Old houses get cracks in their plaster walls and ceilings there is just no denying it. Some of those cracks are a sign of trouble brewing while others are completely innocuous. So, how do you know which cracks are which and when you need to take action?
In this post I’ll help you diagnosis plaster cracks and know when it’s time to do some serious work or just learn to be at peace with things. You can fix plaster cracks of any kind, but it’s important to know if your repair is going to be merely cosmetic or you have some bigger issues to address.
What Causes Plaster Cracks?
That depends on the kind of crack. Historic lime and gypsum plasters are naturally brittle so they require different care than modern drywall. That doesn’t mean they are inferior to drywall. Far from it. Plaster walls are actually far superior to drywall in a lot of ways like sound dampening, insulation, strength, and even filter carbon dioxide from the air!
There are several factors that can cause cracks in lime plaster walls:
- Shrinkage: As lime plaster dries, it will shrink slightly. This can cause cracks to form, especially in large areas or thick layers of plaster.
- Temperature and humidity fluctuations: Extreme temperature changes or high humidity levels can cause the plaster to expand or contract, leading to cracks.
- Foundation movement: If the foundation of a building shifts or settles, it can cause the walls to crack.
- Impact damage: Physical force, such as from furniture being moved or objects being knocked into the wall, can cause cracks in plaster. (Young children fall into this category as well.)
- Age: Over time, plaster can become more brittle and prone to cracking due to age and wear.
It’s important to note that not all cracks in plaster walls are cause for concern. Small, hairline cracks are often normal and do not indicate any underlying issues. However, if you notice large or deep cracks, or if the cracks are accompanied by bulging or sagging in the plaster, it may be a sign of a more serious problem and it would be advisable to seek the advice of a professional.
Fixing Plaster Cracks
If you’re one of the unfortunate few who have fallen victim to plaster cracks then don’t worry, they can be repaired. Repairing cracks in plaster is usually pretty simple compared to larger issues like crumbling of sagging plaster. I’ve posted about that more involved process here.
- Dig out the Crack: Digging out the crack a bit to remove loose plaster and widen the crack a bit gives more “tooth” the patch you’ll be doing meaning it will hold on better. A putty knife or scraper works best for this.
- Clean the Area: Wipe the area with a damp cloth to remove any remaining dust or dirt.
- Fill the Crack: Once you have removed all the loose plaster, you can begin filling the crack. Use a premixed joint compound for small cracks or something like Patching Plaster for larger cracks. If you have sanded texture to your plaster you can add sand to the joint compound or use Patching Plaster which is a ready to mix powder that has sand in it already you just have to add water. Apply the compound to the crack using a putty knife or trowel.
- Smooth the Repair: Smooth things out as much as possible to eliminate sanding. Fill in any gaps or holes and spread the compound in at different angles. Use a wet sponge to smooth out the surface and remove any excess compound.
- Let Dry: This may take several hours or even a day, depending on the size of the crack and the humidity level.
- Sand Smooth: Once the compound has dried, you can sand the area to smooth out any rough spots or unevenness. Use a fine-grit sandpaper and sand lightly until the surface is smooth. For sanded finishes skip this step.
- Prime & Paint: Finally, you can paint over the repaired area to match the rest of the wall or ceiling. Be sure to prime the area first and then apply two coats of paint, allowing each coat to dry completely before applying the next.
Very large cracks (wider than 1/2″) may require application of a fiberglass mesh tape prior to filling to avoid further cracks from shrinking of the plaster later.
By following these steps, you should be able to effectively repair plaster cracks in your walls and ceiling. Not only will this improve the appearance of your home, but it will also help to prevent further damage and protect the value of your property.
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I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.