Corrosion problems.

Q In examining masonry lintels on the top floor of a building, I noticed that instead of the brick being supported directly on the angle, there was a gap of almost 1/2-inch between the bottom of the brick and lintel in many locations. In fact, it seemed that the brick was not even being supported

The "shims" were brown in color and had a very rough texture and a layered appearance. The angles were severely corroded. In some cases, the remaining thickness of the angle was less that 3/16 inch. The bed joint in the masonry between these windows was very wide and appeared to have been pointed, indicating that the masonry moved upward.

What caused this gap?

A Without seeing the condition, it is difficult to know exactly what occurred; however, I have seen a condition similar to what you described. In that case, the gap was caused by corrosion of the steel angle.

When steel corrodes, the resulting rust scale occupies more space than the steel. In fact, the corrosion byproducts can be 10 times greater than the volume of the steel that is corroding. The corrosion lifts the masonry above the lintels (sometimes exceeding 1 inch.). This action is often referred to as "rust jacking."

Depending on the exposure, it is possible that the corrosion product has washed or fallen out of the joints, leaving only isolated portions of rust scale to support the masonry wall. A roof leak or some other directed water flow moving through the wall system may--over time--carry away the rust scale.

If the gap is caused by rust jacking, the lintel angles likely have significant pitting of the steel. Depending on the magnitude of this corrosion or pitting, the angles may need to be replaced with new steel versions. This change can be accomplished by first shoring masonry above the lintels so that they can be removed and replaced. The angles should be covered with a proper flashing and weep system to direct any water that penetrates the masonry back to the exterior, and to prevent water from reaching the surface of the angles, thereby reducing the corrosion rate.

The movement may have damaged ties between the veneer wythe and the backup. This possibility is especially the case if the wythes are tied using brick headers. The stability of the wall should be evaluated. If the bonding between the wythes has been compromised, remedial anchors can be installed through the veneer wythe. These anchors are generally installed in the "T" joint created by the intersection of the head and bed joints, as shown in the illustration. The hole created is pointed following the installation of the anchors.

Norbert V. Krogstad is a consultant at Wiss, Janney, Elstner Associates Inc., Northbrook, Ill.