Options for Repairing Concrete Floors and Subfloors

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Concrete floors and subfloors can be repaired using one of three common methods. All of these involve covering the existing concrete slab with a new coating of concrete or a concrete-like topping and finishing the new layer as desired. These methods can be used on interior and exterior surfaces and are intended for surface restoration only; they are not suitable for repairing significant cracks or other structural problems in existing concrete slabs.

When to Repair Concrete Floors

Concrete floors should be repaired with a surface topping only when the concrete slab contains surface, or hairline, cracks or has cosmetic surface flaws. If the concrete floor to be repaired is heaving, has large or wide cracks, or is damaged due to freeze damage, then other alternatives should be considered instead of resurfacing.

Micro-Toppings

Micro-topping treatments are made with very thin layers, no thicker than 1/8 inch, of polymer-modified concrete containing sand and are applied with trowels or brushes, depending on the final look desired. Because micro-toppings are so thin they are not self-leveling. They also dry very quickly, so the final texture is limited to how the micro-topping is applied over the concrete floor. The treated surface can cure in a day, and usually can be walked on within 36 to 42 hours of being applied.

It is important to seal micro-topping finishes, as they are porous and tend to collect dirt that is difficult to remove once embedded in the material. Micro-topping treatments may include two or more base coats and, in some cases, a very thin top coat without sand, if a very smooth finish is desired.

Stamped Concrete

Stamped concrete surface treatments have been widely used for exterior surfaces but have 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 concrete starts as a thin layer, typically 1/4 to 5/8 inch, of concrete that is applied to an existing 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, as with new concrete installations.

A stamped concrete treatment is similar to a micro-topping but contains more sand and provides a rougher concrete surface finish. A coat of concrete sealer is applied after the pattern has been created.

Self-Leveling Underlayment and Topping

Self-leveling treatments can be applied over most concrete floors and are thick enough to help correct uneven surfaces and relatively deep surface damage. Like other repair treatments, self-leveling concrete can be colored with tints during the initial mixing, or the treatment can be colored 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 concrete can be divided into two main groups: underlayments and toppings. Underlayments are installed over an existing concrete subfloor to smooth it out and correct any surface irregularities prior to the installation of other floorcoverings, while toppings act as the actually finished floor without the need for an additional floorcovering.