These joints are taped with scrim - a very open-weave, self-adhesive tape. Most modern ceilings are built from sheets of plasterboard nailed to the joists. ![]() The room above would traditionally have had floorboards. The plaster was squeezed between the laths so that 'nibs' formed - ridges of plaster that squeezed through the laths and set hard, holding the ceiling plaster in place. This was a time-consuming method of building walls and ceilings, as individual laths (thin strips of wood) had to be nailed to the joists and then covered with layers of plaster. The depth of the joists will vary depending on the age of the building (older ones are often deeper than modern ones) and their length. Part of my plaster ceiling repair has a top coat of vinyl spackling compound and part has a top layer of latex caulk.Both, lath-and-plaster and plasterboard ceilings are fixed to the joists that support the floor above. In my case, since the mix of colors in my paint job hides surface defects I went ahead and used both techniques, to see which method survives the test of time. The downside is that the top surface won’t be quite as smooth. This will probably require several layers. However, if you want to try to avoid the reappearance of the crack you can rely on the caulk to form the top surface. This will delay the day when the crack eventually becomes visible. This spreads the separation over a wider area so that the spackling layer will create a bunch of very small microfractures rather than one big crack. The benefit of having the caulk under the top layer of spackling is that the caulk will tend to stretch as the crack widens. This will allow you to apply a layer of drywall mud, or spackling compound, which can be sanded. The caulk will shrink, which is actually good. In my case the paint job has a mottled surface that will hide the imperfections in the surface layer, so it should not be noticeable. ![]() The surface will look like it has been repaired. You can sand plaster down, but you can’t sand caulk. The reason caulk is not usually used in a plaster ceiling repair is that you cannot get the surface of the caulk to be completely smooth. Using a wide putty knife that I wetted down, I spread this caulk to cover the exposed area. Then I caulked the crack with your basic latex caulk. I Begin the Plaster Ceiling Repairįor my repair I cut away all the loose surface plaster with a utility knife. The problem is the compound used to repair this is even weaker than the plaster, since it lacks the fibers, and as the house continues to settle the crack will reappear. Once dried you sand this down and all looks good. The traditional plaster ceiling repair method is to mix up some plaster, or drywall compound, or use spackling compound to fill in the crack. The moisture from the shower had penetrated into the plaster enough to weaken the bond between the finish layer and the base plaster. It was this finish layer that was sticking to the paint. It lacked fiber, so it didn’t have much strength, but it could be smoothed out to provide a very flat, even surface. The fibers were usually animal hair and they did not allow for a smooth surface, so a second, finish layer was laid down. This layer had a lot of fiber mixed in with it, to bind the plaster together and give it some strength. They laid a thick, heavy layer down directly onto the lathe. ![]() When they applied my plaster (back in 1906) they did it in two coats.
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