Plastic Dimple Drainage Board
Keeping your basement dry requires a comprehensive below-grade drainage solution. Typically, that includes an air gap membrane, dimple board and footing drain.
These materials create a tight bond with foundation walls, blocking water, harmful soil vapors and pests from entering a structure. In addition, they relieve hydrostatic pressure and extend the lifespan of waterproofing membranes.
Types
The most common type of drainage board is a plastic sheet molded into a series of raised knobs, or dimples. The height and depth of the dimples vary among manufacturers, but they all function to promote drainage and reduce hydrostatic pressure. Plastic Dimple Drainage Board Unlike fluid-applied membranes that oxidize and crack, drainage boards stay stable for the structure’s lifetime.
They protect against vapor intrusion from ground water and prevent backfill material from touching foundation walls in both vertical and horizontal applications. They also eliminate the need for costly full-height gravel and meet dual code mandates for drainage and damp proofing.
Like air gap membranes, these membranes are placed in the basement wall with the dimples facing the foundation to direct groundwater toward perimeter footing drains. Construction moisture and vapor from the interior can condense against the surface of the dimpled membrane and fall freely to the drains, too.
These composite membranes consist of a heavy-duty impermeable polymer sheet cuspated under heat and pressure to create the high-flow dimpled core, wrapped in a non-woven filter fabric that retains soil or sand particles and allows filtered water to pass. They are typically used in place of a conventional drainage aggregate/sand filled system. They’re particularly useful for retrofitting damp basements when excavation isn’t feasible. They can be installed with or without a waterproofing membrane.
Applications
Dimple drainage boards, also known as dimple mats, dike board, permeable drain boards and water boards, are often used in combination with waterproofing membranes as part of a complete system to protect and drain foundation walls. They are lightweight, durable and can be installed quickly, reducing construction time. They are non-toxic and environmentally friendly, promoting drainage to keep the soil hydrated. They are also resistant to plant roots and are able to resist high water flow rates, preventing the clogging of the drain system.
In addition to a sloping site, the use of air gap membranes, drain tile and dimple boards, helps reduce intermittent hydrostatic pressure against the foundation wall by diverting moisture away from the footings. In many cases, keeping moisture out of the foundation through proper grading and other measures isn’t possible.
Drainage boards are an easy way to prevent moisture from seeping into the concrete wall and causing costly damages. They are mechanically affixed to the exterior of your poured foundation wall up to the level where you can see the finished foundation, or final grade height. They are bonded to the waterproofing membrane underneath and can be fastened with liquid adhesives, screws or bolts. These plastic sheets are a popular alternative to spray-applied waterproofing membranes, which dry out, crack and oxidize over time.
Installation
Typically, dimpled drainage membranes consist of an extruded dimple plastic core attached to a filter fabric. The dimples provide a free-draining space to promote the flow of water away from the foundation wall and High quality drainage membrane building site. The dimples also prevent contaminated soil and water vapors from entering the concrete wall or basement.
A non-woven, needle-punched PP geotextile covers the dimples and filters the subsoil water. This filtration protects the waterproofing membrane from soil particles, which could block the gap created by the dimples. It also releases the hydrostatic pressure from the concrete wall, which extends the life of the below-grade waterproofing membrane.
The permeability of dimpled drainage boards can be tailored to match the needs of any project. Some have a three-dimensional space to allow fluids to drain easily while others are impermeable, making them ideal for use in applications where moisture is problematic.
When installed with the dimples facing the foundation wall, a plastic drainage board acts as the first line of defense against moisture. Its dimples promote the flow of groundwater down to a footing drain, thereby keeping the wall dry. It also directs construction moisture from inside a concrete wall, as well as water and vapor from indoor spaces, down to the footing drain. This helps to eliminate cold, damp floors and improve interior comfort.
Maintenance
Plastic dimple drainage boards are used as a barrier to prevent moisture from entering the foundation and wall. These dimpled plastic sheets are placed on top of the spray-applied waterproofing membrane, and they move any water that collects either through condensation or from a leak away from the wall and toward a foundation drain. They are usually made of polypropylene and may be covered with an engineered textile.
These sheets are lightweight and simple to install, making them a good alternative to traditional aggregate drainage layers. They also help reduce intermittent hydrostatic pressure that can put strain on the waterproofing membrane system. They can be used on projects of all sizes, from small residential basements to enormous commercial projects that extend 50 feet below grade.
When installing a dimple drainage board, it should be attached to the waterproofing membrane system by using a butt joint. Then, it should be secured to the wall with a termination strip. The termination strip helps protect the drainage sheet from concrete backfill, and it also prevents it from shifting during construction.
The dimples on the drainage board can also resist unavoidable outside pressure and impact force during construction, such as vehicles or worker stepping on the basement floor and concrete pouring impact force. This will help protect the waterproofing membrane and keep the walls stable.
