How Long Should Concrete Cure Before Applying Sealer? 

 July 23, 2023

By  Dale Keese

There’s more to pouring concrete than just mixing it with water, gravel or sand and cement. While that’s important, you need to apply a sealer so that it can be protected. If you’re not sure when or how to do that, here’s a simple guide.

Concrete needs to cure for 28 days for an inch of slab thickness after pouring cement so that it can dry, no matter the type of concrete sealer you’re using. The moisture needs to be out of the concrete’s system before sealer can be applied to make it more durable and avoid cracks due to wear and tear.

There are a couple of other decisions you need to make before you head off to buy a  concrete sealer from a general retailer. And here is the information that will help you make them.

How Long Does Concrete Take to Cure Before Sealing?

Sealing concrete is a critical part of the process. It is highly recommended because the sealing helps protect the concrete from wear and tear. It also helps avoid cracks that will happen inevitably over time. And if you do it right, you can keep it functional and well for more than a couple of decades. What do we mean by “keeping it functional and well”. Here’s what.

After pouring concrete, there is the process of curing and then there is sealing. Wet concrete will contain excess moisture. During the curing process, which takes about a month (or 28 days to be precise), moisture evaporates and the concrete becomes solid. That’s when you should do the sealing.

If you do it before curing is complete, the moisture does not evaporate properly and the pathway won’t have the strength that it should have. This means it could become uneven or break and crack ahead of time.

Sealing is a little like painting walls regularly to protect the surface from moisture. So, you need to wait for the concrete to dry and get rid of the moisture but once that happens, you need to seal it so that the moisture in the atmosphere doesn’t find its way back. But it’s not just about picking any concrete sealer. You need to know which one suits you best depending on whether the concrete is interior or exterior.

What Does ‘Curing’ Concrete Mean?

Curing of concrete is essentially the process of maintaining the moisture content of concrete that has been freshly poured to complete the hydration process and ensure that the concrete hardens properly.

Curing helps to increase the strength, durability, volume stability and resistance to abrasion, scaling, freezing and thawing of the hardened concrete, while reducing the permeability.

What Is the Process of Curing Concrete?

There are different methods of curing concrete and the process of curing concrete, as well as the method used essentially depend on the climatic conditions and type of work. The commonly used concrete curing methods include:

Sprinkling Water: The sprinkling method is mostly used for curing floor slabs and the method includes sprinkling water on the concrete surfaces continuously that allows the concrete to cure properly. However, before you start sprinkling water on the concrete, it should be allowed to set sufficiently. While water can be sprinkled by hand, you can use a perforated plastic box to do it too.

Shading: This process essentially prevents the water from evaporating from the concrete surface by shading it and protecting it from direct sunlight, heat and wind in dry weather. And, it helps to preserve the heat of hydration of the concrete and prevents it from freezing in the cold weather. Shading is typically done by stretching canvas that is stretched on frames and is mainly used for large concrete surfaces.

Covering with Gunny or Hessian Bags: A common method of curing used for structural concrete, this process uses canvas, hessian or empty cement bags to cover the exposed concrete surface to prevent it from drying out. The bags are then wetted periodically, ensuring that the concrete surface is wet at all times and should not be allowed to become dry even for a short time while it's curing.

Ponding: The best method of curing, this is suitable for flat surfaces such as roof slabs, floors, roads, etc. In this method, first, when the concrete is placed, the surface is covered with moist canvas or hessian, which is removed after 24 hours. Then, small ponds of sand or clay are built across the concrete area and water is filled in the ponds, which are replenished 2-3 times a day depending on the weather conditions. And, once the curing is complete, the ponds are broken and the water drains out.

Membrane Curing: This process comes under moist curing where the concrete surface is wetted and then covered with a layer of waterproof material for around 7 days. The membrane, usually in the liquid or solid form consisting of wax emulsions, plastic films, bitumen emulsions and bituminized waterproof papers prevents the water from evaporating from the concrete surface.

Steam Curing: In this method, steam is sprayed on the concrete surface to retain the moisture and also increase the temperature of the concrete. In this method, the concrete develops strength very quickly and is best used for precast concrete.

What Happens If Concrete Is Not Cured?

Curing concrete is very important in developing the pore structure, as well as the microstructure of the concrete, which in turn helps to make the concrete strong and durable. If the concrete is not cured properly, it results in a defective microstructure and in turn, the strength, abrasive resistance and durability of the concrete are affected. Inadequate curing causes the concrete to develop thermal and plastic shrinkage cracks and the surface layer can lose its strength.

Why Does Concrete Need Sealer If It’s Already Cured?

Curing freshly poured concrete is necessary to ensure that it hardens properly while making it strong and durable in the long run. However, it is recommended to seal cured concrete as sealing provides continuing, long-term protection from pitting, spalling, cracking, staining, mold, mildew, dusting, efflorescence, salt damage, freeze-thaw damage and deterioration due to water absorption and surface abrasion, thereby prolonging the life of the concrete.

Frequently Asked Questions

Can I Put Concrete Sealer on Fresh Concrete?

No, you cannot. Fresh concrete is damp and contains moisture. If you apply a concrete sealer on this surface, the moisture will remain trapped inside and form air bubbles.

These bubbles will lead to cracks in the surface and your concrete pathway will be damaged long before it is expected to. So, wait for about 30 days to make sure that the concrete surface dries up completely. Use this time to pick the right kind of sealer for the look and functionality you expect from your pathway.

How Do You Know If Concrete Is Dry Enough to Seal?

As mentioned before, the thumb rule is to wait for about a month for the concrete to dry. But sometimes, weather can wreak havoc. And since you can’t tell by looking at it, experts have a few ways of making sure the sealer is not applied prematurely.

They usually do a test to check the moisture content and it is called the “relative humidity test”. During this test, single-use L6 sensors are placed at different depths of the concrete slab and the relative humidity is measured.

These sensors are quite easy to use and install in the concrete slab. They are left to do the job for about 24 hours after which the readings are checked.

How Do You Prepare Concrete for Sealing?

You start by cleaning the surface to make sure debris like dry leaves or dirt is removed. Then you pick the right type of concrete sealer and start applying it like paint. That means you can either use a brush or a roller to get a nice, consistent finish.

Apply the sealer to the surface of the concrete until it is covered and make sure you don’t leave any spots that make the concrete vulnerable. After that, wait 24 hours for the sealer to dry and check to see if you did a good job. If yes, pat yourself on the back. If not, repeat the process till all the missing spots are eliminated.

About the author

Hey, I'm Dale Keese.. thanks for reading.. hopefully this article can save you some time and trouble with your sealing job. I'm also in the process of making some video walk-throughs for youtube so check back soon! thanks

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