Common Areas of Cracking in Bricks and Mortar
Some of the most common places to look for cracks and loose brick include:
- Above and below doors and windows
- In the angles of bay windows
- Around corners
- Along the edges of coined corners
- Archways-above, in the corners, and in the center
- Above garage doors
- Throughout walls over 25 feet long without expansion control joints.
- Fireplaces and chimneys
Area Specific Issues
There are several reasons why cracks occur at doors and windows. The main reason for this is that they are the weakest part of the wall and pressures release at these locations easily. Brick receives its strength from the inter-locking of the brick by staggering each course instead of just stacking them. At the edge of a door or window, the brick stop and do not inter-lock. This edge creates a cold joint between the brick and framework of the door or window that allows brick to shift more easily.
Bay windows disperse their weight unevenly due to their design. The steel does not flow straight through them preventing even distribution of pressure. Though connected, the separate panels carry their weight independently; this allows them to shift. As they shift, the pressures increase. As with the doors and windows, the angles of bay windows are not inter-locking and have a cold joint of mortar. These cold joints tend to separate or crack.
Generally, the corners will be the strongest part of the masonry structure. The reason for this is that the corners are supported from two directions. This prevents them from pushing in easily; however, this also makes them vulnerable to cracking because if one side of the corner becomes loose due to a crack anywhere on that wall, it will pull on the other side of the corner; causing a break and cracking. Another reason for corners to crack is their initial construction. Sometimes as the brick veneer is being laid, the bricklayer may place excess mortar behind the wall filling the gap between the brick and the wood behind it. This will make the corner stronger if and only if there is a proper water barrier protecting the wood. Brick and mortar absorb moisture. This moisture soaks through the masonry, the excess mortar behind the brick, and into the wood. Wood swells and gets larger as it absorbs water. As this wood swells, it pushes out on the brick. Eventually this pressure will break the bricks and mortar around them and up the corner of the home.
Coined corners also require a water barrier but do not always have one in place. They can absorb water causing swelling and ultimately cracking. They also are susceptible to many of the problems like doors or windows because they do not interlock with the wall. The coined corner steps out away from the original line of the wall.
Archways face many problems that cause them to fail. One of the most important is gravity. Although gravity is the primary thing that holds an arch together, it can also pull it apart. When the supports at the ends of an arch become loose, the gravity pushing down on all of the weight above it will force the arch to spread. Pouring a concrete beam inside of the arch can prevent this. This does add weight to the arch, but it serves as a backbone as well. Before the weight can spread the arch, it must first break the beam. Sometimes, bricklayers or builders try to cut corners and support archways with a wood beam. This is fine, but creates a problem when they fill in the gap with mortar. Again, anytime you fill in between the brick and wood, you need to have a water barrier to prevent swelling.
The reasons for cracking above garage doors are the weight above the door, length of the lintel, gauge of the lintel, number of (if any) lags to support the lintel, and if one or more sides of the lintel are supported by a corner. There is generally a large amount of weight suspended above the lintel on a garage door. The longer the door, the longer the lintel needs to be, and the weight increases. Therefore, the longer the lintel, the more support it will require for carrying the weight above it. These supports are the lag-bolts that tie the lintel to the wood beam behind. The more lags in the lintel, the more rigid it becomes. Without them the lintel is allowed to bow and flex. The gauge or thickness of the lintel will help, but will not support it alone.
The wood and sheetrock in a house has a large amount of flexibility. This allows it to move or bend without cracking. Masonry has some flexibility, but is much more rigid. It can only flex slightly before it breaks. People talk about using a softer mortar to allow for more flex. Softer mortars are still mortars, but have a lower crushing pressure. This means that it will crumble easier, or potentially fall down. The proper way to allow for the flexing in masonry is not to use a soft mortar, but is to utilize expansion control joints. These are cold joints that have no rigid obstructions such as mortar in them. They are filled with a flexible material such as caulking or polyurethane that moves with the brick as needed. Walls over 20-25 feet should have expansion control joints. As this is a fairly new process (about 20-30 years old), not all homes have them.
About the Author:
James R. Nech – Owner of Alamo Masonry, created the Custom Color Matched Mortar System in 1998. This system allows Alamo Masonry to match the mortar used in the repair to the original mortar of your home both in color and in texture.
This article was reproduced with permission from James R. Nech of Alamo Masonry Repair.