Hairline cracks generally fall into the static crack category — they don't move and they're not going to. They're typically surface cracks that were caused by one-time events, like drying shrinkage.
Hairline cracks are commonly observed in freshly placed concrete and their occurrence is owed to the phenomenon of plastic shrinkage. As the name implies, these cracks are very small- about 0.003 inches (0.08mm) in width and can be very shallow.
No, hairline cracks in concrete are generally not a problem as they do not impact the strength and longevity of the concrete. Generally, cracks less than 0.3 millimeter wide don't impact the structure. Hairline cracks can grow over time and weaken the structure, such as in a home foundation.
While nearly invisible, it is important to remember that plastic shrinkage cracks don't just exist on the surface, they extend throughout the entire thickness of the slab. An excessively wet mix is a contributing factor to shrinkage in concrete.
A concrete slab will shrink about ¼ inch for every 100 square feet of surface space. When concrete dries and shrinks, cracking can occur hours after being poured. Any crack that is ⅛ of an inch or smaller on your patio or driveway is considered standard.
The 28-day curing time is a common requirement, but don't expect all cracking to be completed by 28 days. Drying shrinkage cracking can take place months after a concrete slab is placed.
To avoid water seepage and further damage, it's critical to seal any cracks that develop. This article will discuss why cracks happen and how to quickly repair them.
If water evaporates too quickly, it will weaken the finished product with stresses and cracking. To put it simply, the goal is to keep the concrete saturated during the first 28 days. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible.
Yes, the concrete expands and contracts with time. It is different from the process of curing and hardening. Concrete shrinks slightly in volume in the latter due to drying and water evaporation once it sets and hardens completely.
As the water leaves the concrete, it creates a volume change, known as drying shrinkage. If the concrete is not strong enough during the curing process to withstand the tensile forces of this volume change, the concrete will crack.
The most commonly used grout to fill concrete cracks is Portland cement mixed with water. You need to add enough water to make a good quality grout mix. Besides cement grout, you can go with any other filler material or sealant to fill out the cracks.
Cracks up to ¼ inch in width can be filled with sealant.
Like spider web cracks, these small cracks do not indicate a larger problem, and they often show up soon after the concrete is poured.
Concrete caulk or filler is best for cracks no wider than 1/2 inch. This thick material is injected into the crack with a caulk gun or by directly squeezing it out of the tube. You can use concrete caulk on both vertical or horizontal cracks. Our top pick is Sikaflex Pro Select Self-Leveling Sealant.
Hairline cracks of less than one millimetre in width or slight cracks of between one and five millimetres are generally not a cause for concern. If you begin to notice these, they can generally be filled and painted over as they're a crack in the plaster but not in the wall itself.
Concrete is porous by nature and, even though the moisture near the surface of the concrete evaporates as it cures, moisture from below the concrete or within the concrete will tend to osmotically migrate up through the concrete capillaries, to escape through the path of least resistance.
Concrete is by design a porous material and water can pass through it by hydrostatic pressure, water vapor gradient or capillary action. Water can also enter at cracks, structural defects or at improperly designed or installed joints.
While its optimum strength is known to peak roughly a month after its installation, concrete will continue to harden and develop as time goes on. However, while concrete does continue hardening, it doesn't necessarily benefit its structure, as it essentially becomes unnecessary.
The hardening, or curing, continues as long as moisture remains in the concrete. If too much water is lost from the concrete through evaporation, the hardening process slows down or ceases.
The issue of adding too much water
Too much water added to the mix means that excess water is retained inside the concrete after the curing process has finished. This will often result in the formation of small cracks as the water eventually evaporates over time, which reduces the compressive strength of the concrete.
Moist curing is a common method of concrete curing. It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.
No matter how sturdy a concrete foundation is, it can develop cracks or fissures. The cause of unwanted cracks in concrete can be due to prolonged exposure to natural environmental forces such as: Topsoil and subsurface earth layer erosions. Repeated wetting and drying from rainwater seepage.
Ultrasonic testing of concrete is an effective way for quality assessment and uniformity, and crack depth estimation. The test procedure has been standardized as “Standard Test Method for Pulse Velocity through Concrete” (ASTM C 597, 2016).