1. Pressure washing a concrete manhole with a 5,000 PSI pressure washerSurface Preparation: The rehabilitation process begins with surface preparation. Surfaces can be prepared by water blasting, pressure washing, abrasive blasting, acid etching, hand or power tool cleaning, or any combination of these. Regardless of what method or methods are used, all unsound concrete, contaminants, dirt, and debris must be removed prior to mortar application. The most common method of surface preparation is pressure washing at 4,000-5,000 PSI.

  2. Leak in a concrete manhole between the concrete wall and sewer pipeLeak Correction: A variety of methods may be used to stop leaks, including:

    • Urethane Grout Injection: A hole is drilled into or near the leak site, and grout is injected to stop leaks.
      • Advantage: Effective
      • Disadvantages: May be costly and time-consuming if there are many leak sites
    • Hydraulic Cement: Water is mixed with hydraulic cement, such as Mainstay ML-10 Hydraulic Cement Mortar, to create a fast-setting mortar used to stop individual leaks.
      • Advantages: Effective and inexpensive
      • Disadvantage: May be time-consuming if there are many leak sites.
    • An alternative method used to stop leaks in brick manholes is to spray an initial layer of mortar, allow it to harden, and return later to fix any remaining leaks with hydraulic cement.
      • Advantages: Cost- and time-effective
      • Disadvantage: Requires making a separate trip to the manhole
  3. Spraying restoration mortar using shotcrete equipment onto corroded manholeMortar Application: For cases where corrosion is not present, the application of a restoration mortar such as Mainstay ML-72 Sprayable Microsilica Restoration Mortar alone can smooth the substrate, increase structural integrity, and prevent inflow and infiltration (I&I). Ideally, all surfaces should be saturated, with little water remaining on the surface prior to application of a restoration mortar. Mortar can be applied pneumatically to the substrate using low- to medium-velocity wet mix shotcrete nozzles, centrifugally using a mortar spinner, or by hand using a trowel. Application thickness depends on the condition of the structure being treated and the final structural properties desired.

  4. Sponge finishing concrete manhole after application of restoration mortarMortar Finishing: Extensive finishing is not usually required. However, most contractors will use a pool trowel (a trowel rounded on each end) to "knock down" the mortar profile followed by sponge finishing to produce a smooth, lightly textured surface. Mortar may be finished using a broom, sponge, or brush, depending on the surface texture desired. If the mortar is to be topcoated with additional mortar, it is usually recommended that the surface be finished to a coarse broom finish. If the mortar is to be topcoated with a corrosion barrier coating, it should be finished to a smooth, somewhat grainy texture using a trowel and a sponge.

  5. Spraying 100% solids epoxy corrosion barrier over restoration mortarCoating Application: In cases where a manhole has experienced or will experience corrosion, the combination of a cement mortar and a protective coating, such as Mainstay DS-5 100% Solids Epoxy Coating, is required to both restore and protect the manhole from future deterioration. When restoring corroded manholes using this method, the protective coating should be applied to the mortar as soon as it is finished. Depending on jobsite requirements, the protective coating may be applied one to two hours after the mortar is finished. In any event, the protective coating must be applied to the mortar while it is still soft enough to indent with a fingertip. The protective coating is usually applied by the use of an airless spray pump. The coating may be hand sprayed using a spray gun, or it may be centrifugally applied using a Mainstay coating spinner. Other equipment, such as a whip hose, heater, or plural component equipment may be used.

  6. Applying flexible epoxy to the joint between the manhole frame and grade ringsFlexible Joint Sealant Application: One significant source of inflow and infiltration in manholes occurs at the joint between the manhole cast iron frame and the concrete grade ring(s) or bricks used to bring the manhole frame to a specific elevation. Cracks and expansion around the manhole chimney may also occur if the manhole is located in an area of heavy traffic. Expansion, cracks, and leaks at this location can be easily stopped with the application of a flexible joint sealant, such as Madewell 806 Flexible Joint & Manhole Chimney Seal.

Manhole before

Manhole after