By: Scott Thome
How can a contractor make a seamless transition from an existing concrete floor or patio to a freshly poured addition? How can superficial construction errors on a new concrete surface be renovated? How can old concrete that is stained or chipped be rehabilitated so it looks like new? By applying a colored, cementitious topping over new or existing concrete. As long as the underlying concrete is structurally sound, it can be given a fresh new appearance without sacrificing durability and abrasion-resistance by resurfacing with a polymer-modified topping. Toppings can update the appearance and improve the performance of outdoor and indoor surfaces without the expense, disruption and delays of removing the existing slab and starting over.
There are various types of cementitious toppings. It is important to understand how they differ to select the correct product for the project at hand.
Self-leveling overlays are specifically designed to level and resurface interior floors. They provide a hard surface similar to a flat-troweled concrete floor. Because they can be applied in thin coats they are ideal for refurbishing floors in homes with existing thresholds and fixtures. They can be integrally colored or serve as a base for decorative acid staining.
Other topping materials have been developed for both indoor and outdoor use. These offer excellent moisture and freeze-thaw resistance. They are available in different grades suitable for stenciling, imprinting and broom finishing, giving designers, contractors and owners more texturing options. Because of their versatility these toppings can be used in projects ranging from resurfacing a driveway to expanding a patio or pool deck.
Several steps go into making a resurfacing project a success. First, evaluate the slab and determine that it is structurally sound and suitable to accept a topping. Second, prepare a project mock-up and obtain the customer's approval so there is documented agreement on the color, texture and finish. Next, survey the job site to see what surface preparation is necessary, what obstacles might exist and how much material will be required. (Order 10 percent extra to account for spills and waste, and don't forget to order sealer and finishes so everything is there when needed.)
Surface preparation and cleaning are critical. The majority of failures are due to improper surface preparation. Concrete must be at least 28 days old. The surface must be open and rough for a topping to adhere, so some grinding or sandblasting might be required. A heavy broomed finish is a good surface on which to install a cementitious topping. In addition, the surface must be clean. It should be free from oils or finishes, curing membranes, dirt, dust, grease or any other contaminants. Fill all spalls with patching material and pressure wash the surface with water only.
For overlay surfaces that will be textured, a base coat of the topping needs to be applied first. All working joints in the original slab need to be reflected through the topping. They can be formed in the topping or saw cut after the base material has set. They should be the full depth of the topping, at least as wide as the old joints, and placed precisely over the existing joints.
For a stenciled surface, apply water-resistant paper stencils to the base coat. Tape each stencil so that it overlaps the edge of the preceding stencil. Start pattern placement at form lines, which are straight, instead of at walls, which may not be. Also, mask off areas such as borders that will be finished later in a different color or pattern. Divide the work area into sections that can be easily completed in the desired time period. Walls, joint lines or other features define natural stopping points where work can be resumed later without affecting the finished appearance.
Apply the next layer of the cementitious topping with a hopper gun modified so it sprays down onto the floor. Material flow and air pressure should be tested on a piece of cardboard before spraying the topping on the concrete. A crew of three is required. One operates the hopper gun, another uses a trowel to knock down the high points of the topping and the third mixes the material to keep the hopper supplied. Care should be taken to avoid stepping on and tearing the stencil. A more natural, varied look can be achieved by hand-brushing color onto specific areas of the stenciled surface, replicating the look of brick or stone. Different color effects are achieved by spraying toppings in multiple colors.
When the topping has dried to the point where it cracks when the edge of the stencil is lifted gently, it is time to remove the stencil. The surface needs to be plastic enough to release the stencil, but hard enough to support the person removing it. After the stencil is removed, brush off excess material and detail the grout lines by hand. Extra material can be removed from joints with a toothbrush or small scraper. This attention to detail pays off by making a project look cleaner and more realistic.
Cementitious overlays can also be imprinted to replicate the appearance of stone, wood or other textures using techniques reviewed in last month's column. A multi-component, stamp-grade topping must be used. Depth can be added to the pattern by using imprinting tools and embossing skins with antiquing release agents that provide realistic, subtle variations.
After the topping has been applied, colored and textured, it is not completed until it is sealed. The right sealer protects the surface from automotive oil, grease and food stains with a low-maintenance protective film that resists abrasion and freeze-thaw cycles. A sealer can enhance the surface color and improve its durability. Water-based sealers will have minimal effect on color. Solvent-based sealers will make the color appear darker at first, but will lighten as they cure. Sealers are available in matte, semi-gloss or gloss finishes.
Cementitious toppings should be sealed once they are sufficiently cured. The surface must be cleaned of dirt and debris before the sealer is applied. Excess antiquing release agents must be removed from imprinted surfaces before sealing. The topping must be dry in order to avoid creating a white haze.
To prepare for sealing, adjoining areas should be masked. Sealer can be spray-applied over plain or stenciled overlays. For toppings that have been imprinted, the sealer should be sprayed, then rolled with a lint-free paint roller. This will keep the sealer from collecting in the depressions created by the imprinting tool.
Sealer should be sprayed starting at the house or a wall and moving outwards. A brush or small hand roller can be used to apply the sealer right next to house or wall so no areas will be missed. Two coats should be applied. The second coat can normally be applied within an hour or two of the first one. To make the application even, the second coat should be applied at a 90-degree angle to the first.
The sealed cementitious topping can be maintained easily by sweeping regularly and cleaning off spills when they occur. It can even be scrubbed with a stiff-bristle brush and detergent. Sealer should be reapplied every year to areas such as driveways that are subject to harsh abrasion or high traffic. Patios and similar areas should be resealed every four or five years. This will restore the color of the topping.
As with all decorative concrete techniques, training and experience are critical to ultimate success. Take time to learn resurfacing and stenciling techniques. Take advantage of manufacturers' training programs to gain hands-on experience and experiment in a risk-free environment with different textures and colors. Done carefully and correctly, resurfacing with cementitious toppings is an excellent option for upgrading concrete surfaces and adding additional revenue to your business.
For more information call 800-800-9900 or see www.scofield.com.
Scott Thome is director of training and product services for L. M. Scofield Company, and is based in the Douglasville, Ga. headquarters outside Atlanta. In addition to supervising product testing, his responsibilities include developing curricula for the Scofield Institute and monitoring training standards. He has been involved with the International Cement Mason's Apprenticeship Training programs. His professional affiliations include the ASCC/DCC, ICRI and others. Thome worked with Sika Corp. for 12 years before joining Scofield. He has management and sales experience, and holds a masters' degree in industrial management from the University of Wisconsin.