What is a Lintel and What is Lintel Lift (or Rust Jacking)? (Encore)
For thousands of years the openings in brick and stone (masonry) walls have been topped with an arch to provide support for the masonry above. In arch construction, the masonry that forms the arch, is generally wedged in place. The masonry around and above the arch confines the wedged masonry such that the wedged masonry is compressed and cannot move. The most common failures for an arch are the removal or damage of the keystone (usually the unit at the top and center of the arch), the overloading or crushing of the masonry material, or the inadequate confinement at the bottom of the arch to restrain the outward thrust of the arch.
More modern construction methods, over the past two hundred years or so, have commonly utilized a steel member to support the masonry (brick, stone, or block) above. When loose steel members are built within the masonry and are supported at each end on the masonry, rather than fastened back to and supported by a steel structure, they are called loose lintels. Loose lintels are commonly steel angles (L-shapes) or wide flange beams with a plate (I-shapes with a wide plate welded to the bottom). Figure LL-1 shows a window with a loose lintel.
If the steel material of the lintel has not been adequately protected from prolonged and repeated exposure to excessive amounts of moisture, the steel material will corrode. Adequate protection is commonly comprised of a drainage system (flashing to direct the water in the wall to the exterior and weep holes) and a paint or zinc galvanize coating on the steel. Unfortunately, there have been many masonry walls constructed without adequate protection of the steel from prolonged and repeated exposure to excessive moisture.
Although minor surface corrosion may at first provide a natural protective coating for the steel (as we learned in science class), more severe corrosion causes the steel material to expand and in the most severe situations to expand and delaminate. The expansion and/or delamination of the steel material increases the thickness of steel member causing the brick, block, or stone above the thicker steel to be lifted. This is commonly called lintel lift or rust jacking. Figures LL-1 and LL-2 show lintel lift and the resulting cracking from lintel lift at a window opening. When lintel lift occurs the masonry and the lintel need to be removed, an adequate drainage system installed, a properly coated steel lintel installed, and the masonry re-built.