Myths and Facts

Myths and Facts about Injection Grouting for Municipal Applications

Over the years, there have been myths and misconceptions about injection grouting. Below are factual explanations about the longevity, effectiveness, and overall use of injection grouting for municipal applications – mainlines, laterals, lateral connections, and manholes.

When this myth was originally addressed by NASSCO in 1980, treatment costs were approximately $1.00/1,000 gallons. The myth was not true then, and over 30 years later with thousands of pipes sealed, the myth needs to be given an indecent burial. Even as treatment costs, labor and equipment costs continue to rise, grouting continues to be a cost-effective trenchless rehabilitation option by reducing transportation and treatment costs and stabilizing soils in structurally sound pipes and structures.

Thousands of grout trucks have been sold over the past 40 years. This raises the question: If pipe joint sealing is not cost effective, why do municipalities and contractors invest $500,000 or more in grout rigs if it is not a cost-effective option?

A typical example of cost of grouting vs. cost savings is as follows:

Anytown, USA had 615,000 gallons of unwanted groundwater infiltration entering through 100 joint defects in 12” clay pipe mainlines.  At a conservative rate of $4.00 per 1,000 gallons treated, that amounts to clean groundwater treatment costs of this single section:

  • $2,460 per day
  • $74,000 per month
  • $885,000 per year

Anytown air tested, sealed, and re-tested all 100 joints. The cost of the injection grout alone was around $5,000 which paid for itself in less than four days. Adding in the cost of contractor equipment and man hours, the project paid for itself in less than 30 days and saved the city hundreds of thousands of dollars per year from grouting this one section of pipe.

There is no question that injection grouting is a cost-effective, long-lasting solution for sealing infiltration and stabilizing soils.

In January 1995, Bob Madsen, Senior VP of Madsen/Barr Corp. presented “unfortunately some of the advertising in the liner industry infers that there is no leakage between the host pipe and the liner.” He continues, “It cannot be emphasized enough that the pipe-to-manhole connection and the lateral connections need to be sealed (after lateral reinstatement)”.

It is known that water can flow between the annulus of the liner and host pipe interface and field-proven options for annulus/lateral sealing primarily involve using injection grouting.

Grouting is a complimentary technology to lining – not competitive. Injection grouting is often utilized before or after cured-in-place-pipe (CIPP) lining of mainline pipes for a holistic approach. By eliminating infiltration before lining pipes, maximum performance is achieved by creating an infiltration-free environment for the lining process. Grouting after lining seals the annulus space between host pipe and liner. If this space is not grouted, infiltration will continue to enter the system at the next point of entry.

In 2018, a third-party study was conducted to perform testing and field analysis regarding how relative humidity affects acrylamide grout that has been injected underground. It was confirmed that relative humidity (RH) is a constant 100% for depths consistent with underground sewer systems. In the lab analysis, AV-100 (acrylamide grout) validated zero desiccation over time, meaning its properties – the ability to seal and eliminate infiltration – are permanent and will not change its structure.

It is proven that acrylamide grout, when mixed and applied properly underground, can last 50+ years at 12% concentration (and has 362-year half-life at 20% concentration per the Department of Energy!).

Download the White Paper: Zero Shrinkage of AV-100 Chemical Grout Due to Consistent Relative Humidity in Soils and the Case Study: Acrylamide Provides Lasting Help for United States Government (DOE).

Even though in some cases flows to the treatment facility did not substantially change post-grouting, grouted joints have remained intact and leak-free. This phenomenon could have resulted from incorrect flow monitoring or from sealing only the visibly leaking joints, and not air-testing and sealing all joints that were not air-tight – if the joint leaks air, it will leak water. NASSCO recommends testing and sealing all structurally sound joints in areas having excessive infiltration – certainly in each manhole-to manhole run after the pipe run has been cleaned and winches have been set up.

It is important that a daily log of each pipe joint sealed, including the amount of grout injected into each joint, be submitted to the specifying agency for approval. Ultimately, results are dependent upon value engineering, comprehensive infiltration analysis, appropriate rehabilitation procedures, exacting specifications, and competent full-time inspection.

FALSE. The use of acrylamide grout has never been banned in the United States. In a notice dated December 2, 2002, the EPA announced the withdrawal of a 1991 proposal that would have banned grouts that contained acrylamide and the acrylamide derivative N-methyloacrylamide (NMA). Through the combined efforts of NASSCO and member industry companies, the EPA was correctly educated on the safety and benefits of these products and determined they were safe if increased worker safety training was available. The Safe Operating Practices Program – originally created by Avanti – was developed in cooperation with suppliers and customers as a tool to protect employees and the environment from potential hazards associated with the use of acrylic injection grouts. The SOPP is now available as a NASSCO Grouting Unified Safe Operating Practices Program (USOPP). Get your USOPP certification here.

While grouting in hilly or clay soil areas is more difficult than sealing pipe joint that are surrounded by a sand of stone backfill material, it can be extremely successful if done properly. Sealing in a clay or hilly area may take more time and require use of grouting additives such as latex to ensure a sealed pipe joint. Hill-based cities such as Chattanooga, Denver, and Louisville are a sampling of cities with hills that have been grouting successfully for over 20 years.

Residual grout left inside the pipe is normal and expected and does not affect the final seal.  It is created from the void space between the packer elements and the inside of the pipe and provides absolutely no benefit to the sealing of the joint or defect. The pipe joint “seal” is created from the grout injected outside the pipe into the surrounding soil. This is why it is imperative that the correct amount of grout is pumped into each joint.

If a packer has a one-gallon void space, and only one and a half gallons of grout is pumped into the joint, only a half gallon of grout makes it outside the pipe. Low void packers help minimize this issue, but a good rule of thumb is to pump a half gallon of grout for every inch diameter of pipe (12” pipe = 6 gallons of grout).

The first grouting specification from NASSCO was released in 2014. In 2021, the specification was updated into two different specifications: Pipeline Packer Injection Capital Grouting and Pipeline Packer Injection Pre-Rehabilitation Grouting v2.10. These specifications were prepared by a committee comprised of representatives of NASSCO members and peer-reviewed by industry professionals. To download the specifications, visit