Glossary of Terms for Concrete Construction

A

Abrams’ Law-The rule of concrete stating that with given materials, curing, and testing conditions, concrete strength is inversely related to the ratio of water to cement. Low water-to-cement ratios produce higher concrete strengths

Accelerator – Chemical substance added to a concrete mix that reduces the set time by increasing the rate of hydration.

Aggregate – a mixture of sand, rock, crushed stone, expanded materials, or particles, both enhances the structural performance of concrete and improves cement paste’s formation and flow. Aggregate usually constitutes about 75% of concrete volume.

Air-entraining- Air-entrained concrete contains minute air bubbles that are distributed uniformly throughout the cement paste. Entrained air can be produced in concrete by use of an air-entraining cement, by introduction of air-entraining admixture, or by a combination of both methods. Air-entraining admixtures are used to stabilize microscopic air bubbles in concrete. Proper air-entrainment, with appropriate volume and spacing factor, will dramatically improve the durability of concrete exposed to moisture during cycles of freezing and thawing. Entrained air also improves concrete’s resistance to surface scaling causes by chemicals deicers.

Acid etching- Application of muriatic or phosphoric acid to clean or profile a concrete surface. Used as an alternative to abrasive blasting for surface preparation.

Acid stain – (or chemical stain) A stain containing inorganic salts dissolved in an acidic, water-based solution that reacts chemically with the minerals in hardened concrete to produce permanent, transparent color that will not peel or flake. Gives concrete an attractive variegated or marbleized appearance. Colors tend to be earth tones, such as tans, browns, reddish browns, and greens.

Acrylic Sealer- An acrylic solvent or water-based sealer that forms a protective film on the surface of the concrete that imparts a sheen that highlights the beauty of regular and decorative concrete.

Admixture – An ingredient in concrete other than water, portland cement, and aggregate used to modify the properties of concrete in its freshly mixed, setting, or hardened states. May be added to concrete at the batch plant or on the job site. Prepackaged admixtures are available for convenient job site addition, giving contractors the ability to modify the concrete they receive when necessary, such as extending the amount of time available for decorative stamping.

Air content- The amount of entrained or entrapped air in concrete, usually expressed as a percentage of total volume.

ASR (Alkali -Silica Reactivity) – Alkali-silica reactivity is the process in which certain minerals (mostly glass type silica) in the presence of moisture are broken down by the highly alkaline environment of concrete producing a gel that expands creating tensile forces in the concrete matrix which cause cracking of the concrete. The cracking then allows more water to infiltrate into the concrete creating more gel, more expansion etc. Ultimately the concrete fails or disintegrates.

Antiquing- A color layering technique for giving decorative concrete surfaces an aged or mottled appearance.

American Concrete Institute (ACI) – An international organization providing education, certification, and information about concrete.

American National Standards Institute (ANSI) – The United States representative in the International Organization for Standardization (ISO).

American Standard of Testing Materials (ASTM) – An organization that serves as a standardized testing center to evaluate the performance of a variety of building materials.

Apron – A slab of concrete, often at an entrance for vehicles, that extends beyond a building’s entrance.

B

Bleed water (bleeding) – Water that rises to the surface of freshly placed concrete due to segregation. Bleeding may interfere with finishing operations. If a dry-shake color hardener is being applied to the concrete surface, some bleed water is needed to wet out the hardener sufficiently so it can be floated into the surface.

Blistering – The formation of blisters in toppings or coatings and the loss of adhesion with the underlying substrate. On concrete surfaces, this is often caused by moisture or moisture vapor transmission problems.

Bond – The degree of adhesion or grip of a material (such as coatings, toppings, repair mortars, or sealers) to an existing surface.

Bonding agent – An adhesive agent used to increase the adherence of coatings or toppings to the existing surface. Also used to bond new concrete to old. Also known as a primer.

Bond breaker – A material that prevents adhesion of materials to a concrete substrate.

Broadcast – To hand toss a dry-shake color hardener, decorative aggregate, or other dry material in a uniform layer over fresh concrete, overlays, or coatings to add color or traction. (Also see seeding.)

Broom finish – Surface texture obtained by pushing a broom over freshly placed concrete.

Bull float – A tool comprising a large flat rectangular blade made of wood, resin, aluminum, or magnesium. Used to eliminate high and low spots in freshly placed concrete slabs, embed large aggregate at the surface, bring a layer of paste to the surface needed during final finishing, and float in dry-shake color hardener. Long handles either clip on or screw into the float head so it can be pushed out onto the slab while the user stands at the perimeter.

C

Calcium chloride – An accelerating admixture to reduce the set time of concrete in cooler, damp weather conditions by increasing the rate of hydration. Calcium chloride can cause a mottling or dappling of the surface color and corrode steel reinforcement in a concrete slab.

Cast in place – Concrete placed and finished in its final location.

Cement – Cement is not the same as concrete, but rather one component of concrete. Cement, a combination of finely ground materials, hardens when mixed with water to become the “glue” in concrete.

Cementitious – A material containing portland cement as one of its components or having cement-like properties.

Chairs (supports) – rebar support chairs allow the reinforcement bars to be supported at a sustained level throughout a concrete slab.

Chalking – Loose, powdery substance caused by deterioration of a concrete surface or degradation of a coating or overlay.

Compressive strength – The maximum compressive stress concrete or cementitious overlay materials are capable of sustaining, expressed as pounds per square inch (psi).

Concrete – Concrete is not the same as cement. Concrete is a combination of cement as a binding agent, chemical additives, water and mineral. This combination, when properly mixed and placed, hardens into an excellent building material for a wide variety of uses.

Concrete countertops – A handcrafted alternative to manufactured countertop surfaces. Can be precast in a shop in molds built to the customers specifications or cast onsite, by setting a mold on top of the base kitchen cabinets and then filling with concrete. The use of stains, pigments, decorative aggregates, and epoxy coatings can give concrete countertops the look, texture, and feel of quarried stone such as marble, granite, and limestone.

Consistency – The ability of fresh concrete to flow. The usual measure of consistency is slump.

Control (or contraction) joint – Sawed or tooled groove in a concrete slab used to regulate the location of cracking.

Construction Joint – are surfaces where two successive placements of concrete meet. They are typically placed at the end of a day’s work, but may be required when concrete placement is stopped for longer than the initial setting time of concrete. In slabs they may be designed to permit movement and/or transfer load.

Crack chasing –Routing out cracks in concrete with a saw or angle grinder before filling with a repair material.

Cracks, moving – Cracks in concrete that are still moving, or active. Often they are structural in nature and continue through the entire depth of the concrete.

Cracks, static – Random, non-moving hairline cracks that only affect the concrete surface (also see craze cracks and plastic shrinkage cracks).

Crazing – A series of fine, random cracks caused by shrinkage of the surface mortar.

Crusting – A condition that occurs when the surface of freshly placed concrete dries too quickly, often due to exposure to direct sun, wind, or high temperatures or with stamped concrete.

Cubic Yard – Unit of measure for ready mix concrete. Concrete is ordered, sold, and batched by volume.

Curing – Action taken to maintain favorable moisture and temperature conditions of freshly placed concrete or cementitious materials during a defined period of time following placement. Helps to ensure adequate hydration and proper hardening.

Curing compound – A liquid that, when applied to the surface of newly placed concrete, forms a membrane on the concrete or penetrates the concrete to retard the evaporation of water.

D

Darby – A longer version of a hand float, ranging in length from 2 to 4 feet. Useful for leveling problem areas.

Decorative aggregate – Richly colored natural stones, such as basalts, granite, quartz, or limestone, used to enhance exposed-aggregate concrete or decorative toppings.

Decorative concrete – Concrete that has been enhanced by color, pattern, texture, or a combination of ornamental treatments.

Degreaser – A chemical solution for removing grease, oils, and other contaminants from concrete surfaces.

Delamination – A separation of a coating or topping from a substrate or the layers of a coating from each other due to poor adhesion. Or in the case of a concrete slab, a horizontal splitting or separation of the upper surface.

Densifier – A penetrating liquid chemical hardener applied to concrete to help solidify and densify the surface and provide extra protection from water penetration and staining. Often recommended for polished concrete, because hard concrete produces a better polish.

Dry-shake color hardener – A mixture of coloring pigments, cement, aggregates, and surface conditioning agents. Applied as a dry shake to stamped concrete or stamped overlays to produce a colorful, wear-resistant surface.

Drying shrinkage – A decrease in the volume of concrete as it dries, due to loss of moisture. See also plastic shrinkage cracks

Dyes – Translucent color solutions containing very fine pigments that penetrate into the concrete surface. Will not chemically react with concrete (like acid stains will). Both water-and solvent-based dyes are available, with colors ranging from soft pastels to bolder hue

E

Edger – A tool used on the edges of fresh concrete to provide a clean, finished edge.

Engraving – The use of special tools and equipment to cut or route out patterns and designs in hardened concrete. Usually the concrete is stained first to give it color, so the routed areas look like grout lines.

Efflorescence – A crystalline deposit of salts (usually white in color) that forms on the concrete surface when soluble calcium hydroxides leach from the concrete and combine with carbon dioxide in the atmosphere. On colored concrete, especially darker tones, these white deposits can be particularly unsightly.

Epoxy injection – A method for sealing or repairing cracks in concrete by low-pressure injection of an epoxy adhesive.

Epoxy resins – Organic chemical bonding systems used in the preparation of protective and decorative coatings for concrete, adhesives for injection of cracked concrete, or as binders in epoxy mortars.

Evaporation retarder – A waterborne, spray-applied film that temporarily reduces moisture loss when applied to the surface of freshly placed concrete.

Exposed aggregate – A decorative surface formed by removing the surface mortar from a concrete slab (either by scrubbing, pressure washing, or abrasive blasting) to expose the underlying aggregates. (Also see surface retarder.)

F

Feather edge – To smoothly, seamlessly blend the edge of a topping or repair material into the existing concrete.

Fibers – Tiny filaments made of polypropylene, polyolefin, nylon, polyethylene, polyester, or acrylic used alone or in conjunction with rebar or welded wire mesh to reinforce concrete.

Finishing – Leveling, smoothing, compacting, and otherwise treating the surface of newly placed concrete or concrete overlays to produce the desired appearance and service properties.

Film-forming sealer – A type of sealer that blocks the penetration of water and contaminants by forming a barrier on the concrete surface. May also impart a gloss or sheen, which enhances colored or exposed aggregate concrete. See also membrane.

Flashing (or flash broadcasting) –A technique for applying accent colors of dry-shake hardenerto concrete surfaces before stamping. Results in subtle, natural-looking color variations.

Flexural strength – The ability of hardened concrete or an overlay to resist failure in bending.

Float finish – Surface texture (usually rough) obtained by finishing with a bull float or hand float.

Floor polisher – A walk-behind machine used in the production of polished concrete. Most machines are equipped with a planetary drive system, a large primary polishing head (from 17 to 36 inches in diameter) fitted with three or four smaller satellite heads that hold the diamond abrasives. When the machine is operating, the satellite heads rotate in the opposite direction of the primary head to eliminate linear grinding marks in the floor. (Also see diamond grinding, dry polishing, wet polishing).

Fly ash – A supplementary cementitious material (SCM) Fly ash is a byproduct resulting from the combustion of ground or powdered coal; sometimes used as a cement replacement in concrete.

Form liner – Material used to line the interior face of formwork in order to impart a smooth or patterned architectural finish.

Fresno – A large trowel (about 2 to 4 feet in length) used for final finishing after bull floating. Long handles (like those used for bull floats) either clip on or screw into the blade. NOTE: Fresnos should never be used on air-entrained exterior concrete as it seals over the top of the slab trapping bleed water below the surface.

Finishing – The treatment (compacting, leveling, smoothing, etc.) of recently placed or fresh concrete to ensure the planned-for surface.

Flatwork – Mostly flat-surfaced concrete work, including sidewalks, driveways, basements and concrete floors.

G

Gauge rake – A tool with an adjustable depth gauge designed for application of high-build coatings or cementitious toppings at a preset, uniform thickness.

Gravel Mix – A concrete mix that utilizes either pea gravel or larger smooth gravel as its coarse aggregate. This mix is typical for exposed aggregate finishes.

Grade – A building site’s (or building’s) existing or proposed ground level or elevation. Also used in categorizing building or construction levels, e.g. above grade, on grade, or below grade.

Granulated blast furnace slag – A supplementary cementitious material (SCM) formed when molten blast furnace slag is rapidly chilled. Ground granulated slags are sometimes used in concrete mixtures as a cement replacement to help reduce permeability and improve durability. May also slow setting and extend the working time of the concrete. Mitigates the potential for Alkali-Silica Reaction.

Grinding – A mechanical surface preparation method using rotating abrasive stones or discs to remove thin coatings and mastics or slight flaws and protrusions.

Grout – A mixture of cementitious materials and water, with or without aggregate, proportioned to produce a creamy consistency. Can be purchased preblended in a multitude of colors to define joints and sawcuts in decorative concrete slabs or walls, especially those with stone, brick, or tile patterns

Groover – A tool with a V-shaped bit used to create control joints in plastic concrete.

H

Hand float – A smaller handheld version of the bull float, ranging in length from 12 to 18 inches. Especially useful for floating along the perimeter of forms or to work in tight spots.

Hard-troweled finish – Surface finish obtained by using a trowel with a steel blade for final finishing of concrete. Often used where a smooth, hard, flat surface is desired.

High-pressure water blasting – A process for cleaning or roughening concrete surfaces using a stream of water delivered at high pressure.

High-volume low-pressure (HVLP) sprayer – A spraying device that applies high-solids paints and coatings at low pressure and low velocity, to reduce overspray.

Hopper gun – A gravity-fed system for spray application of coatings or toppings. The material is placed in a hopper attached to a spray gun, which is powered by an air compressor. Often used to apply spray-down systems.

Hover Trowel – A patented lightweight power trowel developed specifically for precision finishing of epoxy, polymer modified, and cementitious overlay systems.

Hydration – The chemical reaction between cement and water that causes concrete or other cement-based materials to harden.

I

Integral color – A coloring agent premixed into fresh concrete or cementitious toppings before placement.

Iron oxide – An inorganic pigment often used to color decorative coatings and toppings.

Isolation Joint – Isolation (or expansion) joints separate or isolate slabs from other parts of the structure such as walls, footings, or columns; and driveways and patios from sidewalks, garage slabs, stairs, light-poles and other points of restraint. They permit independent vertical and horizontal movement between adjoining parts of the structure and help minimize cracking when such movements are restrained.

Joint (control, expansion, or isolation) – Formed, sawed, or tooled groove in a concrete slab used to regulate the location of cracking (control joint) or to allow expansion or movement of adjoining structures. In decorative concrete, joints can also double as delineating design elements in a pattern.

Joint filler – A compressible material used to fill a joint to prevent the infiltration of debris.

K

Kerf – A cut in a concrete surface made by a saw or router.

KCMMB Mix – A concrete mix specification designed by the Kansas City Metro Materials Board for longer lasting concrete by creating a mix design requirement of specific materials and hard rock aggregates that can mitigate the effects of salts, deicers, and alkali-silica-reactivity.

Kneeboards – Boards used by concrete finishers to kneel on when hand floating or troweling concrete flatwork.

Knock-down finish – Achieved by applying a decorative topping with a hopper gun and then using a trowel to knock-down the material to produce a smooth or lightly textured surface.

L

Laitance – A thin layer of fine, loosely bonded particles on the surface of fresh concrete, caused by the upward movement of water. Laitance must be removed before application of a decorative coating or topping.

M

Marbleize – To give concrete surfaces the look and gloss of marble, through a combination of color layering and finishing techniques.

Margin trowel – A steel trowel with a small, rectangular flat blade about 5 to 8 inches in length and a short handle. It has multiple uses, including scraping off concrete from finishing tools and applying patching materials.

Masking – Covering select areas of a concrete surface with an adhesive stencil, tape, or other medium before applying a decorative treatment that will affect only the exposed areas.

Material safety data sheet (MSDS) – Information sheets containing pertinent chemical ingredients, product handling and safety guidelines.

Membrane – Formed over a concrete surface to provide protection and enhance color. Typically clear plastic like acrylic, polyurethane or epoxy.

Microtopping – An ultra-thin polymer-based decorative topping, generally less than 1/4-inch total thickness. Typically applied by trowel or squeegee, and given a texture or smooth finish. Pigments can be incorporated into the mix or broadcast onto the surface for a marbleized appearance.

Mil – A measurement equal to 1/1,000 (0.001) inch. Commonly used to denote coating thickness.

Mix design – Specific proportions of ingredients (cement, aggregates, water, and admixtures) used to produce concrete suited for a particular set of job conditions.

Mockup – An architectural concrete sample made using the same materials and methods proposed for an actual project. Often required for quality assurance on large projects, to ensure that architectural requirements and industry tolerances are met. The size should be sufficient to adequately demonstrate all decorative treatments.

Moisture vapor transmission – The migration of moisture vapor to the surface of a concrete slab, caused by vapor pressure differentials in the concrete and the surrounding atmosphere. Can contribute to the failure of impermeable coatings or other floor toppings that do not permit moisture to escape.

N

Neutralize – To return concrete to the proper pH after acid etching, generally by washing the surface with a mixture of water and ammonia or sodium carbonate. Ideal pH is 7.0 (neutral), but a pH range of 6.0-9.0 is acceptable for most coatings. ASTM D 4262, “Standard Test Method for pH of Chemically Cleaned or Etched Concrete Surfaces,” covers the procedure for determining the acidity or alkalinity of concrete surfaces prepared by chemical cleaning or etching prior to coating application.

Notched-squeegee – A rubber squeegee with notches or serrations on one or both edges. Used for smooth and consistent spreading of epoxy resin products or other low-viscosity coatings.

O

Opacity – The ability of a coating to hide the color of the underlying surface. See translucent.

Overlay – A bonded layer of material, ranging from 1/4 to 1 inch or more in thickness, placed on existing concrete surfaces to beautify, level, or restore.

P

Patterned Concrete – See Stamped Concrete

Penetrating sealer – A sealer with the ability to penetrate into the concrete surface to increase water repellency. Penetrating sealers chemically react with the concrete preventing water and salt penetrating down through the concrete.

Permeability – The degree to which a membrane or coating will allow the passage or penetration of a liquid or gas.

Pervious Concrete – Pervious concrete is a special type of concrete with a high porosity used for concrete flatwork applications that allows water from precipitation and other sources to pass through it, thereby reducing the runoff from a site and recharging ground water levels.

PH Test – A test performed on the concrete surface to determine the level of acidity or alkalinity. Typically performed prior to applying sealers or coatings.

Pigment – A finely ground natural or synthetic particle adding color and opacity to a coating or topping.

Placing – The physical introduction of the concrete mixture into the final location where it is to harden and cure.

Plastic – A condition of freshly mixed concrete indicating that it is workable and readily moldable.

Plastic shrinkage cracks – Irregular cracks that occur in the surface of fresh concrete soon after it is placed and while it is still plastic.

Plasticizer – Water reducing admixture that allows an increased slump without increasing the water to cement ratio.

Polar Set – A non-Chloride (non-corrosive) accelerating admixture to decrease the set time of concrete in cooler, damp conditions by increasing the rate of hydration.

Polished concrete – A high-gloss finish attained by using special floor polishers fitted with diamond-impregnated abrasive disks (similar to sandpaper) to grind down surfaces to the desired degree of shine and smoothness. The resulting surface is very low-maintenance and can be stained to replicate the look of polished stone.

Polymer modified overlay – A cement-based overlay with polymer resins added to improve performance, wear resistance, and aesthetic qualities. Overlay manufacturers use different types of polymer resins, often blending them to produce proprietary products with unique characteristics. Many of todays decorative overlays use acrylics or vinyl blends because these resins provide excellent bond strength and UV resistance.

Polymer stain – An acrylic-urethane based stain available in a broader palette of colors than acid stains. Very low in volatile organic compounds, with workability characteristics similar to latex paint. Can be applied to concrete surfaces by brush, roller, sponge, cloth, or commercial sprayer.

Pop-out – A pit or crater in the concrete surface, ranging in size from 1/4 inch to several inches in diameter, that results from the fracturing of unsound aggregate particles due to expansion pressure. Usually caused by porous aggregate having a high rate of absorption.

Portland cement – A hydraulic product that sets and hardens when it chemically interacts with water. Made by burning a mixture of limestone and clay or similar materials.

Pozzolan – A siliceous and aluminous material that, in the presence of moisture, chemically reacts with calcium hydroxide to form compounds possessing cementitious properties.

Primer – The first coat of material applied to a concrete surface to improve bonding or adherence of subsequent coats. See also bond coat.

Pump-up sprayer – An airless sprayer often used to apply sealers and liquid release agents.

Q

Quilting – texture design. See Stamped Concrete

R

Raveling – The dislodging of aggregate at the edges of joints or scored patterns in concrete, generally caused by sawcutting joints too soon after concrete placement.

Ready-mixed concrete – Concrete that is batched or mixed at a central plant before delivery to the job site for placement.

Rebar (or reinforcing bars) – Ribbed steel bars installed in cast-in-place concrete to provide flexural strength. Rebar come in various diameters and strength grades.

Re-entrant corner – An angle in a concrete slab that points inward. Often vulnerable to cracking, unless a control joint is installed.

Reinforced concrete – Concrete construction that has steel rebar or welded wire mesh embedded in it to provide greater tolerance to tension and flexural stress.

Reflection cracking – The occurrence of cracks in overlays and toppings that coincide with the location of existing cracks in the substrate.

Release agent – A powder or liquid parting agent applied to stamping mats or texturing skins before stamping to keep the mats from sticking to fresh overlay or concrete surfaces.

S

Sack – A quantity of Portland Cement. One sack weighs 94 pounds.

Sack Mix – The amount of sacks of cement in a cubic yard of concrete. Specified when ordering, concrete is typically referred to as 5 sack mix (or 5.5 sack, 6 sack, etc.) The sacks on cement needed in a mix are usually specified in either the plans or the specifications of a project. More sacks = more strength.

Salt finish – A textured, decorative finish obtained by broadcasting rock salt onto fresh concrete and then using a roller or float to press the salt particles into the surface. After the concrete sets, the salt is washed away to reveal a speckled pattern of shallow indentations.

Sandblasting – A method of abrading or profiling a surface with a stream of sand ejected from a nozzle at high speed by compressed air.

Sandblast stenciling – A technique for patterning existing concrete surfaces by applying resilient adhesive stencils followed by sandblasting to lightly remove concrete in only the exposed areas.

Saw-cutting – Using a concrete saw with abrasive blades or disks to cut joints or score patterns into hardened concrete.

Scaling – The flaking or breaking away of a hardened concrete surface, often due to exposure to freezing and thawing. Contrast to spalling, the flaking or chipping of concrete.

Screeding – The operation of forming a surface by the use of a screed or strike-off and screed guides.

Sealer – Solvent- or liquid-based material used to protect and enhance the appearance of decorative concrete.

Seeding – Broadcasting decorative aggregates on the surface of freshly placed concrete or toppings.

Segregation – The separation of the components of wet concrete caused by excessive handling or vibration.

Self-leveling overlay – A flowable, polymer-modified cementitious topping with the ability to self level without troweling. Used to smooth and level existing concrete surfaces. Can also be enhanced by staining, dying, or sawcutting.

Set – The condition reached by concrete when plasticity is lost, usually measured in terms of resistance to penetration or deformation. Initial set refers to concrete that has reached first stiffening. Final set occurs when concrete attains full rigidity.

Setting – The chemical reaction that occurs after the addition of water to a cementitious mixture, resulting in a gradual development of rigidity.

Set retarders – a chemical admixture that slows down the set time of concrete. Used in hot conditions to keep concrete mix from setting too quickly for proper strength gain.

Shotblasting – An abrasive blasting method using round iron shot to clean and profile concrete surfaces.

Skid steer loader

Skim coat – An overlay layer applied very thinly with a squeegee or trowel.

Slag – see Granulated blast furnace slag.

Solvent – Liquid typically used as a carrier for sealers and curing compounds.

Spalling – A breaking away of concrete at joints in floors or slabs. Typically occurs at joints that are installed improperly or don’t adequately support the loads applied to them.

Spalling- is caused by water entering concrete and forcing the surface to peel, pop out, or flake off. Concrete spalling is most likely to occur on exterior surfaces that are exposed to freeze and thaw cycles. Causes include: high water cement ratio in the concrete mix, lack of air entrainment, improper finishing, and inadequate curing.

Spray-down system – A decorative overlay applied as a splatter coat or a knock-down finish to a thickness of about 1/8 inch. Often used in conjunction with paper or adhesive stencils. Available pre-colored or can be integrally colored during mixing.

Slump – A measure of consistency of freshly mixed concrete, as determined by the distance the concrete slumps after a molded specimen is removed from an inverted funnel-shaped cone.

Stamped concrete – Concrete flatwork that is patterned with platform tools, stamping mats, or seamless texturing skins to resemble materials such as brick, slate, stone, tile, and wood planking.

Stamped overlay – Similar to conventional stamped concrete, but can be applied to existing concrete. A cementitious topping is applied at a thickness of 1/4 to 3/4 inch and then stamped to mimic brick, slate, and natural stone. Color options include dry-shake color hardeners, colored liquid or powdered release agents, acid stains, dyes, and tinted sealers.

Stamping mats – Rigid or semi-flexible polyurethane tools for imprinting stone, slate, brick, and other patterns in stamped concrete surfaces. Stamping mats usually imprint a shallower pattern than platform tools.

Stenciled concrete – A decorative surface treatment using heavy-duty paper stencils with stone, tile, or brick patterns that are lightly pressed into fresh concrete, followed by the application of dry-shake color hardeners. When the stencils are removed, the uncolored concrete mimics mortar joints. Another technique, for use on existing concrete, is to apply adhesive stencils and then color, etch, or sandblast the surface. (Also see sandblast stenciling.)

Straightedge – A rigid, straight piece of wood or metal used to strike off a concrete surface to proper grade before the floating operation.

Strike off – To level off freshly placed concrete to the correct elevation.

Substrate – An existing concrete surface that receives an overlay, decorative or protective coating, repair procedure, or other resurfacing treatment.

Superplasticizers – High range water reducer that reduces water content by 12 to 13 percent and can be added to concrete with a low-normal slump and water to cement ratio to make a high flowing slump concrete.

Surface retarder – A chemical applied to the surface of newly placed concrete to delay setting of the cement paste so it can be removed easily later by scrubbing or power washing to produce an exposed aggregate finish.

T

Tamper (or pounder) – A handheld impact tool used to firmly press stamping mats or texturing skins into fresh concrete to ensure a complete imprint.

Technical data sheet – Contains important specifications and manufacturer guidelines for product usage. Includes such data as coverage rates, recommended applications, product limitations, surface preparation guidelines, mix ratios and required mixing times, pot life, application procedures, cure times, performance data, and precautions.

Texture roller – A cylindrical tool similar in appearance to a paint roller used to impart a stone-like texture to stenciled concrete. It is rolled over the stencil and the fresh concrete to texture only the exposed surfaces.

Texturing skins – Flexible skins for adding seamless textures to concrete surfaces without leaving deep pattern lines. Generally thinner and more pliable than stamping mats. Often used to texture slab perimeters and vertical faces, such as stair risers. Can also be used to fix blemishes from non-uniform stamping.

Tint – A diluted color wash used to add hints of color to decorative concrete.

Trowel – A flat, broad-bladed steel hand tool used to compact the paste layer at the surface and provide a smooth, flat finish. Also useful for applying topping or repair materials. Available in different shapes (with rounded or square edges) and lengths (ranging from 8 to 24 inches). Smaller trowels are useful for borders, work in restricted areas, or to work in flashing accents of dry-shake color hardener.

Trowel finish – The smooth or lightly textured surface finish obtained by troweling.

V

Vapor barrier – A moisture-impervious material, such as plastic sheeting, placed on the subbase under a concrete slab to help prevent moisture vapor transmission.

Vapor-emission test – An ASTM test used to measure the volume of moisture vapor released from a concrete substrate over time (typically 24 hours). Too much moisture emitted from a slab can affect the performance and bonding of overlays, coatings, and sealers. Moisture vapor test kits are available that include small containers of preweighed, unhydrated calcium chloride.

Vertical stamped concrete – A decorative finish for walls and other vertical surfaces using a lightweight cementitious overlay formulated to be applied at thicknesses of up to 3 inches without sagging. While the overlay is still plastic, it can be stamped or hand carved to produce deep-relief stone or masonry wall textures. After the material dries, acid stains or dyes can be sprayed or sponged onto the surface to give it the multi- Volumetric Mixer

X

Xylene – A common solvent. Used as a carrier for solvent based sealers. High in odor and flammability.

W

Water-cement ratio – The ratio of the amount of water to the amount of cement in a concrete mixture. The key to producing high-quality concrete is to keep the water-cement ratio as low as possible without sacrificing workability.

Water reducer – An admixture that either increases the slump of freshly mixed concrete without increasing water content or maintains workability with a reduced amount of water without affecting the strength.

Welded wire mesh – A woven mesh of wire strands, welded at each intersection, used to reinforce concrete slabs. Also called welded wire fabric.

Wet polishing – A method for polished concrete that uses water to cool the diamond abrasives and eliminate grinding dust. Not as commonly used as dry polishing, because the process creates a tremendous amount of slurry (a soupy mixture of water and cement dust) that must be collected and disposed of.

White cement – A portland cement with a low iron content that hydrates to a white paste. Often used in integrally colored concrete to produce pure, bright color tones, especially pastels.

Workability – The ease with which concrete or other cementitious materials can be mixed, placed, and finished.

Working time – The amount of time available for placing and finishing a cement-based material before it begins to set. Often depends on the ambient temperature and substrate temperature.