Polyurethane (PU) foam sealant is widely used in construction, automotive, and insulation applications thanks to its excellent sealing, bonding, and insulating properties. However, during the foaming process, users often encounter certain issues that can affect both performance and finish. Understanding these problems—and knowing how to avoid them—ensures better results and reduces waste.

1. Uneven Foam Expansion

Problem: Foam expands irregularly, creating voids or lumps.
Cause: This often results from improper shaking of the can, incorrect nozzle positioning, or applying the foam in areas with uneven temperatures.
Solution: Shake the can thoroughly before use, apply in layers, and maintain a consistent working temperature (ideally between 18–25°C).

2. Poor Adhesion to Surfaces

Problem: Foam does not bond firmly to substrates such as concrete, wood, or metal.
Cause: Surfaces may be dirty, oily, or too dry. Some materials (like polyethylene) naturally resist adhesion.
Solution: Clean surfaces thoroughly, slightly moisten them with water before application, and use primers when necessary.

3. Over-Expansion and Deformation

Problem: Foam expands too much, pushing out of joints or distorting window and door frames.
Cause: Applying too much foam in one pass or not accounting for its natural expansion.
Solution: Apply foam gradually in layers and avoid filling gaps completely at once. Leave space for expansion.

4. Incomplete Curing

Problem: Foam remains soft or sticky even after several hours.
Cause: Low humidity, insufficient moisture in substrates, or low temperatures can slow curing.
Solution: Lightly mist the surface with water before applying, ensure proper ventilation, and work within recommended temperature ranges.

5. Clogged Nozzles or Valves

Problem: Foam cannot be dispensed properly after the first use.
Cause: Residual foam hardens inside the nozzle or valve.
Solution: Always clean the nozzle immediately after use with PU foam cleaner or acetone. For reusable guns, use professional-grade cleaners to keep the valve system clear.

6. Shrinkage or Cracks After Curing

Problem: Foam shrinks back or cracks appear over time.
Cause: Incorrect mixing ratio inside the can, exposure to UV radiation, or excessive movement of the joint.
Solution: Use high-quality foam sealant, protect cured foam from UV with paint or plaster, and apply in stable gaps.

Final Thoughts

Polyurethane foam sealant is a powerful tool, but success depends on proper handling and environmental conditions. By recognizing these common problems and applying best practices, you can ensure strong adhesion, stable expansion, and long-lasting results.

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