Slip-Casting Polyaspartic Polyurea - Technical Guide for Polyurea

Overview

Polyurea is a two-component polyurethane urea polymer that is sprayed or hand-applied as a liquid and cures within seconds. Because it crosslinks almost instantly, it forms a dense, seamless, chemically-resistant membrane that will not blister, sag or soften the way a conventional epoxy film can.

The Delshine polyurea family covers the full performance range: 100% aromatic spray systems for heavy corrosion service, polyaspartic (3rd generation) systems that cure slowly enough for brush and roller application, single-component hand-applied grades, and pure polyaspartic cast and slip-casting systems. They share a chemistry but they are not interchangeable — each has its own mixing ratio, film build and application window.

Because polyurea cures so quickly, the success of a job is decided long before the gun touches the steel: substrate preparation, primer selection, mixing discipline and equipment calibration determine the result far more than the topcoat chemistry does. This guide walks through each member of the range, the specifications that matter on site, and the practical decisions that separate a five-year membrane from a three-month failure.

Slip-Casting Polyaspartic Polyurea: 10kg/barrel

Product identification

The identifiers below are the ones printed on the drum and quoted on the purchase order. Always order and dispatch by code, because the grade and the zinc or temperature variant cannot be inferred from the trade name alone.

Where this product is used

• Internal lining of crude oil, fuel, chemical and potable water tanks
• Ballast tanks, bilge spaces and other shipboard tank internals
• Chemical bunds, secondary containment and spill containment areas
• Offshore platform decks, risers, splash zones and process equipment
• Water and wastewater treatment tanks, digesters and clarifiers
• Pipeline external coatings, valve bodies and pipe fittings
• Mining, mineral processing and material handling equipment
• Blast walls, shotcrete structures and concrete tunnel linings

How it works in the coating system

The topcoat is the visible, exposed layer of the system. It provides the colour, the gloss and the final resistance to weathering, UV, chemicals and mechanical wear — the properties the specifier and the owner actually see and rely on.

Because it is the only coat fully exposed to the service environment, the choice of topcoat chemistry is the single decision that most affects how a coating system ages. A system that is under-specified at the topcoat will look good on day one and disappoint in five years.

Purpose in the system: The final coat of the system, applied over the intermediate coat.

Technical properties

The values below are the typical published range for this product family. The exact figures for your batch are confirmed on the batch certificate and the current technical data sheet.

Surface preparation

1. Abrasive blast the substrate to at least Sa 2½ (ISO 8501-1) using angular garnet or aluminium oxide media. Polyurea will not adhere to a merely cleaned surface — the mechanical key created by blasting is what carries the load.
2. Remove every trace of dust, oil, grease, salt and soluble corrosion product with a clean, oil-free blast. Vacuum the surface and re-blast any contaminated zone rather than trying to paint over it.
3. Check the steel for pitting. Deep pitting must be welded out and ground flush before coating — polyurea bridges a pit but does not fill it.
4. Round all edges to a minimum 2 mm radius and grind welds smooth. Polyurea applied over a sharp edge will pull back and expose a thin wedge of bare metal.
5. Control the environment. Spray polyurea needs a dry substrate, no dew point within 3 °C, ambient above 10 °C and relative humidity below 75%.
6. Apply the specified primer while the substrate is still metallically clean and slightly tacky. Do not let the primer fully cure before topcoating — intercoat adhesion is better on a B-cured primer.
7. Mask or plug threaded connections, drain openings and vent nozzles before spraying. Polyurea is very difficult to remove once it has cured.

Application procedure

Apply by spray for the best appearance and film uniformity, by roller for large flat areas, or by brush where access is restricted.

Aim for a consistent wet film across the whole area. Overlapping passes should be kept wet to avoid a lap line in the finish.

Plan the work so that the coating is applied in manufacturable quantities — a full kit should be mixed and used within the pot life, and any surplus should be discarded rather than saved.

Mixing, ratio and induction time

Two-pack finishes are mixed at the ratio stated on the data sheet, commonly 4:1 or 5:1 by volume for epoxy and 3:1 for polyaspartic and acrylic polyurethane. Use a proper mixing gauge — a mix that is even a few percent off ratio will cure differently and may not meet the published properties.

Cure, recoat window and service readiness

Surface dry in 2 to 6 hours, recoatable in 12 to 24 hours, and fully cured in 7 days. Do not place the structure into service, immersion or heavy loading before full cure, even though the surface will feel dry much earlier.

Coverage and thickness calculation

Typical dry film thickness is 60-100 µm for a conventional finish and 40-60 µm for a high-build polyurethane finish. At 80 µm, one litre covers roughly 8-10 m². Two coats are usually specified where colour, gloss uniformity or coverage hiding matter.

Technical note. Coverage (m²/litre) = (volume solids × 10) / DFT (µm)

Worked example

Advantages

• Cures in seconds to minutes, so a tank can be returned to service the same day instead of waiting a week for an epoxy to harden.
• 100% solids chemistry — no solvent to evaporate, so there is no solvent-trapped film and no VOC contribution to the plant.
• Outstanding abrasion, impact and chemical resistance, including resistance to hydrocarbons, acids, alkalis and salt water.
• Seamless, pinhole-free membranes that can be built to any thickness in a single pass without the layer-count of a conventional system.
• Excellent UV and weather resistance in aliphatic and polyaspartic grades, with no chalking or yellowing over a service life measured in decades.
• Low temperature sensitivity compared with epoxies — some polyaspartic grades can be applied down to -10 °C.

Limitations and precautions

• Aromatic 1st generation polyurea discolours badly under UV — it must be topcoated with an aliphatic or polyaspartic finish for exterior work.
• Surface preparation is unforgiving. Polyurea applied over contaminated or under-blasted steel will fail at the interface, not in the film.
• Spray polyurea demands correctly calibrated plural-component equipment. A worn nozzle or a mis-set proportioning pump will produce an off-ratio film with poor properties.
• The fast gel time leaves almost no working time — a pause in spraying can leave a cold joint or a wet edge.
• The material is expensive and the equipment is capital-heavy, so polyurea only makes economic sense on jobs where the fast cure or the chemical resistance genuinely pays for itself.

Storage and shelf life

• Store component A and component B separately in their original containers, in a cool, dry, ventilated store between 5 °C and 35 °C.
• Never store A and B at a temperature above 40 °C and never allow the drums to freeze — a frozen component will not mix correctly and must be thawed and re-homogenised before use.
• Keep the drums sealed. Component A of an aromatic system can react with atmospheric moisture and will form a skin in an open drum.
• Rotate stock using first-in-first-out. Typical shelf life is 12 months for unopened drums and considerably shorter once opened.

Safety, PPE and ventilation

• Both components contain isocyanates. Always work with local exhaust ventilation and wear a supplied-air respirator or a properly fitted organic-vapour cartridge mask.
• Wear chemical-resistant gloves, safety goggles and a coverall. Isocyanate vapour sensitises the respiratory system permanently.
• Do not spray near open flames, hot work or hot surfaces. Isocyanate vapour can ignite at elevated temperatures.
• Ensure the spray booth is negatively pressurised so overspray and vapour are drawn away from the operator.
• Dispose of empty drums through a licensed chemical contractor. Do not burn or bury residue.

Quality control and inspection

• Check colour and gloss against the approved sample or RAL reference before starting the full area.
• Measure DFT and check for thin spots, particularly over welds, edges and connections.
• Inspect the finished surface for lap marks, sag, orange peel, dust inclusion and solvent entrapment before accepting the coat.

Pricing and how to order

Delshine quotes this product per square metre at a specified dry film thickness, or per drum/litre depending on the project. The material cost is usually the smallest part of the installed cost — surface preparation, access and application labour dominate. Send us the substrate, the service conditions and the required DFT and our technical team will return a full system recommendation with a firm price.

Polyurea is priced per square metre of applied film, not per kilo of material, because coverage depends entirely on the target dry film thickness. At 2 mm, a kilo of two-component polyurea covers roughly 0.5 m², so a 1,000 m² tank needs close to two tonnes of material including waste. Always quote on DFT plus primer, not on area alone.

Frequently asked questions

The questions below are the ones our technical team is asked most often about this product family.

Related products

These products are normally used in the same system as the product described above.

• Spray Polyurea
• Polyaspartic Polyurea
• Special Thinner for Polyaspartic Polyurea Painting
• Polyaspartic Polyurea

See all products