Polyurethane Resin

What Is Polyurethane Resin?

Types of Polyurethane Resin Systems

• Aliphatic polyurethane: UV stable formulations that hold colour and gloss outdoors, used as topcoats over epoxy bodies and as full system finishes on external bunds.
• Aromatic polyurethane: lower cost than aliphatic, with similar chemical and mechanical properties but a tendency to chalk and yellow under UV. Used indoors and below grade.
• Polyurethane concrete (PUC or PUMA): cementitious polyurethane hybrids, the standard PU flooring across food and beverage production, with outstanding thermal shock resistance and high tolerance for substrate moisture.
• Polyurethane screed and self smoothing PU: pourable systems for substrate levelling layers and low build floor finishes where flexibility is part of the design case.
• Moisture cure single pack polyurethane: for repair and detail work where mixing two components on site is impractical.
• Two pack high solids polyurethane: the workhorse for protective coating duty where a balance of flexibility, chemical resistance and build is needed.

Polyurethane Key Features

Polyurethane Applications

• Food and Beverage: polyurethane concrete production floors, ingredient stores, dairy and brewing halls, and any area subject to hot CIP, steam and chilled handling.
• Power Generation and Transmission: outdoor transformer bunds, generator yard aprons and external standby fuel compounds, where UV and seasonal cycling drive material choice.
• Oil, Gas and Petrochemical: outdoor tank bunds, tanker offload aprons and forecourt surface bunds where weather exposure is part of the design case.
• Chemical Processing: external reagent compounds, dosing skid surrounds and process areas with significant thermal movement.
• Agriculture and Aquaculture: silage clamp surrounds, AD plant external bunds, fertiliser compounds and aquaculture tanks exposed to UV.
• Sewage and Waste Water Treatment: external storm tank tops, channel covers and trade effluent bunds with thermal cycling.
• Nuclear Facilities: selectively, on outdoor decommissioning yards, fuel store roofs and exposed support structures.

Polyurethane Chemical Resistance Profile

Polyurethane resists well:

• Hydrocarbons: diesel, kerosene, lube oils and most lubricants.
• Dilute acids and alkalis at moderate concentration.
• Hot water, steam and hot CIP chemistry, especially in PU concrete.
• Most cleaning chemistry in food, beverage and industrial production.
• Salts, brine and aqueous solutions.
• Routine sanitisers such as sodium hypochlorite and peracetic acid at use concentration.

Polyurethane has limitations against:

• Concentrated mineral acids above moderate strength, where vinyl ester or novolac is the better answer
• Strong oxidising chemistry at high concentration
• Some polar solvents — DCM, DMF, acetone — at concentration
• Hot caustic, where alkali combines with elevated temperature
• Hydrofluoric acid, requiring rubber bunding or specialist alternatives

Polyurethane Build Up Methods

Polyurethane Application Conditions

• Air temperature: typically 5–30°C, with cold-cure variants for work in lower temperatures.
• Substrate temperature: at least 3°C above dew point, with continuous monitoring across each working day.
• Relative humidity: more sensitive than epoxy; most PU systems require below 75% RH during application and cure, with higher humidity causing surface defects and accelerated cure on aromatic systems.
• Substrate moisture: under 4% on standard PU; PU concrete tolerates higher moisture, often up to 6–8%, which is one of its operational advantages.
• Pot life: typically shorter than epoxy, often 20–40 minutes once mixed, demanding faster placement and tighter batch control.
• Recoat window: system-specific, often tighter than epoxy, with missed windows requiring mechanical keying.
• Application equipment: roller, brush, airless and plural-component spray for coatings; trowel and screed bar for PU concrete.
• Mixing discipline: exact ratios, mechanical mixing, and immediate placement once the catalyst is added. PU is unforgiving of partial or rushed mixing.

Polyurethane Advantages and Limitations

Advantages

• The most flexible chemistry in our range, with crack-bridging and substrate movement tolerance no rigid system can match
• Excellent thermal cycling and thermal shock resistance, particularly in PU concrete form
• UV stability with aliphatic systems, retaining colour and gloss across years of external exposure
• Wide operating temperature range, with PU concrete spanning sub-zero to 130°C
• Outstanding abrasion and impact resistance under daily traffic and wash-down
• Tolerant of higher substrate moisture in PU concrete form, opening up applications where standard epoxy will not cure
• Available across multi-coat coatings, mortars, screeds and self-smoothing systems

Limitations

• More moisture-sensitive during application than epoxy, demanding tighter humidity and substrate moisture control
• Shorter pot life than epoxy, requiring faster placement and stricter batch discipline
• Aromatic PU systems chalk and yellow under UV; aliphatic must be specified where appearance matters
• Higher cost per litre than basic epoxy, justified by performance rather than headline rate
• Generally lower hardness than premium epoxy, with abrasion performance dependent on the specific formulation
• Limited resistance to concentrated acids, strong oxidisers and aggressive polar solvents

How Polyurethane Compares to Other Systems

• Versus Epoxy Resins — polyurethane is more flexible, more UV stable and better at thermal cycling; epoxy is harder, more chemically resistant for general duty and more cost-effective. We often pair them, with an epoxy body coat under a polyurethane topcoat.
• Versus Polyurea Resins — polyurethane is conventional cure, applied as multi-coat or self-levelling at standard pace; polyurea is rapid spray-applied with much faster return to service, at higher capital cost and less variant flexibility.
• Versus Vinyl Ester Resins — polyurethane is the natural choice for movement and weather; vinyl ester handles concentrated acids, oxidisers and FRP/GRP lay-up duty that polyurethane cannot reliably hold.
• Versus Novolac Epoxy Resin — polyurethane handles thermal cycling and substrate movement; novolac handles hot acid, hot solvent and elevated-temperature chemical attack. The two solve different problems.

Polyurethane FAQs