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Demystifying Plaster Repair

Plaster repair expert, Rory Brennan of Plaster Magic (and appearances on This Old House®), joined us all the way from Vermont on Thursday, April 6 to present a seminar at Jefferson Park Library about how to repair cracks, holes, and bulges in plaster walls and ceilings.

The seminar was a full-house with 74 attendees! Many bungalows and vintage homes in Chicago still retain their original plaster walls and ceilings, so it’s no surprise that the topic is of high interest to our members.

If you registered for the seminar online, you received a follow-up email with links to the information presented at the seminar. But we want to make sure all our members get this valuable information! Below are the links we emailed to registrants, as well as some extra advice from the notes we took during the presentation:


Instruction sheet for repairing cracks in plaster (click images below to enlarge, or click here for printable PDF):

Here are the notes we took while Rory explained each of the steps:

  • Typically, lath are 1¼" wide and ¼" apart

  • Vacuum the dust after drilling (there will be dust, no matter what!)

  • When spraying with conditioner, you can use a straw at the tip of the spray nozzle to get into holes, or you can drill the holes bigger

  • After clamping, clean the area with a wet sponge

  • Never sand plaster (it creates dust), just scrub with a wet sponge (that should be all you need)

  • Remember that the joint compound is cosmetic, not structural

  • Joint compound should be applied 3 times, and each time the layer should be so thin that you can see underneath it (it's best to build up thin, even layers than to apply one thick, uneven layer)

(Rory also said one way to avoid creating cracks is to never nail into plaster! Use screws to hang artwork on plaster walls--screws will be more secure, while nails will damage the plaster.)

To fix bulges in a plaster wall:

  1. Clamp bottom of bulge

  2. Cut 3/8” slit along bottom

  3. Drag out the debris from inside the bulge with a wire (you can use a wire hanger)

  4. Clamp the top of the bulge and continue clamping down the rest of the bulge, working from the top downwards

  5. Now you can proceed with the Plaster Magic repair method above


Instruction sheet for patching holes in plaster (click images below to enlarge, or click here for printable PDF):

  • When mixing the patching plaster, it should be the consistency of peanut butter.


If you missed the presentation, have no fear, because the Plaster Magic website has links to Rory's instructional YouTube videos, here! Here's a good one to start with before assessing your plaster problem--the anatomy of a lath and plaster wall:

And here's Rory's step-by-step, start-to-finish instructional video for repairing plaster cracks and holes:

You can explore the rest of Plaster Magic's website for other resources and product information.

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