I am a plaster restoration contractor in Greensboro, N.C.
After more than 25 years of plaster restoration, I have concluded that there is a common defect that can indicate a real safety issue involving certain plaster ceiling systems.
Under-engineered Attachment System as a Singular Cause of Failure and Collapse
The fact that plaster ceiling systems fail* and collapse* is not a new issue. However, my theory that under-engineering (which is a widespread condition) ***is ***a major factor in attachment failure and ceiling collapse…often the only factor…is new.
Though plaster may collapse and break off of from ‘traditional’ wood lath and cause damage, my concern is with plaster-over-gypsum lath ceilings, especially ones that used 4 x 8’ gypsum lath. (I refer to these ceiling systems as ‘transitional’ ceilings because this combination of materials and techniques was employed after the time of ‘traditional’ plaster over wood lath, and before modern drywall.)
Why is this a Safety Issue?
These ceilings concern the home inspector because **when **they collapse, it tends to be ***complete, sudden and monolithic. ***Therein lies the safety issue. Such a collapse involves hundreds of pounds of material, in addition to insulation which may also contain asbestos. (The failure and collapse occur at the point of attachment to the joists.)
My first experience with a ‘failing’ plaster-over-gypsum rock ceiling system was here in NC. A client called me to come and look at the ceiling in his grandmother’s room. O***ne-half*** of the ceiling was hanging at a 5 degree angle, leaving an 8" gap the length of the room. The ceiling attachment system (between the lath and joists), was in an advanced stage of ‘failure’.
We removed the ceiling completely and dry-walled it. ** Fortunately, the grandmother had been moved out of the room and the ceiling had not collapsed on her.
The construction was three-coat plaster-over-rock/gypsum lath. It was attached by means of a ‘clip’ system to the joists, but had weakened and relaxed over time with the weight of hundreds of pounds of plaster.
Over the years, I have seen and remediated numerous such ceilings in the ‘process ***of failing,***’ though they had not collapsed. I have also seen various attachment systems for that ‘transitional’ time period; the three most common being smooth nails, angled metal clips and wires. I have observed all three methods of attachment showing signs of failure.
What Should a Home Inspector Look For?
The age of the home should be your first clue. Transitional ceilings span roughly the period from the 1920’s to the 1960’s.
One way attachment failure can be observed is to look at a ceiling from the attic side (especially towards the middle of the ceiling), moving back the insulation. There should be no space between the joists and the back of the gypsum rock. Any space there indicates the extent to which the attachment system has been compromised.
A more obvious indication of attachment failure is the presence of straight cracks, either running the length of a ceiling (the most serious safety problem) or following a zigzag pattern. Because the transitional period for plaster-over-gypsum rock spans almost 40 years and different sizes of gypsum lath were used, one sees different patterns of cracking in these ceilings, following the joints in the gypsum rock.
Rarely, a ceiling may show circular or curving cracks. This usually will be a ceiling in the later part of the transitional period and also indicates a serious condition.
Another indication of a failing attachment system is ceiling repairs that do not last. This is because the plaster or drywall contractor did not understand the underlying cause of the crack and did not properly anchor the ceiling back to the joists before taping and mudding.
Signs of failure can be detected by home inspectors with a trained eye in most cases. As with any potential safety issue, recommendation should be made for further evaluation/remediation by a knowledgeable plaster repair person as these ceilings have been known to collapse.
**Can Collapse Be Predicted? **
Though these cracks are indications of attachment failure, one cannot predict when or if these ceilings will ‘collapse’. However, the state of failure, if not remediated, is a progressive one. Given enough time, collapse will eventually occur.
An early client, M. Rothrock of Greensboro, N.C., shared a story with me as I was remediating the living room ceiling in her father’s home (this one was attached by wires and was about 3" away from the joists as seen from the attic side)
The neighbor’s house, built at the same time in the 40’s by the same contractor, experienced a total collapse of all the ceilings in the house shortly after construction. Besides a number of similar stories from clients, I have found a number of instances online of property being damaged and in one case, a small child being killed by what appears to be this type of sudden monolithic ceiling collapse.
Visit my website at Transitional Ceilings](http://estateplaster.com/TransitionalCeilings.aspx) For pictures and links to stories of pertinent ceiling collapse cases. In some, engineers or architects describe the cause of particular collapses and corroborate my conclusions here.
Estate Plaster Inc
- *For this discussion, a ceiling attachment system that has **failed, or is in a state of failure, *means that it is in a compromised state where it is observed to be in the process of failing at what it was intended to do; that is, hold the ceiling securely to the joists. When I use the word collapse, I am referring to a ceiling or part of a ceiling that has completely fallen to the ground.
*** Estate Plaster Inc. has developed remediation techniques that do not require the removal of the ceilings in most cases. If a ceiling can be re-secured, it saves time, trouble, as well as money for a client. Proper remediation may also decrease failure and collapse due to contributing causes, such as water damage, storms or factors related to heating/cooling cycles and the affects of vibration or impact. *