When the concrete surface is not appropriately hardened, rainfall may wash out cement from its surface and expose aggregates, see Figure-2. This may not affect the structure's safety, but it can lead to uneven surface and color streaking if the concrete is integrally colored.
How long does concrete take to dry after rain? Once the concrete has been finished (between 4-8 hours after pouring) and has set hard enough for walking on, the effects of rain should be minimal. The curing process is a chemical reaction, with ready mix concrete taking up to 28 days to fully cure.
Concrete typically takes 24 to 48 hours to dry enough for you to walk or drive on it. However, concrete drying is a continuous and fluid event, and usually reaches its full effective strength after about 28 days.
Ultimately, rain can 'water down' and therefore weaken the concrete mixture, making it less useful in your project. This can also lead to cracking, dusting, scaling and streaking, which can cause structural and aesthetic damage.
If the rain begins after 2-4 hours from concrete placement, the surface needs to be covered; otherwise, the concrete surface will suffer damages. If rains pound on concrete 12 hours after placement, the likeliness of any damage is negligible.
Concrete that is not moist-cured at all dries too rapidly, and reaches less than half its potential design strength. It will also have a greater number of shrinkage cracks.
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.
If it loses too much moisture through evaporation, it will not cure properly and will become prone to cracks. Many construction specialists recommend watering it down five to ten times per day, for the first week, starting 2-4 hours after it has been poured.
Pouring concrete into the rain is not advisable, but to pause and wait until the pouring of the concrete is complete. If you are already concreting concrete, remove the surface water before you finish the installation, or wait until it passes and clears the atmosphere.
To protect your new slab and ensure an exceptional finished product you should wait 24 hours for foot traffic (including pets), 10 days to drive light vehicles or add furniture, and 28 days for heavy pick-up trucks and RVs. After 28 days the concrete is cured and you will have a strong and stable slab.
After pouring and finishing the slab, you should wait 24-48 hours before removing concrete forms. You can remove the formwork once the concrete has enough strength to keep it from cracking. Concrete naturally contracts as it cures, so it should pull away from the forms and make them easier to remove.
If your concrete is exposed to the elements, you won't be surprised to learn that the concrete will dry faster in warmer, sunnier conditions.
Retarder can slow the cure of concrete made in the winter mix. For a contractor, Fore-times it is necessary to need slightly water reduce more work time for your surface than what would normally be required. When this is the case, the use of retarder will help to slow the setting of the concrete overlay product.
Warm temperatures cause cement to set faster, and the faster cement sets, the faster it begins to cure. At 80 degrees, concrete usually sets in about four hours. At 90 degrees, you can expect it to set in 2.5 hours, and at 100 degrees, your concrete will set in roughly an hour and a half.
DO spray new concrete with water. One of the most common methods for curing concrete is to hose it down frequently with water—five to 10 times per day, or as often as you can—for the first seven days. Known as “moist curing,” this allows the moisture in the concrete to evaporate slowly.
Concrete that has had water standing on it for it's entire life crumbles quickly but not all standing water is the same. If the puddle is in a shady area and deeper than 1/4” it will shorten the life of the slab.
If your concrete mix is too wet it will also be more porous once cured, making it difficult to achieve the desired finish and potentially making it not fit for purpose. In short, a concrete mix that is too wet could seriously impact the durability, longevity and strength of your project.
“If the surface of a floor slab is colder than the dew point temperature of the ambient air above the slab, moisture will condense on the surface of the slab. This condition, commonly called “sweating,” typically occurs when warm, moist air flows into a building that has relatively cool floors.”
Water is mixed into concrete to activate the cement binding agent and as the mix dries, it hardens. The drying, or "curing," should be gradual, otherwise cracking may occur. To prevent cracks, plastic is placed over the curing concrete to trap the water inside and regulate its temperature, ensuring gradual curing.
Effects of too much mixing water
Lower compressive strengths. Segregation of the concrete mix under certain conditions resulting in variable quality throughout the concrete mass. Cracking - with too much water, there will be lower tensile strength, and a tendency towards high shrinkage and subsequent cracking.
When too little water is used or if water evaporates out too quickly, the cement never reaches a full chemical cure, causing a weakened product.
Vrydaghs said this is called “sweating,” and is caused by hydrostatic pressure pushing water and moisture through the concrete from below the surface. The more likely cause is that the concrete is colder than the air, causing condensation, making it appear wet, Vrydaghs said.
Rain can weaken the concrete surface and compromise its strength since it can wash off the cement in the mix. This can lead to issues like cracks in the concrete and delays in the curing process, both of which can lead to a poorly finished surface.