We all know that if we’re planning to pour concrete, it can be hard to schedule the pour, especially if your pour involves professionals and must be scheduled a few days ahead of time. Even if you’ve checked the weather forecast before pouring your concrete, sudden showers can pop up, especially in the summer.
They form out of nowhere, rain like gangbusters for a few minutes (just enough to ruin your day), and then disappear. Then the sun comes right back out as if nothing happened.
So, can you pour concrete in the rain? The quick answer is yes, providing you take the necessary precautions so the rainwater doesn’t fall directly onto the freshly poured concrete. Protecting the concrete for a least 4 to 5 hours from being rained on will prevent any damage.
Fall can be just as bad. You may have planned your pour for a day or two after a cool weather front has passed through with its attendant rain, only to find out that the low-pressure system that brought the front has also brought some wrap-around showers as the system moves, bringing an unwanted rain surprise.
Since it’s still harder to predict the weather for a certain place, there is always a chance that something could rain on your concrete parade. Even if you’re doing the pouring yourself, you’ll probably need a helper or two, and it’s not like you can just call your buddy and have him come over to help without much notice. You’ll need to know what to do in case some unwanted heavenly water shows up during your job and what preparations you need to make.
Will Rain Ruin Fresh Concrete?
Rain can cause problems with freshly poured concrete. Rain, especially hard rain, will tend to weaken the strength of the concrete. Problems such as scaling and dusting can develop, especially near or on the surface. Craze cracking can occur, leading to worsening cracks if a freeze happens soon after the pour. If your concrete mix is colored, the rain can wash out some of the coloring agent, leaving streaks in the color or other undesirable results.
If you had time to work through the finishing process and the concrete has stiffened, rain may cause little damage or none at all. The stiffening usually occurs between four and eight hours after it’s mixed. Actually, once the concrete is set, a little extra water can actually help the curing process.
True, water is an integral part of any concrete mixture, but only in a certain ratio to the other materials. More water is likely to not only ruin the surface of the concrete slab in places but may also affect the internal concrete structure.
If it rained before you start your pour, any water on your base surface can be absorbed by the fresh concrete you pour and change the ratio of water to cement in the mix. If you plan to pour a slab a day or two after it rains, cover the base gravel or ground with a plastic tarp to keep it from getting wet when it does rain.
How Do You Protect Freshly Poured Concrete from Rain?
The best thing you can do is to have some heavy plastic sheeting or large tarps at the ready in case you get caught by an unexpected shower. Make sure you seal the edges of the plastic around the edges so the water can’t sneak in underneath.
Some people just try to work the rainwater into the surface, but this is one of the worst things you can do. Another mistake is to try to throw dry cement onto the wet concrete to try to soak up the rainwater. This actually may further weaken the top layer of the concrete and will certainly interfere with the finish.
The best thing you can do if your concrete slab gets rained on is to use a float to push any water off the slab before you start the finishing process. You’ll need the float in the finishing process anyway, so you should have one handy.
How To Pour Ready Mix Concrete in the Rain – A Guide to Pouring Concrete in the Rain
Of course, rain doesn’t work on your schedule, or you wouldn’t be reading this. Following are some tips to help and some things to avoid minimizing the chances of your concrete becoming damaged. Included are some repair tips in case the worst happens.
>>> How Does Rain Affect Freshly Poured Concrete?
Light sprinkles or drizzles may not cause any damage. Unfortunately, those hit or miss summer showers usually feature a downpour, however brief, which will tend to drive the water right into the cement. It can cause pitting from the individual drops and change the actual mix of the concrete, weakening it. It causes the surface to become soft and may cause flaking. Thicker slabs may only suffer surface damage. A thin slab may become ruined entirely.
>>> How Long Does Concrete Take to Dry?
You’ve probably heard about concrete both curing and drying. They aren’t the same thing. Curing refers to the hardening process that starts as soon as the concrete is poured. This can take as little as 28 days to complete. However, there is still water contained in the slab that needs to evaporate, and this process can take months to complete, especially if the slab is exposed to the weather.
Concrete is usually deemed fit to be walked on within 24 to 48 hours. This depends on the mixture used. After seven days, the concrete is considered to be partially cured to the point that a vehicle can drive over it as long as it is not too heavy or large.
The actual full curing and drying times are also affected by how thick the slab is. Of course, the thinner it is, the faster it will cure and then dry. A typical rule of thumb is that each inch of concrete slab thickness takes about 28 days to dry. These approximate times are meant for concrete that is kept inside in a warm place with low relative humidity.
This time will be lengthened if the slab is outside exposed to the weather. The sealant itself should be left to cure and dry for at least 24 hours. The drying time should be listed on the product label.
>>> How Concrete Cures and Dries
All types of concrete contain three basic materials: cement, water and aggregate. When the cement is mixed with water, it causes a chemical reaction that binds the elements together. This reaction caused the concrete to harden. During this curing process, the concrete will become porous, and part of the water in the mixture will become part of the concrete as it fills the tiny holes.
The drying process consists of this water slowly evaporating up through the surface, drawing up more water from deeper inside the slab. The less humidity in the surrounding air, the more quickly this water will evaporate. In humid conditions, the concrete stops drying, at least temporarily.
>>> How to Protect Concrete When It Rains?
As has been mentioned, it’s important to keep enough thick plastic or tarps to cover your entire slab including the sides just in case the skies should open up unexpectedly.
Being careful to stick to the correct ratio of ingredients when mixing the concrete can help as well. If you add too much water, it will take longer for the extra water to evaporate, leading to a longer drying time. You can add more cement to your mix to speed up the drying time, but this can lead to shrinkage as the concrete dries, possibly causing cracks.
Lightweight concrete or concrete containing lightweight aggregate tends to absorb more water. Try using synthetic aggregates that won’t absorb water.
You may be tempted to use curing or sealing agents. These can actually make it harder for water to evaporate from the slab’s surface, lengthening the drying time.
Sealing can be done, but sealants should only be used after the concrete has dried thoroughly, or else you risk sealing in extra moisture. Wait at least 30 days. You may need more time if your slab is subjected to rain during the drying time or a humid atmosphere.
>>> How to Know if Rain Has Damaged Your Concrete
If the surface of the concrete appears uneven or you see lumps and bumps in the concrete, there may be damage. However, you may not be able to tell right away if your concrete has been damaged. Cracks tend to develop as the concrete dries. Surface problems such as scaling will become apparent more quickly.
If the top was damaged by the rain it will grow to look rough and powdery and may be brittle. The edges can be affected similarly and display a rough edge. Flaking as the concrete dries and a pitted surface will be visible.
Scratching the concrete with a screwdriver will often let you know if it is damaged, especially if you are experienced in pouring concrete and can compare. There are test kits available that will help you assess your concrete’s health, including a test involving a core sample.
Thicker slabs may just suffer some surface damage. In this case, you can grind off the surface layer once it’s fully dry and replace it, sometimes as little as 1/8 inch. The surface damage may just need to be ground off, which should leave a polished finish. A thin slab may have to be replaced entirely.
A few tiny cracks can be repaired with mortar and a sealing compound. Widen the crack with a grinder, then fill it. After the mortar is hard, apply a coat of sealant.
If you do need to replace the surface or just make a new surface, this is possible. Once it’s dry, clean it with a broom and then pressure wash the surface. Use a de-greasing product if necessary. Prime the surface and coat it with a bonding adhesive. Pour a layer of new concrete and use a trowel to create a smooth finish. It should be ready to be used after 12 hours or so, but it will take a week or a week and a half to really get strong.
If in doubt about whether your concrete is damaged, consult your concrete supplier. They can usually tell you what to look for or perhaps even send someone out to assess any damage.
Tips for Pouring Concrete in the Rain
As has been mentioned, keep enough thick plastic or tarps available to cover your entire slab in case of rain. If you are having a concrete company do the pour, this is usually where problems with rain show up the most. Pours usually have to be scheduled a few days ahead of time, and we all know how quickly the weather forecast can change.
If you suspect rain is on the way, cover the site with plastic ahead of time to keep the ground dry. If rain starts to fall during the pour, you’ll need not only tarps or plastic but some boards to construct a sort of shelter over the concrete. If it rains during the pour, use your finishing float to keep pushing any water off the edges of the slab.
If you don’t have a float, you can slide a regular garden hose carefully across the surface, using it as a squeegee. Avoid pouring concrete on very wet surfaces or puddles. Again, don’t try to work or mix the rainwater into the concrete, as it will cause problems and potentially weaken much of the slab.
If you have to pour concrete during your rainy season and you dodged a bullet with your actual pour, be mindful of your weather. If your area is prone to pop-up showers, watch the weather conditions carefully and be ready to cover the concrete if a shower should creep up. Once the concrete has been finished and has been set hard enough to walk on, you won’t have to worry so much. This usually occurs between four and eight hours after finishing, depending on the temperature and humidity.
Pouring concrete can be a tricky process. The warm temperatures that summer brings that are good for drying concrete also mean more likelihood of unexpected, brief rain showers. The best you can do sometimes is make your best guess and try to avoid pouring concrete on a day when there’s a chance of rain but be prepared ahead of time to deal with the problem should it happen. If your concrete does show signs of damage, it usually can be dealt with.