Commercial buildings constructed in the past 30 years experience a myriad of below-grade water infiltration problems at the lower levels, basements, and elevator pits.
After original construction, the building's foundation starts the settling process, and is moved by periodic ground shifts. The areas that are affected by water infiltration are the interior slab-to-wall joints and interior belowgrade walls exhibiting stress cracks, including elevator pits. In most cases, the exterior belowgrade walls would have some damp-proofing applied such as asphalt emulsion sealers, some form of membrane, and if thought of at the time, a protection board installed to ensure that during the backfill process the membrane would not be damaged by the impact of stones and hard soils. If these damages do occur, then not too far off in the future, moisture from sprinkler systems and rainfall will wick through the damaged dampproofing materials, through the cracks, and into the exterior of the belowgrade structures.
At slab-to-wall joints, a rapid setting hydraulic cement commonly called “water plug” can be installed and is very effective where there is hydrostatic pressure. This material contains hydraulic cement, selected silica sands, accelerators, adhesion additives, and shrinkage compensation additives. The wall-to-slab joint must be cut by a diamond blade or by chiseling to provide a minimum opening of ¾ inch, making the opening in the shape of an inverted V with the wide part of the V away from the worker.
This guarantees that the inside of the opening is wider than the outside so the hydraulic cement effectively bonds to the slab and wall substrates. This hydraulic cement also can be used to repair voids, honeycombs, and holes in concrete walls. On the downside, with its high strength of more than 8000 psi, and when movement or cracking occurs in the area installed, the concrete surrounding the repair will crack and deteriorate around it.
Coatings with acrylic modifiers
Belowgrade walls of commercial structures, such as buildings and parking garages, experience stress cracks wicking efflorescence to the interior of the structure. A commonly used material for interior belowgrade use to prevent moisture infiltration is a portland cement-based high-build waterproofing coating with acrylic modifiers. It allows vapor transmission while providing effective performance in resistance to standing water, moisture dampness, and hydrostatic pressure. This material is packaged in liquid and powder to provide a base coat, waterproofing coat, and topcoat. Its high strength is more than 4290 psi, and it is applied by parging a wall to effectively fill static cracks and voids.
Other than belowgrade concrete walls, the coating with acrylic modifiers is used effectively in damp-proofing the exterior of CMU block walls and its interior. It provides outstanding protection against positive or negative side water penetration. The downside of parging this material is its properties have no crack spanning capabilities (like elastomeric coatings), should cracks result due to ground movement of the structure after its construction.
These two types of materials—rapid setting hydraulic cement and a portland cement-based high-build waterproofing coating with acrylic modifiers—provide the protection needed belowgrade when filling cracks and voids.
— Rafael A. Rivas is president of National Association of Waterproofing & Structural Repair Contractors Inc. (NAWSRC), Baltimore, Md. For more information on waterproofing, contact NAWSRC at 410-931-3332 or email@example.com.