Polyurethane (PU) Grouting and Injection
What is PU Grouting?
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.
LE FONG USES ONLY THE CLOSED CELL FOAM FOR ALL OUR PU GROUTING TREATMENT
INDUSTRY SPECIALIST IN PU GROUTING SERVICES
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