There are numerous reasons why the plaster along the exterior walls of your home will crack and the interior walls will look very unsightly. It is important to determine the cause of any cracks you find so you can effectively repair them. Some of the most important causes of these cracks are listed below.
1. Structural cracks
Structural cracks, as the name implies, are caused by structural weaknesses in a building that are further worn down by certain conditions, such as a bathroom shower. A steam shower or steam room enclosure should be properly fortified with tile.
The most important structural cracks include:
o Settlement resulting from inadequate or incorrectly located foundations, the use of undersized or incorrectly spaced members, omission of bracing, or shrinkage of wood
o These cracks are usually large and well defined, and extend across the surface and through the plaster
o They can start near the corner of a door or window, or go up and down the corner where two walls meet, or along the joints between the walls and the ceiling
2. Map and shrinkage cracks
Poor workmanship and the use of poor quality plastering materials are the main causes of what are known as “map cracks” and “shrinkage cracks”, that is, shrinkage in the plaster itself. There are ways to distinguish between these two types of cracks in plaster. :
o Cracks in the map are usually caused by improper bonding between the plaster and the base
o They are less noticeable than structural cracks and go through the plaster, but do not extend over the entire surface like the latter
o They are formed by a series of cracks that extend at various angles and span areas generally 6 inches or more wide
o Shrinkage Rifts, on the other hand, resemble map rifts, except the rifts themselves and the areas they enclose are much smaller.
o They differ from map cracks in that they do not go all the way through the plaster and are generally limited to the finish coat.
o Careless workmanship is often the cause of these cracks.
o Steam from a sauna can dilate these cracks; an infrared sauna unit is the best way to go
3. Loose plaster
Sometimes the keys or rivets that hold the cast to the base break or become loose, causing the cast to bulge and crack. On ceilings, around plumbing, bathroom and kitchen fixtures, it will often hang in this condition for a long time before falling off, held together by hair or fiber from the plaster. Occasionally, the nails or fasteners used to hold the lath in place can corrode and break, allowing the part of the plaster covering the loose lath or laths to sag and crack.
Tools needed for repairs
For small cracks and holes, a small diamond-shaped mason’s trowel or wide-bladed putty knife, for plastering larger areas, a plasterer’s trowel and a shallow pan.
Materials needed
o Plaster of Paris or commercial repair plaster
o A small amount of regular glue if needed
or clean water
mix the plaster
o All mixing boxes and utensils must be clean and clean water from your glass sink, bathroom vanity or bathtub must be used in the mixing.
o Special care must be taken so that no traces of old set plaster remain in the mixing box.
o The water should be placed in the mixer box before the dry plaster is sifted into the water.
o The mixture should then be shaken well to dissolve any lumps.
o It should be of a consistency such that the putty can be picked up with a wide-bladed knife and forced into the crack or break in the wall.
Use plaster of paris
If only a small amount of fresh plaster is needed, plaster of paris alone can be used. Plaster of Paris sets very quickly. If it is to be used without a retarder, only mix as much as can be put in 10 minutes or less.