Foams

Straw type application is more popular for generous filling applications as the straw is a set diameter delivering a high volume of foam. Delivery is controlled using a very simple push cap attached to the straw nozzle. Hand held foam cans are best suited for single use jobs as they are more prone to becoming blocked once started, especially if the can is not used for a few days after the initial application. Professional trade applicators often prefer using a foam gun which is attached to the canister by a screw thread. Foam guns have a flow adjustment screw which limits or increases the amount of foam being dispensed, this subsequently affects the bead width making neat, measured beads possible and avoiding excess foam being applied. In the case of foam canister systems which are typically used for adhering insulated roof panels to flat roofs the foam gun is attached to a flexible hose which is connected to the canister. These systems usually have a gun with a long wand to allow the user to apply the foam while walking in an upright position making the operation much more comfortable. It is essential that any foam gun systems are flushed through after use with a suitable foam gun cleaner to prevent blockages caused by foam curing inside the gun. Different formulations and qualities of expanding foam can yield varying fill capacities; in some cases a greater expansion can be achieved by a more open cell structure causing large air pockets in the cured foam which can necessitate re-application and lead to poor surface appearance, particularly when sealants have to be applied over the top, acoustic properties of the foam may also be compromised. Expanding foams can also be used to help reduce the spread of fire inside buildings when they are used to fill gaps around door frames, windows and pipe penetrations. The fire rating capabilities of expanding foam are typically categorised as B3 – high flammability, B2 – normal flammability and B1 – low flammability but certification such as BS476: part 20 and BS EN 1634-1 may also be documented. For any fire resistant applications a minimum of B1 should be considered but this rating alone does not qualify the foam as suitable in fire resistant applications as different joint configurations and base materials can dramatically affect the performance of the foam. Expanding foam is very easy to apply but for one common mistake, failure to moisten the base material. All polyurethane foams require moisture to cure and therefore substrates MUST be moistened using a water sprayer before application, failure to do so results in poorly cured foam and compromised performance.

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