Hairline plaster-wall cracks may be serious
QUESTION: Thanks for your weekly column. I find it interesting and very informative. I live in a 1,000-square-foot bungalow in River Heights that was built in 1948 with plaster walls and ceilings. I am seeking advice on the best method to repair hairline cracks in the walls and ceilings, prior to painting. What method and products would you suggest? I am sure the answer would be of interest to many Winnipeggers who are thinking of renovations. Thank you in advance. Leanne Pauch.
ANSWER: While I rarely address questions of a purely cosmetic nature, this is one that may often go deeper than what appears on the surface. Sometimes this type of repair is simple and only superficial in nature, but other times requires more extensive renovations to prevent a quick reoccurrence.
Cracking in old plaster walls and ceilings is inherent, as anyone who lives in a home built before the 1970s can attest. Often, these small cracks are simply the result of the older surface layer or plaster drying out and losing its flexibility. When this happens, any small movement in the home or seasonal changes in temperature and relative humidity can cause the old walls to crack. Other times, the substrate behind the surface plaster can become loose or damaged due to moisture or excessive movement and it will cause cracks to occur time and time again.
The first thing to determine before deciding on whether your cracks are serious or just cosmetic in nature is to determine the composition of different layers behind the thin surface plaster.
If your home was built in the 1950s or early ’60s, like many homes in your neighbourhood, it’s likely that you have long, narrow sheets of gypsumbased plaster lath behind the plaster topping. This material is quite durable and may be covered with a thin mortar layer before the plaster, or it may have the top coat applied directly to the surface. This can often be determined by removing a return air register in a wall or looking for any damaged or cut wall sections. If this is the situation in your home, looking at the direction and length of the cracks is your next step.
If the cracks are thin, short and rather random in nature, these are likely cosmetic in nature. These can often be repaired by chipping or sanding off any loose paint or plaster and patching with typical plaster patch or drywall compound. The patching compound should be applied in several thin layers and finished by sanding with fine-grit sandpaper. If the cracks are long and very straight, this may be an indication of loose plaster lath and further repairs will be required before patching.
Because most older plaster lath was attached with simple nails, the sheathing can become loose from the studs or ceiling joists over time. If this occurs, reattaching the wall or ceiling sheathing to the framing with drywall screws will be necessary to prevent frequent reoccurrence of the cracks. These drywall screws can be installed right through the surface of the old plaster, but pre-drilling small holes with a masonry drill bit will ensure the screws don’t snap when installing.
Once the plaster lath sheathing is secured, proper patching may require removal or countersinking of older loose nails if they pop through the surface of the plaster.
The other type of plaster substrate is in older homes, typically built before the end of the Second World War. This is comprised of older wood lath covered with layers of mortar and plaster. This wall and ceiling covering is very durable but is prone to various severities of cracks developing due to shrinkage and movement.
Once older wood lath pulls away from the studs or framing behind, there is not much that can be done to fix it. The best way to ensure a longlasting repair is to install new drywall directly over the old plaster with long drywall screws. This will require a bit of extra work in locating the framing behind the old plaster, but this is critical in ensuring proper securing of new drywall over top of the old plaster walls and ceilings.
Once new drywall is installed over top of the old, deteriorated plaster, typical drywall compound and tape can be used to cover the seams and screws, which should be applied in successive layers. Once the final layer is applied, it can be sanded smooth before priming with drywall primer paint. Final touch-ups are still possible after priming to ensure an extra-smooth surface before application of finish paint or wallpaper.
Wall and ceiling cracks in older homes are not normally of major concern, but may require substantial repairs to ensure a long-lasting finish. Determination of the difference between superficial, cosmetic cracks and serious damage may require the expertise of an experienced painter or contractor, but repairs should be possible no matter what level of damage has occurred.
If your home has pre-Second World War plaster-on-wood-lath walls such as shown, and the plaster is merely cracked, the best repair is to install drywall over top using
extra-long drywall screws to fasten directly to the studs behind the lath.