Saturday, September 10, 2016


Two very common construction defects that we encounter during our forensic investigations are the so-called mortar bridging and mortar droppings.  These defects have been known to the construction industry for many-many years, but despite the awareness, they continue to occur quite frequently.  The main reason for that is that it is a challenge even for a good mason to manage the mortar.   
Imagine what this means if a not-so-good mason builds the wall.  This blog deals with these mortar handling issues as they relate to the anchored masonry veneers that are so popular with homes built during the past twenty years.

This picture clearly displays a problem that we call mortar bridging and mortar dropping.  This occurs when sloppy workmanship results in mortar getting behind the brick. The problem is that this prevents water from freely draining out of the wall system.  In fact, it even bridges the gap between the brick and the framing, allowing water to wick into wood materials, causing lots of problems.

Anchored Masonry Veneer
Masonry (brick or stone) veneers cover areas of the exterior walls at many condominiums, single family houses, commercial buildings and other structures.  The brick or stone is nonstructural and is attached back to the structure with corrugated brick ties.  Openings in the brick are spanned with primed steel angles.  The brick wall typically bears on top of the post-tensioned slab and is installed between 1-inch and 2-inches from the exterior wood stud walls, depending on the design.
Properly detailed brick veneer functions like a rain screen.  The key is making sure there is an unobstructed path for water to flow out at the bottom of the wall.  This path starts with the airspace behind the brick. Water freely flows down through this space, gets collected by through-wall flashing at the bottom of the wall, and drains out through weep holes.


                                    Brick veneer rain-screen assembly

The purpose of the cavity weep system in an anchored brick veneer is to provide a means to drain and dry the air space between the brick and the weather-resistive barrier.  The cavity weep system (the 1-2 inch air space, flashings, drainage nets, and weeps) is critical to ensuring the durability of anchored brick veneers and the underlying building envelope components and framing.  The proper installation of a weep system is prescribed by building codes and is well documented in industry standards.

                                                Basic Cavity Wall Design

Unfortunately, many installed cavity weep systems for brick veneers do not comply with industry standards and the building code requirements for such systems.  This typically results in diminished capacity of the brick veneer to drain and dissipate absorbed moisture and incidental water penetration.
At one recent forensic inspection, we found that excessive mortar droppings were blocking the drainage path and weeps at the bottom of all walls and above all fenestrations that were subjected to our intrusive examinations.  To prevent mortar droppings, standard industry practices include either mortar dropping devices at the base of the brick walls or cleaning out the air space from the mortar droppings during construction on a daily basis.  Some typical specifications regarding daily cleaning are provided here:
The contractor shall carry out work in as clean manner as possible and shall remove excess materials and mortar droppings daily.
Where bricks walls and partitions are to receive plaster, excess materials and mortar dropping shall be removed and the surfaces shall be brushed clean.
During cleaning operations, adjacent work shall be protected and any damage resulting from improper protection shall be made good by the contractor at this own cost.
The contractor shall carry out the work in a clean manner and shall remove excess material mortar droppings excess materials mortar droppings shall be removed and the surfaces shall be brushed clean during cleaning operation adjacent work shall be protected and any damages shall be made good at the cost of the contractor resulting from improper protection.

Applicable Code and Industry Standard References
1403.2 Weather protection.
Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing, as described in Section 1405.4. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1405.3.
Source: International Code Council (ICC), 2012 International Building Code (IBC), Chapter 21, Section 1403

1404.4 Masonry.
Exterior walls of masonry construction shall be designed and constructed in accordance with this section and
Chapter 21. Masonry units, mortar and metal accessories used in anchored and adhered veneer shall meet the physical requirements of Chapter 21. The backing of anchored and adhered veneer shall be of concrete, masonry, steel framing or wood framing.
Source: International Code Council (ICC), 2012 International Building Code (IBC), Chapter 14, Section 1404 Maintain a maximum distance between the inside face of the veneer and outside face of the solid sheathing of 1 in. (25.4 mm) when corrugated sheet metal anchors are used. Maintain a maximum distance between the inside face of the veneer and the wood stud or wood framing of 41/2 in. (114 mm) when other anchors are used. Maintain a 1-in. (25.4-mm) minimum air space.
Source: Masonry Standards Joint Committee, BUILDING CODE REQUIREMENTS FOR MASONRY STRUCTURES, 2006

                                           Example of mortar bridging

Defects Associated with Thru-Wall Flashings installed at the Base of the Masonry Veneer Wall
Through-wall flashings are one of the components of the cavity wall system where we also see very significant defects. The first step to detailing the base of a brick-veneer wall is to install a through-wall flashing, which extends down the sheathing and out across the support ledge (often a concrete extension of the foundation, but may also be formed with angle-iron).
Through-wall flashing can be made with metal, but is usually formed with a flexible rubber-based membrane, such as the one shown in the photo below.

                                       Flexible rubber through-wall flashing

1.    Weather-resistive barrier. Next, a weather-resistive barrier, such as building paper, must be applied over the framed wall assembly. The courses of the weather-resistive barrier must be applied "shingle fashion," with the lowest course applied first, overlapping the vertical leg of the through-wall flashing. The upper courses are installed afterwards, overlapping each lower course.
2.    Air space. The brick must be installed with a 1-inch air space behind it to allow water that seeps into the brick to freely drain. The illustration above shows a mortar mesh installed in the air space at the base of wall. This helps to stop mortar droppings from clogging the weep holes.
3.    Weep holes. Water that collects on the through-wall flashing must be able to drain out through weep holes, which are formed by an "open" head joint (as shown in the illustration above), or with rope inserted into the  mortar joint (as shown in the photo below). In this illustration the open head joints have been filled with an open-weave mesh. This is a good idea for keeping mud wasps from building their nests in the weep holes, and to prevent other obstructions from blocking the free flow of water.

Weep holes: Rope inserted in the head joist between bricks will allow water to weep out of the base of the wall assembly

As far as installation construction defects, many installers do not understand how to install flashings around windows and doors so that when water runs downhill (as it surely will).  The moisture should be guided down and out, instead of into the wall cavity.  When installers install flashing by “reverse lapping” at the sill flashing paper (which is often done) water is drawn into the walls instead of out of walls.  See figure below.

Water stained sheathing and rusted fasteners below window shown in photo above.  Note that the weather resistive barrier is reverse lapped with window sill flashing, allowing the moisture from the flashing to impact the sheathing.

Installers also often rely on caulking to create a weather-resistant joint, instead of proper flashing. Caulking will deteriorate with age and weather, and is subject to proper installation to provide the water resistance; proper flashing can last considerably longer and is not subject to deterioration from most climatic stressors (wind and rain).

Installation construction defects also relate to the interconnection of windows and doors to the building structure relative to the vapor retention barrier and wall insulation. The vapor retention barrier is typically initially installed in continuous sheets, and then cut out for window and door openings. Construction defects occur when the “X” cut typically made at these openings extend beyond the opening size required for the windows and doors, thus creating locations where water will pass through the envelope, unimpeded; moisture will condense in this area. Moisture also infiltrates the wall cavity if insulation is not uniformly installed in all areas around windows and doors.

Management of the Mortar
Cavity bridging can be found in any cavity built building, from residential housings to infill walls to high rise buildings.  Bridging materials found in contemporary buildings are generally of mortar and brick debris discarded during construction.  In older buildings built with lime mortar, the bridging materials generally found are a build up of decayed mortar within the cavity.

So, are there any ways of managing the mortar droppings and bridging?  There are two major issues when it comes to managing mortar within the wall cavity: the need to ensure weep hole function and the need to address mortar bridges throughout the entire height of the airspace.
As stated earlier, mortar droppings are excess mortar that fall to the flashings. Mortar droppings that obstruct a properly detailed and constructed flashing system are blocking the weeps and they are preventing the drainage system of the wall from functioning as was designed.  An initial means of protecting weeps from mortar droppings was to place pea gravel in the cavity.  We quickly learned that this did not resolve our issues — we merely raised the location of the solid ledge of mortar to the top of the pea gravel.
A huge improvement over pea gravel came when commercially available drainage materials were introduced to the marketplace.  These products come in various configurations, all of which break up mortar droppings in one manner or another to reduce the opportunity of creating a solid obstruction above the weeps.  See figure below showing the installation of one of these types of drainage materials.

                                              Installing a drainage net

The second issue is mortar bridging when mortar makes contact with the backup.  (see photo). A mortar bridge will impede the flow of moisture to the flashing level, and it will make it harder for air to flow within airspace.  Moisture can pond on top of mortar bridges.   
If moisture is collecting at locations where insulation joints are not properly sealed, moisture will have the opportunity to get behind the insulation and cause the rotting of the sheathing, wood framing and so on.  Due to these construction defects, mold has been surfacing as the number one concern in all building envelopes. 
                                            Mortar bridging in cavity walls

Practices to prevent mortar bridges have included the use of pull-boards and back parging.  Pull-boards are a hassle, and this practice can disturb bricks.  Back parging can increase the amount of mortar droppings.  
Another method that has been developed is to add-head joint type weeps at the bottom and the top of the wall, sometimes with plastic or mesh inserts.  This practice greatly improves cavity ventilation, yet cannot compensate for a severely obstructed cavity.   Some practices to avoid are shown in the figure below.

Responding to this challenge, several companies now manufacture products that are installed throughout the full height of the airspace to assure a clean cavity. By installing a full-height drainage material that does not allow mortar to make contact with the backup, a continuous drainage area is the result. 

Additionally, these products make smaller cavities possible, which allow increased insulation or overall wall thickness reduction. Even though these products have quite different physical properties, the concept is still the same: full-height airspace maintenance that prevents both mortar droppings and mortar bridging.

Clogged weep tube.  The tube is also located much higher above the flashing than is allowed.  This home had moisture intrusion problems in that area.

Weep holes are essential for the good health of your building.  Because brick is not waterproof and is actually porous it allows as a reservoir for water and also allows the movement of water through the wall. This means that when it gets wet a masonry wall can absorb and store significant amount of water.  The weep hole is designed to ensure that that stored water can escape and allow for air to enter behind the wall to assist in keeping the structure dry.  Unfortunately, this opening is also a convenient entry point for unwanted pests such as mice, roaches, snakes, spiders and other unwanted critters.
A big problem we see is that the specifications do not dictate what drainage product to use to keep the cavity free from mortar droppings.  Many specs we reviewed classify pea gravel placement the same as mortar net, for example.  Since this is a cost issue for the mason, he will of course use pea gravel which is not as effective in keeping the cavity area open from mortar droppings.

                                                   Weep drain clogged with organic growth

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