Concrete overlay is done over existing concrete floors for repair and decorative reasons. It could be colored or cementitious based. A well-designed and constructed concrete overlay floor provides excellent performance, in many cases extending the life of the floor surface for years. Depending on the manufacturer, the overlay products vary in the mixture and proprietary blends. There are different blends of portland cement, different aggregates and polymer resins with polymer-modified additives in each product. Concrete overlays can be applied as thin as a feather finish depending on the desired finish.
All concrete overlay types fall into two divisions- the bonded and the unbonded. Bonded overlays become part of the underlying existing floor slab. They are placed on top of the existing concrete pavement and ensure a full bond between new and old concrete layers. They are 2 to 5 inches thick and are usually applied to strengthen an existing pavement or for preventive maintenance. Bonded overlays cannot be used if the existing floor is in poor condition. An unbonded concrete overlay consists of a concrete layer that is placed on the top of existing floor slab with an interlayer to separate new overlay and existing concrete. These generally are 4 to 11 inches thick.
Advantages of concrete overlay of floors
A concrete overlay can fix underlying problems, or add creativity to an otherwise bland-looking appearance, it offers many advantages;
- Correct surface deficiencies
- Improve skid resistance
- Improve surface drainage
- Improve structural capacity
- Enhance appearance
- Reduce surface roughness
- Comes in several different colors and textures
Factors to consider for concrete overlay of floor
The surface on which the overlay is applied must be leveled and cleaned so cracked or surfacing up can be avoided. One must look for overlay blends that are strong and made out of high-quality ingredients such as polymer resins, a mix of cement and sand, and other additives. Here are a few factors that should be kept in mind before the execution of concrete overlay.
While deciding on the concrete overlay, it is important to analyse what type of conditions your flooring will face. For example, if it is for floors that are exposed to heavy foot traffic and extreme conditions you will need durable overlays that are built to withstand wear and tear. The overlay will vary according to flooring conditions.
Floor surface evaluation
A common method for floor surface evaluation is deflection testing, particularly with the falling weight deflectometer. Curing is recommended for all overlay projects. In addition to the surface evaluation of the existing floor slab, the degree of support beneath the floor surface layers should also be evaluated.
Estimate of traffic
The quantification of traffic over the design life of the floor is required for all thickness design procedures. The average annual daily traffic and the percentage of trucks are the minimum traffic parameters required for floor pavement design.
Concrete strength is a key design input, particularly flexural strength. The experts should verify that the design strength is achievable with the available materials. The modulus of elasticity of the concrete is another material property input for most designs of overlay. Another material property that is mainly used in mechanistic-based design procedures is the coefficient of thermal expansion (CTE).
You should look for a concrete overlay that is stain-resistant and water-resistant.
Different types of concrete overlay for floors
Each concrete floor overlay type offers different decorative options and performance attributes, which are described below.
Self-Leveling Concrete Overlay
A self-leveling overlay can be applied over most concrete floors and are thick enough to help correct uneven surfaces and relatively surface damage of old and worn out surfaces. It can be colored with tints during the initial mixing, or colored can be applied after it is applied and cured using dyes. One of the most important characteristics of self-leveling concrete is that it can provide a very dense and durable concrete floor. Most self-levelers can go down 1/4 inch to 1 inch, with the ability to be feathered into the existing floor to make a very gradual transition. Self-leveling overlays are especially useful when substrate conditions are old or worn concrete surfaces or unlevel floors, and concrete surfaces that are damaged by other floor treatments. Typical applications include commercial building lobbies and corridors, retail spaces, residential floors, restaurants, and warehouse floors.
Micro-Topping Concrete Overlay
Micro toppings paper-thin polymer-based products that work on vertical as well as horizontal floor surfaces. They are applied in one or more layers with a trowel or squeegee. The total thickness achieved with this type of overlay is 1/8 inch. Micro Toppings are strong and can reach upto 3000 psi.. Before the micro-topping is applied you will need to verify that your surface is clean and free of debris. It is important to remove residues of chemicals, concrete traces, or any other chemical reaction that are showing up on the surface.
Spray-down Concrete Overlay
Spray-down overlays offer many different kinds of finishes. Using an air-powered hopper gun, these are evenly sprayed onto the surface of the concrete. A splatter coat can be created for a textured, slip-resistant, surface or for a smoother surface. A trowel can be used for a final look. A very popular technique for sprayed-on concrete overlays is to use paper or stick-on stencil patterns. Spray-down overlay comes in textured form that is durable, non-skid, and great for pool decks, walkways, patios, and driveways.
Stamped Concrete Overlay
Stamped concrete overlay is widely used for exterior surfaces but has recently become popular for interior floors as well. Stamped concrete provides a low-cost, durable solution, offering an ample range of colors and patterns from which to choose. Stamped overlay comes as a thin layer, typically 1/4 to 5/8 inch, of concrete that is applied to an existing floor slab, then is textured with a stamping tool to create the appearance of natural stone, tile, or brick. The concrete can be tinted or dyed. For the final finish a coat of concrete sealer is applied after the pattern has been created.
The application method of concrete overlay
- Before the overlay can be applied, the surface of the slab must be properly cleaned, patched, and primer applied
- Cleaning involves removing any anti-adherents and then pressure washing to eliminate loose debris creating a clean palette for applying bonding primer.
- Expansion joints should be thoroughly cleaned and free of all debris before overlaying
- Lay a piece of string in the expansion joint and apply the overlay
- Pour on the proper depth and smoothen properly to eliminate any random show-through or weak pockets
- Texture the surface of the overlay by hand brush or trowel as per requirement
- Leave it for overnight curing or some time lesser depending on the overlay type chosen
- Fill with a concrete filler and allow it to dry according to the manufacturer’s instructions
Given above is a brief overview of concrete overlay application, there can be few changes in the application method depending upon the overlay type selected and materials used.
A concrete overlay can improve aesthetics, reduce surface roughness, and provide a variety of creative alterations for your floors. It’s really important to hire professional contractors with experience in installing concrete overlays.