Well sealing foam: What you should know about this sealant

Well sealing foam is a real specialist when it comes to sealing in the water and wastewater sector. Polyurethane foam (PU foam) is particularly suitable for wells, cisterns, manhole rings or sewage pipes. But it can do much more than many people think. In this text, you will learn everything you need to know about the application, processing, properties and limitations of well sealing foam – including practical tips, a checklist and an FAQ section.

What is well sealing foam suitable for?
The most important properties of well sealing foam
Is well sealing foam UV-resistant?
How to work with well sealing foam – practical tips
How much well sealing foam do I need?
Safety during use
Checklist: Using well sealing foam correctly
FAQ: Frequently asked questions about well sealing foam

What is well sealing foam suitable for?

Well sealing foam always comes into play when a waterproof connection between components is required. The foam is mainly used in civil engineering, sewer construction and well installation for bonding concrete rings, well shafts and shaft necks.

It replaces conventional sealing materials such as mortar or sealing slurry. Its dimensionally stable, waterproof structure makes it ideal for handling standing or slightly pressurised water.

Typical application examples:

Sealing of cisterns, sewer manholes and domestic sewage treatment plants
Pipe penetrations in the water and wastewater sector
Sealing against wastewater and surface water

→ Tip for professionals: Well sealing foam has also proven its worth when renovating old well constructions or installing retrofit rings.

The most important properties of well sealing foam

Resistance to rotting and decay

Well sealing foam is permanently resilient. Most products are resistant to microorganisms, fungi and bacteria, such as those found in waste water systems. Even household wastewater containing faeces is not a problem.

Chemical resistance

Thanks to its polyurethane base, well sealing foam is resistant to diluted acids and alkalis. This makes it a safe sealant for systems with biologically aggressive contents.

In the construction of wastewater pipes, these properties permanently protect the soil from contamination and keep the wastewater and its sometimes harmful substances where they belong: in the wastewater pipe.

This also works the other way round. The well sealing foam also ensures that no impurities from the surrounding soil enter the inside of the water pipe.

Adhesion to many materials

It adheres to concrete, plaster, masonry, brick, wood, metal and many plastics. It is not suitable for PE, PP, Teflon (PTFE) and very oily substrates.

Dimensional stability & waterproofness

The foam is waterproof, but technically not 100% waterproof. The waterproofness is only created by mechanical pressure, e.g. when a shaft ring is placed on the foam while it is still fresh. This compacts the cell structures – water molecules then have no more room.

This effect is, therefore, based on a physical interaction between the material and the installation method. It is, therefore, crucial to put on the next ring while the foam is still sticky.

Pressure resistance

Well foams are tested for long-term tightness up to 0.5 bar water pressure (approx. 5 m water column). Some manufacturers have also tested their foams up to 0.8 bar (approx. 8 m water column). It is worth taking a look at the product data sheet here.

Is well sealing foam UV-resistant?

No. PU-based well sealing foam is not UV-resistant. It yellows in sunlight, becomes brittle and can decompose over time. This mainly concerns applications above the earth’s surface.

How to protect well sealing foam outdoors:

Paint over with weatherproof paints
Cover with sealing compound (e.g. silicone, acrylic, PU)
Use sheathing or cover strips

→ Important: UV radiation is not an issue when used underground.

How to work with well sealing foam – practical tips

Working with well sealing foam is just as easy as with other PU foams. The usual processing instructions for 1-component PU foam apply. Firstly, here is a brief summary. You will find explanations of the individual points directly below:

1. Preparation: Clean substrates, moisten slightly if necessary (not wet!).
2. Observe temperature:
   - Adhesive surfaces: +5 to +35 °C
   - Can: +5 to +25 °C (ideally 15-25 °C)
   - Ambient temperature: between +5 and +30 °C for optimum curing
3. Shake can well: Approx. 30 seconds upside down
4. Inject evenly: Do not apply an excessive amount – the foam expands
5. Place the foam so that it cannot be pushed away to the outside, i.e. in the inner “bead” of the manhole ring.

6. Work quickly: Apply the next manhole ring while the foam is still sticky
7. Wait for curing: 6 to 20 hours, depending on the product and environment
8. Remove residues cleanly: Cut off with a sharp knife after curing

Important: Well sealing foam hardens due to humidity. An excessively humid environment can shorten the open time.

Pay attention to the level of humidity!

Well sealing foam is usually offered as a 1-component PU foam. This means that it needs moisture from the environment in order to foam up and harden properly.

In order to extend the sticking time (readjustment time) of the well foams, the environment should not be too humid. Separate moistening of the applied foam is, therefore, not advisable with well sealing foam.

This is where well sealing foam differs from other assembly foams, which should be slightly moistened to improve the foam quality and shorten the curing time.

Once the foam has hardened, you can cut off any excess PU foam with a sharp knife. If necessary, seal these interfaces again with silicone if the pressure of the shaft ring is not sufficient.

Pay attention to the processing temperature

The temperature should also be right for working with PU foam. It should be between 5 and a maximum of 35 degrees Celsius on the adhesive surface.

The PU foam can itself may have a temperature between 5 and 25 degrees Celsius. If the can has become too warm or too cold, you can slowly bring it to the optimum operating temperature of approx. 15 - 25 degrees Celsius with cold or warm water.

Shaking improves the quality of the construction foam

Screw on the PU foam gun or the adapter tube. Shake the can vigorously approx. 30 times. This ensures that the contents of the can mix well. This improves the foam quality.

Apply the well sealing foam evenly

Then spray the foam as evenly as possible into the joint to be sealed or onto the manhole ring. When doing so, you should hold the can head downwards. After foaming, the well sealing foam continues to swell slightly.

The fresher the foam, the better!

The next shaft ring should be fitted within a few minutes. In general, the quicker you place the ring on the freshly applied foam, the better.

In any case, you should fit the ring before the foam is tack-free to ensure the necessary stability of the well or shaft. The product data sheet provides information on the exact time period.

Observe the curing times

Depending on the product used, it must cure for between 6 and 20 hours before well sealing foam is waterproof and fully resilient. During this time, it expands even further. This also fills small cavities and leaks. The foam then retains its shape and no longer changes its volume.

How much well sealing foam do I need?

A standard 750 ml can is sufficient for approx. 30 linear metres of foam line. With 500 ml cans, the yield is approx. 20 linear metres.

Formula: 1 ml foam ≈ 0.04 linear metre foam strand

→ Tip: Plan according to the circumference and diameter of your manhole rings – this avoids interruptions during work.

Safety during use

Well sealing foam contains propellant gas – just like other PU foams. Therefore:

Ensure good ventilation, especially in shafts or narrow working areas
Strictly avoid naked flames and sparks
Do not smoke during processing
Wear protective equipment: Gloves, safety goggles, breathing mask if necessary
Minimise the risk of explosion: Do not use electric tools with sparks
Ventilate regularly if you use several cans in succession

Checklist: Using well sealing foam correctly

✔ Clean substrate, moisten slightly
✔ Shake can, pay attention to temperature
✔ Apply foam evenly – do not overfill
✔ Fit the manhole ring immediately
✔ Ensure UV protection for outdoor applications
✔ Allow 6-20 hours curing time
✔ Do not forget ventilation and safety

FAQ: Frequently asked questions about well sealing foam

Is well sealing foam waterproof?

Waterproof yes – but it only becomes completely watertight if it is mechanically compacted, for example, by the weight of a manhole ring. Pressing them together ensures that moisture can no longer penetrate.

How does well sealing foam become waterproof?

This is how the sealing of well shaft rings with well sealing foam works: the weight of the shaft rings used ensures that the foam is compressed and compacted in such a way that water absorption is no longer possible. There are simply no more water molecules to fit between them!

Its water-repellent effect is not only due to its chemical properties, but also to the physical pressure exerted by the setting rings.

To achieve this effect, you should ensure that you fit the next shaft ring in good time. In good time means: before the foam stops sticking! Once the well sealing foam is tack-free, it is possible that the tightness will suffer.

Is well sealing foam resistant to splash water?

The fact that well sealing foam is waterproof means that it does not dissolve even when constantly exposed to water. This means that it can withstand water for a certain period of time, even splash water does not bother it, but regularly acting pressurised water penetrates into the cell chambers of the foam.

How long does well sealing foam harden?

Depending on the product, humidity and temperature, between 6 and 20 hours. During this time, it expands and fills cavities. It then retains its shape.

Can well sealing foam be painted over?

Yes, and this is also advisable for above-ground use. A simple covering with PU, acrylic or silicone sealants protects against UV damage and extends the service life.

Do you need special products for drinking water wells?

Yes. In this case, the foam should be coated with a compound suitable for drinking water after application. This protects the water quality.

Which well sealing foam is suitable for which manhole ring?

This question is easy to answer: The tightness of the ring and foam are tested together. Therefore, simply pay attention to test certificates or approvals.

How long does well sealing foam last?

When properly processed and installed in a protected location (e.g. below ground level), well sealing foam lasts for many years – usually just as long as the surrounding components.

Conclusion: Well sealing foam is a real problem solver

Whether you want to seal a well, install a shaft or protect a cistern connection from moisture: well sealing foam is a versatile, durable and easy-to-use helper. If you pay attention to proper use and select the product for the intended purpose, it will serve you well for many years.

Autor: Antje Ebner

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