Concrete is a hard, durable, long-lasting surface, but that’s only if it cures. Fresh concrete is more sensitive than you may realize and requires a longer cure time than what many people, even professionals realize. In fact, most sources say concrete cures within four to seven days, but the real answer to how long concrete takes to cure: 28 days. Yep, almost a full month.
That doesn’t mean it’s wet for 28 days, of course. It just means you have to follow a set time frame when it comes to caring for the slab and set up proper conditions to ensure a strong, stable, long lasting concrete surface, and that’s what we’re going to break down for you.
What Does “Curing” Actually Mean with Concrete?
Curing concrete isn’t just making sure the slab is dry – that happens in around 48 hours in most cases. In fact, keeping moisture in the slab is essential to a proper cure because it’s about making sure the chemistry involved takes place in the right time frame. The cement and water binds with sand and gravel and crystalline structures form within the slab in a reaction called hydration. The crystals grow out like little “fingers” wrapping around the sand and gravel, giving the concrete its durability, strength, and hardness.
Curing serves three key purposes:
- Holds moisture in the substrate to facilitate crystal structure growth and development;
- Slows and delays the shrinkage that comes from drying as drying too soon can lead to cracking on the surface;
- Improves impact-resistance, water-resistance, and wear-resistance;
How to Properly Cure Concrete
The hydration reaction requires specific moisture and temperature conditions for the best results.
- Moisture: The cement reacting to water causes the curing process, so if there’s less water in the mx, the concrete will cure. However, there are fewer crystalline bonds, so it may not be as strong as you need it to be. On the other hand, too much water either within the slab or introduced to it during the cure process means it will take longer and may cause cracking and flaking along the top.
- Temperature: This doesn’t refer to the air temperature, it refers to the slab temperature. Heat leads to moisture evaporation, which can allow your concrete to cure more quickly, while the hydration reaction stops almost completely at 40 degrees Fahrenheit.
So, how can you find that perfect balance to achieve hydration and avoid cracking and structural problems?
- Spray concrete with water several times over the course of a week or cover with polyethlyne sheets or a concrete insulation blanket to hold in the moisture and heat if needed;
- Use a concrete curing compound that optimizes water retention;
- Avoid walking on it for 48 hours and avoid allowing vehicles or equipment to roll on it for at least 7 days
If you plan on grinding and polishing the slab, you’ll want to wait the full 28 days. This way, any cracking and drying will be complete, it will be strong, and you’ll have a better idea of what kind of tooling you’ll need to use.
Get the Surface Preparation Equipment You Need
Once your slab is fully cured, we have everything you need to give it the finish you want. From coatings and densifiers to concrete grinders, reach out to our team today to get a quote on the gear you need at 815-472-9711.