Epoxy and Polyurethane Selection Guide: System-Level Decision Framework and Scenario-Based Comparison

In industrial protective and floor engineering, "epoxy or polyurethane" is the most frequently asked and also the easiest-to-get-wrong question. Many projects decide by habit: all floors use epoxy, all outdoor use polyurethane — resulting in either outdoor epoxy yellowing and chalking, or low-temperature polyurethane softening and poor abrasion resistance. Epoxy and polyurethane are not about "which is better", but "which is more suitable" — they chemically follow two different routes (epoxy is epoxy ring-opening amine addition, polyurethane is isocyanate and hydroxyl addition), and their performance profiles are naturally complementary. This article provides a system-level decision framework: first break down the mechanism differences, then score item by item across six dimensions of "medium, weathering, temperature, load, displacement, schedule", and finally land on a scenario-based selection table and supporting solutions, helping you turn selection from "by feel" into "by matrix".

As a technical supplier of industrial protective coating, Kexin New Materials (kexinMaterials) provides both epoxy and polyurethane systems. This article does not favor either side, but only gives executable conclusions based on working conditions, for engineers and procurement to reference.

I. Mechanism Differences Determine Performance Profiles

Epoxy: the epoxy group (—CH—CH—) of epoxy resin (bisphenol A, etc.) undergoes ring-opening under amine curing agent, and adds with amine hydrogen to form a three-dimensional cross-linked network with ether bonds, hydroxyl groups, and benzene rings as the skeleton. Characteristics: strong adhesion, high cross-link density, chemical resistance (especially alkali and water resistance), low shrinkage, but the aromatic structure makes it poor in UV resistance, high brittleness, and almost no displacement follow-up.

Polyurethane: polyisocyanate (—NCO) and polyol (—OH) add to form urethane bond (—NH—COO—). By using isocyanate types (aliphatic HDI/IPDI vs aromatic TDI/MDI) and soft-hard segment microphase separation, weathering, elasticity, and abrasion resistance can be tuned. Characteristics: extremely wide adjustable range — from hard-brittle to high-elastic, outstanding abrasion resistance and elasticity, aliphatic PU is weather-resistant and non-yellowing, but its strong alkali and temperature resistance are generally inferior to epoxy.

One-sentence profile: epoxy is strong in "adhesion + chemical resistance + rigidity", polyurethane is strong in "weathering + elasticity + abrasion resistance". Selection is about seeing which side the working condition needs more.

II. Six-Dimension Decision Framework

Break selection into six measurable dimensions and judge each one.

1. Medium (Chemical Exposure)

• Long-term contact with strong alkali, solvent oil, salt spray, alternating acid and alkali: prioritize epoxy (ether bond alkali resistance, dense shielding).
• Only atmospheric exposure, rain, mild chemicals: polyurethane is sufficient, and has better weathering.
• Strong oxidizing acid, high-temperature strong corrosion: both need upgrading (phenolic epoxy, vinyl ester, lining, see epoxy chemical resistance performance https://www.psste.com/epx-chemical-resistant/).

2. Weathering / UV

• Outdoor, daylight roof, exposure: must use aliphatic polyurethane (HDI/IPDI); epoxy will yellow and chalk outdoors (see aliphatic and aromatic polyurethane https://www.psste.com/epx-aliphatic-aromatic/ and polyurethane varnish yellowing resistance https://www.psste.com/epx-pu-varnish/).
• Indoor, underground, inside tank: weathering not sensitive, epoxy has higher cost performance.

3. Temperature

• Medium temperature (≤ 80–100℃ depending on system), need thermal cycling resistance: epoxy (especially phenolic epoxy) is more stable.
• Room temperature, need low-temperature flexibility: polyurethane (especially polyether type) is better.
• Low-temperature construction: both have low-temperature curing agents available (see epoxy curing agent selection https://www.psste.com/epx-curing-agent/).

4. Load / Abrasion

• Heavy-duty forklift, steel wheel, high-frequency traffic: epoxy self-leveling/mortar has outstanding abrasion and compression resistance; polyurethane elastic topcoat resists impact but slightly lower compression resistance.
• Pedestrian, light load: both are fine, polyurethane feels more elastic underfoot.

5. Displacement / Elasticity

• With expansion joints, cracks, shock absorption needs: polyurethane elastic layer (elongation at break can reach hundreds of percent) or elastic epoxy (see elastic epoxy expansion joint treatment https://www.psste.com/epx-elastic/) is more suitable; rigid epoxy does not follow displacement.

6. Schedule / Odor

• Fast schedule, low odor: water-based or high-solid systems; both polyurethane and epoxy have water-based versions; water-based polyurethane floor see epoxy and polyurethane floor elastic coating https://www.psste.com/epx-pu-floor/.

The table below gives an overview of the six-dimension comparison:

III. Scenario-Based Selection Table

Give conclusions directly by common working conditions:

IV. Compatibility Is Better Than Going Solo

The optimal solution is often a composite system of "epoxy primer + polyurethane finish", leveraging each other's strengths:

• Anti-corrosion配套 (ISO 12944-5 approach): Epoxy zinc-rich primer (cathodic protection) + epoxy micaceous iron oxide intermediate coat (flake shielding) + aliphatic polyurethane topcoat (weathering decoration). This is the classic three-layer heavy anti-corrosion, primer and intermediate strong adhesion and chemical resistance, topcoat weather-resistant non-yellowing.
• Floor配套: Epoxy primer + epoxy leveling/self-leveling + aliphatic PU finish (outdoor) or epoxy finish (indoor); joint nodes treated with elastic epoxy/PU.

Interlayer compatibility of the配套 is a prerequisite. Same manufacturer, system verified by配套 has the lowest risk; cross-system mixing must first do small-sample verification (whether it bites through, whether adhesion meets GB/T 5210 pull-off method requirements).

V. Common Selection Errors

• Error 1: Outdoor use of ordinary epoxy. Yellowing and chalking within months, should change to aliphatic PU topcoat.
• Error 2: Strong alkali environment using ordinary PU. PU ester bond alkali resistance is inferior to epoxy, long-term under alkali liquor choose epoxy.
• Error 3: Large displacement joint sealed with rigid epoxy. Must crack, should use elastic epoxy/PU.
• Error 4: Only look at unit price. Epoxy unit price is low but outdoor life is short, comprehensive life-cycle cost may be higher; calculate by full life cycle.
• Error 5: Ignore VOC and schedule. Indoor/food plant need low odor low VOC, choose water-based or high-solid (refer to GB 30981-2020 and GB 50325 approach).

Kexin New Materials (kexinMaterials)It is recommended to first sort out the working conditions for key projects (six dimensions: medium, temperature, load, displacement, weather resistance, construction period), and then allocate the "primer/intermediate coat/topcoat" roles between epoxy and polyurethane accordingly. If necessary, apply a 1–2 m² sample panel and confirm after one working condition cycle before implementation.

VI. Quick Decision Checklist

Your actionable checklist:

1. Outdoor/UV exposure? Yes → Topcoat must be aliphatic PU.
2. Strong alkali/solvent/salt spray? Yes → Primer priority epoxy.
3. Expansion joints/cracks/vibration damping? Yes → Add elastic epoxy or PU elastic layer.
4. Heavy load and high frequency? Yes → Epoxy self-leveling/mortar load-bearing.
5. Strong corrosion beyond boundary? Yes → Upgrade epoxy (phenolic/vinyl ester/lining).
6. Low odor/low VOC requirement? Yes → Water-based or high-solid system.
7. Tight schedule? Yes → Choose fast-cure/high-solid, verify pot life (see two-component coating mix ratio https://www.psste.com/epx-mix-ratio/).

The more "yes" items satisfied, the more you should take the composite route of "epoxy primer + intermediate coat + PU topcoat" or "epoxy load-bearing + elastic joints".

VII. Standards and Testing Correspondence

Selection conclusions must be verified by standards:

• Weather resistance: ISO 11341 / GB/T 1865 xenon arc weathering; aliphatic PU far superior to epoxy in gloss and color retention;
• Salt spray: ISO 9227 (equivalent to ASTM B117);
• Adhesion: GB/T 5210 pull-off method;
• Abrasion: GB/T 1768;
• Hardness: GB/T 6739 pencil hardness;
• Flexibility/elongation: GB/T 528 / ASTM D412;
• VOC: GB 30981-2020, GB 50325.

Ground the "selection conclusion" in these measurable indicators so engineering acceptance has a basis.

VIII (Supplement). Quick Selection by Industry Scenario

Electronics plant: epoxy self-leveling + anti-static; pharmaceutical/food: low VOC epoxy/water-based PU, hygienic grade non-porous; automotive plant: epoxy floor + aliphatic PU equipment finish; petrochemical tank farm: phenolic epoxy/vinyl ester + lining; bridge steel structure: zinc-rich primer + micaceous iron oxide intermediate + aliphatic PU topcoat; underground garage: epoxy primer + intermediate + epoxy/PU topcoat; outdoor platform ramp: epoxy primer + PU elastic/wear-resistant topcoat. Remember the three tips: choose epoxy for indoor heavy load, choose PU for outdoor weather resistance, choose special epoxy for corrosion upgrade.

IX (Supplement). Cost and Service Life Trade-off in Selection

Low unit price does not mean low cost. Ordinary epoxy used outdoors, after several years of yellowing and chalking requiring rework, the life-cycle cost may exceed aliphatic PU; high-solid/solvent-free although higher unit price, saves process steps and complies with low VOC, overall superior. Reverse-engineer materials based on design life (e.g., ISO 12944 durability grade 5–15 years) to avoid paying repair costs for saving material costs.

X (Supplement). Minimum Verification List for Selection Implementation

Do three things before implementation: one, list the six working condition dimensions (medium, weather resistance, temperature, load, displacement, schedule) and tick; two, define primer/intermediate/topcoat roles according to the matrix in this article; three, apply 1–2 m² sample panel, verify through one working condition cycle with no cracking, delamination, gloss loss, then sign technical agreement. Kexin Materials (kexinMaterials) provides working condition diagnosis + system solution + process card integrated delivery for key projects, bringing selection from paper to replicable processes.

XI (Supplement). Common Cross-System Compatibility Traps

Trap 1: PU applied before epoxy cured, amine migration causes yellowing; Trap 2: PU topcoat incompatible with epoxy intermediate causing biting; Trap 3: aromatic PU topcoat used outdoors, inevitable yellowing; Trap 4: ordinary PU misused in strong alkali environment. Cross-system must verify adhesion (GB/T 5210) and aging with small samples before large-area application.

XII. Quick Selection by Medium Environment

Contact with strong alkali, salt spray, mineral oil: epoxy priority; outdoor UV exposure: aliphatic PU priority; strong oxidizing acid or high-temp concentrated acid: phenolic epoxy/vinyl ester/lining; expansion joints and vibration damping: elastic epoxy or PU elastic layer; low odor low VOC: water-based or high-solid. Use medium environment as the first filter for selection, then discuss cost.

XIII. Quick Selection by Structural Part

Floor: epoxy self-leveling/mortar load-bearing, outdoor add PU topcoat; wall equipment: epoxy or PU both ok, outdoor use aliphatic PU; steel structure bridge: zinc-rich primer + micaceous iron oxide intermediate + aliphatic PU topcoat; tank inner wall: phenolic epoxy or lining; expansion joint: elastic material. The part determines stress and exposure, and is the coordinate of system design.

XIV. Standard Template for Selection Documents

Recommended technical specification includes: six working condition dimensions, medium matrix, environmental grade (ISO 12944), design life, film thickness and number of coats, key indicator thresholds (adhesion/abrasion/elongation/weathering hours), VOC limits, acceptance method and sample requirements. Templating makes selection comparable and auditable, and facilitates supplier quotation and accountability.

XV. Arbitration Principles for Common Selection Disputes

Disputes often stem from "save money" vs "durable". Arbitration principle: safety and compliance non-negotiable (VOC, food contact); outdoor weather resistance non-negotiable (must be aliphatic); corrosion upgrade by matrix not luck. Insist on non-negotiable items, optimize negotiable items by life-cycle cost, is the basis of objective arbitration.

XVI. Compatibility Decision of Epoxy and Polyurethane in Steel Structure Anti-Corrosion

Steel structure: atmospheric zone uses zinc-rich primer + micaceous iron oxide intermediate + aliphatic PU topcoat (ISO 12944-5); buried or immersed zone uses coal tar epoxy or solvent-free epoxy; high-temperature zone uses silicone or heat-resistant epoxy. Decision by environmental grade (C1–C5, Im) and part, not a uniform paint. For compatibility decision see epoxy micaceous iron oxide intermediate coat and epoxy chemical resistance.

XVII. Compatibility Decision of Epoxy and Polyurethane in Flooring

Flooring: indoor heavy load uses epoxy self-leveling/mortar; outdoor and ramp use epoxy primer + PU topcoat; joints and vibration damping use elastic epoxy/PU elastic layer; low odor uses solvent-free or water-based. Decision by load, weather resistance, displacement three dimensions, see dedicated articles. Floor compatibility is the most common implementation point of this selection framework.

XVIII. Cost Quantification Method for Selection Errors

Convert selection error into: rework material + construction + downtime + brand. Example: epoxy misused outdoors, chalking rework in 3 years, unit annual cost may double. Quantification method supports "spend when should" with numbers, and facilitates reporting to management. Cost is the last check of selection decision.

XIX. Documentation and Handover of Selection Conclusion

Selection conclusion documented as: condition table + medium matrix + system structure diagram + indicator threshold + acceptance method + sample requirements. Documentation aligns procurement, construction, acceptance three parties, and facilitates later maintenance and expansion. Kexin Materials (kexinMaterials) delivers the document package together with the system solution, ensuring consistency from selection to operation.

XX. Application Decision of Epoxy and Polyurethane in Automotive Plant

Automotive plant: workshop floor epoxy self-leveling load-bearing; equipment exterior aliphatic PU weather-resistant; conveyor line area elastic PU vibration damping. Decision by part stress and exposure, mixed use most economical. Automotive plant is a typical field of epoxy+PU composite, selection logic replicable to other manufacturing plants.

XXI. Decision of Epoxy and Polyurethane in New Energy Field

Lithium battery workshop needs anti-static epoxy; photovoltaic bracket uses zinc-rich + micaceous iron oxide + aliphatic PU; energy storage container interior uses chemical-resistant epoxy. New energy superimposes safety and weather resistance requirements, stricter selection. New energy is the fastest growing compatibility market, decision must be forward-looking.

XXII. Evaluation of Supplier Capability in Selection

Evaluate supplier: complete formulation and TDS, compatibility verification data, engineering cases, testing and compliance documents, technical service response. Capability determines compatibility implementation quality. Include supplier capability in selection to avoid "right material, poor service" failure.

XXIII. Review and Iteration of Selection Conclusion

After project commissioning, review: difference between actual and预设 conditions, failure points, cost deviation. Review feeds back to selection template, making next time more accurate. Selection is not one-time, but a "hypothesis—verification—correction" loop. Establish annual review mechanism with key customers for continuous optimization.

XXIV. Boundary of Selection FAQ Quick Reference

This article provides framework not replacement for specific TDS. Final selection subject to supplier technical documents and sample verification. Framework helps avoid detours, but execution must land on data and samples. Treat quick reference as start not end, is responsible selection attitude.

XXV. Summary of Common Misunderstandings in Epoxy and Polyurethane Selection

Misunderstanding list: epoxy outdoors, ordinary PU in strong alkali, rigid for large displacement, only look at unit price, cross-system mixing. Summarize into checklist, verify item by item before selection to avoid pitfalls. Misunderstandings mostly from empiricism, checklist systematically avoids. Post list in technical review meeting to reduce low-level mistakes.

XXVI. Integrated Delivery of Selection and Construction

Selection implementation relies on construction, integrated delivery reduces disconnect. Delivery includes system solution, process card and on-site training, so design intent implemented into process. Integrated delivery is more reliable mode, making selection not just on paper, but landing on replicable construction quality.

XXVII. Standard Reference List in Selection

Key standards: ISO 12944 (system and environmental grade), GB 30981 (VOC), GB 50209 (floor acceptance), GB/T 5210 (adhesion), GB/T 1768 (abrasion), ISO 11341 (weather resistance). Standard list makes selection traceable and auditable. Referenced standards must indicate version in technical agreement.

XXVIII. Applicability and Limitation of Selection Framework

This framework applies to most industrial anti-corrosion and flooring scenarios, but extreme conditions (ultra-high temp, strong oxidation, nuclear grade) still require customization and special verification. Know limitation not blind use, complex projects please supplier co-design. Framework is start, rigorous verification is end.

XXIX. Balance of Selection and Cost

30. Cross-disciplinary Collaboration in Selection

Collaboration involves three parties: process, structure, and procurement. Process defines the medium, structure defines load and displacement, and procurement defines supply. Collaboration reduces rework; team operation beats going solo. Write collaboration into the project kickoff meeting and clarify interfaces. Cross-disciplinary information alignment is the key to successful selection in complex projects, and also the reverse lesson of many failed projects.

31. Knowledge Accumulation Mechanism for Selection

Accumulation includes templates, cases, and reviews. Templates speed up work, cases provide evidence, and reviews enable correction. Accumulation becomes organizational assets, allowing newcomers to get up to speed quickly. The mechanism ensures knowledge does not leave with individuals. Archive every selection into the database, and over time form the enterprise's proprietary capability. Knowledge accumulation is implicit competitiveness and should be institutionalized for continuous value growth.

32. Key Points of Customer Communication in Selection

Communicate with data to explain price differences: why outdoor must use aliphatic, why strong alkali requires epoxy. Data builds trust, and professionalism shows value. Avoid empty talk; speak with standards and sample blocks. With proper communication, the owner understands and approves the technical solution, reducing later changes. Communication is a soft skill for selection implementation, equally important as technology, and must be deliberately practiced.

33. Applicable Boundaries of the Selection Framework

The framework applies to most industrial anti-corrosion and floor coating, but extreme conditions such as ultra-high temperature, strong oxidation, and nuclear grade still require customization and special verification. Know the boundaries and do not apply blindly; for complex projects, invite suppliers for collaborative design. The framework is a starting point, and rigorous verification is the end. Clarifying boundaries means both daring to use the framework for efficiency and knowing when to escalate, which is maturity.

34. Integrated Value of Selection and Construction

Selection is realized through construction; integrated delivery reduces disconnects. Delivery includes supporting schemes, process cards, and training, so that the design is implemented into the workflow. Integration ensures selection is not just on paper, but lands in replicable quality. The value lies in single responsibility and clear traceability. Integration is a standard capability of mature suppliers and a guarantee of project success.

35. Standard Reference List for Selection

Key standards: ISO 12944 system and environmental class, GB 30981 volatile organic compounds, GB 50209 floor acceptance, GB/T 5210 adhesion, GB/T 1768 abrasion, ISO 11341 weather resistance. The list makes selection traceable and auditable. Referenced standards must indicate the version to avoid using outdated in place of current, ensuring compliance and validity.

36. Visualization Tools for Selection Decisions

Make the six-dimensional decision into a scoring sheet or matrix diagram, so selection results are visualized, facilitating review and reporting. Tools lower the professional barrier, allowing non-technical people to participate. Visualization also exposes weight conflicts and promotes discussion. Tools are the carrier of the framework; using them well turns selection from metaphysics into engineering, with more stable and controllable quality.

37. Final Checklist for Selection

Checklist: outdoor exposure? strong alkali medium? expansion joints? low-odor requirement? frequent heavy load? Tick item by item, and the conclusion emerges. The checklist compresses the framework into executable actions, directly usable in review meetings. Put the sheet on the wall, and selection misses nothing. The checklist is the implementation carrier of this article; use it well, and even complex conditions can quickly yield a reliable scheme, reducing internal disputes and rework.

38. Continuous Improvement Mechanism for Selection

Selection is not a one-time action, but a cycle of hypothesis, verification, and correction. Review each project and feed successes and failures back into the template. The continuous improvement mechanism lets organizational capability snowball. Institutionalize the mechanism, and even newcomers can produce veteran-level results. Improvement is slow but steady, and in the long run is the invisible base of competitiveness. Write improvement into the quality manual, and a year-by-year rise in selection level can be expected.

39. Risk Prediction in Selection

Predict risks: misusing epoxy outdoors, misusing ordinary polyurethane in strong alkali, using rigid material for large displacement. Prediction eliminates failure in advance. Risk prediction relies on the framework and experience, and is written into technical review. Accurate prediction means fewer pitfalls. Make the prediction list-based and go through item by item in review meetings. Risk prediction is the moat of mature selection; small effort avoids large loss, and professional value is evident here.

40. Organizational Building of Selection Capability

It is recommended that enterprises build a selection knowledge base, case base, and training mechanism, turning individual capability into organizational capability. Building makes selection replicable and auditable. Investment in capability building reduces error rate and cost in the long term. Incorporate building into strategic planning for continuous value growth. Selection capability is invisible competitiveness, becoming more important as the market matures. With building in place, enterprises are more composed and robust in competition.

41. DFT Equivalent Conversion for Epoxy and Polyurethane Selection

Selection is not only about defining the system, but also the film thickness. Dry film thickness (DFT) is determined by volume solids and wet film thickness: DFT (µm) ≈ volume solids (%) × wet film thickness (µm) ÷ 100, and verified by thickness measurement per GB/T 13452.2. Epoxy self-leveling can reach several hundred microns in a single coat, while aliphatic PU clear coat is often only 30–60 µm and requires two coats; confusing the two leads to systematic insufficient film thickness. In heavy corrosion environments, determine the total DFT target (e.g., medium C5-M can reach above 320 µm) according to ISO 12944 environmental class (C3–C5, Im), then allocate to primer/intermediate/topcoat layers. Binding "system selection" with "film thickness determination" gives the supporting scheme a quantifiable acceptance baseline, and avoids misattributing weather or chemical resistance failure to the material itself. When film thickness is insufficient, even the best system cannot reach design life, so film thickness should be a hard indicator in the selection report rather than a suggested value. In composite systems, each layer's film thickness must also coordinate with interlayer division: thick epoxy primer/intermediate and thin aliphatic PU topcoat is the classic allocation; if reversed—thickening the weather-resistant topcoat while thinning primer/intermediate—it wastes weather resistance and weakens barrier. Film thickness allocation should return to the division principle of "primer/intermediate resist chemical, topcoat resists weather," not merely meeting total thickness. At design stage, use volume solids to back-calculate each coat's wet film; during construction, use wet film gauge for real-time control—these are the two handles for film thickness implementation, both indispensable.

FAQ

Q: Which is better, epoxy or polyurethane?

A: There is no absolute good or bad, only suitability. Epoxy excels in adhesion, chemical resistance (especially alkali), stiffness, and cost-performance; polyurethane excels in weather resistance without yellowing, elasticity, and adjustable abrasion. For outdoor exposure choose PU, for strong alkali and heavy load choose epoxy; the optimal is often a composite system.

Q: Can epoxy be used for outdoor floor coating?

A: Not recommended to use ordinary epoxy as outdoor topcoat; under UV it yellows, chalking, and loses gloss. Outdoors should switch to aliphatic polyurethane topcoat (HDI/IPDI system), with epoxy still usable at bottom for adhesion and chemical resistance.

Q: Why "epoxy primer/intermediate + polyurethane topcoat" for anti-corrosion systems?

A: This is the classic three-layer concept of ISO 12944-5: zinc-rich epoxy primer (cathodic protection) + micaceous iron oxide epoxy intermediate (flake barrier) + aliphatic PU topcoat (weather-resistant decoration). Each plays its strength: primer/intermediate strong chemical resistance and adhesion, topcoat weather-resistant and non-yellowing.

Q: For strong alkali environment, choose epoxy or polyurethane?

A: Choose epoxy. Epoxy ether bond resists alkaline hydrolysis, with better alkali resistance than polyurethane (PU contains ester bond prone to alkali hydrolysis). For long-term alkali liquid, electroplating, sewage, etc., prioritize epoxy system.

Q: How to select for floor expansion joints?

A: Use elastic materials: elastic epoxy (strong adhesion, good compatibility with epoxy) or polyurethane elastic layer (higher elongation, weather-resistant). Rigid epoxy cannot directly seal joints, or it will certainly crack. See elastic epoxy expansion joint treatment for details.

Q: Can polyurethane be used for heavy-load floor?

A: Yes, but depends on type. Rigid/high-solids PU has good abrasion; elastic PU has lower compression resistance than epoxy self-leveling/mortar. For high-frequency heavy forklift, steel wheel, epoxy mortar/self-leveling is more stable; for impact resistance and shock absorption, PU elastic topcoat is better.

Q: Can epoxy and polyurethane be directly mixed in a system?

A: Yes and common (epoxy primer + PU topcoat), but interlayer compatibility must be verified; do a small sample first to confirm no lifting and adhesion meets standard (GB/T 5210). Same-manufacturer systems with proven compatibility carry lowest risk.

Q: How to select for low odor and low VOC?

A: Choose water-based or high-solids systems; both epoxy and polyurethane have water-based versions; also meet limits of GB 30981-2020 and GB 50325. Indoor, food, and pharmaceutical plants need special attention.

Q: Which to choose when schedule is tight?

A: Look at fast-cure and pot life. Both have fast-cure/high-solids products; key is accurate ratio and use within pot life (see two-component coating mixing ratio). Epoxy self-leveling cures faster; some PU systems also fast-cure; arrange process per TDS.

Q: Should samples be made for selection?

A: For key projects, it is recommended to make a 1–2 m² sample, and after one working-condition cycle (temperature change/media/load) confirm no cracking, no delamination, performance meets standard before large-area application, which avoids most selection mistakes.

Further Reading

• Epoxy Floor Coating System: Primer/Intermediate/Topcoat Three Layers and Film Thickness Grading
• Aliphatic and Aromatic Polyurethane: Essential Difference in Weather Resistance and Yellowing
• Epoxy Chemical Resistance: Crosslink Network, Media Tolerance Matrix and Selection Boundaries

Further Reading

• Zinc-Rich Epoxy Primer Technical Analysis: Zinc Content, Solids and Cathodic Protection Mechanism