Dare Concrete - Outer Banks, North Carolina
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Decorative Concrete & Resurfacing Options

Concrete Décor

Stamped Concrete

Overlay Systems:
-Thin-Crete

-Spray Deck

Coloring Systems:
-Integral Colored Concrete

-Acid-Staining
-Color Hardener

Sealing Concrete

Stenciling Patterns Into Concrete:
-Sandblasting Method
-Stenciling On Fresh Poured Concrete

Brushed Finishes

Architectural Walls - Stone-Crete

Surface Preparation

Maintaining Decorative Concrete

 

SURFACE PREPARATION

Knowing what you're working with - both internally and externally is a key to successfully preparing a concrete surface for accepting cementitious toppings. A slab may look clean and sound, but that doesn't necessarily mean it is. Your system will only be as good as the surface underneath. Below are a few steps to ensure proper surface preparation.

1) Start with a walk - Depending on its condition, every concrete surface requires some preparation to create a proper texture, or profile, for applying coatings. A visual evaluation is the first step. Walking the floor to carefully note differences in surface cleanliness, grade and condition is a must. Look for any existing sealers, grease, oil, effervescence, curing materials and dirt that need to be removed. Excessive laitance or a weak layer of cement on the surface must be removed down to solid concrete. Coatings and overlays will simply not bond properly to weak concrete. A few tests can help gauge the slab's structural integrity. Take a screwdriver or nail, and pry up test areas of the surface that appear loose or soft. Strike a ball peen hammer against the concrete surface to indicate hardness. Hollow spots can be determined by sweeping a surface with a metal chain or golf club and listening for pitch changes.

2) Evaluating moisture and vapor transmission - Moisture is a huge problem when it comes to surface preparation. Moisture can basically do three things to concrete: it can hurt the concrete itself when the alkalinity reacts with the aggregate; it can destroy certain polymers; and it can expand to remove toppings from the surface. Excessive vapor transmission occurs when a water source under the slab is combined with concrete that is usually permeable. That source could be a high water table, broken water pipe, landscape sprinkler or rain. Overly permeable concrete usually results from a water-cement ratio that is too high. The excess water leaves the slab, during the curing process and creates capillaries that serve as a pathway for water vapor to be drawn up through the slab. The most cost-effective method of determining if moisture vapor is passing through the slab is the calcium chloride test. To solve this problem, applying a waterproof product that penetrates the concrete to form a permanent gel-like barrier, which can never be worn away. In one application, the product holds the hydrates in, thus waterproofing the concrete internally as well as externally.

3) Repairing the cracks - All concrete surfaces crack. It is important to repair cracks because, if left, they will spread and cause concrete to become unstable. Coatings, too, will fracture along joints or cracks that are not properly addressed. The key in making repairs is to determine the kind of crack you're dealing with. A cosmetic crack, which does not go all the way through the slab, will be addressed differently than a structural one. Cosmetic cracks are the easiest to handle - cut the crack and seal it with a hard filler material. Structural cracks are more difficult. Most often, you should square cut the crack, and then apply a flexible epoxy resin or sealer. Most cracks that occur in the slab are not moving cracks, but some do move or vary in size because of seasonal differences in temperature, moisture levels, stress loads and other factors. You should design your system to honor the cracks, to allow the floor to move.

4) Cleaning the surface - Once you've got a handle on the slab's character and condition, and have repaired and solved any problems, the next step is to clean and condition it thoroughly. To ensure a bond between the topping and the concrete, the slab must be absolutely free of dust, dirt, oil, grease, paint, curing components, coatings and all other contaminants. To determine if the surface is clean use the water drop test by applying a small amount of water onto the floor. If the water doesn't penetrate into the pores, neither will a coating. Cleaning a slab may be as simple as scrubbing the surface with an aggressive nylogrit brush and then applying commercial cleaners. The surface can then be rinsed with a pressure washer and allowed to dry. Pressure wash works well for chemicals and oils. Degreasers worked in with a floor scrubber/polishing machine can adequately remove dirt and grime. Detergents and cleaners can also be effective as long as the grease and contaminants are water soluble or emulsifiable by the detergent or cleaner. They work best for removing superficial grease, although more than one treatment is often necessary. High levels of contaminants may require grinding.

5) Knowing what you're removing - Removing previous coatings and flooring products depends on the type and nature of the material to be removed. For thin sealers, concrete grinders or brush blasting with a shot blaster are appropriate. For epoxy, mastic and thick coatings, concrete grinders with aggressive cup wheels or scarifiers can be used. Machines with carbide-tipped slicers can quickly remove thick coatings. Hand-held or ride-on floors scarpers can effectively remove such materials as carpet, parquet flooring and other thick materials. If the surface is delaminated, shot blasting, scarifying or other chipping methods must be used. Shot blasting works well as long as the material is not rubbery. Muriatic acid can be used to clean and profile concrete surfaces. Through advances in technology muriatic acid is also offered in a gel. This gel keeps the acid on top of the slab where the profiling is obviously needed.

6) Creating a surface profile - Creating a profile is an essential ingredient in the job's eventual outcome. It's one of the keys to getting cementitious topping to bond. Profiling the surface mechanically includes grinding, sandblasting, shot blasting and using other tools. Chemical profiling includes acid washing, chlorine washing and other chemical methods to remove surface imperfections. The preferred method for large or difficult surfaces is mechanically profiling. Shot blasting is one of the most popular and cost-effective methods of creating a profile, and it is most suitable for 1/8-inch or thicker toppings. Scarifying can resurface horizontal surfaces and smooth faulted joints, and cut deep into the concrete to create non-slip surfaces. Grinding creates less of a profile but it's often used for edges.

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