Holding Back the Waters: Exterior Basement Waterproofing


Table of Contents

Proper basement waterproofing addresses all of these ways of water movement, and an important part of waterproofing is exterior waterproofing.

Water is the enemy of your basement and its possessions, and sometimes it seems you need a miracle to keep it out. It has a lot of ways of getting into your basement. Water moves several ways:

  1. water flow (this could be leaking pipes, backed up sewers, or flooding, among other things)
  2. capillary action (did you know that concrete is essentially a wick? Water can seep through even solid concrete.)
  3. vapour diffusion (water in vapour form is a part of any but the driest air; it moves through a house through the “stack effect” of differential pressures between inside and outside, and warm and cold)

Exterior Basement Waterproofing

Your basement is waterproofed by both interior and exterior measures. Both are important, and they are complementary. This blog post discusses exterior waterproofing; a later post will look at interior basement waterproofing.

Exterior waterproofing consists of two major elements: a perimeter drain system and waterproofing the exterior faces of the walls. When a house is built, these measures should be properly completed, although they do not always meet the required level of quality. Later in a house’s life, the exterior waterproofing will need re-doing. How long after initial construction this happens depends on the quality of the initial work.

Proper rework of exterior waterproofing requires excavation. The footing needs to be exposed. The foundation walls will need to be cleaned prior to a sprayed or rolled on polymer being applied. Be sure that the material used for waterproofing is true waterproof emulsion, not a damp proofing. They look similar, but the proper waterproofing is thicker. This polymer coating, once dry, is covered with a dimple board product that will facilitate downwards draining and that will protect the polymer waterproofing.


A perimeter drain system is then placed, or, in the case of a reworking of an existing waterproofing, replaced. [The image shown shows a house in the initial stages of having its waterproofing redone. The material along the basement walls has been removed down to the footings, the old perimeter drain is being removed (some still is in view on the right), and the walls have been prepared for re-surfacing. In this case, the wall on the left side of the image has also now received a waterproofing polymer.]

waterproofing work in progress

The perimeter drain system consists of drainage pipe (sometimes called “weeping tile”) placed around the footings. The drain pipe needs to be properly sloped to create continuous drainage. It leads to either a sump pump or to daylight, depending on the surrounding ground level of the building. The drain pipe is covered with 3/4″ clean rock back fill rising up from one foot to up to 60% of the wall height (depending on soil conditions). The rock fill is then covered with a non-woven [geo-textile][https://en.wikipedia.org/wiki/Geotextile] to prevent soil migration, yet still allow water movement down to the drain. All that is covered with soil backfilling, ideally with a soil with a high clay content to resist water infiltration.



The image below shows the completed exterior waterproofing system (omitting the sump pump, and not to scale).


This completes a description of typical _exterior_ waterproofing, but notice that all of this waterproofing is built along the vertical face of the building wall. It remains possible for water to travel beneath or around this system of protection, and to arrive _underneath_ the building floor. From there, water can move upwards through capillary action to saturate a floor. To deal with this situation, interior waterproofing is required, to complement the exterior waterproofing. Neither interior nor exterior waterproofing is in itself a complete solution. Interior waterproofing is described in another blog post.

Waterproofing your basement is critical to protecting your investment in your home. Contact Master Drain today to discuss the basement waterproofing requirements for your house.

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