Why Does My House Plaster Crack?

Your house plaster is cracking?  Sorry to hear it, but it is in fact a very common problem, especially in wood framed houses.
Before I tell you why plaster cracks, let me assure you up front.  Home plaster walls and

ceilings CAN be repaired, and the motivated homeowner can learn to do it himself.
Plaster has a tendency to crack in wooden houses because plaster is not very elastic.  In
other words, you really can’t get it to stretch – and say unbroken.  Several forces can work
against the integrity of plaster, leading to subtle movement in the house structure.  This
stress shows up in cracking or buckling of the wall or ceiling plaster.
In the USA where I live, the framing lumber used in most wooden buildings is somewhat wet.  Even kiln dried lumber has moisture, so wood in your ceiling joists and wall studs shrinks over time.  For perhaps years, the lumber is slowly drying and moving.  And the movement can be activated further by the change in seasons of the year.
In old houses with wood lath backing for the plaster, cracks are common.  In this case, the lath nails may loosen, resulting in plaster no longer tight against the wall.  Bulges and cracks form.
Sometimes the ceiling joists old houses really aren’t strong enough to support properly the full weight of wood lath and plaster.  So they sag and this too leads to cracking.
Houses near streets with heavy traffic may suffer from the vibration.  If you can sometimes hear the windows rattle a little, this means your whole house is being shaken, however subtle it may seem.  Low frying large aircraft transmit shock waves to houses below.

Ground tremors from earthquakes can lead to major plaster problems.  Fortunately, most parts of the US don’t have to worry about these very often.
Water intrusion, leaks from roofs or plumbing, can wet and soften plaster.  Cracks may show up as the plaster loses its strength.
In the USA since the late forties onward for some years, the most popular home plaster system was known as rock lath and plaster.  This represented an improvement over the older wood lath and plaster systems, but even this advance led to its own problems.  Since the seams between the rock laths were not reinforced with any kind of tape before the layers of plaster were troweled on, it is common to see cracks in this plaster forming over the seams.  I have repaired many thousands of square feet of ceilings and walls that were done in this way.
As I have perfected my methods of treating plaster cracks, I have also instructed clients in methods of plaster repair they could use in their own homes.  The results were a nice
improvement in the look and feel of their interior walls and ceilings, and the experience of pride in doing it all themselves.


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