How To Repair Old Plaster

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. 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 contraction and expansion that often occurs in older homes during changing weather conditions. In fact, as the plasters 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. Assesing – 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 smalls cracks is the focus of this writing 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, peeling paint 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 paints 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. You’ll need a good gauging plaster mixed to the consistency of creamy peanut butter split 50/50 with lime. 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 and lime 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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by Scott Sidler

Scott is the owner of Austin Home Restorations, a company that specializes in renovating and restoring historic homes in Orlando, FL and the creator of The Craftsman Blog. When not working on, teaching about or writing about old houses he spends time fixing up his own old bungalow with his wife Delores and their son Charley.

http://www.austinhomerestorations.com

16 comments

  1. homesower on said:

    Good article. I am faced with a few ceiling cracks. I have been ignoring the for 15 years but would love to finally fix them properly.

  2. John Cadd on said:

    I am renovating an Edwardian house with a modern Limelite plaster.It`s breathable plaster and also insulates the walls. The dining room had hollow sounding plaster on brick walls. I cut a number of trangular holes about 4 inches each side to remove the hollow parts and attach the rest more firmly . The worst wall was all hollow (loose Drummy Render). Lime plaster does not stay attached to brick sometimes (often ). I cut a slot about 3 feet wide with a multi tool and then straight down to form a big oblong shape about 4 feet high. The section just fell off in one piece with a thud. The multi tool avoids any damage you might get with hammers and chisels . I had to remove 8 layers of gloss paint from the plaster walls in the kitchen. The house is becoming breathable once more after many years abuse .

  3. John Cadd on said:

    In a loft room I moved a doorway along the passage to avoid the door opening near the top of the staircase. It`s a lath and plaster wall.I had some spare uprights to make the supports. I started replacing the laths with the original nails.That`s a very noisy job. Then I switched to an experimental way with Sikaflex polyurethane sealant/glue. Much too expensive normally but a beautifully silent , simple way to rebuild a wall. Testing a few laths later in the week I found the sealant laths took about 3 times as much force to shift compared with the old nails. The nails were in very usable shape considering they had been there for one hundred years .
    30 years ago the roof was changed from terra cotta to concrete tiles. The electrician told me the loft was a mess! I discovered the plaster torching had been left there all that time. Over 6 tons of it hidden in every cavity and all held up by those tiny lath nails. Not one scrap was resting on a strong joist. All just hanging on old laths and nails .

  4. mike on said:

    My house was built in 1923. I have had plaster issues for decades. The roof leaked before I purchased the house ruining many ceilings. Covered all ceilings with sheetrock and then joint compound with several layers of vaneer plaster as there were high and low spots. They look great painted different colors. No white ceiling paint in my house.
    I used hundreds of plaster buttons to re-secure the wall plaster whereever needed.
    Anyway, my house was always very dusty. I finally realized, while skim coating the walls with plaster, that the old plaster behind the wood trim was/is deteriorating. The dust falls out from behind the wood at the seams due to random vibrations. I ran a thin bead of paintable tan colored caulking at every wood to wood and wood to plaster seam. My dust problem has disappeared and the house is much less drafty.

    • Interesting solution. Very creative! You have to be good at improvising with an old house.

    • Amy Hogg on said:

      We have the same problem with dust coming out from under the baseboards! Most of our baseboards are missing quarter round so I’m hoping it gets better once we get it installed.

      • Mike on said:

        The reduction of dust has been incredible!
        Apply before paint, use your finger to press deeply into seams and cleanup with a damp rag You cannot see the caulk at the wood to plaster seams. If you caulk the wood and stain it, use a caulk as close to the color of the stain as possible and it’s almost invisible. I got lucky, nobody ever painted my woodwork. It had a thick coat of something very dark on it (shellac?) and was severely alligatored wherever the sun hit it. Had to use a chemical stripper to remove.

  5. Amy Hogg on said:

    We recently bought a house built in 1900 and the ceiling in the living room (16′ x 20′) is loose. From the way he described it I believe the lathe has detached from the beams above it. My contractor said that this is fairly uncommon and he suggested drywalling over it. After reading this post I would prefer not to. Would he be able to use the process that you describe in “dealing with cracks” to fix this problem? I also have a built in bookcase in which the plaster is crumbling in all of the corners. I could use the Big Wally’s plaster magic that you describe in another post, right? Thanks for the advice!

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