Determining the best grout for curtain grouting depends on a few factors.
- type of leak(s)
- size of voids
- presence of water
- soil properties
- structure conditions
Leak Features
The type of leak has a significant impact on the choice of curtain grout. Point leaks, such as a distinct hole in a wall, or a poorly sealed pipe penetration can usually be grouted with a higher viscosity chemical grout. This can be either a plural component geotechnical polyurethane, such as a CJGrout 35NHV61, or an expansive prepolymer.
Water weeping through a wall usually requires a grout that will thoroughly coat the exterior of the structure. Depending on the nature of the weeping, a single component chemical grout or acrylate grout is typically best. The benefit of curtain grouting is that it provides a positive side seal. This is enhanced by grout penetrating the leaks through the full thickness of the structure. If it’s larger flowpaths, such as course honeycomb, expansive prepolymer works well. If it’s small cracks or deteriorated mortar joints, acrylate works great.
Size of Voids
The larger the voids, the more likely that a plural component geotechnical polyurethane is best. Plural component polyurethanes, such as CJGrout 35NHV61 provide excellent bearing capacity, and expand significantly. The expansion means that less liquid volume of grout has to be placed to fill the voids.
Plural component polyurethanes aren’t great at penetrating very tight cracks, though. So, secondary grouting with a single component prepolymer or acrylate is typically used to chase any residual leaks after bulk void filling is done.
Soil characteristics have a big impact on grout choice if there aren’t any voids. More on that below.
Presence of Water
For leaks above the water table, a hydrophobic material is best. Hydrophobic materials, such as all the various CJGrout plural component polyurethanes, and many single component prepolymers, don’t shrink or swell depending on moisture levels. Historically, hydrophobics grouts haven’t had great elongation, so would tear in dynamic environments. Manufacturers have responded by developing relatively high elongation hydrophobic grouts, such as Mountain Grout Ultra.
Hydrophilic grouts are great for use below the water table. They have excellent elongation, and tend to get drawn into tight cracks & leaks as they seek out water during injection.
Soil Properties
In general, the smaller the soil grain size, the lower the grout viscosity needs to be, if the goal is to permeate out into the soil to create a grout curtain. The best grout for curtain grouting where the goal is to just coat the wall and not permeate out into the soils, is a higher viscosity grout. The larger the soil grains, the higher the grout viscosity needs to be, and the faster the reaction time needs to be.
For structures backfilled with poorly graded stone, a thick, fast grout is best. For fine grained soils such as sands & silts without voids against the structure, a very low viscosity grout will perform best. The lowest viscosity grout out there is acrylate. Note that acrylate is effectively the same viscosity as acrylamide, but unlike acrylamide, acrylate is safe to handle.
Structure Conditions
The last really important consideration for selecting the best grout for curtain grouting is the condition of the structure. A resilient wall such as newer poured concrete, will tolerate expansive grouts a lot better than an old leaky brick wall.
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