Processing PU foam correctly
7 simple tricks that are a matter of course of PU foam professionals
Shake the PU foam can hard
Apply the construction foam upside down
Wet the 1C PU foams
This is how PU foam adheres correctly
Ensure that the processing temperature is correct
Differentiate between 1C and 2C PU foam
Differentiate between adapter and gun foam
1. Shake the PU foam can hard
Just before they are used, PU foam cans must be shaken thoroughly, at least 25 times, to ensure that the viscous PU foam and the propellant are mixed perfectly. In this way you create a homogeneous mass and the propellant can fulfil its three important functions.
- It triggers the viscous PU fluid.
- It transports the PU from the can.
- It acts as an expanding material and cell creator for the PU foam that exits the can, thereby creating the required fine-pore structure that insulates so efficiently.
If the can is used for a longer time, re-shake now and again.
What happens, if you forget to shake the can?
The PU foam and the propellant will not form a homogeneous mass and the PU foam only expands slightly.
2. Apply the construction foam upside down
PU foam professionals know that assembly foam cans need to be held with the valve facing downwards. This is the only way to empty the can properly.
Why? In contrast to classic aerosol cans, assembly foam cans do not have a riser tube that pumps the fluid content outwards when the spray head is pressed. Because PU foam is viscous, a transport tube of this kind would become clogged.
Instead, the construction foam can should be emptied upside down. This causes the viscous mass to sink downwards. An adequate amount of PU foam collects at the valve, and you can apply the foam easily and evenly.
3. Wet the 1C PU foam
Most 1-component PU foams need a certain amount of moisture from the environment to harden. Therefore, the surfaces and the freshly applied PU foam should be moistened with water - for example with a plant sprayer.
A general rule is that a PU foam can with 750 millilitres (ml) of foam requires about 60 ml of water to harden correctly.
But, be careful! There are now PU foam on the market that do not need moisture to harden. Therefore, always check the instructions by the manufacturer on the packaging.
What happens, if there is not enough moisture.
After this, the foam hardens more slowly and expands less. In a worst case, it may expand later.
1C foam hardens from the outside where moisture impacts first then inwards. If it is too dry, the outer layer of the foam develops a hard skin, whilst the active PU foam underneath in the foam core remains unhardened. If the humidity increases later, this foam can expand weeks later and deform the parts.
4. This is how PU foam adheres correctly
PU foam adheres to almost all surfaces that are strong, clean and free of dust and grease. Only silicon, oils, greases, polyethylene, Teflon or similar surfaces are not suitable for PU foam.
One special case are materials that can actively absorb moisture, for instance plaster. These surfaces must be dampened enough to ensure that the PU foam finds adequate moisture for its hardening process.
Otherwise, it could impair the adhesion and edge adhesion. We recommend a prior coat of primer or bonding agent in this case.
5. Ensure that the processing temperature is correct
Conventional 1-component PU foams should be processed at a temperature between 5° and 30° Celsius so that the hardened PU foam has the required quality.
At temperatures below 5 degrees, the foam hardens more slowly. This affects the cell structure. The hardened foam can become brittle.
If the PU foam becomes too warm during processing, it may lose structural stability. This is similar to how cream behaves on a hot waffle.
Therefore, ensure that the environment and also the material onto which the foam is applied do not reach a temperature above 30° Celsius.
These temperature specifications only apply to foam that has not yet fully reacted. Once hardened, PU foam is temperature resistant from -40° C to +80°C.
Tip: Warm up cold foam and cool down warm foam carefully
You can warm up cool PU foam cans in lukewarm water.
Never place cans into hot water or heat otherwise, for instance on a radiator or with a torch! Why? Otherwise, the propellant in the can may expand too quickly and the can could burst.
Foam that is too warm can be brought down to the right temperature in a cool water bath.
Tip: Use the special winter foam
If the outside temperature lies permanently below the optimum processing temperature for PU foam, it is recommended using so-called winter foams. Winter foams are specially developed for frosty temperatures and, depending on the formula, deliver high-quality insulation and foaming results in temperatures up to -10 °C.
6. Differentiate between 1C and 2C PU foam
1-component PU foams and 2-component PU foams differ with respect to their hardening behaviour: 1C PU foam requires moisture to harden. 2C PU foam requires another reaction partner. This is located in the can and must be activated just before it is applied. 2-component PU foam is very strong and hardens very quickly and evenly. This helps to control the hardening process. A typical use for 2C assembly foam is the fitting of doors.
7. Differentiate between adapter and gun foam
If a PU foam gun is used for the work, we speak of gun foam. If you find an adapter tube on the case, you have adapter foam in your hand.
1C PU foam cans with an adapter and safety valve
1-component PU foams with an adapter are a practical solution for people that only use construction foam occasionally. The adapter tube is simply screwed to the valve of the PU foam can just before use.
1C gun PU foam
People who use 1C PU foam on a regular basis usually prefer working with a separate PU foam gun that is screwed onto the construction foam can. The benefits lie in the easier dosage of the construction foam.
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