The Problem
by David Campbell — Many apartment units of a four story apartment complex in Minneapolis, Minnesota had experienced a history of water infiltration during heavy rains. It appeared as though the water was somehow entering the exterior wall system and migrating down into apartment units at various levels. The exterior walls were wood frame construction with a stucco finish and the windows were hollow aluminum frame units.
The Investigation Begins
Inspec, Inc., which provides various engineering and architectural services, was hired to investigate the problem, determine the cause(s), and make remedial recommendations. The investigation started with a systematic progression of spray bar water testing at various suspect windows. By process of elimination it was determined that the primary source of the infiltration was isolated to the window sills. This was confirmed by flooding the window sill tracks with water, which recreated the infiltration into the wall system between the window unit and the framed rough opening.
In addition, the exterior finish materials were removed around the window in order to examine installed flashings and weather resistant barriers (WRB). Next, one window unit was completely removed and more closely examined for possible installation or design defects.
It was discovered that some of the factory installed gaskets, which provide a thermal break between the exterior and interior window components, had shrunk over time as much as one half inch. It was also discovered that silicone sealant had not been installed at the base of the aluminum jamb plates.
The Cause
By removing the aluminum jamb plate it was revealed that, in section, the operable window sills are comprised of two main chambers with a smaller chamber between them created by the thermal gasketing.
The window sill tracks are designed to drain through holes down into the corresponding chamber below, where the water then passes from chamber to chamber toward the exterior following the chamber floor slope. Once in the exterior chamber the water discharges through weep holes to the exterior of the window.
Since the silicone sealant was not installed at the bottom of the jamb plate, the water that accumulates within the two main chambers also drains out the chamber ends at the jamb and enters the wall system between the window unit and the framed rough opening. In addition, the water in the middle gasket chamber enters the wall system in the same way only through the opening created by the shrinking gasket at each jamb.
Remedial Recommendations
Since the apartment complex had 375 window units that needed to be repaired, the conventional approach of removing each unit in order to install the missing silicone and fill the gasket opening would be cost prohibitive, not to mention the collateral damage and tenant inconvenience that would also occur. For those reasons, Inspec devised a solution that did not require the removal of the window units. Somehow a more cost-effective, yet elegant, solution had to be developed that left the windows in-place.
Inspec decided to inject an expansive grout into the jamb ends of each of the three sill chambers. This could be accomplished without removing the window by reaching to the outside of the window from the interior. Since some of the chamber interiors could still be wet from the previous rains, Inspec decided to use a hydrophilic grout, which bonds well even to wet surfaces. However, since hydrophilic grout expands to many times its liquid volume before it solidifies, a “containment dam” first had to be injected. The containment dam limited this expansion and avoided filling the chamber completely, which would prevent the sills from draining. A quick setting foam product was chosen as the containment dam material.
Finally, new exterior weep holes would be drilled in the exterior chamber to weep the middle portion of the chamber occurring between the two foam containment dams.
Mock-up Testing
Since Inspec was not aware of any other examples of similar window injection, the team decided to test the procedure on a mock-up window first. One window was temporarily removed, taken into the building garage, and mounted upright in a wood frame to simulate the in-place condition. The window was injected with the containment dam foam first, and then the hydrophilic grout. Since hydrophilic grout not only adheres to wet surfaces but actually requires adequate moisture in order to completely activate, or “kick” Inspec had a special wand fabricated which would evenly distribute water into the chambers prior to the grout injection.
Once the jambs had been injected, and the hydrophilic grout had adequately cured, Inspec simulated an extreme rain event by keeping the sill tracks and the chambers completely filled with water. After 30 minutes the team observed no water leakage at the jamb ends of the window, indicating that the injection technique worked.
Refinement
The procedure was refined further and used to repair the in-place windows of the apartment building. Injection holes were drilled in the exterior face of the sill frame and the containment dam foam was injected. Next, the hydrophilic grout was injected in the sill frame between the containment dam and the window jamb, until foam was observed coming up through the existing weep holes located in the sill tract at the jamb ends. Finally, new weep holes were drilled down through the sill tracks and also through the exterior side of the sill frame in order to maintain the draining of the sill tracks after the new repair.
Conclusion
The cost of repairing the windows using the conventional method of first removing the window from the building would cost an estimated $650,000 (375 windows @ $1730/window). The cost using the injection method was $150,000 (375 windows @ $400/window) representing a savings to the owner of $500,000.
Since the repair was made, the windows have been exposed to numerous rain events over an extended period of time without any reported leaks, it is reasonable to assume that grout injection is a viable repair technique as an alternative to more conventional methods and could be used for repairing windows with similar infiltration failures at great savings to the building owner.
David Campbell, AIA, RWC, GRP is a firm associate with Inspec, Inc. He is a licensed architect, a registered waterproofing consultant and an accredited green roof professional. Inspec, Inc., is an independent and award-winning engineering and architectural firm.