To understand why it happens, you need to know one thing about concrete: it's strong in compression, but weak in tension. That means while it can carry heavy loads, it doesn't handle movement, heat, or uneven support very well. Over time, those stresses add up and cracks appear.
Shrinkage is a main cause of cracking. As concrete hardens and dries it shrinks. This is due to the evaporation of excess mixing water. The wetter or soupier the concrete mix, the greater the shrinkage will be.
Deep Cracks: If you can see significant depth into the crack, it's more than just a surface issue. Cracks with Accompanying Damage: Look for other signs like water pooling, sinking sections, or concrete spalling (flaking/chipping) around the crack.
One of the main reasons behind concrete cracking is 'shrinking', caused by excessive water in the concrete mix. When excess water from the cement evaporates, it leads to shrinking, which ultimately creates cracks in the concrete. The key to preventing this is maintaining a proper water-cement ratio.
It's common for concrete to crack due to the shrinkage that occurs when the concrete dries and hardens. As concrete dries, water evaporates from the mixture, and the size of the concrete slab shrinks. The loss of material creates stress on the concrete.
A good material proportion “rule of thumb” regarding concrete mixtures is the 10:20:30:40 mixture ratio which is about 10% cement, 20% air and water, 30% sand, and 40% stone based on the absolute volume of the concrete mixture.
Characteristics of structural cracks
The following procedure is recommended for cracks that are ½” wide or less and ¼” deep.
The short answer is that concrete can crack AT ANY TIME starting just hours after it is poured. Have you ever heard someone say … “Well I thought I'd get at least a few years out of the concrete before it started to crack …. “ This is a very common misconception.
Can you pour concrete over cracked concrete? Pouring concrete over cracked concrete before at least repairing the cracks is not going to go well. If the issues that caused the cracking to occur on your existing concrete surface are still present, they will affect your new concrete surface, too.
Identification of Structural Cracks
Width and Depth: If the crack is wider than 3mm and seems to go deeper than just the surface, it's likely structural. Location: Cracks around windows, door frames, and load-bearing walls are often a red flag. Pattern: Vertical, diagonal, or stepped cracks usually indicate movement.
Some foundation cracks are normal and may not require action. Cracks in a home's foundation are a typical sign of an underlying structural problem. But not all foundation cracks are an issue to be concerned about. A cracked foundation warrants an inspection when combined with other symptoms.
In addition to length, keep an eye out for width as well; any cracks wider than ¼ inch should be addressed immediately. In some cases, these large cracks may even begin to form small holes throughout their surface area.
Too much water in the mix increases shrinkage, making cracks more likely. Even with good finishing, an overly wet mix can cause more noticeable new concrete curing cracks.
Cracking can be performed in several ways, but two of the main methods include using a catalyst or using steam. These are called catalytic cracking and steam cracking. Both cracking methods involve heat. During cracking, the hydrocarbons are heated up in order for them to break down.
Almost all concrete cracks over time, but not all cracks are serious. Small, surface-level cracks (like shrinkage or crazing) are often cosmetic. Deeper or wider cracks (settlement, heaving, or structural) may require professional attention. Caulking and maintaining cracks early helps prevent expensive repairs later.
The ASTM C 94, Specification for Ready Mixed Concrete, indicates that the concrete shall be discharged on the job site within 90 minutes and before 300 revolutions after water was added to the cement. The purchaser may waive this requirement, when conditions permit.
Those thin, hairline cracks that appear within the first month of a new concrete installation are typically shrinkage cracks. They're usually no wider than 1/16 inch and don't extend through the full depth of the slab.
Identifying Concrete Damage: 10 Major Signs
For hairline cracks, choose a liquid concrete crack filler or thin caulk, which can flow easily into the crack and fill it.
Concrete won't bond to another concrete material if you don't apply an effective concrete adhesive. With the right concrete adhesive, your concrete repairs can stand the test of time.
Hairline cracks are usually cosmetic and caused by normal concrete shrinkage or settling. Structural cracks are deeper, wider, and can indicate foundation movement or pressure from hydrostatic forces. The orientation, width, and location of a crack can help determine its seriousness.
Key Takeaways. 4 inches is the minimum, but 6-8 inches is better for heavier loads. A compacted gravel base (3-6 inches) prevents cracking and settling. Rebar or wire mesh reinforcement increases strength and longevity.
Cracks wider than 1/8 inch or those that are horizontal are known as structural foundation cracks. As the name indicates, these cracks pose a severe threat to the structural integrity of the foundation.