Normally, concrete walls require a minimum amount of maintenance. Cut out cracks to a depth of 1 inch and a width of at least ½ inch. Wet down before filling with a sand –cement mortar (two parts sand, one part cement). Repair large broken areas by cutting out sufficiently to expose reinforcing rods or mesh that will bind the new concrete to the remaining wall. Thoroughly clean and wet the cut surfaces of the wall, then coat with a slurry of neat cement and water prior to placing new material. Most defects that cause appreciable problems, such as leakage, aredue to the expansion and contraction of the building members with temperature changes. Efflorescence Efflorescence on walls always indicates trouble. It usually appears as a light powder or crystallization after the evaporation of water, Excess moisture in the walls may come from defective flashings, gutters, downspouts, copings, or improperly filled joints. Locating the source of the moisture can require a bit of work. The water may not be entering the wall at the point where the efflorescence occurs. Streaks on the wall from the top down or wet patches some distance from the top may indicate defective gutters or copings. Patches from efflorescence are sometimes caused by opened joints. Water may also enter through windowsills or around windows and door frames. Efflorescence close to the ground may indicate ground water drawn up by capillary action. Concrete walls that have an “open” texture may be made more durable, more attractive, and more watertight by painting with portland cement paint. Cracks Lack of adequate expansion and contraction joints is a common cause of cracking. Other common causes are settlement, poor materials, structural weaknesses in the foundation, excessive floor loads, and poor workmanship in the original construction. Horizontal movement cracks are usually long, wide cracks that occur along the line of the floor or roof slab, or along the line of lintels over
windows. Vertical and diagonal movement cracks generally occur near the ends or offsets of buildings. They may also be found extending from a windowsill to the lintel of a door or window on a lower floor. These vary from 1/8 to 3/8 inches in width. Do not use brittle materials to repair such cracks; use a flexible compound. Shrinkage cracks are fine, hairline cracks. In repairing shrinkage cracks, do not chisel them out and fill them. Instead, scrub with a grout made with 65 percent cement and 35 percent sand mixed to a consistency of heavy molasses. Wet the wall and scrub in the mixture, then cure it with water. Postpone shrinkage crack repairs until the wall is at least one year old to avoid repeating the repair job. In special cases, such as when the concrete is exposed to severe weathering or corrosion, you should repair broken or spalled concrete as soon as practicable to prevent progressive deterioration that might result from the rusting of the reinforcing steel. Seal cracks to water that would promote corrosion and subject the concrete to the danger of further deterioration of freezing and thawing. Spalled and Eroded Surfaces Treat spalled and eroded surfaces that cannot be renewed by brush coats of thick cement water paint by plastering them with a mix of one part portland cement, two to two and a half parts of masonry sand, and 10 percent hydrated lime. Apply the plaster in layers 3/8 to ¾ inch thick and then cure it. Prior to beginning the plaster work, (1) remove all loose and fractured surface material with a hand chisel or air hammer, (2) clean and repair all exposed steel, and (3) roughen the remaining smooth surfaces with a wire brush or by sandblasting. Patch all deep recesses. After the patches have attained an initial set, saturate the defective surface with water for an hour or two before plastering.