Damp proofing isn't the same as waterproofing. The asphalt coating on the exterior of the foundation won’t prevent water from leaking into your basement.
It’s not easy to figure out the best way to waterproof a foundation. There are plenty of different products and techniques devoted to waterproofing foundation walls, along with strong opinions favoring one method over another. How do you know what will work best for waterproofing your basement? Like many tricky home improvement issues, this can’t be resolved with a single “silver bullet” product or treatment. The best approach to waterproofing a foundation usually involves a combination of strategies that are explained below. Let’s assume that the type of foundation we’re talking about is a basement foundation with either concrete block or poured-concrete walls.
Exterior foundation drains eventually clog. It’s standard procedure to install plastic drain lines around the exterior of a foundation, but plant roots and silt cause this type of drain to stop working.
When a house is being built, foundation walls are accessible and clean – ideal conditions for applying a waterproof coating. The traditional exterior coating for a new foundation is an asphalt-based compound applied by brush or spray equipment. It’s important to point out, however, that this treatment is referred to as “damp-proofing,” not waterproofing. Damp proofing is intended to keep out soil moisture, but not liquid water that enters the basement through gaps, cracks and holes left by form ties.
In many areas, it’s a code requirement to apply a damp-proofing treatment to the exterior of the foundation. The builder is also supposed to install perforated plastic drain pipe near the footing to carry water away from the foundation. Unfortunately, these drain lines (aka exterior French drains) don’t end up being very effective. They can be crushed during the backfill process and often clog quickly with silt and plant roots, even when installed correctly. With exterior drains that don’t work and a “waterproof” coating that doesn't stop water leakage, an exterior coating shouldn't be your only line of defense against a wet basement.
Waterproof coatings often fail. Moisture seeping through a foundation wall can destroy the bond between the paint and the concrete.
There’s no doubt that the technology associated with paints and coatings has advanced in significant ways. Today’s paints, sealers and waterproof coatings are better than ever before. Some foundation waterproofing compounds are designed to be applied on the exterior of the foundation wall, while others are meant for the interior. Either way, the goal is the same: establish an impermeable barrier to water.
Unfortunately, this foundation waterproofing strategy doesn't have a good chance of success. By holding water back, a major buildup of hydrostatic pressure occurs against the foundation wall and against any thin membrane or coating. Water under high pressure can actually bow or buckle foundation walls (causing foundation cracks that become leakage points). Before this happens, even tiny gaps or cracks in the foundation (or the waterproof coating) will begin to leak because of high water pressure. Essentially, holding back the water in one area ensures that leaks will occur elsewhere.
Interior drains feed a sump pump. The most effective way to keep a basement dry is to capture ground water in a perimeter drain system and then pump it to the exterior.
One technique that has proven effective in keeping basements dry is an interior drain system connected to a sump pump (see drawing). This foundation waterproofing strategy actually harnesses the power of hydrostatic pressure instead of fighting it. Unlike an exterior drainage system, the WaterGuard® interior French drain system from Basement Systems can’t clog with plant roots or silt because of its location. It is typically installed where the basement’s slab floor meets the foundation wall – the most leak-prone area in any basement. WaterGuard® drain lines capture groundwater before it gets to the basement floor and convey it to a sump pit. When the water in the sump pit reaches a certain level, the sump pump comes on automatically to pump the water outside.
Another option for interior drainage is our CactusBoard basement footing and wall water drainage system - designed to keep basement floors dry. CactusBoard comes with a 20-year transferable dry basement floor warranty. This foundation waterproofing solution creates a space between the edge of the basement floor and basement walls. Water from the perimeter and walls is drained into stone aggregate under the floor and into a sump pump basin where it is then pumped outside.
It’s always smarter to have two lines of defense instead of one. A well-installed damp proof coating on the exterior of the foundation will help prevent soil moisture from seeping through foundation walls. An interior drain, like CactusBoard or WaterGuard®, combined with a sump pump system captures and controls water that leaks in from around and under the foundation.
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