How to Waterproof Your Foundation with DELTA®-MS: A Complete Below-Grade Guide

Why Below-Grade Foundation Waterproofing Matters

Water is the single greatest threat to any foundation. When soil becomes saturated after rain or snowmelt, hydrostatic pressure builds against your foundation walls. Without a proper drainage and waterproofing system, that pressure forces moisture through concrete, block, or poured walls — leading to efflorescence, mold, structural cracking, and costly repairs that can run into the tens of thousands of dollars.

Below-grade waterproofing addresses the problem at the source: on the exterior of the foundation, before water ever reaches the wall. It is the most effective and longest-lasting approach available, and DELTA®-MS dimpled membrane is one of the most trusted products for the job.

What Is DELTA®-MS?

DELTA®-MS is a high-density polyethylene (HDPE) dimpled drainage membrane manufactured by Cosella-Dörken. It is designed specifically for below-grade foundation protection — the portion of your foundation that sits underground, from the footing up to grade level.

The membrane features a distinctive pattern of raised dimples on one side. These dimples do two critical things:

• Create an air gap between the membrane and the foundation wall, so any moisture that does reach the wall drains downward rather than being held against the concrete.
• Provide a drainage plane that channels water down to the footing drain or weeping tile, where it is safely directed away from the structure.

DELTA®-MS is UV-resistant, rot-proof, and rated for long-term underground use. It does not rely on coatings or adhesives that can crack or degrade over time.

View the DELTA®-MS Below-Grade Foundation Protection membrane →

Air-Gap Technology: How It Works

Traditional waterproofing coatings (tar, asphalt, or elastomeric paint) are applied directly to the foundation wall and rely on a continuous, crack-free bond to keep water out. The problem: concrete moves. Seasonal temperature swings, soil settlement, and normal curing shrinkage all create micro-cracks that allow water infiltration over time.

DELTA®-MS takes a fundamentally different approach using air-gap (or drainage-gap) technology:

1. The membrane is installed with the dimples facing the foundation wall, creating a continuous 8 mm air gap across the entire surface.
2. Any water that migrates through the soil and reaches the membrane face runs down the dimple channels by gravity.
3. At the base of the wall, water exits into the footing drain system and is carried away from the building.
4. Because the wall surface stays dry within the air gap, there is no hydrostatic pressure buildup and no sustained moisture contact with the concrete.

This system works even if the foundation wall develops minor cracks — because the membrane manages water before it can enter the wall, not after.

When Do You Need Below-Grade Waterproofing?

Below-grade waterproofing with DELTA®-MS is appropriate in the following situations:

• New construction: The ideal time to install — the foundation is exposed before backfill, and installation is straightforward.
• Foundation excavation and repair: If you are already digging to repair cracks, replace a footing drain, or address structural issues, adding DELTA®-MS at the same time is highly cost-effective.
• Chronic wet basement problems: If interior drainage systems and sump pumps are not keeping up, exterior waterproofing addresses the root cause.
• Finished basement projects: Protecting the foundation before finishing the interior prevents future moisture damage to framing, insulation, and drywall.

Step-by-Step Installation Overview

Note: This overview is intended as a general guide. Always follow the manufacturer's installation instructions and consult a qualified contractor for your specific project conditions.

Step 1 — Excavate to the Footing

Excavate the soil around the foundation down to the top of the footing. The trench should be wide enough to work safely and to install the membrane without obstruction. Remove any loose soil, roots, or debris from the wall surface.

Step 2 — Clean and Prepare the Foundation Wall

Brush or pressure-wash the foundation wall to remove dirt, efflorescence, and loose material. If there are active cracks or significant structural damage, repair these before proceeding. A clean, sound surface ensures the membrane seats properly.

Step 3 — Apply a Drainage Board and Dampproofing (If Required)

In some applications, a dampproofing coat is applied to the wall before the drainage membrane. Check local building codes and the project specifications — some jurisdictions require a base dampproofing layer beneath the drainage membrane.

Step 4 — Install DELTA®-MS Membrane

Unroll DELTA®-MS along the foundation wall with the dimples facing the wall. Start at one corner and work horizontally. Key installation points:

• Overlap adjacent sheets by at least one row of dimples (approximately 50 mm / 2 inches) to maintain a continuous drainage plane.
• At the top of the membrane, use DELTA® Termination Bar or an equivalent mechanical fastener to secure the membrane to the wall and prevent soil from entering the air gap.
• At the bottom, allow the membrane to extend over the footing and into the drainage aggregate or weeping tile trench so water exits cleanly.
• At corners, cut and fold the membrane carefully to maintain full coverage without gaps.

Our DELTA®-MS Installation Kit includes the termination bar, fasteners, and tape needed to complete a professional installation.

Step 5 — Install or Verify the Footing Drain

DELTA®-MS channels water downward — it must have somewhere to go. Confirm that a functioning perforated drain pipe (weeping tile) is in place at the base of the footing, surrounded by clean drainage aggregate (washed gravel) and wrapped in filter fabric to prevent clogging. If no footing drain exists, install one before backfilling.

Step 6 — Backfill

Backfill the trench with clean, well-draining material. Avoid large rocks or debris that could puncture the membrane. Compact the fill in lifts to prevent settlement, and slope the finished grade away from the foundation at a minimum of 6 inches over the first 10 feet to direct surface water away from the building.

Common Mistakes to Avoid

• Installing the membrane backwards. The dimples must face the wall, not the soil. Reversed installation eliminates the air gap and defeats the purpose of the system.
• Skipping the termination bar at the top. Without a proper termination, soil and insects can enter the air gap, clogging the drainage channels over time.
• No footing drain. DELTA®-MS manages water along the wall, but it needs a functioning drain at the base to remove that water. Without one, water will pool at the footing.
• Insufficient overlap at seams. Gaps between sheets allow soil fines to enter the drainage plane. Always overlap by at least one full row of dimples.
• Backfilling with large rocks or sharp debris. Heavy or angular fill can puncture the membrane during compaction. Use clean granular fill.
• Ignoring surface grading. Even a perfect below-grade system is undermined by surface water draining toward the foundation. Always ensure positive grade away from the building.

DELTA®-MS vs. Other Waterproofing Methods

For most new construction and excavation projects, DELTA®-MS offers the best combination of performance, longevity, and ease of installation.

Shop Foundation Waterproofing Products

Ready to get started? Browse our full selection of foundation waterproofing materials:

• DELTA®-MS Below-Grade Foundation Protection Membrane
• DELTA®-MS Installation Kit (termination bar, fasteners & tape)
• Shop All Foundation Waterproofing Products →

Have questions about your project? Contact our team — we're here to help you choose the right system for your foundation type, soil conditions, and budget.