Water Retention in Split Faced Block Buildings

One must stop the water from coming in, AND get rid of the retained water.

By William Decker, CRI, CCI, CMI

If you have lived in or near the north side of Chicago, you are probably well aware of some of the problems that exist in some of the newer apartments, condominium buildings and single family houses that have been constructed of split faced concrete block.  This material is very porous and, in most cases, was not properly detailed with flashing and drainage planes.  As a result, most of these buildings have water intrusion problems.  The problems can present themselves as water stains on the walls and trim, buckling of hardwood floors, water drips from light switches and electrical outlets and can lead to rot of the wooden structural members and harmful mold growth.

Water Damage and Rust in Split Faced Concrete Block Building  Wet Split Faced Block Building in Chicago


Most of my client are primarily concerned with a) stopping the water from coming in, and b) fixing the cosmetic damage.  But they are missing a crucial step in the middle, having the water that remains in the wall removed.  Once the water intrusion source has been repaired, the walls themselves must be dried.  In a commonly seen 3 unit, duplex-down condominium building with split faced block on 3 sides, there can be as mush as 2,500 - 3000 gallons of water that is retained in the porous block and the open cells at the center of the block.

Recently, I accompanied a friend of mine who is a contractor who specializes in fixing split faced block buildings. We decided to run a little test.  Using a drill and a special masonry bit, we drilled a little hole into the mortar joint of the building.  The results can be seen here:

Water Logged Split Face Block Building Chicago - YouTube

This was the amount of water that was found in only one of the block cells and there are hundreds, if not thousands of these cells in a typical building.  If not dried, this water will only come back, over the years, and cause more damage.

Drying the wall

Once the water intrusion has been stopped, the wall must be dried.  This is a multiple step process.

Weep wicks, or better yet, ventilation ports, should be installed at the joist pocket flashing levels all around the building.  Weep wicks are sections of rope that should be placed in the wall when it is being built.  These wicks draw the water down and out by capillary action, where the water will evaporate.  The evaporation action creates a suction that draws more water out.  Weep wicks should be a regular construction detail and serve to remove any wall moisture that may form under normal circumstances.

Ventilation ports are small plastic assemblies, similar to plastic steel wool or corrugated cardboard, that fit into the mortar joints between the block or in bricks.  They provide a clear water and air channels that allow water in the wall to drain out as well as provide ventilation into the wall to promote drying.  These vents should also be installed at the joist pocket levels which is where most of this moisture tends to accumulate.

The drying can be further sped-up by the temporary use of industrial strength type de-humidifiers inside the building.  This will dry the interior air and draw the moisture out of the masonry.  In most cases, the interior insulation and drywall must be removed anyway, because of their water damage and as part of the mold remediation process.  These de-humidifiers should be run after the drywall has been removed and before any wall replacement work is done.  If fully and properly de-humidified, many problems with minor buckling of hardwood floors solve themselves.  Drying out the masonry also tends to dry out the hardwood floors and they un-flex themselves.

Final Thoughts

With split faced block building problems, it is especially important to approach the situation in a planned and managed manner.  A professional Home Inspector, one who is experienced with thermal imaging and building science principles, can do the initial evaluation of the property and determine the extent of the problem and the most cost effective methodology to address that building's specific needs.  The masonry and flashing contractors should also be specifically experienced with split faced block problems and will work with the inspector to develop the best repair plan.  Once the repair work is completed, the building must be properly dried.  This takes time, often lasting 2 to 4 weeks, during which time the interior of the building will have the wet drywall and insulation removed.  If the water problem has been of long duration, repair could also include replacing some of the rotted wood furring strips and rusted electrical conduit and boxes.  If there has been significant mold formation, this will have to be professionally removed by a contractor who is specifically trained in mold remediation.  Finally, and only after all these steps have been completed, the drywall, flooring and wooden trim can be re-installed and painted.  Remember, saving a little money up front will most probably mean that the problem will come back.  It is always better to do it right the first time.