Expansion Joint Waterproofing with Polyurea: Methods and Steps

Expansion joint waterproofing polyurea work deals with the one place where a concrete structure is meant to move. A spray membrane bonds well to flat concrete. However, a joint opens and closes with heat, load and settlement. So it needs its own product and its own detail. This guide explains the options Krypton Chemical documents and the steps on site. It also shows how joints differ in tanks, roofs and floors.

Contents

• Why joints are the weak point of liquid membranes
• Expansion joint waterproofing polyurea options from Krypton
• Step-by-step expansion joint waterproofing polyurea
• Expansion joint waterproofing polyurea in tanks, roofs and floors
• Expansion joint work by Target in Egypt
• Frequently asked questions
• Request a joint survey in Cairo

Why joints are the weak point of liquid membranes

A liquid membrane bonds fully to the concrete below it. In fact, that is its strength on a flat slab. At a joint, though, the two sides move apart and back again. As a result, a thin film over that gap carries all the movement in a very small strip.

For this reason, Krypton’s car park roofs page names a common mistake. It is “bridging movement joints or penetrations without a designed detail and compatible reinforcement.” In other words, the membrane alone is not the joint solution. The joint needs a filler or a band, and the membrane must then tie into it.

Expansion joint waterproofing polyurea options from Krypton

Krypton documents several joint products. Each one, however, has a different job, so it helps to read them side by side.

Product	Type (per TDS)	Intended use (per TDS)
Rayston Flex 70	Two-component modified-polyurea mastic, from cartridges with a pump	Expansion and working joints outdoors: roofing, water treatment structures, bridge decks, foundations
Rayston Flex Joint GEO	TPE band with geotextile strips on both sides	Expansion joints in walls, roofs, terraces, water tanks, water treatment plants, pools, basements
Geomax	Polyester/polyamide geotextile	Reinforcement; also “an inner stopper when filling expansion joint spaces”
Rayston Flex 90	Modified-polyurea mastic	Joints and cracks in concrete floors

Rayston Flex 70: polyurea mastic

The Rayston Flex 70 datasheet describes a “polyurea mastic, mechanically applied”. It comes in prefilled cartridges. Also, it needs a dedicated pump from Krypton. Key values from the Rayston Flex 70 datasheet (PDF):

• Elongation at break of 690% and tensile strength of 20 MPa.
• Watertight to EN 1928 (60 kPa, a 6 m water column).
• No cracking when folded at −45 °C.
• Gel time of about 12 seconds at 25 °C.

Rayston Flex Joint GEO: elastic band

Meanwhile, this band suits wide joints and joints with large movement. Its datasheet lists a 170 mm width and a thickness of about 1.5 mm. It also reports water pressure resistance above 3 bar (DIN EN 1828). On dry concrete you bond it with epoxy glue. On damp concrete, however, the datasheet uses a flexible waterproof mortar instead.

How much mastic do you need?

The Flex 70 datasheet gives a theoretical yield table. For example, one 1.7 kg cartridge fills about 11.8 m of a joint 12 mm wide and 10 mm deep. However, this figure does not include losses. So Krypton advises a site test first.

Geomax and Rayston Flex 90

Geomax can act as a stopper inside a joint, so the liquid does not run away. Note, though, that its datasheet is written around Impermax membranes, which are polyurethane. So confirm its use in a polyurea system with Krypton. Rayston Flex 90, finally, is for floor joints only.

Step-by-step expansion joint waterproofing polyurea

1. Open and clean the joint

First, open the joint to its design width. Then remove dust, oil, old sealant and water. The Flex 70 datasheet says the joint must be clean and free of water, and it needs no special primer.

2. Check the weather

Next, check the air. For Flex 70, air should be between 10 °C and 40 °C, with humidity below 70%. For the GEO band, apply between +5 °C and +30 °C, and not when rain is expected within 24 hours.

3. Place a stopper or backing

Then set the depth of the filler. Geomax is one documented stopper. Otherwise, follow the backing that the project drawing shows.

4. Fill or band the joint

After that, fill the joint fully with Flex 70 and cut off the excess. The datasheet says you can cut it with a steel blade after 60 seconds. Or, for a band, press GEO into fresh glue or mortar. Then add a second layer on top. Join two pieces with a patch or a hot-air welded overlap of at least 40–50 mm.

5. Tie in the main membrane

Next, bring the main membrane up to the joint detail as drawn. In short, the detail decides where the membrane stops, laps or passes over.

6. Cure and protect

Flex 70 resists rain drops after 5 minutes and light foot traffic after 1 hour. The GEO band takes about 3–4 days to cure at 20 °C. Also, its datasheet asks you to protect the band from mechanical damage.

Expansion joint waterproofing polyurea in tanks, roofs and floors

Each place puts a different load on an expansion joint waterproofing polyurea detail:

• Tanks. The GEO band lists water tanks and permanent immersion. For negative water pressure, its datasheet calls for a metal plate on one side.
• Roofs and podiums. Flex 70 lists roofing. Both products accept outdoor use.
• Floors. Wheels cross the joint all day, which is why Krypton has Rayston Flex 90 for concrete floors.

For more on this, see our pages on repairing expansion joints and filling joints.

Expansion joint work by Target in Egypt

This section lists project records only. It is separate from the product guide above. Target Engineering’s presentation lists “Expansion Joints treatment by using Polyurea” on these projects:

• Wadi El-Natroon lifting station (7, 8), contractor SIAC, consultant Hydro.
• El-Mostakbal Tanks, contractor SIAC, consultant Space.
• Ministry AFF, New Capital, contractor SIAC, consultant ECG.
• Mansoura 1, contractor TIBA, consultant Five Plus.

The records name no product for these joint works.

Frequently asked questions

Is polyurea a joint sealant?

Some polyurea products are. Rayston Flex 70 and Flex 90 are polyurea mastics made to fill joints. A spray membrane, by contrast, is a surface layer. It bridges fine cracks but does not replace a joint detail.

How much movement can a joint take?

The datasheets give material values, such as 690% elongation for Flex 70. They do not give a joint movement rating. So the joint size comes from the structural engineer.

Can old mastic joints be repaired?

Yes. The GEO band datasheet lists the “repair of expansion joints made with mastics or water-stop-like joints”.

What about joints in tanks?

Treat them first, then apply the main lining. Our hot and cold applied polyurea article explains the lining methods.

Request a joint survey in Cairo

Send us photos, joint widths and drawings. We will inspect the joints and propose an expansion joint waterproofing polyurea detail with its datasheets. You can also read the Rayston Flex Joint GEO datasheet (PDF).

• Office: 48 El-Horreya St, Heliopolis, Cairo
• Phone: +20 120 226 9326
• Email: admin@targetsw-eg.com
• Online: contact Target Engineering

For more background, read our polyurea waterproofing guide. For concrete repair practice in general, the International Concrete Repair Institute is a useful source. Target also works from offices in Abu Dhabi and Kenitra.