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Last edited 07 Oct 2020
Sealants are typically used to close openings between spaces that are too small for other materials such as concrete, timber or mortar to be used. They have a wide range of properties in terms of strength, flexibility, appearance permanence, solubility, corrosion resistance and so on.
Expanding foam filler is a common type of polyurethane filler. It can be sprayed into gaps such as those around windows and doors to stop draughts, fill gaps and dampen sound. It is designed to adhere to a variety of common building materials and can be water resistant.
 Expanding foam characteristics
Foams can be divided into two different ways: type and purpose.
- Type of application: handheld dispenser or gun grade applicator.
- Purpose of application: Filling voids or securing materials through adhesion (these foams have a lower expansion rate).
Expanding foam filler is made up of materials that expand under different conditions, depending on its composition. One type of expanding polyurethane foam requires moisture in order to expand, which can make it sticky during the installation process. Another begins to expand when two different chemicals are mixed together. Dampening the surface that will be treated can help the foam set more quickly.
There are several differences between types of foam which should be clearly marked on the containers:
- Indoor or outdoor use.
- Sandable or paintable.
- Presence of HCFCs or CFCs (no longer permitted).
- Gun grade or handheld.
 Possible dangers of expanding foam
It’s important to proceed with caution with the application process, since the chemicals can be toxic if they are not used properly. However, the substance should be safe once it has fully expanded and dried.
Cured foam should be protected from daylight or other light since this can degrade the effectiveness of the product over time. Dried foam can be painted, or otherwise covered, to protect it from light.
Expanding foam should be used relatively quickly once a can or gun is started, since the chemicals may not retain their effectiveness over time. It can also be difficult to remove or clean foam. There is a special type of chemical that can be used to clean wet foam, and in some instances, acetone can be used.
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