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How To: Fix Plaster Cracks

plaster cracks

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:

  1. Shrinkage: As lime plaster dries, it will shrink slightly. This can cause cracks to form, especially in large areas or thick layers of plaster.
  2. Temperature and humidity fluctuations: Extreme temperature changes or high humidity levels can cause the plaster to expand or contract, leading to cracks.
  3. Foundation movement: If the foundation of a building shifts or settles, it can cause the walls to crack.
  4. 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.)
  5. 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 a bit to give more “tooth” to the repair
  1. 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.
  2. Clean the Area: Wipe the area with a damp cloth to remove any remaining dust or dirt.
  3. 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.
  4. 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.
  5. Let Dry: This may take several hours or even a day, depending on the size of the crack and the humidity level.
  6. 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.
  7. 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.
filling plaster cracks
Some cracks are small enough they can be filled without needing sanding

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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9 thoughts on “How To: Fix Plaster Cracks

  1. I have an old house with various cases and degrees of cracked plaster. I always use mesh tape and 99% of the time they never return. However I have years of drywall experience(tho not my first trade) and know most all of the tricks. But all the tricks have a mostly flat learning curve as well imo. If anyone asks me I tell them the first trick is don’t be afraid to try it.

    1. I carve out cracks to at least one inch wide to expose the lathe, clean and apply plaster glue. Then I make plaster the original way from the components and key-in the new plaster, feathering the edges over the old.

  2. Thank you Scott! I do have cracks in my plaster and wondered what the best way would be to fix those, then your article! My 1908 home is in Central Montana and has been empty for over 8 years before I moved in last year. I believe most of the cracks are from the extreme temperatures and just age. The plaster may also be thicker than normal as a Stanley stud finder will not work.
    I would also like to thank you for sharing your expertise and experience on restoring old windows. People have told me I should replace them, but I refuse to do so. I just received your book Old Windows Made Easy and started reading it last night. Looking at my double hung windows with ropes really intimidated me, but after reading the first third of your book, I’m no longer afraid to get started on restoring my windows! Again, many thanks!

    1. I’m in the middle of restoring my windows, using this book as well. I have 15 windows in my home and so far I’ve done 4. Getting more confident with each one; and they look so good when finished! This book has been so helpful. Good luck with your windows!

  3. Do you have any before and after pics of lime plaster repair? Our old house had very visible patching before the walls were redone in recent years. Now I see the cracks happening again above windows and don’t want to replace whole walls. Would love to see if this repair could be tackled by ourselves . Thanks , Marilyn

  4. My house was built in 1929 & some of the walls have stucco plaster. How do you repair cracks in stucco plaster. It is a very thick stucco.
    Thanks for your suggestions.

  5. N O P E . . if you do not use plaster washers the cracks will return . .

    you NEED to stabilise the plaster . . . if there are cracks the Keys are broken and gravity is in effect . . . plaster washers pull the plaster back against the lath . . .

    1. Do you have a plaster washer to show us?
      1. Where can you buy them?
      2. Does the washer go in the area to be plastered or next to it, in the nearby area where existing plaster was not removed?
      Thanks, Sher

  6. I highly recommend Big Wally’s Plaster Magic. I’ve used it to repair plaster cracks, holes , plaster that has separated from the lath with excellent results on the plaster walls of our 113 year old house. And I’m a DIY amateur.

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