Can You Pour Self-leveling Concrete Over Existing Concrete?

Self-leveling concrete can be a great solution to uneven concrete slabs or surfaces, but it’s not always the best option out there.

In short, self-leveling concrete can be a great way to even out the imperfections on your existing concrete surfaces. But there’s a little more to it than that.

A-1 Concrete Leveling has been repairing concrete for over 30 years, and in this time we’ve seen a lot of good applications of self-leveling concrete over top of existing concrete. We’ve also seen quite a few that have crumbled away relatively quickly.

This article will walk you through when it makes sense to pour self-leveling concrete over your existing slabs and when it doesn’t, and give you some alternatives to consider if you’re not sure if self-leveling concrete is the right route for you. 

Related Resource: Top 4 Problems With Using Self-Leveling Concrete

How Does Self-Leveling Concrete Work?

Self-leveling concrete is a cement-like compound similar to concrete, but it is much thinner, flows more easily, and sets up faster. 

When mixed with water, it can be poured over existing concrete slabs where it will spread and even itself out, creating an even surface texture.

Using Self-leveling Concrete Over Existing Concrete Slabs

Self-leveling concrete is designed to be used over existing concrete to achieve a flat surface, either as a standalone floor or in preparation for flooring to be installed on top.

But to ensure a quality application that will last, the existing concrete must be prepared beforehand.

Prepping Existing Concrete for Self-Leveling Concrete Compounds

To ensure the area is prepped for a self-leveling compound, the existing concrete must be: 

• Completely clean 
• Primed with the recommended primer
• Free of any holes or cracks where the compound can leak out 

Extra care must be taken to remove any loose debris, chipped concrete, stains from oil or grease, or dried paint, as these imperfections can cause the self-leveling concrete to chip, crack, or deteriorate.

Self-Leveling Concrete Dry Times

Each self-leveling compound is different and cures at varying timelines. Some are ready for use within 12 hours, and others require waiting 24-48 hours. 

Heating, ventilation, and other similar factors where the self-leveling concrete is applied can also influence the time it takes for the compound to dry.

Top 4 Problems With Using Self-Leveling Concrete

Learn about the common problems you can run into when using self-leveling concrete on uneven slabs.

Outdoor Self-Leveling Concrete: Can You Use Self-Leveling Concrete Outside?

Using self-leveling concrete outdoors is usually not a good idea. The natural expansion and contraction of the concrete due to freeze-thaw cycles and moisture absorption can cause the self-leveling concrete to crack or crumble away.

Alternatives to Self-Leveling Concrete

• Concrete Leveling

  
  Concrete leveling is a way to raise sunken or settled concrete slabs back up to their original position. While it does not change the surface texture, it’s used to even out the concrete and eliminate trip hazards, redirect water flow away from buildings, and fill voids underneath slabs.

Pro Tip: Concrete leveling can also be done on interior concrete, like on sunken basement or garage floors.

• Resurfacing

Professional resurfacing can be a more permanent fix for uneven surface texture on exterior concrete slabs, but it is a much more expensive and involved process. 

• Patching Compounds

Additional concrete and patching compounds are sometimes used as temporary fixes for divots, chipping sections, or trip hazards. But as with self-leveling concrete, they tend to chip and crack away with the expansion and contraction of the existing concrete.

• Concrete Grinding

Concrete grinding can be a cheap and easy way to eliminate trip hazards and uneven concrete, but it’s not recommended in all situations because it exposes the concrete to potential damage.

Best Uses for Self-Leveling Concrete

When concrete is poured, sometimes it can be finished with dips or other imperfections. Self-leveling concrete compound is intended to even out these dips and inconsistencies in the concrete’s surface, especially before installing new flooring. 

With this in mind, the following is a list of the best use cases for self-leveling concrete:

• Interior projects, as the temperature fluctuations outside can cause premature cracking
• Filling in dips in the surface of concrete, like concrete floors in preparation for flooring
• Pours ¼ inch deep or less, although this can vary by compound
• Standalone interior floors

When To Avoid Self-Leveling Concrete

There are many times when self-leveling concrete is not the right choice. Here are some of them:

• Outdoor Concrete Slabs

As mentioned above, the freeze-thaw cycles and constant moisture absorption for outdoor slabs cause concrete to expand and contract, meaning self-leveling concrete will likely crack off when used outside.

• Thick Pours

If a thick layer of self-leveling concrete is needed to cover the imperfections in the concrete surface, it will likely end up crumbling away.

• On Settled Concrete

To even out settled concrete and get it to a level position, you would likely need to use a lot of self-leveling compound in a thick layer that can chip or crack off.

Self-leveling concrete won’t address the actual reason why the concrete is settling, so there is also a possibility that the slab itself will keep settling.

• Vertical Surfaces

Self-leveling concrete isn’t a good fit for walls or any non-horizontal surface as these do not allow the compound to cure properly.

• Large Surface Areas

The short working time of self-leveling concrete (usually around 20 minutes) can make installing it over a large area tricky.

Should You Use Self-Leveling Concrete Over Existing Concrete?

Now that you know what self-leveling concrete is and when to use it, you’re ready to decide if it’s the right option for you, or look into the alternatives for fixing uneven slabs.

You want your repair to stand the test of time, so making sure you’re using self-leveling concrete correctly and for the right application can save you lots of headaches and additional costs down the road.