Well foam: what you need to know about this sealing material

What is well foam used for?

Wells, cisterns, water pipes, waste water pipes. Well foam was developed to facilitate waterproof adhesion of concrete rings and well shafts. It is a universal foam that can be used to seal standing or slightly pressing water. This special polyurethane-based foam is ideal for sealing, connecting and adhering well shaft rings, shaft necks and concrete rings.
It can also be used when setting sewer shafts and domestic sewage plants. Today, well foam is used instead of traditional water-impermeable materials, such as mortar or silting, when sealing objects in the sewer and civil engineering sector and in the sanitary sector.

The most important properties of well foam

Decay and rot-proof

Well foams are chemically resistant to diluted acids and alkalis, and therefore to normal household waste water that may contain bacteria and faeces. It is durable in the long-term, and is also decay and rot-proof.

Suitable for water and waste water

When construction waste water pipes, these properties protect the ground against contamination and keep the waste water and its partially harmful constituents where they belong: in the waste water pipe.

And this principle also works vice versa. The well foam also ensures that no soiling from the surrounding ground can enter the inside of the water pipe.

If you are constructing a drinking water well, you should cover the foam with a compound approved for drinking water after positioning the shaft ring.


Well foam has a further benefit. It adheres to almost all materials and is therefore universal. For instance, for concrete, masonry, wood, plaster, plastics and even metal. It does not adhere to smooth materials like PE or PP. Also, oily surfaces are not suitable because they impair the adhesion of the foam.

Is well foam waterproof?

Well foam is usually used to seal pipes and shafts. However, this does not mean that it is absolutely watertight itself. Hardened PU foam always has a mixture of closed and open cells, which is why it is not completely watertight, but waterproof. This means: well 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.

Despite this, wells and shafts can be made watertight using well foam.

Preferably under pressure: this is how foam becomes watertight

How well shaft rings work with well foam: 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. No more water molecules can fit between them any more!

The water-repellent effect of well foam does not only come from its chemical properties, but from the physical pressure of the stacking rings.

To ensure this effect, you should ensure that the next shaft ring is set in good time. This means: before the foam no longer adheres! If the well foam does not adhere, its tightness may be compromised.

Is well foam UV-resistant?

Well foam is polyurethane-based and is not permanently light-resistant. This means that, if exposed to UV light, it will initially turn yellow before becoming brittle and ultimately the upper layer will degrade.

As long as the foam remains underground, its sensitivity to light is irrelevant because it is protected by the earth. If it is used above ground, it should be protected against UV light. This is best achieved by using paint or sealing agents on the foam. Most paints and sealing agents are suitable for this. If protected in this way, the sun cannot compromise the well foam.

What well foam is best suited for which shaft ring?

This question is easy to answer: the tightness of the ring and the foam is tested jointly. Therefore, simply check the test certificates or approvals.

How to work with well foam - important tips

The well foam is as easy to use as other PU foams. The conventional processing instructions apply for 1-K PU foam. 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 properly. This improves the quality of the foam.

For more information about working with 1K foam, klick here

Apply the well foam evenly

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 fresher the PU foam, the better!

The next shaft ring should be positioned within a few minutes. The general rule here is: the quicker the ring is placed on the fresh foam, the better!

Always position the ring before the foam loses its adhesive strength so that the well or shaft has the necessary stability. The product data sheet states the exact time intervals.

Ensure that there is enough moisture!

Well foam is usually offered as a 1-K PU foam. This means that it needs moisture from the environment to foam and harden.

To prolong the open period of the well foam, the environment may not be too moist. It is therefore not advisable wetting the applied foam separately.

This is the difference between well foam and other assembly foams that need added moisture to improve the quality of the foam and shorten the hardening time.

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.

Observe the hardening times

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.

Ensure that the processing temperature is correct

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 – 25 °C gradually by placing it into cold or warm water.

How many cans of well foam do you need for one shaft ring?

Well foam is usually available in 750-millilitre cans This yields an average foam strand of 30 metres. The number of rings you can set with this amount of foam depends on the circumference of the shaft rings.

Some manufacturers also supply 500 ml cans. The foam yield here is lower. For more details, please check the product data sheet.

Safety tip: Ensure that rooms are well ventilated

When working with well foam, it is very important to ensure good ventilation. Space inside shafts is often very tight. The smaller the space in which you are working, the more careful you must be. This especially applies if you use several cans.

The reason? When working with well foam, the propellant exits the can. This is not usually a problem, but in tight spaces this gas can mix with the air to form an explosive mixture, which is why you should always avoid all ignition sources and possible sparks. Open flames are also prohibited; please remember that some electrical devices may give off sparks.


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