Mounting foam is an indispensable tool for sealing, insulating, and installing everything from windows and doors to pipes and wall gaps. However, even experienced professionals can encounter issues if they overlook some key best practices. At Tegra State, we believe that understanding these common mounting foam mistakes—and how to prevent them—ensures a job well done, every time.
1. Choosing Wrong Type of PU Mounting Foam
It is fundamentally important to choose the right mounting foam for the job. Some polyurethane foams are more flexible than others or have different secondary expansion rate. Using high secondary expansion mounting foam for installing doors may damage the frame or wall during its curing time.
Low secondary expansion foam is used for doors and windows’ installation. High secondary expansion PU mounting foam – for filling bigger hollow parts and gaps, i.e. around sewer pipes. Glue-foam is perfect for bonding construction materials and elements or gluing interior details.
2. Skipping Surface Preparation
Applying foam to dirty, greasy, or dusty surfaces is a recipe for poor adhesion. Always ensure surfaces are clean and free of contaminants before starting. This simple step maximizes the mounting foam’s grip and long-term performance.
3. Forgetting to Moisten the Surface
For one-component polyurethane foams, moisture is essential for proper curing. Skipping the step of lightly misting the substrate can result in uneven expansion, voids, and reduced insulation effectiveness. Always moisten the surfaces before and after application—unless you’re using PU foam specifically designed for sub-zero temperatures, in which case moisture can actually hinder performance.
4. Incorrect Gap Filling With Mounting Foam
Overfilling or underfilling gaps is a common pitfall. Too little foam leaves thermal bridges and potential for drafts or moisture ingress, while too much can cause excessive expansion, leading to structural stress or deformation. Apply polyurethane mounting foam in layers for deep gaps, allowing each to expand before adding the next, and always leave space for the foam to expand as it cures.
5. Using the Wrong Mounting Foam for the Season
Not all foams are created equal—some are formulated for summer, others for winter, and some are multi-season. Using summer PU foam in cold weather can prevent proper curing and adhesion. Always check the product’s recommended temperature range and select accordingly to ensure reliable results.
6. Improper Storage and Handling
Mounting foam cans should be stored upright and at the recommended temperature. Exposure to extreme cold or heat can degrade the product, affecting expansion and curing. Before use, shake the can thoroughly—about 30 times—to ensure the ingredients are well mixed. If polyurethane (PU) foam is used without shaking the can, several issues can arise due to improper mixing of the chemical components inside:
Inconsistent Mounting Foam Quality
PU foam cans contain a mixture of chemicals (isocyanate and polyol, typically) that need to be thoroughly mixed to react properly. Without shaking, these components remain separated or unevenly distributed, leading to foam that may not expand correctly, has poor structure, or is overly dense in some areas and weak in others.
Reduced Expansion
The polyurethane foam may not expand to its full potential, resulting in lower yield and insufficient filling of gaps or spaces. This happens because the propellant and reactive ingredients aren’t properly blended.
Poor Adhesion and Strength
Uneven mixing can lead to mounting foam with reduced adhesive properties and structural integrity, making it less effective for sealing, insulating, or bonding.
Wasted Product
You may get less usable mounting foam from the can, as the reaction won’t occur efficiently, potentially requiring more cans to complete the job.
7. Cutting or Disturbing PU Mounting Foam Too Soon
Patience pays off. Cutting or shaping mounting foam before it’s fully cured can collapse the structure and compromise the seal. Always follow the manufacturer’s curing time instructions before trimming or finishing the foam.
8. Neglecting to Protect Cured Polyurethane Foam
Once cured, polyurethane foam is sensitive to UV light and weather. Leaving it exposed can cause degradation, colour change, and crumbling. Always cover cured foam with protective tapes, coatings, or sealants as soon as possible to preserve its insulating properties.
9. Not Wearing Personal Protective Equipment (PPE)
Safety should never be an afterthought. Always wear gloves, goggles, and a respirator when working with mounting foam to protect yourself from chemicals and airborne particles. We provide the possibility to access and complete a compulsory PU training for those who need it. All information can be found here.
Conclusion
Mounting foam is a powerful ally in construction and renovation, but only when used correctly. By avoiding these common mistakes—cleaning and moistening surfaces, choosing the right polyurethane foam, applying in layers, and protecting the finished work—you can ensure durable, energy-efficient, and professional results every time. At Tegra State, we’re committed to helping you build better, safer, and smarter.
