Construction Joint Waterproofing 101

Every time concrete is poured against a previous pour, a construction joint is created. These joints are planned and necessary — but they are also one of the most common places for water to enter a basement, water tank or retaining wall. Here is how to keep them dry.

Why joints leak

A construction joint is a plane of weakness. Even with good workmanship, the bond between old and new concrete is rarely perfectly watertight. Shrinkage, vibration and hydrostatic pressure open micro-gaps along the joint, and water finds them.

Two approaches: proactive and reactive

Proactive: injection-hose systems

The modern best practice is to cast an injection hose into the joint during construction. The hose is laid along the joint and its ends are brought out to accessible termination points using hose connectors.

• If the joint later leaks, resin is injected through the hose, which distributes it along the entire joint and seals it from within.
• Because the hose is already in place, the repair is fast, clean and re-injectable.

This is the lowest-risk option because it builds the cure into the structure before a leak ever appears.

Reactive: drilled injection

When no hose was installed and a joint starts leaking, the joint is sealed by drilling and injecting just like a crack:

1. Drill holes that intersect the joint at depth, staggered along its length.
2. Fit packers.
3. Inject a polyurethane resin — a foaming PU for active water, a flexible PU where movement is expected.
4. Work along the joint until it is fully sealed.

Choosing the resin

• Active, flowing water: a fast hydrophobic foaming PU chokes the flow.
• Damp or weeping joints: a flexible PU seals while tolerating slight movement.
• Dormant, dry joints needing strength: epoxy, though this is less common for joints than for structural cracks.

Detailing that prevents trouble

• Install waterstops at joints in water-retaining structures.
• Keep injection-hose termination points accessible and clearly marked.
• Don’t rely on surface coatings alone to bridge a moving joint — they will tear.

The takeaway

Construction joints don’t have to be a weak point. Plan for them with injection hoses on new work, and treat them decisively with resin injection on existing structures. Either way, the goal is the same: seal the joint along its full length, not just at the surface.

Need help specifying an injection-hose system or a joint-sealing resin? We’re a WhatsApp message away, with samples on request.