Whether you’re a contractor or a weekend DIYer, worksite schedules aren’t easy to change up. Different build components from footings, foundations, floors, walkways, walls, and even roofs all involve planning, prep work, and scheduling of materials such as concrete. A weather delay can put a project off by weeks or more! The big question for many is, can you pour concrete in the rain?
You can pour concrete in the rain by taking some extra steps to prevent rainwater from being worked into the pour and weakening or damaging the concrete. Rain within 4 hours of pouring can expose the aggregate and cause scaling or dusting. After 10 hours though, light rain will do little to no damage.
In this article, we’ll discuss pouring concrete in the rain, how rain can affect the pour, how to protect the work from the rain, plus how to fix any rain damage. We’ll also provide tips for pouring in the rain to keep your project on schedule. By the end of the read, you’ll be better prepared to meet the curveballs Mother Nature has up her sleeve.
- Can You Pour Concrete In The Rain?
- What Happens if It Rains After Concrete Is Poured?
- How Long After Concrete Is Poured Can It Be Rained On?
- Can You Pour Concrete After It Rains?
- How to Protect Concrete From Rain
- Tips on Pouring Concrete in the Rain
- How to Fix Water Damaged Concrete
- Can You Pour Concrete on Wet Ground?
- Can You Pour Concrete in the Cold?
Can You Pour Concrete In The Rain?
Pouring concrete in the rain is problematic on a number of fronts. Moving heavy equipment around waterlogged worksites or walking on wet slippery surfaces is a recipe for disaster and injury. Pouring concrete onto water-saturated ground can result in poor quality and weakened slabs or surfaces.
Additionally, the type of pour also affects the decision to pour concrete in the rain. Taking all that into consideration, the answer is, yes – with recommendations and planning.
Water is a key part of the process of making concrete. Too much and the concrete pour is soupy, there’s greater shrinkage and cracking, and it has less strength. Too little and the concrete is difficult to pour and won’t cure properly either, resulting in a weaker product.
Concrete is a mixture of cement, sand, aggregates (stone), binders, water, and other materials. Sand and stone are also known as ballast. The ratio of dry materials like cement, sand, and stone depends on what the concrete will be used for – footings, foundation walls, residential or industrial floors. The amount of water is based on the amount of cement in the mix and is also a ratio.
The water to cement ratio (w:c) is based on the weight of each. The amount of water added during the mixing process greatly influences the quality of the concrete; the less water used during the mixing, the stronger and more durable the cured product.
The ratio is commonly between 0.4 and 0.6 depending on use, yearly temperature fluctuations, and ground conditions. The greater the water ratio, the more permeable the cured product and the greater susceptibility to freeze-thaw damage.
A gallon of water weighs 8.345 pounds, so if a cubic yard of concrete mix contains 220 pounds of cement, the weight of water for a 0.4 w:c ratio would be 88 pounds (220×0.4), or 10.55 gallons (88÷8.345). If your mind bends to metric, a 0.4 w:c ratio means 40kg (1kg = 1 liter) of water is mixed with 100kg of cement.
Water mixed into the concrete differs from rainwater hitting or pooling on the pour. Properly mixed concrete may displace water resting on plastic sheeting (moisture barriers) or trapped in forms or post holes. However, it is best to remove the water first to prevent it from becoming trapped or mixed into the pour.
Pouring in heavy rain is not advisable as it can alter the water ratio of the mix and weaken it. However, a light or intermittent shower or drizzle may have little impact on the curing process.
Additionally, if it starts raining after the concrete initially starts to set, about 30 to 60 minutes, rain becomes more of a finishing than weakening concern. Rain before the concrete fully sets, about 8 to10 hours, can damage the surface finish, making leveling difficult, and weaken the surface and upper portion of the pour if it sits or is absorbed.
Pouring foundations, small pads up to 10’x10’, or even walls in the rain is doable as the pour surfaces are easy to cover before and after the rain starts. They also don’t require a lot of time (if any) to finish.
Pouring concrete for piers or fence posts in the rain is possible too. However, if the ground is saturated but the hole contains little or no water, use dry quick-setting concrete to fill the hole after the post is leveled and set.
The greatest concerns are preventing water from collecting inside the forms and mixing into the pour to weaken the concrete. Being able to access the pour areas safely is another concern. Larger surfaces are more difficult to protect, so may need to be rescheduled.
Concrete protected from rain will set and finish as it should. Pouring cement onto saturated ground, into water-filled forms, or left to set and cure in the rain will be weaker, pitted, susceptible to cracking, and structurally compromised.
What Happens if It Rains After Concrete Is Poured?
Concrete that has set and is curing should be kept moist for a week or more to slow the curing for a stronger product. It can be wetted every 2 to 3 hours depending on the temperature, covered with moistened sand or fabric and a plastic layer, or coated with a curing compound to slow evaporation. However, a torrential downpour on unprotected concrete up to 24 hours after it has set, can still cause surface damage.
The amount and force of rain are important factors. The greater the force and volume, the more damage it will inflict. Rains within 4 hours of pouring the concrete can leave marks in the surface, cause pooling, wash away cement to expose the aggregate, soften and reduce its strength, cause scaling, or dusting.
Rains between 4 and 10 hours of placement may cause less structural damage, but can still make finishing difficult, damage the surface, and can weaken the pour. Much depends on the quantity and force of rain before the concrete fully sets. Never work rainwater into the surface of the concrete or sprinkle cement powder onto puddles.
How Long After Concrete Is Poured Can It Be Rained On?
Once the concrete is poured, placed, screeded, leveled, and smoothed, it’s usually allowed to set up. The size of the pour determines how long the pour-place-leveling stage takes. The ratio of cement to ballast and water to cement ratio, along with the temperature and additives influence the speed at which concrete sets up. Concrete doesn’t need to dry; it needs to cure.
Concrete will begin to set up usually within 1/2 an hour of pouring. The sheen stage is a process that begins as the concrete sets up and can take anywhere from 2 to 4 hours (sometimes longer) for water bubbling out of the concrete to evaporate. Once the sheen of bleed water has disappeared, the concrete surface can be floated, grooved, edged, and finished as necessary.
Concrete usually fully sets 8 to 10 hours after it’s poured and will fully cure over the following 28 days. Do a scratch test to check the surface hardness using a screwdriver or trowel. If the surface marks easily with little or no pressure, protect it from rainwater.
The longer rain holds off after the concrete is poured, the better. Rain during the screeding or leveling stage can compromise the strength of the concrete. Precipitation resting on the surface can easily be worked into the mix during the screed, leveling, or vibration process, altering the water to cement ratio.
Rain can pit or damage the concrete as it sets up and hardens. However, if the concrete has been finished and is nearing the end of its hardening or setting period (10 hours), light rain will likely do little if any damage.
If it rains the day after the concrete has been poured, there probably won’t be any damage. After 24 hours, new concrete slabs should be sprayed with water several times a day for a week or more if the temperature is above 75°F to help the curing process, so rain will only help. The critical time, when you don’t want much precipitation, is before and during the pouring, placement, and leveling of fresh concrete.
Can You Pour Concrete After It Rains?
Concrete is heavy. Moving and placing it when the ground is dry is hard work, doing that on saturated ground is even more difficult. Light rain dampening the ground is very different from a torrential summer thunderstorm, so the amount of rain prior to a pour can impact the job.
You can pour concrete after it rains provided the ground will support the weight of the concrete. Cement mixed with water creates a chemical reaction that cures and hardens. Too much water from the oversaturated ground, though, can weaken the concrete, so it’s common to use a plastic moisture barrier between the wet ground and the pour.
Pools or lakes of rainwater collected within formed areas will mix with the pour, altering the water-cement ratio and weakening the concrete. Before filling forms with concrete, remove all collected water, and also keep it away from the edge of the slab or pour area. A wet jobsite is an ingredient for disaster and injury.
How to Protect Concrete From Rain
Minimizing the effects of rain before and after a pour is part of successful planning. Formed footings, foundations, and walls can collect and hold rainwater, as can floors or pads ready for concrete.
The concrete site may be elevated so runoff won’t flood a portion of the site. Unfortunately, footings and foundations tend to be in excavations which can be submerged, while pads may only be slightly above or below ground level.
If you’re preparing for a pour and the forecast or weather pattern (or your joints) predict rain, cover the work area with plastic or tarps to protect it. Tent the plastic so it sheds any water away from the formed area.
On the pour day, if the sky or forecast looks ominous, make sure to have a roll or two of plastic sheeting and some 2x4s for elevating the poly off the concrete so it doesn’t sag with water. If heavy rains are predicted and the pour has a large surface area, it is wise to postpone if possible.
Should you be lucky enough to get the finishing stage completed before it rains, covering it for 6 to 12 hours with plastic won’t hurt, especially if it looks like rain. Once the concrete has set up – 8 to 10 hours after the pour – rain won’t do much damage, just don’t leave puddles on it.
A light rain as the surface of the concrete pad cures is helpful since it should be kept wet for the first week or so. An alternative to wetting the concrete as it cures is to seal it to protect the surface. Concrete should be protected from rain for 24 hours after it is sealed, though.
Tips on Pouring Concrete in the Rain
Weather forecasting has come a long way but it’s still not perfect. The best practice when planning a concrete pour is to prepare for the worst, and hope for the best – something I’ve heard many people say. Some concrete sites are easier to protect than others from the rain, but precautions can be taken for all. Remember, preparation is the key.
Here are 10 tips to consider when the forecast forewarns that it may rain on your concrete pour:
- Scope out the work area ahead of time for gullies, swales, and downspouts that can flood the jobsite. Redirect, or use excavated material to prevent extra water into the area.
- Dig a bit deeper in one area outside the pour zone to collect rain and runoff.
- If rain is predicted prior to the pour, cover the forms or formed area to keep water out. Saturated ground can alter the water-cement ratio.
- Always remove collected water from pour areas, so the concrete isn’t weakened.
- If a torrential downpour is predicted, reschedule the pour.
- Recheck forms and forming stakes and braces, and relevel or reinforce if necessary. Rain can soften soils and allow forms to shift.
- Make sure to have tarps or plastic sheeting and 2x4s available to cover the pour if rain shows up.
- If it rains during the pour, push water off the edge of the slab so it isn’t trapped or worked into the concrete.
- Never work rainwater into fresh concrete, push it to the edge with a float or sponge it off.
- Don’t throw dry cement powder onto the concrete surface to soak up rainwater. It will damage the finish and weaken the pour if worked in.
How to Fix Water Damaged Concrete
Rain damage may be in the form of craze crackling, surface scaling, dusting, dimpling, discoloring, pitting, or exposed aggregate, all of which can be aggravated by impact traffic and freeze-thaw cycles. A scratch test using a set of hardness tools or even a screwdriver will help determine how large an area has been compromised and how best to fix the damage.
A hand grinder with a diamond-concrete disc for small areas or an industrial size diamond head grinder for larger areas will remove the damaged or weakened surfaces. Once removed, cleaned, and a bonding agent applied, the area can be resurfaced with an overlay of concrete or a polyurethane sealer.
Water that has pooled or formed a pond on the surface of the concrete, could cause subsurface damage due to oversaturation. Similar damage can occur if the concrete is poured onto saturated ground or into water-filled forms. The additional water weakens the concrete by changing the cement to water content. The weakened area may need to be cut out, or the whole pour hammered out, removed, and redone.
Can You Pour Concrete on Wet Ground?
Pouring concrete on wet ground occurs quite often. The greatest concern with saturated ground is standing water and moisture being sucked up into the pour and compromising the strength of the concrete. Another concern is machines and workers becoming mired in mud. If rain is forecast prior to a pour, cover the ground and formed area to minimize moisture collection and retention.
You can pour concrete on wet or saturated ground but it may cause some problems. To minimize potential damage caused by moisture by wet ground altering the water to cement ratio, remove standing water from the pour site and off the edge of the slab area.
Use a wet-dry vacuum or bucket to remove water from post holes, forms, or depressions before pouring concrete. Consider rolling out a plastic moisture barrier and pouring the concrete on it to limit the effect of saturated ground.
Keep in mind, though, that most concrete isn’t poured directly onto the ground. It often has packed gravel under it and may even have a moisture barrier and/or a layer of rigid insulation. Footings below frost level commonly are poured directly onto undisturbed soil. They may, however, be on compacted gravel, especially if the excavation is too deep.
Can You Pour Concrete in the Cold?
You can pour concrete in the cold, but it requires additional steps. The best temperature range for the chemical reactions for concrete to set and cure properly is between 50°F and 60°F. Pouring concrete in temperatures below 40°F requires precautions to prevent it from freezing before it sets. Curing problems due to the cold include cracking and strength issues.
Snow and standing water (ice) must be removed and the formed area warmed above freezing to prevent concrete cracking when the ground thaws, or weakened due to improper curing. Additionally, the surface concrete may harden before the base concrete due to the cold slowing the setting process, further weakening the pour.
Forms and tools also need to be above freezing. Use an infrared or dial pocket thermometer to check temperatures.
Tenting the pour area with tarps or plastic and using ground heaters, warming blankets, heat lamps, or hot-air blowers is common practice for warming the ground and concrete after it is poured. The travel distance from the concrete plant is another concern. Concrete traveling an hour won’t be as warm as when mixed, making it more susceptible to the cold, so mixing with hot water is normal.
Additives that won’t damage metal mesh or rebar are often used to speed up the setting process. Once poured, the concrete needs to stay above 50°F for 48 hours to strengthen properly. Moisture must still bleed out and evaporate off or be sucked up as the concrete sets; don’t allow it to turn to ice. Forms should also be left on the pour longer to ensure it is fully set, otherwise, it may collapse or crack.
Pouring concrete in the rain requires planning and preparation to prevent from rainwater being absorbed into the mix and weakening the concrete. Using tarps or plastic to keep the worksite dry 24 hours before and after the pour will ensure the concrete is strong and holds its finish.
Hopefully, you have a better understanding of the requirements for pouring concrete in the rain and how to protect it and repair it, if necessary.