PU Grouting and Injection

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PU Grouting / PU Injection

What is PU Grouting?

Polyurethane (PU) grouting is a term used for a specific technique used to stop water seepage from cracks, to fill voids under slabs, concrete joints or walls that are caused by water damage. The procedure involves injection expanding polyurethane or PU into the space created by the water damage. This method is effective when used on the side of any water leakage area. For example, in an inter-floor ceiling leakage problem, a PU grout can be injected into the lower floor ceiling to prevent further water leakage.


Causes for Concrete Cracks

  • Moisture permeates the tiny breaks in the concrete substrate and in colder climates enlarges them to full-fledged leaking cracks by expansion/contraction resulting from freeze/thaw cycle of the moisture.
  • As the ground around the footing or foundation stabilises, any movement can cause the rigid concrete substrate to separate at these tiny breaks in the concrete, enlarging them to a water-leaking size.


Low and High Pressure Injection

The repair of the concrete structures mentioned above is suitably accomplished using low-pressure injection of the damaged areas with a liquid polymer, which hardens with time. Other applications, such as those involving very thick-walled structures (e.g. dam repair) or where a high volume of water flow must first be stopped may be better suited for high-pressure injection.

Low-pressure injection, here defined as 20-40 psi, utilizes surface ports placed directly on the surface of an otherwise sealed crack as the entry point of the liquid polymer. This technique can be utilized at up to 250 psi of injection pressure.

High-pressure injection at 250 psi -100 psi psi utilises injection packers which are typically placed in holes drilled at 45 degrees to intersect the interior of the crack. Until recently, this technique has traditionally been used in in commercial and civil projects, but as the technology is more readily available the use of polyurethane foam repair is preferred. The disadvantages of this approach is the extra cost of packers but it’s worth it in the long run.

The secret to effective polyurethane foam injection, low-pressure introduction of the liquid polymer into the crack. Low pressure (20-40 psi) allows the applicator to properly monitor the injection process. At this pressure range, the applicator can be confident that the crack has been saturated with the liquid polymer up to that point when liquid begins to collect at adjacent surface injectors.

Polyurethane foams are classified as hydrophilic or hydrophobic. Both a hydrophilic and a hydrophobic react with water (typically that present in the crack, although they can also be mixed with water immediately before injection). A hydrophilic foam system will entrap any excess water present within its structure during foam formation. Both can be formulated to be flexible but a hydrophilic system is typically more resilient than its hydrophobic counterpart. The disadvantage of a hydrophilic foam is that it can lose any excess water due to evaporation under dry conditions and subsequently shrink (growing again when exposed to more water) Recently, a hydrophobic formulation has been introduced with claims of being as resilient and flexible as a hydrophilic without subsequent susceptibility to shrinkage with time.


Guide to Use of PU Grout

PU Grouts are usually injected under pressure as a liquid resin into or in the vicinity of the leak. Once the resin contacts water, a chemical reaction occurs. Depending on the material formulation, the grout/water combination forms either an expansive closed cell foam or a gel. The foam created can be flexible and resilient (hydrophilic) or ridged, meaning the cell structure of the foam crushes when compressed (hydrophobic).

In most manhole leak scenarios, the water flow or leak can be used to pull the grout into the structure. To accomplish this, a hole is drilled in the vicinity of the leak and the chemical grout is injected through the wall into the water source. As the resin reacts with the ground water, it is pulled back into the structure and seals the leak from the outside in, thus creating a seal through the entire wall. PU Grouts can also be injected directly into the defect in cases where the leak is not strong enough to pull the grout into the structure. The expansion of the foam helps drive the grout through the structure to seal the defect. Hydrophilic polyurethane resins that produce gels are typically installed by injecting water along with the resin through a manifold that briefly mixes the two prior to being injected. These gels are non-expansive but can be produced at water-to-resin ratios as high as 15 parts water to one part resin.



Both hydrophilic and hydrophobic chemical grouts will seal leaks in all types of concrete structures initially. The issue is how to create a permanent seal. Let’s look at the basic properties of both hydrophobic and hydrophilic chemical grouts. The properties of each type can be used to reduce the cost of installation and improve the quality of the repair long term.


Hydrophilic – Latin (hydro)=water and (philic)=affinity

Hydrophilic chemical grouts can produce either closed cell foam or a non-cellular gel when mixed with water. The reaction time is typically 30-45 seconds for foams and 12-15 seconds for gels. When activated, foams expand in volume between 5 –8 times. The volume of gel produced is relative to the ratio of water mixed with resin during installation. Hydrophilic Gels can shrink after cure in the absence of water. Hydrophilic chemical grout likes water and is able to bond to wet surfaces tenaciously; water-scavenging agents that seek out water as they react and allow the resin to work its way into water filled pores that exist in wet concrete surfaces. Hydrophilic chemical grouts are flexible and resilient after full cure and will allow movement to occur in the structure without damaging the seal or bond.


Hydrophobic – Latin (hydro)=water and (phobic)=fear

Hydrophobic chemical grouts require a catalyst that is blended into the resin prior to installation. The dosage of catalyst added to the resin controls the reaction time and the volume of foam produced. Using the maximum dosage of catalyst, (10% by volume) hydrophobic resins have an aggressive expansion; the reaction time is 10-12 seconds and expansion can be as much as 29 times in volume. Hydrophobic chemical grouts repel water after activation. When injected into a wet crack or joint hydrophobic resins can trap water in the pores of the wet concrete. This trapped water becomes a bond inhibitor. Hydrophobic resins cure rigid and do not recover from compression. If the structure moves there is good chance the cell structure will be damaged and leaks will reappear. Hydrophobic chemical grout is low viscosity and permeates loose and non-consolidated soils readily.

Knowing the basic differences in hydrophobic and hydrophilic chemical grouts is a crucial step in making the correct choice of repair material.


What to Do

If a leak repair project involves a non-structural defect in a concrete or masonry structure, a hydrophilic chemical grout should be used to seal the leak unless job conditions dictate otherwise.

Gels should be used only in below grade structures where either moisture from the interior (like in a manhole) or from ground water is present to keep the cured gel hydrated. Gels will shrink if water becomes absent, but provide a low-cost alternative to foams.

Foams are appropriate for above grade or below grade installation. They are typically 85% air filled after cure and have excellent elongation, compression and rebound for use in expansion joints, cracks, or any other non-structural defect in concrete structures.

Use the aggressive expansion of hydrophobic chemical grouts if repairing a gushing leak that is impractical to repair with milder expanding hydrophilic resins. In below grade structures, this is a good way to fill voids that may be present outside the structure. Once the leak is reduced to a manageable level, hydrophilic resin should be injected into the defect to back up the hydrophobic material.

Inject hydrophilic gel into gushing leaks neat or with a 1:1 water-to-resin mix ratio to shut down gushing leaks. This is a case where you push in as much material as possible as fast as you can. If a high volume pump is available, less material will be used to stop the leak because it reduces the dilution of the resin in the mass of water source.

Use “Activated Oakum” (dry oakum soaked in hydrophilic resin) to reduce the flow in gushing leaks. If the leak can be slowed, a hydrophilic resin may be used to complete the repair.


What to Avoid

Avoid installing gels in expansion joints or cracks that are subject to movement. Gels form a solid material with little or no cellular structure to disperse tension under compression. This tension can split the gel and damage the seal.

Avoid installing hydrophobic grouts for repairing minor leaks in cracks or joints. The repair will be temporary.

Don’t get in a hurry when repairing tight cracks and minor leaks. These can be the most difficult to repair long term.



As our infrastructure ages, grouting will continue to maintain its value as one of the easiest, most cost-effective and longest-lasting repair solutions available.


How do we inject a PU grout?

A hole is drilled into the lower floor ceiling, and the PU grout is injected through this hole using either low and high pressure (depending on the type of ceiling structure). Once injected, the grout will expand to fill up the void or cracks caused by water damage.


What kind of PU grout is durable?

There are two kinds of PU grouts in the market – the open cell foam and the closed cell foam. Traditionally, the open cell foam is naturally more porous and is only useful as a temporary solution of a water leakage situation. To ensure a durable and lasting PU grouting, a closed cell foam is needed as the nature of a closed cell foam is sturdy and does not require a second treatment with resin.




If you are looking for a specialist in PU Grouting, you are in the right place! We specialise in PU grouting for the following areas:

  • Seal joints in concrete, cement screed or masonry
  • Seal water-bearing cracks in concrete walls and ceilings
  • Repair of damaged false ceiling due to water leakage
  • Opening and resealing broken or damaged false ceiling due to water leakage
PU Grouting

Seal Joints

Seal joints in concrete, cement screed or masonry

PU Injection

Seal Water-bearing Cracks

Seal water-bearing cracks in concrete walls and ceilings

PU Grouting

Repair False Ceilings

Repair of damaged false ceiling due to water leakage

PU Injection

Reseal False Ceilings

Opening and resealing broken or damaged false ceiling due to water leakage

PU Injection at Meyer Road

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Open vs Closed Cell Foam

Truth and fiction about 1-component PU injection foams


Recently, popular comparisons have been made between 1-component Flexible polyurethane injection foams (HA Flex) and 1-component Rigid polyurethane injections foams from mainly German manufacturers. In these comparisons the shrinkage of the HA Flex foam is emphasized and it is wrongly concluded that the product therefore is not suitable for waterproofing.

When comparing injection resins, a rigid foam injection resin should be compared to a rigid foam injection resin and not a rigid foam open cell water stopper with a closed cell foam flexible injection resin. In order to obtain permanent waterproofing of leaks in constructions, you need to inject with a resin that will react into a closed cell foam, such as De Neefs HA Cut and HA Flex resins. The 1-component open celled foams from the competition are considered as temporary water stoppers which need a second injection with a closed cell flexible 2-component resin to obtain lasting and durable waterproofing.

It is clear that that an open porous foam structure is not a permanent water blocker but only forms a temporary sealing of the leakage. Therefore a second treatment with another type of injection material is always needed in order to eventually stop the leakage. When using open celled 1-component foams, this second injection step is an absolute requirement to obtain lasting and durable waterproofing. When injecting with closed cell foams, this post injection with a 2-component resin is not needed since the result will be a lasting and durable water stop in the crack or joint.

So where does this misconception come from?

When one compares a rigid foam to a flexible foam, it is clear that the properties of both types of resin are completely different. In the reaction that turns the resin into a foam, heat and CO2 is generated – irrespective to being an open or closed cell foam. The CO2 that forms the cells heats up during the reaction and expands. When cooling down this CO2 gas shrinks again. In the case of open cell foams, the shrinking CO2 gas is replaced with air being sucked into the foam through the open cells. Additionally, the foam will not shrink because there is no decrease in internal pressure or volume of gas in the cells.


In rigid closed cell foams, the foam will not shrink because the cell structure is sufficiently strong to absorb the volume reduction of the cooling CO2 gas. In closed cell flexible foams however, the shrinkage is not caused because of a problem with the product, but because the CO2 cools down and the flexible properties of the cured resin causes a closed cell flexible foam to shrink slightly in atmospheric conditions, because air can not be sucked into the foam to replace the loss in volume. Actually we would say, the reason for which HA Flex resins shrink in free foam is an indication of their prime property to lasting waterproofing: CLOSED CELL FOAM What must be understood, is that waterproofing injections are done in confined spaces, never in free atmospheric conditions and therefore cup tests are very unrealistic simulations to what happens in a real injection. The resin is compressed into the crack by means of an injection pump and the secondary expansion of the foam forming reaction will build up the pressure even more, assuring a perfect waterproofing.


The confined foam will only be able to create small closed cells filled with compressed CO2 gas. The cooling down of that gas will not result in shrinkage of the dense flexible foam but in a relaxation of the pressure of the confined CO2 gas. This will pressurise the confined closed cell foam plug within the crack and create a pressure of the foam against the sides of the crack which will ensure the waterproofing of the crack. The pictures below show what happens if a closed cell flexible resin is allowed to expand in confined conditions. The experiment concerns a metal pipe which is completely filled with resin. This resin is allowed to expand in completely confined conditions (picture 1). After curing of the resin, the pipe is opened by removing the end caps (figure 2). As can be seen in picture 3, the closed cell resin which has expanded in confined conditions is tension inside the pipe and when allowed to relax, increases in volume beyond the original volume of the pipe. This pressure against the sides of the cracks (B>A, D>C) is what makes closed cell resins excellent for lasting and durable waterproofing.


As a result a perfect closed cell foam will fill the crack and ensures a permanent flexible waterproofing without the need for additional injections afterwards.


The open-cell foam like the 1-component rigid open cell foams from the competition will only temporarily block the water and can not be considered.


Permanent solution to the leakage problem due to its open cell structure. However, the De Neef HA resins will form a permanent sealing of the leakage.

Now let us make a comparison between De Neef HA Cut and a rigid open cell foam from the competition

Cell structure and overall foam quality

Ha Cut left vs Open cell foam from completion right Irregular cell and foam formation of open cell foam clearly visible.

Close up of closed cell foam HA Cut.

Close up of open cell foam from the competition. Irregular cell structure clearly visible.

The difference between open and closed cell foams in wet environments becomes immediately clear from the test performed below. Cubes cut out of HA Cut and open cell foam from the competition foam are inserted into water containing a dye to visualise the effect of open cell foam. The photographs to the right clearly show the increased absorption of the open cell foams from the competition compared to the HA Cut foam. The absorption flux graph below shows even more clearly the problem with open cell foams regarding lasting waterproofing and the need for post injecting to obtain lasting results. The graph line for HA Cut shows an initial water absorption caused by cell structure damage due to cutting the sample out of the foam but levels out very fast and remains constant. This is also visible in the photograph where only the outer rim of the foam is stained.

HA Cut foam with dye only on outer rim, where the closed cells were cut to obtain the cubic shape.

Open cell foam from the competition showing dye permeating throughout the foam.

The open cell foam from the competition however shows a graph rising and not levelling out meaning capillary absorption is still ongoing and will continue until saturation and subsequent leaking of the foam. The photograph of the open cell foam from the competition clearly shows dye penetrating to the middle of the foam through the most open cells in the structure. Once these have been saturated, water channels have been created in the cured resin and the injected area will start to leak again.

Why is PU grouting useful in sealing water-bearing cracks in concrete walls and ceilings?

In our hot and humid weather, cracks in concrete walls are common as the concrete walls are subjected to thermal movements and drying shrinkage. Some cracks happen because of nearby construction works or renovation works. Usually, such cracks are minor issues and do not present a problem at the onset. However, these cracks can be a major concern if they become a water seepage problem. Water damage in concrete walls can cause structural issues, especially that of structural integrity.

PU grouting is useful for water-bearing cracks as the closed cell foam that Le Fong uses will fully expand after injection to fill the void in the cracks. Once the foam fills up the void, the crack is covered efficiently, and the water seepage problem is stopped.


We are experts in PU grouting and make use of the latest technology to provide solutions for your water seepage problems. Only high-quality waterproofing materials are used to fill up gaps, voids and cracks in your concrete walls and ceilings to offer permanent solutions.


Call us today to prevent water damage or water leakage issues on your property. We offer an obligation-free waterproofing inspection on your property before we give you our professional recommendations based on our on-site inspection. All our materials are of high-quality and are recognised as the best in the industry.

Denepox 40

An ultra low viscosity, two-component epoxy injection resin for structural injections in concrete, and can be used in a dry or wet environment.

Product Description

Pre-weighted two-component epoxy resin, which cures into a rigid compound.

Field of Application

• Low pressure injection for the structural bonding of cracks and micro cracks in dry or wet concrete.

• Bonding and anchoring.

• Sealing of porous low density concrete.

• Denepox 40 is not suited for applications in contact with moving water.

Product Advantages

• Insensitive to humidity

• Cures in damp/wet environment

• Low viscosity: deep penetration in the cracks.

• Very good adhesion: exceeds the cohesion of the concrete

• Solvent-free

• Long pot life

• Cured Denepox 40 is resistant to acids, alkalis, oils, greases and petroleum derivatives (*)


1. Surface preparation

• Surfaces to be repaired or sealed need to be clean and sound. The concrete surface must be free of dust, laitance, sealers, grease or any other contaminants that might influence bonding of the resin to the concrete.

2. Injection ports

• Entry ports for injecting should be approved devices spaced at appropriate intervals to accomplish full penetration of the resin into the cracks or voids.

Drilled ports

• Drilling of cracks for packers needs to be executed in accordance with local regulations. After drilling the hole, insert packer.

Glued ports (plastic or metal)

• The injection ports should be fixed to the surface of the crack with Multitek Adhesive SDW.

• Apply a layer of Multitek Adhesive SDW, polyester paste or fast curing cement to the surface of the crack.

3. Mixing

• Mix the pre-weighted quantities of resin (A-component) and hardener (B-component) with a low speed mixer (300rpm) until a homogeneous liquid is obtained. Never mix more material than the quantity that can be used up within 60 minutes

• Mixing ratio A/B = 100/30 (mass)

91/32 (volume)

4. Injection

• The crack can be injected with a manual (single piston) pump or a mechanical (single or double piston) injection pump

• Initial hardening time: approx. 24h at 20°C

• Uncured material and equipment should be cleaned with Washing Agent Eco



A-component: Epoxy resin, transparent

B-component: Polyamine hardener, light yellow

Colour: Transparent


Has to be estimated by the engineer or operator and depends on width and depth of the cracks and voids.

Technical Data / Properties

Full chemical or mechanical resistances are only reached after a curing period of 7 days at 20ºC. Mechanical properties of epoxy resins decrease at temperatures higher than 50ºC.


Denepox 40 (3kg set)

A-component: metal pail

Net : 2.3kg (Gross: 2.47kg)

B-component: metal pail

Net : 0.7kg (Gross: 0.78kg)

1 box

5 pails of A-component and 10 pails of B-component

1 pallet

16 boxes of A-component and 8 boxes of B-component


Denepox 40 is sensitive to moisture and should be stored in original containers in a dry area. Storage temperature must be between 5°C and 50°C. Once the packaging has been opened, the useful life of the material is greatly reduced and it should be used as soon as possible.

Shelf life: 2 years.


To be ordered separately

• IP 1C-Manual hand pump.

• IP 1C-Compact electrical airless diaphragm pump.

• Packers and connectors. (Please consult the relevant data sheet).

Health and Safety

Denepox 40 A-component is classified as irritating. Denepox 40 B-component is classified as corrosive. Always wear protective clothing, gloves and protective goggles. For full information, consult the relevant Material Safety Data Sheet.

Elastopack 201


2-component, phthalate free, hydrophobic, flexible polyurethane grout for sealing dry to moist cracks and joints with a non-expanding grout in concrete and masonry structures. Elastopack 201 can be injected or poured.

Product Description

Elastopack 201 is a 2-component, phthalate free, injection grout consisting of a resin and a hardener, which are injected as 1-component system after mixing. After curing, the grout will become a dense and elastic material.

Elastopack is packed in pre-weighted sets composed of:

• A-component : polyol blend.
• B-component : di-isocyanate hardener.
• Mixing ratio A/B : 2/1 volumetric.

Product Advantages

• ADR free transport

• Phthalate free resin, REACH compliant

• Packed as a complete pre-weighted set

• Solvent free • Non-flammable

• Good flexibility

• Low viscosity, fast and deep penetration

• User friendly: Easy to use 2/1 volumetric mixing ratio, used as 1-component

• product after mixing

• Cured resin has a very good all-round chemical resistance(*)

Field of Application

• Sealing of moving or non-moving cracks in concrete or masonry structures.

• Sealing of dry to moist cracks in concrete or masonry structures.

• Sealing of hairline cracks where other resins cannot penetrate.

• Filling of voids which can be subject to movement.

• Filling of joints between horizontal concrete slabs by pouring or pumping.


1. Preparation

• To improve adhesion of the resin to the surface, the surface needs to be sound, clean and free from dust, debris, grease, oils and laitance.

• Low temperature conditions will significantly increase the viscosity and the reaction time of the products. To minimize this effect, store the product at room temperature for a minimum of 24 hours before use.

• Add the complete contents of the A-component to the B-component. Mix thoroughly with a mechanical mixer at moderate speed (500 rpm). Shake A-component thoroughly before adding to B-component.

• Do not pre-mix more material than can be used within the pot life of the product.

2. Injection

• The product is used as a 1-component product after pre-mixing in a 2/1 volumetric ratio.

• The product can be injected or poured into the joint, void or crack to be filled as a 1-component system. Standard 1-component hand pumps or electrical airless diaphragm pumps can be used.

• All pumps and equipment should be cleaned immediately after use with Washing Agent Eco to prevent the material from gelling or curing inside the injection equipment.

Technical Data/Properties


A-component: Yellow transparent liquid

B-component: Dark brown liquid


Has to be estimated by the engineer or operator and depends on width and depth of the cracks and voids, which need to be filled.


3L set

A-component: 2L plastic pail in cardboard box

B-component: 1L metal drum in cardboard box

1 box = 5 x 2L A-component

1 box = 10 x 1L B-component

1 pallet

18 boxes A-component

9 boxes B-component

Total 90 sets (270L)

15L set

A-component: 10L plastic jerry can

B-component: 5L metal drum

1 pallet

30 x 10L A-component

30 x 5L B-component

Total 30 sets (450L)


Elastopack 201 should be stored in a dry area, free from ground. Storage temperature must be between 5°C and 30°C. Once the packaging has been opened, the useful life of the material is greatly reduced and should be used as soon as possible.

Shelf life: 2 years.


To be purchased separately

• IP 1C-Manual hand pump.

• IP 1C-Compact electrical airless diaphragm pump.

• IP 1C-Pro electrical airless diaphragm pump.

• Packers and connectors.

See relevant Technical Data Sheet.

Health and Safety

Elastopack 201 A-component is not classified.

Elastopack 201 B-component is classified as harmful.

All persons in contact with the materials should wear the appropriate protective clothing and gloves. Spills should be washed immediately with abundant quantities of clean water. For full information, consult the relevant Material Safety Data Sheet.