What is the difference between an expansion joint and a construction joint?

An expansion joint is designed to move and take the structure’s expansion and contraction, so it gets an elastomeric sealant or a profile. A construction joint is where a pour stopped and restarted; it is not meant to move, and is treated during construction — or injected if it leaks.

Do you treat expansion joints?

Yes — in roofs, floors and car parks — with a flexible sealant, a waterstop and a metal cover plate, depending on the joint type and its movement.

How are pipe penetrations through a roof sealed?

The pipe is cleaned and prepared, then a suitable collar or sleeve and reinforcement go around it, and the membrane is taken up the pipe high enough and secured with a clamp and sealant. Penetrations that are too close together are grouped or spaced so they can be sealed.

Why does water leak around roof and floor drains?

Because the membrane is not clamped into the drain flange, the drain body sits above the waterproofing level, or there is no reinforcement around it. That is why drains made for the waterproofing system are used, and the area around them is flood-tested.

▽ +09.00Waterproofing · Joints & penetrations

Joints & penetrations

Most leaks start at a joint or a penetration, not in the middle of a surface. Each kind of movement and each penetration has its detail.

Illustration: an expansion joint treated with a cover plate and a flexible seal

Overview Where it applies Systems Execution & QA From our projects References & FAQ

Engineering view

What is joint and penetration waterproofing?

Buildings move: they expand and contract with heat, settle, and their separate parts move relative to each other. A joint is the place designed to take that movement; treated with a rigid material, or coated over as if it were a plain surface, it cracks and becomes a water path.

Every penetration — a pipe, a drain, a base — has its own detail tying it into the waterproofing. This page covers joints and penetrations across all applications; the expansion-joint system has its own technical page.

Problems it solves

What goes wrong

Leaking expansion joints
Sealant torn, debonded or hardened; water runs along the joint.
Seepage at pour joints
A pour joint left untreated during construction becomes a seepage line.
Leaks around penetrations
Pipes, sleeves and drains not tied into the waterproofing.

Diagnose by symptom

From the system’s documented advantages

Key benefits

Lets the structure move without leaking
Replaceable components: sealant, tape and cover
Protects the joint edges from traffic damage

Documented advantages of Expansion joint systems — every system also has limits, listed on its page.

By technology

Available systems

How the system is chosen

Situation	Suitable systems	Why
An expansion joint in a roof, deck or wall	Expansion joints	An elastomeric sealant (PU, or polysulphide where specified) with a backer rod, tape or profile.
A leaking construction joint or crack	Crack injection	Epoxy injection to repair, or PU to stop water.

A starting point only: the final system follows the inspection, the approved specification and the product TDS.

Layers

System build-up

Illustrative drawing, not to scale; materials and thicknesses follow the approved specification and the manufacturer’s recommendations.

System build-up5 layers

Expansion joint systems

Select a layer to see what it does.

Cover plate or profile
In floors and car parks that carry vehicles and people.
Where trafficked
Elastomeric sealantCore layer
Placed to a designed width and depth, bonded to the two joint faces only.
Backer rod
Sets the sealant depth and stops it bonding to the joint bottom.
Joint waterproofing tapeCore layer
Bonded either side with a loop that allows movement, and tied into the surrounding waterproofing.
Concrete either side
Sound, clean and dry edges.

A typical build-up for this application, top to bottom.

System page: how it works and its limits

Brand-neutral

Manufacturers & approvals

Fosroc (Saint-Gobain)Approved applicatorCertificate
AwazelApproved applicatorCertificate

We start from the engineering of the system, then the product. Manufacturers appear here only with their documented relationship; this does not imply a commercial partnership.