Common Plaster Problems

Common Plaster Problems

Posted By: Nyumba Imara Blog on 31st of October 2013

When plaster dries, it is a relatively rigid material which should last almost indefinitely. However at times the plaster work may start cracking due to several conditions.  Some of the conditions that may cause the plaster to crack, efflorescence (that is to lose moisture and turn to a fine powder on exposure to air), separate, or become detached from its lath framework include; •    Structural problems •    Poor workmanship •    Improper curing •    Moisture Structural Problems 1. Overloading Stresses within a wall, or acting on the house as a whole may end up creating stress cracks. Appearing as diagonal lines in a wall, stress cracks usually start at a door or window frame, but they can appear anywhere in the wall, with seemingly random starting points. The weight of the roof, the second and third stories, the furniture, and the occupants may impose a heavy burden on beams, joists, and studs. Even when houses are built properly, later remodeling efforts may cut in a doorway or window without adding a structural beam or "header" across the top of the opening. Occasionally, load-bearing members are simply too small to carry the loads above them and may lead to deflection or wood "creep" (deflection that occurs over time) thus creating cracks in plaster. Overloading and structural movement combined with rotting floorboard, rusted nails, or poor quality plaster results in the plaster detaching from the lath (floorboard) therefore losing its key. When the mechanical bond with the lath is broken, plaster becomes loose or bowed and if repairs are not made, especially to ceilings, gravity will simply cause chunks of plaster to fall to the floor. 2. Settlement/Vibration Cracks in walls can also result when there is settlement in a house. Houses built on clay or black cotton soils are especially vulnerable to cracks when settlement occurs as clay soils are highly expansive. In the dry season, water evaporates from the clay particles, causing them to contract. During the rainy season, the clay swells thus causing a building that is not structurally sound to be riding on an unstable footing. Diagonal cracks running in opposite directions suggest that house settling and soil conditions may be at fault. Similar symptoms occur when there is a nearby source of vibration-blasting or busy highway. 3. Lath Movement Horizontal cracks are often caused by lath movement. Because it absorbs moisture from the air, wood lath expands and contracts as humidity rises and falls. This can cause cracks to appear year after year. Cracks can also appear between rock lath panels. A nail holding the edge of a piece of lath may rust or loosen, or structural movement in the wood framing behind the lath may cause a seam to open. Heavy loads in a storage area above a rock-lath ceiling can also cause ceiling cracks. Errors in initial building construction such as improper bracing, poor corner construction, faulty framing of doors and windows, and undersized beams and floor joists eventually manifest through to the plaster surface.