Can You Pour Cement on Top of Cement?

Yes, you can pour Cement on Top of Cement over existing concrete. As long as your concrete is in mint condition, this task is doable. If you decide to pour a new mixture over an old slab, be sure it is at least 2 inches thick. But if the old concrete is severely damaged—with cracks or signs of crumbing—it’s not a good idea to pour fresh concrete over it.

If your concrete starts looking tired and worn out, it might be time for a refresher. Homeowners may wonder: Can you pour concrete over concrete? This guide will tell you everything you should know about pouring concrete over an existing concrete slab, including the pros and cons, and how to know if you should start from scratch.

Concrete is durable and cost-efficient, with the versatility to be either decorative or purely functional. However, concrete that’s cracked, stained or heavily patched can create structural hazards and harm a project’s overall appearance.

Do you have to remove the old concrete in those cases, or is adding a new layer an option? Learn more about pouring concrete on concrete correctly.

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How to Properly Pour Concrete Over Existing Concrete?

You’ve established that your existing concrete can support a new layer, and now you’re ready to start your pour.

First, however, you’ll need to decide which methods you should use. Should you opt for a bonded or unbonded overlay? Will the concrete need reinforcement, and if it does, which type should you choose? Once you’ve made these decisions, you’ll be ready to begin.

Bonded overlays use an adhesive bonding agent between the old concrete layer and the new to join them together. You can use this type of overlay if your existing concrete is too thin but in good condition otherwise. The new layer will add a minimum thickness of 25 to 50 millimeters and benefit from the base’s strength and stability.

You should only use bonded overlays when the original slab still has structural and functional integrity — that is, when it can still safely support its expected loads and walking, riding or driving on it is still safe and comfortable.

If your current concrete’s condition is stable but unsuitable for a bonded overlay, you can use an unbonded overlay instead. As it does in a bonded overlay, the base slab serves as a stabilizing subbase. However, this technique also uses an interlay layer — typically geotextiles or bituminous materials — to keep the old and new cement slabs from bonding.

While the existing concrete provides stability for an unbonded overlay, the overlay doesn’t use the base’s strength. To compensate, unbonded overlays must be at least 100 millimeters thick. You may also want to use additional reinforcement methods with this technique.

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Reinforcement Methods

Additional reinforcement materials can provide extra strength to your concrete, increasing the weight it can bear and helping to prevent cracks. Consider using one of these options:

• Rebar: Short for “reinforcing bar,” rebar is a type of ridged metal rod placed before pouring and tied or welded into a supporting grid.
• Wire mesh: The wire in this pre-formed grid is a smaller gauge than rebar, making it much more flexible. You should place wire mesh before you begin pouring.

Guide to Pouring Concrete Over Concrete

When you’ve chosen your technique and any reinforcement methods you’ll be using, follow these steps to properly add a layer to your existing concrete:

1. Fix any cracks and pits: If you’re using a bonded overlay technique, you’ll need to start with as solid a surface as possible. You can fix spalling — a patchy and pitted surface — with a concrete resurfacer and patch small pits and cracks with a concrete repair mix. While a resurfacer contains bonding agents that allow it to bond to the concrete, you’ll need to apply a scratch coat or liquid bonding agent before using a repair mix.
2. Measure the area and prepare your frame: Dig a trench for your frame around each side of the existing concrete. Ensure you take accurate measurements of both the surface area you’ll be covering and the final height the concrete will reach after your new pour. If you’re using an unbonded overlay technique, the height will also include the interlay layer. Once you have your measurements, assemble a wooden frame to fit.
3. Clean and prepare the surface: If there are any stains on the current concrete, you can use a detergent or degreaser to remove them or chip away the area with a hammer and chisel. Use a stiff-bristle brush to remove any loose material and follow with a power washer to clear off any remaining dirt or chemicals.
4. Install your frame: Fit your frame into place, checking to be sure it’s level on all sides.
5. Apply the bonding adhesive or interlay layer: Spray the existing concrete with water to dampen the surface. For a bonded overlay, apply a bonding agent. For an unbonded overlay, add your interlay layer so the top surface is level.
6. Pour the concrete and apply the curing compound: Pour your concrete. After you’ve leveled and smoothed the concrete, apply a thin, even layer of curing compound.

Dynamic Concrete Pumping has over 40 years of combined experience in commercial and industrial concrete construction. We’re industry leaders in superflat floor technology, so you can trust us to provide high-quality, award-winning concrete flooring.

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