For thorough basement waterproofing, it’s generally recommended to combine interior and exterior methods to prevent water from getting trapped in the concrete and causing damage over time. While only one type of drainage system is typically necessary, a sump pump can effectively remove water from either interior or exterior drains.
The most common basement waterproofing methods include:
- Exterior waterproofing coating
- Interior sealants
- Interior water drainage
- French drains (interior and exterior)
- Sump pump installation
Key Considerations for Clients
- Sealants Alone Are Temporary: Advise clients that relying solely on interior sealants is only a temporary measure. To prevent long-term damage to basement walls, an exterior sealant or membrane should always be added.
- Foundation Coating vs. Drainage: Sometimes, a client may only want to seal or coat their foundation to save costs. However, it’s crucial to explain that this will not protect the foundation from continuous contact with water on the outside. Waterproof coatings should ideally be paired with a drainage system to guide high volumes of water away from the home.
- Cost Factors: In general, interior basement waterproofing typically has lower costs, while many exterior waterproofing methods are more expensive. Other factors influencing costs include the basement size, the home’s age, and its geographic location.
- Permits and Licenses: Waterproofing jobs requiring excavators or other heavy equipment may necessitate permits or licenses, adding to the overall cost.
- Gutter System Upgrade: If the basement only experiences dampness and isn’t prone to major floods, improving the rain gutter system might be a more cost-effective solution than full exterior waterproofing. This includes moving gutters farther from roof edges, extending downspouts away from the home, or connecting downspouts to existing drains to prevent water buildup around the foundation.
Tools and Materials Required
Basement waterproofing jobs typically require the following tools and materials:
- Excavator (for exterior work)
- Breaker hammers or sledgehammers (for interior concrete work)
- Shovels
- Compactor
- Hydraulic cement (for crack filling)
- Waterproofing paint
- Concrete sealer
- Perforated corrugated pipes (for drainage systems)
- Landscape fabric (filter fabric)
- Gravel (for drainage systems)
- Grit sand (for compacting soil with high clay content)
Pro Tip: For businesses, professional-grade tool and large equipment rental (including excavators, trailers, trucks, etc.) can be a valuable asset.
Exterior Basement Waterproofing Methods (Typically More Complex and Costly)
Exterior waterproofing methods are generally the most involved. The process starts with excavation around the perimeter of the home, digging down to expose the foundation footings. Once exposed, the foundation must be thoroughly cleaned and dried before any coatings or membranes are applied.
There are several exterior waterproofing coating options, each with distinct advantages and materials:
- Liquid Synthetic Membranes:
- Materials: Polyurethane and rubberized asphalt.
- Application: Easiest to apply, as they come pre-mixed and are painted directly onto cleaned, excavated foundation walls.
- Durability: Materials like polyurethane can deeply infuse concrete, offering protection for up to 25 years.
- Synthetic Sheet Membranes:
- Materials: Thermoplastic, bituminous, and PVC.
- Application (Thermoplastic): Applied to foundation walls and then melted in place to form a polymer against the concrete surface. Useful for flexible ductwork or protecting pipe plugs, sump pits, or tanks.
- Solid Bentonite Sheets:
- Material: Rolled membrane with a clay-based concrete adhesive.
- Mechanism: The material expands as it dries, filling any empty spaces left during application.
- Durability: Bentonite waterproofing often lasts the lifetime of the concrete structure, especially in below-grade applications exposed only to water and soil.
Drainage System Integration:
Waterproof coatings should always be paired with a drainage system, most commonly French drains. These are installed in the perimeter trenches before backfilling. The drain should be surrounded by gravel before adding any soil for backfilling.
Backfilling Process:
Once the waterproofing coating is set and the drainage system is installed, the trench should be backfilled with soil in 6-inch layers. Each 6-inch layer must be compacted with a compactor before adding more soil. This process continues until the trench is fully backfilled and densely packed. Grit sand can be helpful for compacting soil with high clay content.
Interior Basement Waterproofing Methods (Typically Lower Costs)
Interior waterproofing begins with digging a trench around the edges of the basement floor. If a sump pump is being installed, a sump pit is also excavated. Once the drainage system and pump are in place, the basement walls are sealed, and any removed wall material (like wood paneling) is replaced.
- Interior Sealants:
- Application: Applied to the interior walls and floors of the basement to prevent moisture seepage.
- Purpose: Typically used as a temporary solution or in conjunction with other, more robust waterproofing methods.
- Preparation: It’s crucial to fill any cracks in the basement walls before applying sealant to prevent larger amounts of water from collecting in the wall and causing further damage.
- Cost: Waterproof paint costs $1-$6 per square foot and is the least expensive option. It prevents water from seeping through but won’t plug existing cracks alone. Concrete sealants vary: acrylic sealants ($3-$4 per square foot) are good for long-term projects with less frequent reapplication, while silicate and epoxy sealants can cost up to $5-$7 per square foot.
- Interior French Drains:
- Installation: Dig interior trenches by breaking up concrete with a jackhammer or other breaking hammer, creating a continuous channel along the perimeter of the basement interior.
- Function: Designed to collect water and direct it away from the basement.
- Reliance on Pumps: Unlike exterior systems that can rely on gravity, interior French drains do not push water away themselves; they rely on pumps (like a sump pump) to carry the water farther away into deeper soil.
- Sump Pump Installation:
- Timing: Best installed simultaneously with an interior French drain to avoid excavating concrete twice.
- Process: Excavate a pit slightly larger than the sump pump tank in a basement corner, ensuring it connects to the French drain channel. Install the sump pump and tank in the pit, connecting the perforated pipe from the drain to the tank.
- Discharge: Connect the sump pump to a discharge pipe positioned away from the home. When activated, the sump pump pumps water away from the foundation, preventing the French drains from overflowing.
Finishing Interior Drainage:
After the interior French drains and sump pump are installed, backfill the drains with gravel before relaying cement to fix the basement floor. Once the cement is set and dry, the sump pump and drainage system should operate as intended.