Waterproof adhesion with PU foam
Wells, cisterns, water pipes, waste water pipes. Well foam was developed to facilitate waterproof adhesion of concrete rings and well shafts. It can also be used when setting shaft rings, drain shafts and domestic sewage plants. But how should it be used properly?
It is resistant to diluted alkalis and acids
This special foam meets the usual civil engineering requirements. Thanks to its special formula, it is resistant to thinned alkalis and acids. It is even resistant to bacteria and faeces. This either protects the fresh water against contamination or keeps the waste water and its constituents where they belong in the waste water pipe.
However, hardened PU foam always has a mixture of closed and open cells, which is why it is not completely watertight, but waterproof. Water absorption lies below one percent. This means: construction foam does not dissolve, even if exposed permanently to water.
It is resistant to splashwater
This means that it can withstand water for a certain amount of time, even splashwater is no problem; however, regular exposure to pressurised water will lead to penetration of the cell chambers of the foam. This is one of the reasons why window joints need to be sealed more tightly.
Preferably under pressure: this is how PU foam becomes watertight
And how does well foam work that is used for sealing well shaft rings? Here, the weight of the inserted shaft rings ensures that the foam is so compressed and compacted that it is no longer possible for water to be absorbed.
The physical pressure is decisive
The water-repellent effect of well foam does not come from its chemical properties, but from the physical pressure of the stacking rings.
Well foam adheres to almost all surfaces and is therefore universal. It does not adhere to smooth materials like PE or PP. Modern polyurethane-based well foams often only develop their highest resistance, if they are constantly ‘flooded’. They are usually watertight up to a water pressure of 0.5 bar.
Protect well foam from light
PU foam is decay and rot-proof.
However, like all other PU foams, well foam is not light fast. This means that if it is used above ground, it should be protected against UV light. Paint or sealing agents can be applied over this foam, for instance, silicone, polyurethane, acrylic or MS polymer.
Easy to use
The well foam is as easy to use as other PU foams. The same processing instructions apply. Screw on the PU foam gun or the adapter tube. Shake the can hard about 30 times holding the can head downwards. This will mix the contents of the can well. This improves the quality of the foam.
Apply the foam as evenly as possible into the joint that needs to be sealed or onto the shaft ring. After applying the foam, the well foam will continue to swell slightly.
The next shaft ring should be positioned within a few minutes. The product data sheet states the exact time intervals. The general rule here is: the fresher the PU foam, the better!
Is there enough moisture?
Depending on the product used, the well foam needs to harden for a period of 6 to 20 hours until it is completely watertight and fully durable. It continues to expand during this time. It also fills out all hollow spaces and leaks. After this, the foam retains its form and does not change in volume.
PU foam requires moisture to harden.
This is why some manufacturers recommend spraying the joint with water before apply the foam. Once the foam has hardened, larger pieces of excess PU foam can be cut off with a sharp knife. If necessary, these cut areas can be coated with silicone again.
Tip: Observe the processing temperature
The correct temperature is also important when working with PU foam. The PU foam should have a temperature of between 5 and 35 °C on the adhesion surface.
The PU foam can itself may have a temperature of between 5 and 25 °C. If the can becomes to warm or too cold, it can be brought to the optimum operating temperature of approx. 15 °C gradually by placing it into cold or warm water.