Common Types of Foundation Cracks. Some cracks in the foundation, including hairline cracks, are considered normal foundation cracks. These typically appear due to settling or concrete shrinkage. Other types of foundation cracks might indicate a serious structural problem.
Hairline Foundation Cracks
Typically, these are harmless and can form days or weeks after a new foundation is installed. Hairline cracks are often a result of the concrete or mortar drying out as it cures. In older homes, hairline cracks can appear as a sign of concrete aging and are also not cause for alarm.
Hairline cracks may develop in concrete foundations as the concrete cures. Hairline cracks do not cause problems with the stability of the foundation but do cause leakage problems. If the cracks appear shortly after pouring the concrete foundation, concrete may have been mixed poorly or poured too quickly.
Hairline cracks are common in new construction foundations across the country. They usually appear within one year and caused by the settling and drying of the new foundation.
For hairline cracks, it is not uncommon to see a few develop in a slab over time. Some may even occur during the concrete curing process if the concrete is too wet, dries too quickly, or is exposed to significant extremes in temperature.
Hairline cracks can grow over time and weaken the structure, such as in a home foundation. Some hairline cracks can also cause leaks in a foundation. It's important to watch the cracks to see if they grow. Contact a concrete contractor if you notice cracks exceeding 0.3 millimeter wide.
Generally, cracks with a width of less than 0.3 mm are acceptable and do not affect the structure.
Size matters when evaluating concrete cracks. The National Association of Home Builders (NAHB) standard for cracks in interior slabs requires repairing cracks that exceed three-sixteenths inches wide or high (vertical displacement).
A structural crack is where the foundation wall feels uneven or the width of the crack is about ¼” or wider. If you have a structural foundation crack, you may need an engineer's specifications to do a basement foundation repair.
Stair-step cracks along mortar joints or through the actual brick are almost always a serious matter—especially if the wall is bulging or if the cracks are larger than ¼ an inch. If you notice stair-step cracks in your foundation walls, call a contractor at USS immediately for a free foundation estimate.
Crazing cracks are very fine, surface cracks that resemble spider webs or shattered glass. When the top of a concrete slab loses moisture too quickly, crazing cracks will likely appear. While unsightly, crazing cracks are not a structural concern.
Cracks that are ⅛” or smaller in width and less than ¼” deep can be filled with a product like DRYLOK® Masonry Crack Filler or DRYLOK® Pourable Masonry Crack Filler to seal the area.
Structural concrete cracks have the potential to negatively impact the durability and strength of a concrete structure. These cracks are general recognized as serious if they are progressively widening, retaining dirt, allowing penetration of moisture, or developing in highly visible locations.
It can be heartbreaking, but sometimes your only real choice when dealing with foundation issues is to walk away. If the seller won't make repairs, the damage is too extensive or you can't wait for repairs to be completed, you may have no choice but to give up and find your next dream house.
Here's how to know if a crack is structural: One of the easiest 'tells' for structural damage cracks is that they grow over time. A thin, non-structural crack can quickly become a structural foundation crack if it gets wider after several weeks or months.
The good news is not all foundation cracks affect your home's structural integrity. Sometimes they're just ugly and caused by shrinkage during the concrete curing process. These unsightly, non structural shrinkage cracks (which are often hairline cracks) don't put your home in immediate danger.
Diagonal cracks at the corner of a window or door opening are usually caused by concrete shrinkage and aren't an emergency. Initially, diagonal foundation cracks do not threaten the structural integrity of your home. However, as with any foundation crack, they can worsen over time.
Foundation problems can be a red flag when you''re trying to buy or sell a home, but the good news is that it doesn''t have to be a deal breaker. In many cases, armed with the right information, you can work things out for both parties without too much expense or stress.
Horizontal cracks
They usually occur because of excessive outside pressure, such as shifting soil, water pressure, or other sheer forces to the foundation. Horizontal cracks are much more dangerous than vertical cracks because they can quickly lead to total foundation failure.
Thin hairline cracks can usually be repaired with a vinyl concrete patching compound. If recommended by the manufacturer, apply a concrete bonding adhesive or primer/additive to create the best bond possible between the old surface and the patching material.
No matter what has caused the foundation to crack, or whether it is moving or static, the crack should be sealed.
No wall crack is the same. They can vary in length, width and direction. Typically, larger cracks (those bigger than 15mm in width) are a cause for concern, as they could point to structural issues. You'll want to get these inspected by a structural engineer.
As the shrinkage begins, the concrete will crack where it is the weakest. Cracking typically starts within 12 hours of the finishing process. Weather conditions will slow or accelerate it. Shrinkage cracking is typically planned for and handled with control joints.
Shrinkage: The most common type of cracking in concrete, especially early on, is shrinkage. Concrete is a mix of cement and water. As the concrete hardens, which is caused by the cement and water forming bonds, some of that water escapes through evaporation.
Ask any contractor if they can guarantee that the concrete patio they pour won't crack, and they will all give you the very same answer: No. This is because concrete will crack; no matter what anybody does, there is just no avoiding the fact that concrete cracks.