Install the 20-mil white wall liner over the basement masonry, fasten it with compatible masonry drive pins, and keep its lower edge continuous with the slab perimeter drain or drainage channel. Finish the top with sealed trim strips, seal penetrations and drain transitions for radon control, and verify that the drainage system has a working sump or other approved discharge route. This interior approach manages water that reaches the foundation from inside, but it does not replace correction of major exterior drainage defects or structural foundation problems.
What an interior liner and curtain drain system does
An interior basement waterproofing system of this type has two coordinated parts. The wall liner creates a controlled surface for water moving through cracks, joints, or porous masonry. The wall curtain drain, sometimes called a wall drainage membrane or drainage channel, carries that water to a floor-level collection point.
The liner is not intended to make the foundation wall itself waterproof. Instead, it manages water after it enters the wall or reaches the interior side of the foundation. The system is most useful when the basement has damp masonry, recurring seepage at the wall-to-slab joint, or a planned interior drainage channel.
Before installation, identify whether the problem is ordinary moisture, active bulk water, condensation, plumbing leakage, foundation movement, or groundwater pressure. A liner can conceal symptoms without correcting a leaking supply pipe, a failed window well, a damaged footing drain, or a structural crack. Significant wall displacement, widening cracks, or standing water should be evaluated before the wall is covered.
Materials and preparation
A typical installation includes 20-mil white wall liner rolls, compatible masonry drive pins with washers or retaining heads, sealed top edge trim strips, a floor-level drainage channel or collection detail, compatible sealant, and materials for sealing pipe, wire, and other penetrations. The exact liner composition, fastener type, sealant, and installation spacing are product-specific. Follow the selected manufacturer's instructions rather than treating these materials as interchangeable.
Prepare the wall by removing loose paint, friable mortar, sharp projections, and debris that could puncture the liner. Do not remove sound structural material simply to create a smooth appearance. Mark the location of utilities before drilling. Electrical wiring, plumbing, gas piping, reinforcing steel, and concealed equipment can affect the safe location and depth of masonry fasteners.
Measure the wall height and each section separately. Allow enough material to reach the intended bottom drainage detail and the sealed top trim without stretching the liner. Store rolls where they will not be crushed, folded sharply, or exposed to conditions prohibited by the product instructions.
Installing the 20-mil wall liner
- Plan the layout. Start from a corner or other logical control line. Keep seams, corners, penetrations, and changes in wall plane visible on the layout so they can be treated deliberately rather than cut around at random.
- Set the bottom elevation. Position the lower edge so water behind the liner can enter the floor-level drain or drainage channel. Do not bury or pinch the liner in a way that blocks the designed flow path. The required overlap or insertion detail depends on the drainage product.
- Hang the first roll. Keep the liner reasonably flat, but do not pull it so tightly that normal wall irregularities or future movement transfer excessive stress to the fasteners. Avoid folds that can trap debris or obstruct drainage.
- Install masonry drive pins. Drill only with the bit size and depth specified for the fastener system. Set pins through the liner's intended fastening area and use the compatible washer or retaining head. Overdriving can crush masonry or tear the liner; underdriving can leave a protrusion that damages the finished surface.
- Continue across the wall. Maintain the manufacturer's fastening pattern and keep the liner aligned. At corners, form the liner according to the product instructions. Do not assume that a tight fold, an unsealed overlap, or a cutout around a penetration will remain watertight or radon resistant.
- Complete seams and penetrations. If the product requires taped, sealed, overlapped, or mechanically joined seams, use the specified method. Seal around pipes, conduits, posts, and other interruptions with materials compatible with both the liner and the substrate.
The 20-mil thickness is a product characteristic, not a universal code requirement. A thicker or thinner material may be permitted by a particular system, while a manufacturer's warranty may require a particular thickness or accessory. Verify the product's intended use for interior below-grade walls and confirm whether the installation is approved for the drainage and radon-control goals of the project.
Using masonry drive pins correctly
Masonry drive pins are installed through a predrilled hole or fastening point and driven into concrete or masonry. They are convenient for attaching liner retainers, but the wall condition controls whether they will hold. Old brick, hollow block, weak mortar joints, cracked concrete, and thin parging can provide poor resistance or break during drilling.
Fasten into sound substrate where the system allows it, and avoid placing pins directly over visible cracks unless the manufacturer's instructions specifically address that condition. Keep clear of known utilities and any reinforcing or embedded components. A contractor should stop and reassess if the bit encounters unexpected resistance, a void, or material that begins to spall.
Do not substitute drywall screws, roofing nails, random concrete screws, or improvised washers for the specified fastener assembly. The retaining head must hold the liner without cutting it, and the fastener must be compatible with the wall material and moisture exposure. The appropriate spacing is installation-specific, so use the manufacturer's layout rather than an assumed universal dimension.
Tying the liner into the floor slab perimeter drain
The lower edge is the critical hydraulic transition. Water behind the wall liner must have an uninterrupted route to the floor slab perimeter drain, interior drainage channel, or other designed collection point. If the liner stops above the drain, curls away from it, or is sealed in a way that blocks the opening, water can collect behind the wall instead of reaching the pump.
At the wall-to-slab joint, inspect for existing cracks, open joints, previous coatings, and obstructions. The installation may require a narrow section of slab removal to expose or install a drainage channel. Concrete removal can affect utilities, post-tensioned construction, structural elements, or finished surfaces, so the proposed detail should be reviewed before demolition.
Confirm where collected water goes. A sump pump basin, gravity drain, or other discharge arrangement must be permitted where required and must comply with local rules and the system design. A liner and channel do not solve a drainage system that has no capacity, a failed pump, an obstructed discharge, or an improperly sealed sump cover.
When the existing perimeter drain cannot be verified, do not describe the installation as connected to a functioning drain merely because a channel was placed at the edge. Test the flow path before closing the work. Water testing should be controlled so it does not overload the basement or introduce water where electrical equipment could be affected.
Sealing the top edge with trim strips
Finish the upper edge with a continuous trim strip or termination detail designed for the liner. The trim holds the material in place and helps limit air and moisture movement behind the finished wall. Install it on a sound portion of the masonry, not on loose coating or deteriorated mortar.
Use the sealant specified or approved for the liner and substrate. Run a continuous seal where the system calls for one, tool the sealant without leaving gaps, and treat trim joints, corners, and end conditions as part of the air seal. A mechanical trim by itself is not necessarily an air seal or radon seal.
Keep the top termination accessible until the sealant has been inspected. Do not cover it with framing, insulation, or drywall before confirming that the trim is continuous and that the liner has not pulled away from the fasteners. If the wall will be finished, preserve access to valves, cleanouts, electrical equipment, and drainage components.
Radon mitigation and air sealing
Radon control requires more than installing a white wall liner. The liner, top edge, seams, floor-to-wall joint, sump basin, floor drains, pipe penetrations, and other openings can form part of the pressure boundary. If the goal is radon reduction, use a radon professional or other qualified designer to determine how the interior wall system fits into the mitigation plan.
Seal around penetrations with a material compatible with the liner and masonry. Flexible sealants are often needed where small movement is expected, while larger openings may require a designed sleeve, boot, or mechanical seal. Do not use an unapproved caulk as a substitute for a tested radon sealing component when the mitigation design specifies another product.
Keep the sump basin cover, floor drains, and cleanouts in the mitigation plan. A cover that is airtight in one location can still leave an unsealed pipe opening or perimeter gap elsewhere. Test the basement for radon before and after mitigation using a method appropriate to the project. Local health departments, qualified radon professionals, and applicable state programs can help identify testing and mitigation options.
Radon requirements and mitigation practices can vary by project, state, local program, and system design. The International Residential Code and other model codes may address radon-resistant construction, but a model code is not automatically the rule in every jurisdiction. Confirm current requirements with the local building department or authority having jurisdiction.
Inspection and finished-wall checklist
- Confirm that the wall substrate is sound enough for the selected drive pins.
- Verify that fastener heads hold the liner without tears, crushing, or sharp protrusions.
- Check that corners, seams, penetrations, and transitions follow the product installation instructions.
- Confirm that the liner's lower edge enters or drains toward the intended perimeter collection path.
- Verify that the sump, pump, discharge, or gravity drainage route is operational and legally acceptable for the property.
- Inspect the top trim for continuous attachment and a complete compatible seal.
- Seal penetrations, floor drains, sump covers, and other openings included in the radon-control design.
- Photograph concealed drainage and sealing details before framing or finishing the wall.
- Maintain access to pumps, cleanouts, shutoffs, electrical equipment, and inspection points.
If water continues to appear after installation, determine whether it is entering above the liner, bypassing a seam or penetration, rising through the slab, condensing on a cold surface, or coming from a plumbing source. Do not simply add more sealant over an unresolved drainage or structural problem.
Frequently asked questions
Is a 20-mil liner thick enough for every basement?
No universal thickness applies to every project. A 20-mil liner may be appropriate when the product is specifically designed for the intended below-grade wall and drainage use, but the manufacturer may require a different thickness, fastening method, or accessory for particular conditions. Check the product documentation and local project requirements.
Can masonry drive pins be installed anywhere on a concrete wall?
No. The pin location must avoid utilities and unsuitable substrate, and the fastener must be rated for the wall material. Cracked, hollow, friable, or deteriorated masonry may not provide reliable holding strength. Use the specified bit, embedment, washer, and spacing, and reassess unusual wall conditions before fastening.
Does the wall liner stop basement water from entering?
It does not stop water at the exterior face of the foundation. It guides water that reaches the interior side into a designed drainage path. Exterior grading, roof drainage, foundation cracks, plumbing leaks, and groundwater pressure may still require separate investigation and correction.
How should the liner connect to the slab drain?
The lower edge should remain continuous with the floor-level drainage detail so water behind the liner can flow to the collection system. The exact overlap, insertion, or termination depends on the liner and drain products. Do not block the drain opening or assume that a visible channel is connected to a functioning discharge system.
Is sealing the top trim enough for radon mitigation?
No. Radon control also requires attention to seams, penetrations, sump basins, floor drains, slab cracks, and other openings. The appropriate sealing and testing plan depends on the building and mitigation design. Confirm the approach with a qualified radon professional and applicable local authorities.