DRAINAGE MATS & DIMPLE BOARD
How They Work and Where They’re Used
DRAINAGE MATS & DIMPLE BOARD
Understanding Modern Waterproofing and Drainage Membranes
Modern waterproofing systems depend on two critical components: a waterproof coating and a drainage layer. Together, these elements form a complete system that keeps below-grade walls and slabs dry, protected, and structurally sound.
Drainage mats, dimple boards, and dimpled membranes are made from high-density polyethylene (HDPE) sheets and have dimples. The air gap created by the dimples provide a high volume drainage space between the foundation and the soil or backfill that provides. Most drainage mats have a geo-textile filter fabric that allows water to pass through while preventing soil and sediment from clogging the flow path.
HDPE is one of the most durable and long-lasting plastics used in construction. It’s environmentally friendly, chemically resistant, and designed to withstand years of ground pressure, moisture, and soil contact—making it ideal for both residential and commercial waterproofing applications.
These waterproofing systems are commonly installed in below-grade structures such as basement foundations, under-slab assemblies, shotcrete shoring, blind walls, green roofs, podium decks, and landscaped areas. They can be applied to a wide range of foundation types, including concrete, concrete block, insulated concrete form (ICF), and shotcrete.
What is a Drainage Mat?
A drainage mat is a dimpled plastic sheet with a filter fabric on one side. It is installed over a waterproof coating to protect it from backfill damage and to provide a path for water to drain down to the perimeter drain.
The raised dimples create drainage channels, and the filter fabric lets water pass through while blocking soil and fine particles. This prevents clogging and maintains consistent water flow.
Drainage mats reduce hydrostatic pressure, protect the waterproof coating, and keep the structure dry and stable. They are used behind foundation walls, retaining walls, planters, podium decks, and green roofs—anywhere reliable protection and drainage are required.
What Is a Dimple Board?
A dimple board, also called a dimpled foundation membrane, is a HDPE plastic sheet that creates a permanent waterproof barrier around the foundation. The raised dimples create an air gap that allows water to drain down to the footing while keeping moisture away from the wall surface.
Unlike drainage mats, dimple boards do not have a filter fabric attached. They provide drainage through the open air space formed by the dimples. When installed with a waterproof coating, a dimple board provides extra protection for your foundation and protects the waterproof coating from any backfill damage.
Dimple boards are used on poured concrete, block, ICF, and shotcrete foundations—anywhere long-term moisture protection and drainage are required.
Why Drainage Systems Matter
In a complete waterproofing system, drainage mats and dimple boards work together with waterproof coatings to manage water, relieve hydrostatic pressure, and protect foundation walls from damage.
This combination improves the long-term performance of any structure by keeping water away from the wall, protecting coatings during backfill, and extending the life of the foundation. Whether used in residential or commercial construction, proper drainage is essential for a dry, durable, and stable building.