Question: We have had recurring cracks in our plaster ceiling. Is there a way to prevent this from repeating after patching repairs have been done? Will control joints help?
Lawrence Marmel
Answer: Repairs to cracks in old plaster ceilings may last for several years, but only if they are not caused by ongoing structural movement or loose plaster components. If movement is the root cause, then adjusting the supports under the floor structure will be required to ensure a more permanent repair
This question may be very timely, as I have recently received a record number of inquiries about cracked ceilings and walls for this time of year. Normally, those type of e-mails and calls occur near the end of summer and into the fall, after hot weather has dried out the soil. Last summer may have been one of the driest on record, but a couple of large rainfalls before the cool weather arrived managed to somewhat stabilize a very volatile situation. Based on the ongoing requests, it was only a temporary reprieve.
Cracks in older plaster walls and ceilings are extremely common and often are due to the age of the material and normal deterioration of its components. This material was applied in several layers, of differing composition, with varying techniques. Homes built before 1950 normally have the initial layer of supporting material composed of thin, narrow slats of rough-sawn wood, know as lathe. These small planks were nailed to the wall studs and ceiling joists with narrow gaps in between, with small, smooth nails. Over time, the nails may loosen or rust, the lathe begin to rot, or the mortar layer in between loose its integrity. Once any or all of these occur, the finish layer of plaster will certainly crack or become loose. Once this has progressed to a certain degree, no amount of patching will last very long.
In homes built in the following two decades, the wooden lath layer was usually replaced with a form of drywall. These were typically 12-inch-wide sheets, nailed side by side, perpendicular to the studs and ceiling joists. Once in place, the entire surface was covered with the next two layers, similar to the wooden predecessor. Because of this updated method, homes of that age will rarely have spiderweb surface cracks, or uneven damage due to deteriorated lath. But, they are prone to long, straight cracks, which follow the joints in between the individual drywall underlay sheets. Especially with ceiling cracks, if these long drywall sheets become loose, often from excessive attic moisture or the weight of damp insulation, cracks will form. The good news is that these types of cracks are more easily repaired, but may require re-securing the entire underlying drywall layer with screws. Alternatively, just like with older plaster, a well secured new layer of drywall over top will provide a superior, more permanent, end product.
No matter what the age of your home, or the method used to install the plaster on the walls and ceilings, if the cracks are occurring due to structural movement, then that must be addressed before any repairs are undertaken. Because of the recent drought-like conditions in our area, the expansive clay soil has significantly shrunk in many locations. While a lack of precipitation will usually affect only the top metre or so of earth below grade, the prolonged dry weather has caused shrinkage to soil below some house footings. This can cause home foundations to settle, or sink, often unevenly from one side to the other. Once this happens, it will usually cause bumps in floors, rubbing interior doors on jambs, and of course, cracks in walls and ceilings.
While it may not be possible to replenish the soil moisture to fully stop this settlement, without Mother Nature’s cooperation, other remediation may help. The most successful first step is usually to adjust the teleposts beneath the main beams, which may not have settled along with the foundation. If you still have wooden posts, these should be replaced with adjustable metal ones, to allow for remediation. Also, many older homes had basement partition walls built with little or no space between them and the main floor joists. These can also cause wall and ceiling movement, due to uneven pressure on the floor components, if the foundation settles. Cutting these walls down, and installation of gaps or slip-joints at the top or bottom, may be necessary before tele-posts can be touched.
Adjustable steel columns below beams, or tele-posts, should be lowered very slowly to allow the structural components they support to ease back toward their original positions. If this is done too quickly, it will only cause cracks and loose plaster in additional areas to the ones already present. The goal of adjustments is only to straighten the warped beams they are supporting, reduce the stress on the wooden structural members, and return these to a point where further movement is minimized. It is not possible to get these back to original positions, or to level the floors, but it should be feasible to lessen the problems in the worst locations. This should reduce the stress and strain on the wall and ceiling components, allowing longer lasting repairs to cracked plaster surfaces, without installation of any control joints.
Patching and sanding wall and ceiling cracks may provide a temporary fix, but will not last if structural movement is behind the formation of these cosmetic defects. Professional, careful adjustment of tele-posts, and trimming any improperly built basement walls, will be required to prevent a quick return of the cracks after repairs.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
