Elsewedy Cables Roof Joint Waterproofing
The joints in Elsewedy’s sandwich-panel roofs were closed with hot-spray polyurea in 2018, on the long metal decks of one of Egypt’s cable makers.
01 · Project overview
What is this project?
Elsewedy builds cable and electrical equipment for work across Egypt and well beyond it. The plants that do that sit under long metal roofs. Those roofs are not one skin. They are sandwich panels butted together, and every butt joint is a place rain can sit, then get in.
A hard bead of sealant fights the panel. The panel moves with the sun, the bead cracks, and the leak shows up over the machines. In 2018 those joints were given a sprayed polyurea film, a membrane that can stretch with the metal instead of arguing with it.
| Place | Elsewedy Cables |
|---|---|
| Year | 2018 |
| Scope | Roof joints on sandwich panels |
| System | Hot-spray pure polyurea |
02 · The challenge
What did this structure ask of the membrane?
A sandwich-panel roof is a field of movement. Noon heat opens a joint a fraction. Night pulls it shut. Any seal harder than that movement tears at the edge of the panel. The waterproofing has to cross the gap and stay stuck to both sides, on a rib that is rarely flat and never still.
03 · The solution
Which Krypton system was trusted here?
Hot-spray pure polyurea was trusted because it lands as a continuous film across the joint and gels in seconds, before it can run off a vertical rib. Krypton’s Polyurea Rayston is that film. One pass covers the gap and the metal either side of it, which is the only way a moving joint stays closed.
04 · Application
How is this system built?
Concrete is prepared before any resin goes down. Polyurea Rayston, Krypton’s hot-spray pure polyurea, wants a support that is flat, compact and cohesive. Pull-off strength should be at least 1.4 N/mm2. Cracks are cut out and filled first. High-pressure sand or abrasion opens the pores, and the dust is vacuumed off. Moisture in the concrete must sit under 4 percent. Concrete temperature belongs between 10 and 40 degrees C, and the air should be under 85 percent relative humidity. If damp is suspected behind the slab, two coats of epoxy primer go on, the second one blinded with quartz sand. Metal is cleaned and primed with a polyurethane primer. That bond is what stops a blister when the structure heats up.
A joint in a metal roof opens and closes every day. A hard seal tears. A sprayed film can follow that movement and close the gap without a lap to peel.
Spraying is hot and fast. Both components are brought to about 25 to 30 degrees C before they are loaded. In the machine they run hotter: about 65 degrees C on the resin, 75 degrees C on the isocyanate, and 65 degrees C in the hose. Pressure at the gun is at least 140 bar. The usual build is 1.5 to 2.0 kg/m2, which leaves a film about 1.5 to 2 mm thick. Gel time is about 4 seconds at 25 degrees C. The surface is tack-free in a matter of seconds, not hours. Hardness climbs from roughly 28 Shore A at five minutes to about 88 Shore A after four days. One pass should make the thickness. Where a corner needs a second pass, it should follow within about two hours.
Speed is the practical gift on a crowded site. Upstands, outlets and internal corners can be closed before the next trade arrives. The film itself is elastic. Typical elongation is 324 percent and tensile strength is 16.2 MPa, with tear strength around 69 N/mm. It bridges cracks instead of snapping when concrete moves.
A joint in a metal roof is a moving target. The spray crosses it as one film, so there is no lap sitting there waiting to peel. Typical elongation is 324 percent, with tensile strength of 16.2 MPa and tear strength around 69 N/mm, which is the give a panel joint needs when the sun opens it at noon. The resin is aromatic. A joint left in the weather should take an aliphatic topcoat if the colour has to stay even. Water uptake is very low, about 0.002 kg/m2 per square-root hour. CE marking to EN 1504-2 and European Technical Assessment 16/0148 belong to the product, not to a reading taken on this roof.
Polyurea Rayston technical data sheet
After the spray, walk the joint, not just the middle of the panel. The film has to land on both sides of the gap and stay thick where the metal changes direction. A second pass, if a rib needs it, should follow within about two hours. Where the joint sees the sun, the aliphatic coat goes on before the first summer, because the polyurea underneath will keep its strength and lose its colour. That is the whole of the aftercare on a metal roof.
05 · Results
What does a job like this ask us to stand behind?
The duty on a cable-plant roof is ordinary and strict. Rain stays on the weather side of the panel. A joint that can open with the day and still hold water is what this spray is there to stand behind.
06 · Products
Which products carry this duty?
Polyurea Rayston
Hot-spray pure polyurea. Typical build 1.5 to 2 mm. Elongation 324 percent. Root resistance tested to CEN/TS 14416.
07 · FAQ
Frequently asked questions
How fast does the polyurea set?
Polyurea Rayston gels in about 4 seconds at 25 degrees C and is tack-free in seconds. Full hardness still takes days.
Will the joint split when the panel moves?
Typical elongation is 324 percent. The spray crosses the joint as one film, so there is no lap to peel when the metal opens in the heat.
How thick is a normal spray coat?
The usual rate is 1.5 to 2.0 kg per square metre, about 1.5 to 2 mm. That is guidance from the datasheet, not a reading taken on this job.
Does sunlight damage it?
Colour can shift because the resin is aromatic. Strength stays. An aliphatic topcoat is added where the film remains in the sun.
What moisture can the concrete have?
Support moisture should be under 4 percent, with concrete between 10 and 40 degrees C. Wetter concrete gets an epoxy primer blinded with quartz.