not, tell us how to improve it! We look forward to your feedback. E-mail comments to:


Keep us on your referral list. We are ready to make you look good and get your deals closed promptly! 



Robert Swickard
President of NBI



A friend of mine has a home on a hillside, and his patio has had cracks in its concrete for decades. They probably formed soon after the patio was poured, given the settling that any hillside structure experiences. They haven't gotten any worse since he bought the house, but he does need to keep them clear of debris so grass and other plants cannot take root and expand the cracks.


His experience reminds me that concrete is not quite the "set it and forget it" material you may think it is!


I keep a weather eye on our house's various cracks, and so should you: Change can be so slow you wouldn't notice it unless you know to look for it.





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