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What is a Waterproofing Membrane?

M. McGee
M. McGee

A waterproofing membrane is a layer of material that prevents the passage of water. These materials are used in a huge range of products, but the term is generally used when referring to construction or clothing. In both cases, the membrane is usually placed between two other layers. This both protects the waterproofing membrane and creates a physical part that separates the waterproof and the non-waterproof areas. When used in construction, it isn’t uncommon for there to be multiple layers of waterproofing membrane both inside the building and in the areas around it.

Waterproof is often a matter of degree rather than certainty. Two items that are both waterproof may allow small amounts of water to penetrate them in entirely different circumstances. These substances are in contrast to water-resistant ones, where water can move through them to some degree in any circumstances. For instance, a waterproof membrane may hold water back completely in most situations, but if it gets too warm or cold, small amounts would go through. A water-resistant layer would allow penetration regardless of temperature.


When a waterproofing membrane is used in clothing, it is generally very light and fragile, similar in thickness and weight to a plastic garbage bag. These layers are sandwiched between two layers of fabric and chemically bonded. In is important that the fabric isn’t sewn, as that would create non-waterproof holes in the layer. This multilayer material is then placed inside the clothing, generally along with additional layers of protective padding. These layers are common in jackets and footwear, as they often consist of multiple layers anyway.

In construction, most waterproofing membranes are located around the foundation and basement walls. These layers are generally inside concrete walls, along the outer surface of submerged areas or placed strategically around the building. Since people don’t need to wear them, they are thicker and more durable than those found in clothing, but are still subject to accidental punctures. In addition to synthetic membranes, some buildings use natural material layers to discourage water movement or channel it to specific areas.

When placed inside a wall, the actual construction of a waterproofing membrane is nearly identical to that inside clothing. The membrane is bonded to other materials, often directly to the wall or to a hard secondary material, and placed inside a wall cavity. These layers allow water to penetrate half of the wall, but block it from penetrating into the other half.

Exterior waterproofing membranes usually aren’t sandwiched like interior membranes and are, therefore, designed to be much stronger. Most are placed directly against the outside of the building, preventing water from entering at all. These are common in most new construction and are considered part of a standard building envelope.

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