Construction - Glossary

To find the definition of a term, click on the corresponding first letter of the word above.

Adhesion. The degree of attachment or bonding of one substance to another.

Alligatoring. Mud cracking of the surface of a tar or asphalt roof. Has the appearance of alligator hide.

Ambient Temperature. Temperature of the surrounding air on all sides.

Asphalt. A dark brown to black bituminous sticky substance, solid or semisolid in consistency, found in natural beds and also obtained as a residue in petroleum refining. It consists chiefly of hydrocarbons. The principal ingredient in asphalt mastics.

Breathable Coating. A coating with a perm rating above about 0.5 perm. The opposite of a vaporretarder. The higher the perm rating, the more breathable the coating.

Caulking. A substance to stop and make watertight against leakage.

Chalking. Usually a grayish or white substance, dry, chalk-like residue, forming on the surface caused by weathering.

Coating. A liquid or semiliquid protective finish capable of application to thermal insulation or other surfaces, usually by brush or spray, in moderate thickness.

Combustible. Capable of uniting with air or oxygen in a reaction initiated by heating, accompanied by the subsequent evolution of heat and light. Capable of burning.

Condensation. The process of changing from a gas or vapor to a liquid.

Contaminants. Something that makes a surface or substance unclean, pollutes, soils, stains from an outside source.

Coverage Rate. Quoted either as square feet covered by a gallon (50 ft2/gal) or as gallons used per square (2 gal/square). (A square is 100 square feet.)

Cure. To change the properties of a plastic or resin by chemical reaction, which, for example, may be condensation, polymerization, or addition; usually accompanied by the action of either heat or catalyst or both, and with or without pressure.

Cure Time. The time required to complete the cure process.

Degradation. The deterioration of a substance caused by contact with its environment.

Delamination. The separation of the layers of material.

Dirt Pickup. The accumulation of dirt on the sealant surface during or after sealant cure.

Dusting. A condition that develops in one to seven days on the surface of uncoated and unprotected spray foam due to photo oxidation by ultraviolet light (sunlight). The ultraviolet causes the surface to break down and become a dust or powder, which impairs adhesion of coatings and blows away. When this occurs, the foam changes from its original light color (usually tan) to a rust or dark brown.

Elastomer. A material capable of elongating at least 100% and recovering its original dimensions.

Elongation. Lengthening or stretching ability to accommodate movement.

Expansion Joint. A break in a surface to allow the material to contract and expand without causing damage. It may be a working joint to allow movement or a control joint to isolate a stress.

Film Thickness. The thickness of a membrane, normally measured in mils.

Flash Point. The flash point of a liquid is the lowest temperature of the liquid at which it gives off vapor sufficient to form an ignitable mixture with the air near the surface of the liquid or within the vessel used.

Fluid Migration. The migration of fluids, such as plasticizers, unreacted polymer, or otherliquid formulation additives into or onto porous or microporous substrates. Itis a diffusion-controlled phenomenon, observed with all sealant types,including polysulfides, acrylics, polyurethanes, silicones and oil-basedputties.

Fluid Streaking. The accumulation of dirt in water runoff channels on nonporous surfaces, aggravated by fluid migration from the sealant. Streaking is caused by the migration of free fluids to the sealant surface. Streaks can extend above and below a horizontal joint.

Grout. Cement or mortar used to seal between precast concrete planks in a roof deck.

Gypsum. A fireproof board composed of calcium sulphate and fibers. Used asconstruction panels.

Hardness. The relative resistance of a material to denting, scratching or bending.

Hot Applied. Or "hot mopped." Refers to an asphaltic or tar materialthat must be heated in a kettle to melting and applied to the roof deck by mopor squeegee. Also referred to as "soup." Different from atar-based mastic, which is spread as supplied.

Humidity, Relative. The ratio of actual pressure of existing water vapor to the maximum possible(saturation) pressure of water vapor in the atmosphere at the same temperature,expressed as a percentage.

Impact Resistance. Ability to withstand mechanical or physical abuse under severe service conditions. Resistance to blows, bumps and shocks incidental to use.

Laitance. Surface material on top of concrete made up of fine cement and aggregateparticles. It is loosely bonded and of low strength and must be removed by wirebrushing before coating can be applied.

Light Concrete. A nonstructural concrete using materials such as vermiculite or perlite as aggregate.

Mil. A unit in measuring thickness, being 0.001 inch (British equivalent: Thou.)(Metric equivalent: 0.0254 mm).

Monolithic. Single form or single piece; formed or composed of material without jointsor seams.

Organic. Compounds consisting of carbon and generally hydrogen, with a restrictednumber of other elements such as oxygen, nitrogen, sulphur, phosphorous,chlorine, etc., but not containing atoms or molecules, generally known asmetal.

Parapet. A wall rising above the level of the roof, usually around its perimeter.

Penetration. Any assembly that goes through a roof deck such as a vent, exhaust fan, electrical feed-through, roof drain, stand pipe, etc.

Perm Rating. A measure of a material's ability to pass water vapor

Pinhole. A very small hole or imperfection in a coating through which water or ultraviolet light can enter and cause damage.

Polymer. A chemical compound or mixture of compounds formed essentially of repeating structural units.

Primer. A chemical material that improves the bond of the sealant or coating to the substrate.

R Factor. Resistance of heat flow through a particular thickness of material.

Reversion. Urethane sealants lose their original rheological properties over time(i.e., their ability to actually seal joints).

Scupper. A hole in the wall to allow water to course through.

Shore “A” Hardness. Measure of firmness of a compound by means of a durometer hardness gauge.

Shrinkage Crack. Fine hairline cracks in the surface of newly cured concrete. Overall patternlooks like a crushed egg shell.

Solids Content. The percentage of nonvolatile matter that may be measured in volume orweight.

Solvent. Any substance, usually a liquid, that dissolves other substances. Incoatings, normally a liquid organic compound used to make a fluid coating applymore freely.

Square. A 10-foot x 10-foot area, or 100 square feet.

Structural Concrete. Reinforced concrete with a compressive strength of at least 2500 psi.

Structural Crack. Concrete crack subject to little movement but that must be repaired since itcan go through a full-slab thickness and leak.

Tack Free. A film is considered tack-free when the finger, with a slight pressure, will not leave a mark. The surface will not be sticky.

Tensile Strength. The force per unit area that is applied at the time of rupture of the specimen. It is calculated by dividing the breaking force in pounds by the cross-section of the unstretched specimen in square inches.

U Factor. The overall heat transfer factor for a particular building component, suchas a roof.

UL Rating. A flammability rating system for materials as tested by Underwriters Laboratories. UL classifies or lists materials that pass their specific tests.

Urethane Sealant Reversion. Sealants lose their original rheological properties over time (i.e., their ability to actually seal joints).

UV. Ultraviolet radiation or sunlight.

Vapor Retarder. Those materials or systems that retard the transmission of vapor under specified conditions.

Vent. A breather vent. A device put in a roof system to allow moisture vapor to escape.

Viscosity. The property of resistance to flow exhibited within the body of a material.

Water Absorption. The increase in weight of a test specimen expressed as a percentage of its dry weight after immersion in water for a specified time.

Water Repellency. Control of water absorption through the coating. Water beading is sometimes used as an indication of water repellency.