The Definitive Guide To Concrete Overlays

If you’re planning a decorative concrete or stained concrete project, it’s important to understand what needs to be done to make your concrete slab perfect. Rather than demolishing and replacing your entire concrete floor, a cementitious overlay can be applied on top of the concrete so that it’s level. Cementitious overlays can then be polished or you can apply epoxy over them to create the surface that fits your needs.

What is a Concrete Overlay?

A concrete overlay is a thin layer of cement-based material, often mixed with polymers and aggregates, applied over existing concrete to restore, protect, and enhance its appearance and functionality. Overlays, like the NXT® LEVEL SP, are designed to provide a durable, attractive, and low-maintenance surface suitable for polishing, coloring, and texturing. They can transform rough, damaged concrete into a smooth, aesthetically pleasing finish. The application process includes surface preparation, priming, and applying the overlay in one or more coats, followed by proper curing and sealing to ensure long-lasting performance and protection against wear and environmental factors.

What Is The Difference Between A Concrete Overlay and Underlayment?

Concrete overlay is primarily used to restore, protect, and enhance existing concrete surfaces, providing both aesthetic and functional improvements, such as polishing, coloring, or texturing to meet design requirements. For example, a decorative concrete overlay can resurface an old patio with cracks, giving it a fresh, attractive finish.

The installation process involves surface preparation, priming, applying the overlay material in one or more coats, and curing and sealing. Overlay thickness depends on the type. In its Guide to Decorative Concrete, the American Concrete Institute describes a microtopping as usually 1/8 to 3/16 in. thick and a bonded polished overlay as 3/8 to 1 in. deep. Overlays often include decorative elements and polymers, like NXT® LEVEL SP.

Conversely, concrete underlayment is used to prepare subfloors for installing various types of flooring, ensuring a level and smooth surface. For instance, a concrete underlayment is applied over a plywood subfloor before installing ceramic tiles in a kitchen to prevent cracking. The process involves cleaning and priming the substrate, mixing and applying the underlayment material in a single lift, and allowing it to cure before the final flooring installation.

Underlayments focus on providing a stable base. While overlays are applied over existing concrete surfaces and serve as a finished surface, underlayments are applied over various substrates, including concrete, tile, and plywood, and are hidden beneath the final flooring.

What Is The Process For Applying A Concrete Overlay And How Long Does It Take?

1. Surface Preparation

Surface preparation is the initial step in applying a concrete overlay, essential for ensuring proper adhesion and durability of the new overlay. This involves cleaning, repairing, and profiling the existing concrete surface. Cleaning removes dirt, debris, and loose material, which can be done using pressure washing or scrubbing with a strong cleaner. Repairing involves filling any cracks, holes, or imperfections on the surface to create a smooth base. Profiling, achieved through mechanical methods like grinding or shot blasting, roughens the surface to enhance the bond between the old concrete and the new overlay.

Example: For instance, if you have a driveway with visible cracks and stains, you would start by pressure washing the entire area to remove any surface contaminants. Next, you would fill the cracks with a suitable concrete repair material, ensuring a level surface. Finally, you would use a grinder to roughen the surface, increasing the overlay’s adhesion.

Timeline: Surface preparation time depends on the condition of the existing concrete and the area size.

2. Priming

Priming is the process of applying a bonding agent to the prepared surface to ensure a strong adhesion between the old concrete and the new overlay. This step is crucial as it enhances the overlay’s durability and prevents delamination. The primer should be applied evenly and allowed to dry according to the manufacturer’s instructions.

Example: After preparing the driveway surface, you would apply a concrete primer using a roller or brush, ensuring it covers the entire area uniformly. Allow the primer to dry completely, as the product specifications direct.

Timeline: Priming time depends on the product used and environmental conditions; follow the product’s data sheet.

3. Mixing the Overlay

Mixing the overlay involves preparing the overlay material, which typically consists of cement, sand, and polymers. The mixture must be consistent and thoroughly blended according to the manufacturer’s guidelines to ensure a smooth application.

Example: If you are resurfacing a patio, you would mix the overlay material in a large container, ensuring all components are blended well to achieve the desired consistency.

Timeline: Mixing time depends on the amount of overlay needed.

4. Application

The application step involves spreading the overlay material onto the primed surface. Many products are applied in two coats: the first coat is applied thinly and evenly to fill minor imperfections, and the second coat is added after the first has set, which can be textured or patterned as desired.

Example: For a garage floor, you would first apply a thin coat of the overlay using a trowel, ensuring it covers the entire surface. When the first coat has set, as the product directs, you would apply a second coat, adding texture or patterns if desired.

Timeline: Application time depends on the area and on the drying time between coats that the product specifies.

5. Curing

Curing is the process of allowing the overlay to set and harden properly, which is crucial for its strength and durability. Many products specify how to cure; follow the product’s data sheet.

Example: After applying the overlay to a sidewalk, you would cure it exactly as the product data sheet directs. Some products call for covering and moist curing, others do not.

Timeline: Curing time depends on the overlay product used; follow its data sheet.

6. Sealing

Sealing is the final step, where a sealant is applied to protect the overlay from stains, moisture, and wear. The sealant should be applied evenly and allowed to dry thoroughly.

Example: For a newly overlaid driveway, you would apply a concrete sealant with a roller, ensuring it covers the surface uniformly. Allow it to dry as per the manufacturer’s recommendations before using the driveway.

Timeline: Sealing adds application and drying time, as the sealer’s data sheet specifies.

Total Timeline For Concrete Overlay

This table shows the entire process of applying a concrete overlay. The total time depends on the surface condition, the area and the specific products used. Proper adherence to each step and allowing adequate drying times is essential for achieving a durable and aesthetically pleasing result.

Where Are Concrete Overlays Typically Applied?

Common areas where concrete overlays are used are:

• Interior floors
• Patios
• Garage floor
• Driveways
• Pool decks
• Countertops

How Much Do Concrete Overlays Cost?

Concrete overlay costs vary depending on the condition of your existing slab, and how much work you want to be done in terms of color and decoration, and the thickness of the cement that needs to be applied. Typically, applying a self-leveling cement can increase costs by almost 2x for a project, however, replacing the entire floor means demolition and a new pour, so it is worth comparing the two.

How Long Do Concrete Overlays Last?

When properly cared for, a concrete overlay can last for years. Thickness matters, but the right thickness depends on the overlay type and the product, so follow the manufacturer’s data sheet. An overlay applied thinner than its product calls for will not be as strong and is more likely to crack and break.

If you’re tempted to save money and attempt a DIY concrete overlay project, it’s best left to professional contractors who are experienced. Overlays are unforgiving of shortcuts. Concrete Decor notes that overlays can be temperamental if they are not installed properly and the manufacturers’ technical data sheets are not followed to the letter, and that an overlay is only as good as the concrete under it and the applicator who puts it in. Poor preparation or application shows up as an overlay that chips, flakes, or cracks. An experienced contractor costs more upfront, but preparation and application are in practiced hands.

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