We’ve all been tempted to take a walk or leave a little fingerprint through wet concrete, haven’t we? Maybe you’ve even paved a front path on your home, and the whole family left their handprints to remain forever— or until the new owner replaces it. 😢
Regardless, concrete slabs can take some time to cure, and while it’s fun to make your mark in a little sidewalk square, it’s vital to let the concrete slab of your foundation fully cure before building anything on top of it.
But how long should a concrete slab cure before building on it?
That’s a great question! For which, we hope, we have the answer. Our timeline walks through how long it might take to cure a concrete slab and when the right time to get to work will be.
How Long Does Concrete Take to Dry?
While concrete used for sidewalks or smaller projects might dry within 24-48 hours, larger concrete slabs used for a foundation will take much longer and actually require curing vs. just letting it sit and dry. Here’s a helpful timeline for when concrete might be cured enough to walk on or start working:
- 10 Hours: 5% cured
- 24 Hours: 15%
- 48 Hours: 25%
- 72 Hours: 40%
- 1 Week: 65%
- 2 Weeks: 90%
- 30 Days: 99%
- 48 Days: 100%
Some companies say that you should wait a full 48-60 days to be safe. However, that may vary depending on many of the factors in this guide. You can start framing on a poured concrete slab about seven days after it’s poured when it’s close to 75% cured.
It’s important to note that drying and curing are not the same thing. Yes, there is a difference between drying and curing concrete. In short, drying concrete means the concrete is dehydrated, while curing is the process of hydrating the concrete.
The Importance of Waiting Until It’s Cured to Build
So what can happen if you start building on an uncured slab? We’re sure you can imagine, but here’s why it’s so important to wait until it’s at least 75% cured before you begin building on it.
- An uncured slab is wetter than a cured one, so it’s more susceptible to cracks.
- Uncured concrete can shrink as it loses water, which can cause cracks in walls or floors built on top of the slab.
- If you put flooring on an uncured slab, it might not adhere as well.
- If you paint or put sealant on an uncured slab, it might not adhere as well and could start to peel.
- Uncured concrete can be weaker than cured concrete, so any weight on it could cause damage.
As you can see, it’s best to wait until the curing process is well underway before you start your framing or building project. They say patience is a virtue— that is especially true when it comes to curing concrete.
5 Factors That Can Affect the Curing Process
There are a few factors that can affect how long it will take your concrete to cure. These include:
- Size of the Slab
The larger the slab (or thicker the slab), the longer it will take for the entire thing to cure. This is especially true for commercial builders and large homes.
- The Water-to-Cement Ratio
The lower the water-to-cement ratio, the longer it will take to cure. Curing requires hydrating the concrete, so the less water, the more it will dry out and the worse it will cure. The last thing you want is to start over, so get your ratios right before you begin. You can also adjust as you go, depending on the consistency.
- The Temperature Outside
If it’s too cold out or too dry out, it can take forever to cure concrete. The ideal temperature for cured concrete is 50 degrees and above, with 80-85% humidity.
- Type of Mix Used
There are different types and ratios of mixes you can use for concrete, and some will cure faster than others. The ratios of sand to cement or aggregate will also matter.
- Sealant Applied
There are concrete sealers like these vetted by Bob Vila himself. Some contractors might also apply plastic wrap over the concrete to help seal in the moisture and allow it to cure properly.
Tips for Speeding Up the Drying Process
While many recommend waiting a full 60 days for a concrete slab to cure before building on top of it, there are some ways you can speed up the process and your project timeline.
1) Use Curing Compounds
Curing compounds are a great way to help the curing process along, but they should only be used on horizontal surfaces—not vertical ones. If you use them on vertical surfaces, it can cause staining. Curing compounds work by preventing the evaporation of water from the concrete as it cures. This can help prevent cracks and maintain the moisture longer so it can cure faster.
2) Do It During Warmer Months
As we stated, the warmer the weather and the more humidity in the air, the better and faster your concrete will cure. Make sure the temperature outside (or inside) is at least 50 degrees Fahrenheit.
3) Use Water in the Curing Process
Curing concrete is all about hydration, so keeping the concrete moist will help it to cure faster. After you pour your cement, cover it with a wet burlap sack or apply a light mist of water over it for the first seven days.
4) Cover the Slab While It Cures
Again, this is about keeping the moisture in so the curing process can happen faster. If you can’t keep a burlap sack on it or mist it with water, you can cover it with plastic sheeting. Just make sure there’s no chance of the plastic touching the concrete, or you’ll risk staining.
These tips and tricks can help you ensure a sturdy and stress-free build. Pair these with a reputable concrete specialist, and you should be well on your way to a perfectly cured slab of concrete!
For a Proper Concrete Slab Cure & Installation— Call Perma Pier
If you’re in the market for a new concrete slab, or if you need help with any other foundation repair issues, call Perma Pier of Texas! We offer free consultations, and we would be happy to answer any questions you have about your specific needs. Get a quote for concrete slab installation services!