Cement Board Glossary: Key terms to know

From residential builds to commercial construction, using a cement board underlayment can provide a wide range of benefits. Like drywall, cement board sheets are cut to size and secured to wood or steel framing; however, a cement board’s water resistance makes it the ideal choice for wet applications. While not waterproof, cement boards typically won’t grow mold or mildew and won’t deteriorate when wet — all of which combine to make cement board installation ideal for kitchens and bathrooms, as well as exterior wall cladding systems, such as thin brick, adhered stone and stucco.

The following glossary defines cement board terms related to the products construction, installation, and interior and exterior applications.

• Cement board: A combination of cement and reinforcing fibers formed into sheets of varying thickness that are typically used as an underlayment or substrate.
• Cement board tape: An alkali-resistant tape used to conceal and reinforce corners and joints between two sheets of cement board.
• Cementitious core: The center part of a cement board, consisting of a rigid substrate made of Portland cement, aggregate and glass mesh.
• Control joint: A joint that accommodates movement of cement boards to relieve stress and minimize cracking.
• Fasteners: The variety of products used to mount and secure cement boards to either wood or steel framing.
• Fastener spacing: The maximum distance between fasteners when installing cement boards on walls, floors and ceilings.
• Fiberglass mesh: The material that comprises the exterior surface of a cement board, adding impact resistance and strength.
• Heat shield: The ability of certain cement boards to be used as a wall protector with UL-listed, solid-fuel room heaters and fireplace stoves.
• Polystyrene aggregate: Small, foam-like beads that are mixed with cement to create lightweight cement boards, versus using a heavier crushed-stone aggregate.
• Reinforced edge: A reinforced cement board edge that helps reduce damage from handling and allows fasteners to be installed closer to the edge without fracturing the board.
• Score and snap: The function of cutting a surface with a sharp blade and then breaking it along that cut into the desired size.
• Substrate: The underlying layer used to support the primary layer. For example, cement board is used as a substrate for tile installation in a bathroom or kitchen.
• Underlayment: A general term for the horizontal application of one material under another material during construction. For example, cement board is ideally suited as an underlayment beneath tile or stone on floors.

Cement Board Interior Wet Applications

With its ability to resist moisture and stay intact when exposed to water, cement board is ideal for interior wet areas in kitchens and baths.

• Caulk: A flexible, waterproof material used to seal joints or seams against leakage.
• Foam tile backer: A lightweight, waterproof tile backer board designed for interior tile applications.
• Membrane: An underlayment installed between the cement board and the finishing surface (e.g., tile) to improve waterproofing.
• Notched trowel: A device used to scoop and spread mortar across floors and walls. The notches on the sides of the trowel create a base of ridged mortar, which compresses when a tile is placed to provide a complete bond between the tile and the floor or wall.
• Sealant: An elastic, waterproof material used to seal joints or seams that are prone to expansion and contraction.
• Thin set mortar: A mixture of cement, water and fine sand that is used as an adhesive to attach tile to the substrate.
• Water-absorption rating: The amount of water a material absorbs, as measured by ASTM C473 standard test method for physical testing of gypsum panel products.

Cement Board Exterior Installation

Cement boards provide a lightweight, durable and easy-to-install exterior sheathing designed to withstand prolonged exposure to moisture.

• Base coat: The first layer of stucco, often called the scratch coat, consists of a mixture of cement material, sand and water.
• Cement board masonry veneer wall systems: A complete, engineered solution for installation of adhered veneers in residential and low-rise commercial construction. Cement board masonry veneer wall systems provide the ability to incorporate an effective water-management system for a variety of building exteriors that use manufactured or natural adhered stone, tile and thin brick veneers.
• Cement board stucco wall systems: A high impact, moisture resistant exterior wall finish system incorporating a cement board substrate, air and moisture barrier, reinforced base coat and a polymer-based finish designed to provide increased impact and weather resistance.
• Continuous insulation: A continuous insulation layer over an entire wall, not just in the wall cavities, that creates an exterior envelope, helping to eliminate air/moisture leakage, improve thermal efficiency and reduce thermal bridging.
• Drainage mat: A layer in an exterior wall system that maintains a separation between the materials used for the veneer and the structural wall to drain moisture and dry the building enclosure.
• Finish coat: The final applied coat of stucco that can take on a variety of textures and colors based on the desired aesthetic.
• Flashing tape: The self-adhesive tape used to seal around window and door installations, providing an added layer of protection to the rough opening to prevent water and air from penetrating the structure.
• Modified mortar: A material that contains polymers formulated into the dry mix to increase its performance and strength.
• Mortar: A mixture of sand, cement and water that hardens to bind stone, brick and concrete masonry units when building a wall.
• Optional primer coat: Similar to paint primer in drywall applications, this additional coat is used for stucco systems where there is a concern that the darker color of the base coat will negatively affect the color appearance of the finish coat. Also called thin-set mortar.
• Rainscreen: A wall system where the cladding sits away from the exterior wall’s water-resistant and thermal barriers, creating an air cavity directly behind the cladding. This design allows any water that passes the cladding to still drain away from the building structure.
• Reinforcing mesh: A fiberglass mesh that usually comes in a rectangular or square grid pattern and is used in cement board stucco applications for reinforcement of the stucco base coat.
• Sheathing: The layer of wood board or other panel material installed on the outer studs, joists and rafters of a building to strengthen the structure and create a base for the exterior wall system.
• Thin brick veneer: A type of exterior wall cladding designed to resemble a brick facade without providing the same structural support of a traditional brick masonry wall.
• Thin stone veneer: A type of exterior wall cladding designed to resemble a stone facade used as a protective or decorative veneer for interior or exterior walls.
• Weather-resistant barrier (WRB): A barrier used within an exterior wall system that prevents liquid water from entering the structure while allowing water vapor to escape. Also called “housewrap” in residential construction.
• Weep screed: A piece of metal flashing installed along the base of an exterior stucco wall that acts as a vent, allowing moisture to escape from behind the stucco.

National Gypsum Company is the exclusive provider of high-performance cement board products manufactured by PermaBASE Building Products, LLC. From kitchens and bathrooms to exterior underlayment for thin brick, adhered stone and stucco, PermaBASE® products are lighter, easier to cut and backed by the industry’s best warranties.

Explore the PermaBASE Construction Guide to find out which of our six types of cement board are the best match for your project.