When temperatures dip below 40 °F, the chemical reactions that strengthen concrete slow down and can lead to weaker concrete. If concrete curing temperatures are below freezing, the water inside the concrete can freeze and expand, resulting in cracks in your surface.
Before you start the pour, ensure that any cavities are free from water, and keep them covered as much as possible. If it started raining before you could cover the slab, don't panic. Simply wait until the rain has passed, then pull or push any surface water off the edge of the slab surface before finishing.
The Best Season for Pouring Concrete
Ideally, the temperature should remain within 50 to 60°F for most of the day. Also, make sure that nighttime temperatures don't drop below 40°F, as this may cause the water in the concrete to freeze, putting it at risk of chipping and breaking.
If too much rain falls into the concrete mix – or if it is laid onto wet surfaces or trenches – this will affect the mix, resulting in weak concrete. Rain falling on freshly-poured concrete can cause damage to the surface, making it bumpy and uneven.
Considering all the factors listed above, the best months for pouring concrete would be June, September, and early October. During these months, the weather will be mild and dry. Therefore, the concrete will set properly.
As long as the concrete is given 4 to 8 hours after mixing and finishing to set up, rainwater won't affect it nearly as badly as it could. Some concrete mixes will actually benefit from rainwater on the surface because it's beneficial in aiding the hydration and curing process.
Freshly placed concrete should be protected from rain for at least 12 hours from its placement. After that, the rainfall rarely influences concrete properties.
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.
The general rule of thumb is that concrete takes about 28 days to dry for every inch of slab thickness. Within 24 to 48 hours, the concrete will be ready for foot traffic.
Pouring concrete in the rain can compromise its strength, increasing the tendency for dusting and scaling to develop. Once the damage is done, it can be hard to rectify and will often ruin the appearance of the finished surface. Don't let it rain on your parade.
Most specifications for retail or commercial concrete slabs specify 4 to 6 inches of thickness. Owners and contractors have historically disputed whether a poured slab meets a specification because of its thickness.
Initial Setting Times for Concrete
In standard industrial cases, full strength concrete is recognized at 28 days. At seven days, you should have concrete that is cured to 70% full strength or greater. But to answer the question of, “How long does concrete take to set?” concrete setting time is generally 24 to 48 hours.
Concrete should be left to sit for 2-4 hours after pouring before watering. If it is supposed to rain in that window, the concrete should be covered. Additionally, if you cannot water the concrete as regularly as is recommended, covering concrete helps trap the moisture and slow the evaporation.
If the weight of the concrete deforms the dirt base in any way, the entire concrete structure will be flawed. All of that is not to say that it is impossible to pour concrete over dirt. You can absolutely do it successfully, but you need to follow a specific process.
It is important to keep in mind that dry-pour concrete may not offer the same level of strength and durability as wet-mix concrete. Dry-pour concrete can also be more prone to cracking and shrinkage, which can lead to structural issues and the need for costly repairs over time.
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.
Curing time of concrete is typically 24-48 hours, at which point it's safe for normal foot traffic. After one week, concrete is typically cured enough to handle continued construction including heavy machinery. Concrete is recognized to have reached full strength 28 days after placement.
The dark gray discoloration is caused by varying degrees of hydration of the cement in the concrete, caused by the varying moisture contents in the localized areas of the total concrete.
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 slabs are very porous. This means standing water can easily fill in pores on the surface and eventually break down the concrete. As a result, the concrete may crack, move, or even settle.
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.
After 24 hours, you can safely walk on your new concrete.
If there has been a lot of rain or you've done decorative stamping in the concrete, you should wait longer. Normal foot traffic should be fine on standard concrete at this point, but you should still be cautious about damaging the surface of the new paths.
Any excess water not absorbed by the sand and cement rise to the surface. This leaves a pool of water on the surface of the concrete, which we call bleed water.