Low-Pressure vs High-Pressure Polyurea Equipment

Two-component spray equipment for polyurea coatings, polyurethanes and foams is commonly divided into low-pressure and high-pressure classes. The distinction refers to the fluid pressure at which the A and B components are delivered to the gun and mixed. High-pressure systems rely on impingement mix spray guns driven by heated, high-pressure streams. Low-pressure systems use lower pressures and often a different mixing method, such as a static mixer, a mechanical mixer or low-pressure impingement. The material being sprayed, not preference, decides which class is suitable.

Why pressure matters

In impingement mixing, the energy that mixes the components comes from the velocity of the streams colliding in the mix chamber. Higher pressure and higher temperature (which lowers viscosity) give more mixing energy. Very fast pure polyureas, which gel in seconds, require this energy to mix completely before they react. If they are sprayed at too low a pressure or temperature:

• Mixing is incomplete.
• Film can be soft, tacky, brittle or streaky.
• Adhesion and physical properties can fall below the data sheet values.
• The defect may not be visible until the coating fails in service.

High-pressure equipment

Characteristics

• Proportioners capable of high fluid pressure and significant heat.
• Heated hoses to maintain temperature to the gun.
• Impingement mix guns with air or mechanical purge.
• Higher output for large areas.
• Typically mounted in polyurea spray rigs or fixed shop installations.

Suitable materials

• Fast-set pure polyureas, both aromatic and aliphatic.
• Hybrid polyurea coatings designed for spray.
• Spray polyurethane foam.
• Many fast-set polyurethane elastomers.

Many manufacturers state minimum pressures and temperatures for their high-pressure materials. ArmorThane, for example, specifies that its ArmorShield-class pure polyureas must be sprayed at no less than 2,800 psi and above 66 °C. Other materials have their own published limits.

Low-pressure equipment

Characteristics

• Lower fluid pressure, often with limited or no heating.
• Mixing by static mixers, low-pressure impingement or disposable cartridges.
• Smaller, lighter and simpler units.
• Lower output, suited to smaller areas, patching and detail work.
• Some systems use pressure pots or cartridge dispensers.

Suitable materials

• Slower-reacting polyurethanes and hybrids specifically formulated for low pressure.
• Some polyaspartic and slower aliphatic systems (see polyaspartic coatings).
• Cartridge-dispensed repair materials and joint fillers.
• Some bedliner products sold for low-pressure application (see truck bed liners).

A low-pressure system must not be used for a material whose data sheet calls for high-pressure impingement mixing.

Side-by-side comparison

Selection factors

1. Material data sheet. It states the mix method, pressure, temperature and ratio. This is the deciding factor (see product data sheets explained).
2. Project size and output. Large roofs, containment areas and tanks favor high-pressure output.
3. Site access. Long hose runs need equipment with enough heat and pressure capacity.
4. Finish requirements. Pattern and texture control can differ.
5. Training and support. High-pressure equipment generally needs more training and maintenance.
6. Power and air. High-pressure systems need larger generators and compressors.

Quality control

Regardless of equipment class:

• Spray a test panel at the start of each day and after material changes.
• Record pressures and temperatures for both sides.
• Check ratio when the equipment allows it.
• Inspect cured film for color uniformity, softness and adhesion.
• Measure thickness (see dry film thickness measurement).

Pressure imbalance between the A and B sides is a warning sign; see proportioner troubleshooting.

Misconceptions

• “Polyurea is polyurea.” Formulations vary widely in reactivity and equipment needs. A product for high pressure will not perform as designed through low-pressure equipment.
• “Higher pressure is always better.” Each material has an operating window. Exceeding temperature limits or using a mismatched chamber can cause problems too.
• “Low-pressure means low quality.” Low-pressure materials and equipment are designed to work together and can perform well within their intended uses.

Key terms

• High-pressure impingement. Mixing by colliding high-velocity streams in a small chamber, the standard method for fast-set polyurea.
• Low-pressure application. Application using lower pressures, typically with a static mixer or cartridge system and slower chemistry.
• Gel time. The time from mixing to the point the material stops flowing, which decides equipment choice (see pot life and gel time).
• Fast-set chemistry. Polyurea formulations that gel in seconds and need impingement equipment.
• Slow-set or hand-applied. Formulations designed to be brushed, rolled or dispensed by low-pressure equipment.

Frequently asked questions

Can I upgrade a low-pressure unit to spray pure polyurea?

Usually not. Pure polyurea needs proportioners and heaters designed for the pressure and heat it requires.

Is high-pressure equipment needed for spray foam?

Most spray foam is applied with high-pressure, heated equipment, though some low-pressure foam kits exist for small jobs.

Related entries

• Plural-component spray
• Polyurea coatings
• Proportioner troubleshooting
• Isocyanate chemistry
• Impingement mix spray guns (new)
• Polyurea spray rigs (new)