Water Leak Repair Guide

Water pools at the wall/slab joint where concrete meets exterior stucco. Rainwater enters the unsealed horizontal gap and travels down the foundation wall directly into your basement.

Wall/Slab Gap (Ingress)

Moss & Low Cable Lines

Grab everything in a single, efficient loop through the Lansdowne store:

Sealant cannot just be dumped into a deep void. It requires a closed-cell foam backer rod so it can stretch and compress across seasonal freeze-thaw cycles without tearing away ("3-point adhesion failure").

Confirm each item as you pick it up:

• Sika 10.1 oz. Sikaflex Polyurethane Sealant (2 tubes)
  📍 Aisle 24, Bay 003 Store SKU #1002334816 61 in stock
• Sika 3/4" x 20 ft. Foam Backer Rod
  📍 Aisle 24, Bay 003 Store SKU #376378 11 in stock
• Anvil Steel Wire Scratch Brush
  📍 Aisle 09, Bay 007 Store SKU #1004547963 105 in stock
• Anvil 10 oz. Caulk Gun
  📍 Aisle 09, Bay 008 Store SKU #1006011745 157 in stock
• 3M ScotchBlue 1.88" Painter's Tape
  📍 Aisle 09, Bay 001 Store SKU #315026 725 in stock
• Venom Steel Nitrile Work Gloves (12-Pack)
  📍 Aisle 07, Bay SC2 Store SKU #1014038289 28 in stock
• Flathead Screwdriver / Stiff Putty Knife (to clear rocks/roots)
  Household / Workshop
• Shop Vacuum or Blower
  Household / Workshop
• Mineral Spirits or Soapy Water Spray + Clean Rags (essential for smoothing Sikaflex)
  Tooling / Cleanup

Any dirt, decomposed leaves, or moss left behind will prevent the polyurethane from bonding.

• Dig out the gap: Run a screwdriver or stiff scraper along the entire seam under the stucco edge to pull out trapped dirt, mulch, and dead roots.
• Scrub the green moss: Vigorously scrub both concrete faces with the Anvil wire brush until bare, sound concrete is visible.
• Vacuum completely: Use your shop-vac nozzle directly against the joint to suck out all pulverized dust.

Polyurethane reacts with moisture. Applying it to damp concrete results in outgassing, pinholes, and loss of adhesion.

• Wait for at least 24 to 48 hours of dry weather after cleaning or rainfall.
• Touch check: Reach into the joint with a dry paper towel. If it picks up any dampness, wait another sunny afternoon.

The 3/4" backer rod will compress slightly to fit snug into the 1/2" to 5/8" gap.

• Unroll the backer rod along the seam. Do not stretch it, or it will pull back later.
• Use a blunt tool (like a wood paint stick or putty knife handle) to press the rod into the gap. Avoid sharp screwdrivers that puncture the foam skin.
• Set uniform depth: The top of the rod should sit exactly 1/4" to 3/8" below the top surface of the concrete slab.

Sikaflex is famously sticky and messy. Painter's tape prevents smearing onto the stucco and slab.

• Apply 3M ScotchBlue painter's tape along the wall 1/8" above the gap.
• Apply a second strip on the flat concrete slab 1/8" away from the gap edge.

Now fill the joint to create a continuous, elastic, watertight seal.

• Put on your Venom Steel nitrile gloves. Cut the Sikaflex nozzle at a 45° angle (~3/8" opening) and puncture the inner foil seal with the caulk gun's poker.
• Push, don't drag: Hold gun at 45° and steadily push the bead ahead of the nozzle to force sealant firmly into the crevices against both sides.
• Tooling: Moisten your gloved finger with mineral spirits or soapy water and smooth the bead in one continuous, firm stroke.
• Slope angle: Shape the bead so it slopes downward from the stucco to the concrete to shed water away from the house.
• Peel tape: Pull the painter's tape slowly away at a 45° angle immediately after tooling.

As seen in `crop_2094_tube.jpg` and `crop_2093_tubes.jpg`, low-lying lines can act as water wicks directly through holes in the foundation.

• Inspect open pipe: Locate the cut tube/conduit visible in your photo. Inject Sikaflex deep into the opening to seal off the bore.
• Seal around cables: Where the black coaxial and blue Ethernet cables penetrate the wall, apply a generous 360° collar of Sikaflex.
• Form drip loops: Ensure exterior wires loop slightly downward before entering the hole so dripping water falls to the ground instead of running inside.

Polyurethane cures from humidity in the air over several days.

• Skin time: Protect the joint from direct foot traffic or rain for 24 hours (skins over in ~4 hours).
• Full cure: Reaches full elasticity in 5 to 7 days.
• Gutter check: Look above this corner during the next storm. Make sure gutters aren't overflowing and that downspouts dump at least 6 ft away.