Case Study: Curing Delay in a Water-Based PU Waterproofing System and the Role of Contingency Planning

Megan Chua
Nov 3, 2025
3 min read

Abstract

This case study examines a water-based PU waterproofing curing delay encountered in an enclosed indoor environment, demonstrating how substrate moisture, ventilation, and on-site conditions can alter expected curing behavior. Despite correct product selection and adherence to standard procedures, sections of the membrane failed to cure properly due to environmental factors. The case highlights the interaction between substrate moisture, ventilation, and material behavior—and underscores the importance of contingency planning, close coordination with manufacturers, and adaptive decision-making beyond what technical datasheets alone can prescribe.

Project Context

The project involved the application of a single-component, water-based polyurethane membrane (Sealbond Optimastic PU-W) over a cementitious substrate with wall upstands. The area was located within a fully enclosed, temperature-controlled space, characterized by low humidity and limited ventilation. This environment, while ideal for occupant comfort, introduced curing challenges for a coating system dependent on air movement and evaporation.

After application, the membrane displayed uneven curing: most sections hardened as expected, while some areas remained soft and milky. These undercured zones corresponded to areas where sand had been broadcast for mechanical keying.

Problem Statement

During post-application inspection and water testing, the affected sections softened and detached, prompting an investigation into whether the failure was due to product formulation, workmanship, or external environmental conditions.

Root-Cause Analysis of the Water-Based PU Waterproofing Curing Delay

A joint evaluation between the applicator and the manufacturer’s technical representatives identified multiple interrelated causes:

Residual substrate moisture – The concrete base retained moisture, limiting the membrane’s ability to release water during curing.
Use of sand – Sand broadcast over the surface trapped water beneath the coating, restricting polymerization.
Low air movement and ambient temperature – The controlled indoor climate slowed evaporation, extending curing time beyond expected parameters.
Premature sand broadcasting – The aggregate was applied while the coating was still wet, sealing the film before vapor could escape.

The assessment confirmed that the product was performing within specification; the failure was environmental, not material.

Corrective Actions

A combined set of technical and environmental measures was implemented:

Surface preparation and removal – Uncured membrane sections were mechanically stripped, and the substrate was dried using industrial blowers and controlled heat.
Environmental control – Air movement was increased using portable blowers to maintain consistent temperatures between 25–30 °C and relative humidity below 75 %.
Longer curing - The applied membrane was allowed to cure for at least 3 days given the humidity and temperature to pass the water retention test with no softening or discoloration.

Key Insights

Environmental dependency of water-based PU
- Water-based systems require adequate air exchange for evaporation. In closed spaces, limited ventilation can significantly slow or interrupt curing.
Value of manufacturer collaboration
- Direct engagement with the manufacturer’s technical team helped confirm root causes and refine the corrective process. The collaboration strengthened technical confidence on both sides and prevented unnecessary attribution of fault.
Limits of technical datasheets
- Datasheets define performance parameters under controlled laboratory conditions. Actual field environments require contextual interpretation and adaptive application to achieve similar results.
Contingency as proactive management
- Construction risk management should anticipate environmental deviations by incorporating schedule buffers, drying equipment, and verification tools into the plan.

Recommendations for Property and Facility Managers

Identified Risk	Recommended Contingency	Expected Benefit
Low-temperature or enclosed areas	Use blowers or heaters during curing	Prevents moisture entrapment
Damp substrates	Conduct moisture tests and ensure SSD condition	Ensures proper adhesion and curing
Extended curing period	Allow schedule flexibility for full polymerization	Reduces rework and delays
Gaps between field and datasheet conditions	Engage manufacturer’s technical support early	Improves on-site decision-making

Conclusion

The curing delay in this enclosed-area project demonstrates how environmental factors can override technical compliance. While datasheets provide essential guidance, real-world performance depends on adaptive site management and open collaboration with manufacturers. This case reinforces the value of contingency planning—not as an added cost, but as a form of risk insurance that protects timelines, budgets, and long-term integrity of the waterproofing system.

The water-based PU waterproofing curing delay discussed in this case highlights how even minor changes in humidity or substrate condition can influence long-term performance.