Troubleshooting Common Spray Foam Problems

Spray polyurethane foam (SPF) is a remarkable insulation and air-sealing material, renowned for its high R-value and ability to create a seamless thermal barrier. However, a successful application is a precise science, dependent on the right blend of chemical components, equipment, and environmental conditions. When one of these factors is out of balance, problems can arise that compromise the foam’s performance, safety, and longevity.

One of the most critical aspects of SPF application is the precise 1:1 mixing of its two liquid components—isocyanate (A-side) and polyol resin (B-side). These components must be heated to a specific temperature and metered in exact proportions at the spray gun.

When the two components are not mixed thoroughly or are not in the correct ratio, the foam fails to cure properly. You may observe areas that remain tacky or sticky to the touch long after application (a condition known as “uncured” or “green” foam). The foam may also appear dark and brittle or have a strange, uneven texture and color. This is more than a cosmetic issue; off-ratio foam will not achieve its stated R-value, may shrink over time, and can continue to emit volatile organic compounds (VOCs) at higher levels than a properly cured foam.

• Cause: Incorrect temperature settings on the proportioner, clogged filters, worn-out pump seals, or a malfunctioning spray gun. Poor technique, such as holding the gun too far from the substrate, can also prevent proper mixing.
• Solution: A professional installer will immediately stop spraying. They will check the equipment’s temperature and pressure gauges, inspect and clean filters, and test the spray pattern on a disposable surface like cardboard until a consistent, creamy-yellow, and properly expanding foam is achieved. Remedying severe off-ratio issues often requires physically cutting out the faulty foam and reapplying a new layer.

Professional Insight:
The chemical reaction between the A and B components, known as polymerization, is highly sensitive to temperature and ratio. Resources from the Polyurethane Foam Association (PFA) detail the critical nature of this process, emphasizing that even a small deviation can lead to significant performance failures.

Spray foam is notoriously finicky about its application environment. Both the temperature of the substrate (the surface being sprayed) and the ambient humidity play a pivotal role in how the foam reacts and cures.

Applying foam to a cold surface (typically below 60°F or 15°C) can lead to poor adhesion and “crawling,” where the foam pulls away from the edges as it expands and contracts. The foam may also have a dense, crusty skin with a weak, under-expanded core. Conversely, in conditions of very high humidity, the water vapor in the air can react with the isocyanate, causing excessive gas production. This manifests as a fine, friable, and crumbly foam structure, often with a burnt-like smell.

• Cause: Spraying in an unconditioned space (e.g., a cold attic or damp crawlspace) without proper preparation.
• Solution: Prevention is key. A reputable contractor will climate-control the work area for at least 24 hours before and after application. Substrates should be heated if necessary. In high-humidity conditions, installers may need to adjust the chemical set time or schedule the work for a drier part of the day. If poor foam has already been applied, the only reliable fix is removal and reapplication under correct conditions.

Professional Insight:
The U.S. Department of Energy’s Building America Solution Center notes the importance of ambient conditions, stating that substrate temperature is one of the most overlooked factors in SPF performance.

A properly cured spray foam should be inert and have a very low, benign odor. Persistent chemical smells are a red flag and a common concern for homeowners.

Homeowners may report a strong, fishy, or sweet chemical smell that persists for weeks or months after installation. This is often linked to the amine catalysts used in the foam formula. While some odor directly after installation is normal during the curing process (which can take 24-72 hours), a lasting odor typically indicates an underlying issue, such as off-ratio foam or contamination during application.

• Cause: The primary causes are improper mixing (as discussed in Problem 1) or contamination of the components. Using the wrong cleaning solvents near the equipment can also introduce contaminants.
• Solution: The first step is to increase ventilation significantly. If the odor persists, a professional assessment is required to determine if there are areas of uncured foam. In severe cases, an indoor air quality test can be conducted. Remediation may involve sealing the exposed foam surfaces with a specially designed coating or, in worst-case scenarios, partial removal.

Professional Insight:
The Center for the Polyurethanes Industry (CPI) provides extensive resources on SPF and indoor air quality, explaining the curing process and when odors should be a cause for concern. They emphasize that a properly installed SPF product should not cause long-term odor issues.

Spray foam is intended to adhere tenaciously to the substrate and maintain its volume and shape for the life of the building. When it fails to do so, it creates thermal bridges and compromises the building envelope.

Visible gaps between the foam and wood studs, joists, or other surfaces indicate shrinkage. In larger foam pours (e.g., for insulated concrete forms), cracking can occur. These gaps allow conditioned air to escape and unconditioned air to enter, defeating the primary purpose of the insulation.

• Cause: Shrinkage is almost always a symptom of off-ratio foam (Problem 1). Cracking in large pours can be due to excessive exothermic heat (the heat generated by the reaction) or an incorrect density foam being used for the application.
• Solution: There is no easy fix for shrunken foam. The affected areas must be cut out and resprayed with a correctly mixed batch. To prevent cracking in large cavities, installers use a “lift and wait” technique, applying the foam in several thinner layers to manage the heat buildup.

While this guide outlines common spray foam problems, the overarching theme is that prevention is infinitely better than cure.

 The vast majority of these issues can be avoided by hiring a certified, experienced, and reputable SPF installer. Before work begins, ask your contractor about their certification (from organizations like the Spray Polyurethane Foam Alliance), their experience with your specific project type, and the warranties they offer on both materials and labor. A professional will conduct a pre-job inspection, ensure all conditions are optimal, and use well-maintained equipment.