PU foam post-expansion – how can it be controlled?
Proper application of polyurethane foam is the key to safe installation of window and door joinery. Postexpansion is a natural process that can be controlled by proper application and selection of foams with the right parameters.
Polyurethane foam is an indispensable material in the installation of windows and doors. Its main advantage is its ability to fill gaps and seal elements during the installation of woodwork. However, like any building material, it requires proper application to work effectively. One of the most important parameters to consider when working with polyurethane foam is post-expansion – the secondary growth of the foam. Improper management of this process can result in deformation of woodwork components. In this article, we will discuss the technical aspects of working with foam and how to avoid application errors.
Post-expansion – what is it and why is it important?
Post-expansion is the process of secondary growth of polyurethane foam that occurs after application. As the foam is released from the can, it begins to react with moisture from the environment and from the surface to which it is applied, causing it to expand further. During this phase, a chemical reaction takes place between the isocyanate (MDI) and the moisture, resulting in the release of carbon dioxide, which causes the volume of the PU foam to increase.
This phenomenon is important because excessive post-expansion can lead to deformation of windows and doors, especially if the foam was applied during the installation of components such as window or door frames. High levels of post-expansion can lead to warping, which means that the joinery will not work properly – windows may not close and doors will not sit well in the frame.
Common mistakes in foam application
Incorrect dosage method during application
One of the most common mistakes in polyurethane foam application is applying too much pressure. When the product is released from the can at maximum pressure, the degree of post-expansion increases, which can lead to over-expansion of the foam, warping of the joinery and possible staining of the surface. Therefore, it is critical that the foam gun be operated in a controlled manner.
Lack of adequate surface wetting
One-part polyurethane foam requires moisture to expand and cure properly. Failure to properly wet the surface with water mist during application can result in uneven expansion of the foam – it will cure on the outside, but remain fresh and uncured in the core for an extended period of time, which can lead to subsequent secondary expansion and increase the risk of potential deformation of woodwork. Special Tytan Professional foams such as 65 Pistol Foam and ULTRA FAST 70 Rapid Pistol Foam are designed to minimize this risk. The technical data sheets for these products also contain information on the need for wetting at temperatures above zero degrees Celsius.
Using the wrong product for the job
Low-pressure foams are designed to reduce the risk of deformation of woodwork. Using other foams, such as high-pressure foams, in applications that require a delicate seal when installing windows or doors can result in warping. Titan Professional offers specialized low post-expansion products designed for these applications to ensure safe application without the risk of warping.
Technical aspects of foam application – what do you need to know?
Effect of temperature on foam
Temperature has a significant effect on the performance of polyurethane foam. Applying summer foams in winter or winter conditions in summer can cause inconvenience during the application process and significantly affect the quality of the finished seal. For example, at lower temperatures, summer foam may not expand and cure properly, affecting the quality of its structure. On the other hand, application of foam stored at too high a temperature, such as in full sunlight, leads to increased pressure in the can and excessive post-expansion, and can cause irreversible changes in the product.
Foam storage – valve up
Proper storage of foam is critical to its subsequent performance. Polyurethane foam cans should always be stored vertically, valve up. If the can is stacked horizontally, the liquid components of the prepolymer will interact with the can’s valve, which can be detrimental to the effective application of the product in the field. Improper storage may result in blockage of one of the valve openings, resulting in uneven product flow.
Layered foam application
Proper application of polyurethane foam should be done in layers. Some contractors make the mistake of trying to fill the entire joint at once. Unfortunately, this technique prevents proper wetting and even expansion of the foam within the joint. The use of several thin layers with wetting in between allows a more accurate filling of the joint and ensures a very good quality structure of the cured foam PU without any possible risks of deterioration of the product properties or deformation of the elements.
Avoid additional accessories that alter the flow of the foam
When applying gun foam for window and door installation, avoid the use of additional hoses that come with the application gun and change the way the foam flows. These items can cause low expansion foam to behave like high pressure foam, significantly increasing the post-expansion level and reducing the output of fresh foam from the can.
The key to success is to follow the rules of application and use specific products. This will ensure that each installation is solid and without the risk of deforming the woodwork.