How To: Repair Old Plaster

By Scott Sidler • November 15, 2011

One of the easiest mistakes to make when renovating a historic home is to tear down the old plaster walls and replace them with modern drywall and joint compound. This not only destroys the historic architecture and features that make a historic home great, but it also adds to the overall costs of the project exponentially. Despite the rumors you can repair old plaster yourself.

Lime plaster has been in use for thousands of years from Japan to Egypt and has been employed in many historic structures around the globe. Lime plaster is a far superior product than today’s modern wall coverings. With its crystalline structure, it repels moisture well while allowing for the contraction and expansion that often occurs in older homes during changing weather conditions. In fact, as the plaster’s structure calcifies (ages), it increases in durability and strength!

A Little History First

Traditional lime plaster was used for wall coverings until WWII. It was applied in a 3 coat process over thin wood furring strips called lath that were made of cedar, cypress or some other rot resistant non-staining wood and attached to the studs. The lath was soaked in water prior to installing the plaster to prevent it from sucking too much water out of the the plaster too quickly and spaced similar to the above picture with room between each piece for plaster to be pushed thru when applied. This spacing allowed the plaster to “key” in the lath and gave it extraordinary holding power when done properly.

The plaster was then applied in successive coats, typically 2, and a smooth finish coat was applied on top. Plaster took weeks to dry properly and fully cure before the walls could be painted. The whole process was slow and required a skilled plasterer which cost more money. After WWII, the building industry needed a faster way to cover walls and the relatively new product, drywall (getting its name from the fact that it didn’t go up wet like plaster), slowly crept into everyday use.

The Repair

  1. Assessing – There are many reasons for lime plaster to fall into disrepair. Knowing the cause of the damage is crucial to applying the correct solution to the problem. From water damage to vibrations from nearby traffic to peeling paint, historical plaster damage can be caused by many problems. Is the plaster peeling from the lathe? Is the plaster soggy or crumbly? Are new coats of paint peeling from the walls? If you answered yes to any of these questions; don’t panic. While each condition is unique to each situation, lime plaster can be repaired easily, economically and effectively. A common occurrence in older plaster, cracks are commonly caused by expansion and contraction of an exterior wall. In the case of heavy cracking, it is possible to that the house it settling improperly. This should be inspected by a Building contractor or structural engineer immediately! Repairing small cracks is the focus of this article though.
  2. Dealing With Cracks – This repair can be done by drilling several small pilot holes in the materials at various intervals. By measuring the depth of the penetration, you can determine if the lathe is detached. Many times a few well-placed screws can draw the lathe and plaster back together. In extreme cases of detached lathe, more holes are drilled into the affected area and an elastomeric adhesive is injected between the separations. Clamping washers are then applied to the surface of the plaster to press the loose plaster back tightly against the lathe and allowed to dry. Once the plaster is secured, the holes and cracks can be filled flush with a mixture of lime and gypsum, allowed to dry and then painted. Check out my video on fixing cracked plaster to learn how to do it yourself!
  3. Peeling Paint – Another common dilemma when dealing with older homes is peeling paint, and it can be repaired with just a few simple techniques. More often than not, peeling paint occurs when many layers of paint have been applied to the plaster over the years. Calcimine is the common culprit of many peeling paint plaster problems. Calcimine is a water soluble paint material that was typically used in older paint products. The calcium in the paint reacts with the moisture content of the calcium in the lime plaster and creates a bond between the water molecules. This bond easily allows water to slip in and out of the paint’s surface, so even if you apply new paint, it peels over time. To remedy this problem, the old paint must be removed. A wallpaper steamer is the perfect tool for removing old paint from lime plaster. Gently use the steamer and a plaster knife to remove the paint without gouging the plaster. Once you’ve removed all of the old paint, wash the plaster with a rag and room temperature water. Don’t get the walls too wet; a light wipe down will suffice. Allow the plaster to dry 24 hours before repainting.
  4. Patching – Patching plaster in anything more than small amounts is something best left for the pros, but if you are a brave DIYer then you can try to tackle the task on your own. Old plaster is made from much different materials than current drywall joint compound. For decent sized holes the best thing to use for repairs is called Big Wally’s Patching Plaster. You simply mix with water and apply. Once your plaster is mixed apply it with a putty knife and press it firmly into the supporting lathe. Make sure the plaster isn’t sagging in the hole. If so, your mix is too watery and you should add more plaster until it is firm enough to hold under its own weight. Once the plaster has dried, give it a light sanding to smooth out the surface and wipe it down with a damp rag before painting.

While some damages can be easily repaired, it’s easy to quickly get in over your head when it comes to plaster repairs in a historic structure. Plaster work is an art form and many delicate cornices, crown molding and ceiling medallions were sculpted by hand by skilled craftsmen. So, before you rip that old plaster down to insulate and cover with drywall think twice. You might have a unknown work of art on the walls or ceiling of your home that deserves restoring.

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72 thoughts on “How To: Repair Old Plaster”

  1. I have moisture damage in a plaster ceiling. We have what can be best described as a “snow flake” condition. Need ideas and thoughts on repair options.

  2. I just had a basement put under my 1862 antique farmhouse and some of my plaster walls literally buckled and fell off due to the leveling. It was off by 4 inches! Regardless, I am heartsick about the destruction and my contractor is repairing my guest room this week. My carpenter wants to put up wall board and insulate and I need to discuss who this other workman is that my contractor has. Thanks for printing this article. At least I’ll have a better idea of how my walls should be repaired.

    1. Hi Sara,

      We are so sorry to hear that that happened to you. Maybe you can find a certified preservationist in your area using our directory that could work with your GC on accurate and careful, historically accurate repairs to your home? Best of luck to you.
      -Alyssa at The Craftsman Blog

  3. We just purchased a home built in 1692…yes, you read that right. The walls aren’t drywall. The walls are made up of some sort of thick grey material that crumbles quite easily. We haven’t dug underneath this outer layer to check (as we don’t want to destroy the walls) but, is this lathe and plaster…or something else?

  4. Considering how common plaster is in most homes it really is a good idea to learn how to repair it. I particularly like that the article goes over how you can patch plaster if you’ve encountered any larger holes. Of course, you’ll want to make sure that you have the proper repair supplies, but once you do you’ll at least know how to carry out the repair job.

    1. I would just like to say with plaster lathe on old homes it is forever cracking. The upkeep is never ending. That is why dry wall is an option. Moldings can be repkicated. I spent 2 months restoring plaster moldings and excessive cracks on a ceiling. The job was completed 9/16. I already have a new fineline crack that appears across the ceiling. These historic buildings expand and contract all the time.

  5. Our New England Victorian was built circa 1893. The plaster ceiling in the grand entrance seems to have been covered by some sort of fabric (mesh?) then plastered again? My husband cut the plaster and fabric as it was uneven with the rest of the ceiling and now you can see where the ceiling is smooth due to the removal of the fabric and plaster. Is there a place to purchase this fabric/mesh that we could help rejuvenate our plaster ceilings? Huge thanks!

    1. i wonder if it is this: I have a house built in 1876, all plaster and lath. It had had some serious settling issues, diagonal cracks in many walls. This system worked well for me. The more painted over it is. the more the matt disappears, but at the moment, I have a wall with visual texture similar to suede. JUST REMEMBER this is fiberglass, so suit up, wear a mask and glasses.

  6. My husband and I own a tiny 1924 bungalow and water damage (due to negligence on the part of our warranty company not responding to our reported leak for a full week) was just discovered in our living room. We have a very unusual (and beautiful) rough plaster texture and they are tearing out huge pieces of my walls. I am heartsick. I am also worried that they will not be able to restore it to “pre loss” condition. I want to cry. They commented when they walked in that they’d never seen walls like ours before. This makes me incredibly nervous. Is it reasonable to expect that this can be restored to a point the repairs are undetectable? Ugh.

  7. My husband and I just bought an old farmhouse built in the early 1930s. It is our intent to keep as much of the original character as we can, but the plaster in the kitchen seems to be too far gone. There are at least 20 cracks in the walls, some large, some small. How do you decide when the plaster is too far gone?

  8. Hi! We are looking to buy a house from 1887 with plaster walls inside. We are hoping to update the home a bit, and a main concern is the electrical is currently outside of the plaster, running in tubes around the baseboards in each room with outlets every here and there. Everyone is telling us to remove the plaster and put up drywall so the electrical can go inside the walls, and because they say its easier than constantly repairing the plaster’s cracks and holes. But I also worry removing the plaster will damage the bricks and stone the home is made of.
    What would you recommend? Is there a way to get the electrical inside the plaster walls? Or would it be easier/cheaper to put up drywall? Thank you.

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