Dampproofing vs. Waterproofing: Things You Should Know Before You Spend Millions on a Building
- May 5, 2018
- 2 min read
Both of these systems are intended to prevent moisture from penetrating sub- or above-grade walls and slabs. However, there are critical differences between them. Getting those differences wrong could mean unnecessary money spent on construction at best, to catastrophic issues with the building, at worst.
There are a variety of materials, systems, and applications with varying levels of moisture resistance, but these broadly fall into two categories:
Dampproofing
Waterproofing
Dampproofing is a system designed merely to resist the flow of moisture in a gaseous state. It can only be used in below-grade walls that are not subjected to hydrostatic pressure. These types of systems resist the flow of water vapor through a building component. They are most commonly used to prevent or reduce migration of water by diffusion. The most common form of dampproofing material is bituminous (asphalt) coating, which is either solvent-based (cut back asphalt) or emulsion. These coatings are applied in one or more applications with a brush, spray or trowel. Reinforcements are rarely applied in these systems. If reinforcements are used they typically consist of woven jukes or cotton fabrics that are specially applied over substrate cracks or openings.
A commonly used dampproofing system
Waterproofing systems are designed to resist hydrostatic pressure that is extended by moisture in a liquid state. This means that the primary waterproofing system and any components directly in contact with the surface have been proven in the laboratory and in the field to both have low moisture permeance as well as minimal moisture uptake (except in the case of some negative-side applications, such as bentonite clay systems, which are a discussion for another paper). Waterproofing systems typically use reinforcement membranes that can be adhered to the substrate in a variety of application methods. Typical application methods include hot application with heated asphalt, cold applications with solvent-based adhesives, torch applications or self-adhered membrane sheets.
The decision to use waterproofing or dampproofing systems can be determined by three criteria.
If hydrostatic pressure is present, a waterproofing system is required. Every time.
A waterproofing system is also required for framed-slab constructions.
For retaining walls or slabs-on-grade, the question is whether a slight leak risk is acceptable. If the answer is yes, then dampproofing may be considered. If the answer is no, then waterproofing is required.
Dampproofing Methods
If it is determined that dampproofing is an acceptable method, it can be applied on the following components: slabs on ground, foundation walls and retaining walls with finish bonded to the wall. Dampproofing should not be applied on concrete walls that have a cavity and brick facing because water can flow down these walls and discharge through weep holes into interior surfaces.