I am often called to repair plaster work in older homes. Typically, it’s to repair a cracked ceiling or areas of walls or ceilings where significant reworking of the plumbing or other mechanicals has been done. I’ve developed some efficient strategies for both situations that don’t require rocking over or demolishing the entire surface.
Large Wall Repair
A difficult repair I did on a customer’s plaster wall last summer provides a great example. Some major plumbing renovations had required opening up the wall and demolishing a big section of plaster. On top of that, a drain pipe that had been relocated into the wall cavity couldn’t be pushed back far enough and stuck out beyond the plane of the existing plaster surface. In this case, as it often is, the door casing and baseboard needed to be left in place, and I wouldn’t be able to build up the plaster or joint compound to be too thick along the edges of the trim. All of this meant that I couldn’t easily cover the wall section with board material, so I opted for using metal lath instead.
We settled for having the inside corner of the room just a few degrees out of square. To make that work, I began by ripping a piece of 2-by and installing it even with the plane of the pipe to create a solid attachment for metal lath, which I could then roll out from the corner 2x2 over the drain pipe, and blend into the casing.
Fabric and lath. In previous repairs, I had discovered the use of plaster over wire lath that had been backed with rosin paper to help prevent too much plaster from falling through the lath. Instead of rosin paper, I used FibaFuse Wall Reinforcement fabric, which I use regularly for resurfacing ceilings, as I will explain later in this article. For the wall repair, I stapled the fabric over the opening in the wall, and then covered it with wire lath, securing the lath with screws and plaster washers. As luck would have it, the opening I was repairing could be covered with a single sheet of lath measuring 8 feet by 27 inches—a common size for wire lath.
Primer and base coat. Before applying the plaster over the mesh and ceiling repair, I first had to apply a plaster bonding agent. In addition to helping the plaster bond to a variety of materials, the bonding agent reduces the water absorption out of the plaster, allowing the plaster to cure properly.
I mixed the base-coat plaster to a thick consistency, and I started applying the plaster along the bottom of the wall. Because I used a thick mix, started along the bottom, and had the fabric behind the lath, I was able to build up the plaster to a thickness of at least 1/2 inch and taper it to nothing along the casing. When I returned the next day, the plaster had set up into a solid surface. The blend-in over the drain pipe already looked good.
For the next coat, I applied a thick coat of setting compound, which set up in about an hour. I then applied a thin coat of lightweight joint compound for the final coat. This coat was just a skim coat of compound to smooth and fill in any remaining defects in the surface. When it was dry, I sanded it to a smooth finish with 220-grit sandpaper.
Repairing Ceilings
Large ceiling areas can be repaired with pieces of drywall. On this job, an area of the ceiling above the wall repair had also been demolished, by the same plumber who installed the drainpipe. The plaster and lath was about one inch thick, so I padded out the ceiling joists with strips of 1/2-inch drywall before installing large pieces of the same material to fill in the hole. Note that the plaster around the perimeter should be well secured with screws and plaster washers, and any small areas of exposed lath should also be secured.
Regular drywall can be used as a plaster base, but it—and any exposed wood lath you want to plaster over—must be treated with a bonding agent. Next, I prefill any open joints and the perimeter of the patch with base-coat plaster, into which I embed fiberglass tape. When that has set up, I follow with a coat of setting compound and feather in the patch before resurfacing the rest of the ceiling.
Resurfacing Plaster Ceilings
Many old plaster ceilings have shallow cracks over much of the surface, and it’s time-consuming to apply tape over every crack even when you’re using self-adhesive mesh tape. Then all those taped areas have to be concealed with multiple layers of compound. This is before the spider cracks are even considered.
Spider cracks are what I call the fine cracks that are sometimes all over an old plaster ceiling. They appear to just be cracks in the paint, but I was never sure what to do about them. Was it necessary to reinforce each one? Doing that would be difficult and time-consuming and require a lot of mesh tape.
Prep work. You’re finishing over an existing surface, so if it’s in poor condition, any material applied over it will be compromised. If the base is loose, dirty, or too absorbent, or if it offers poor adhesion or has some other problem, then the new surface may not create the stable, durable finish desired.
To prep the existing surface, I remove any loose plaster or paint and seal any watermarks or stained areas of the ceiling. Often, areas of the ceiling will have separated from the lath, typically because the keys into the wood lath have broken. These areas can be pulled in tight to the lath by using plaster washers.
If the surface is very smooth, first rough it up with a coarse-grit paper (80 grit or coarser). On glossy painted surfaces, I have used paint de-glossers with success, but using a plaster bonding agent, such as Plaster-Weld, is my preferred method.
I suggest V-grooving larger cracks, then filling them with setting compound and covering them with extra-strength fiberglass mesh tape. Areas that are recessed or crowned should be filled or feathered out at this time with a setting compound. Using the setting compound allows me to complete the prep work and move right on to embedding the glass mat I plan on using to reinforce the entire ceiling.
Tip: Prior to starting a job, you should prep a test area to make sure that the method you are thinking of using is going to work. That way, when you start the work, you can feel confident that you will have good adhesion.
Resurfacing. To achieve a new, smooth ceiling surface over old plaster, I begin by coating the ceiling with a thin layer of joint compound. This acts as an adhesive for a fiberglass mat, which serves as a reinforcement to bind small cracks together and create a new, even surface.
My preferred method for applying the joint compound is using a paint roller that has a 1/2-inch nap cover. The skim coat could also be applied with a wide taping knife or even with a paint sprayer capable of spraying joint compound. The compound thickness should be about 1/8 inch (3mm). Edges close to walls and ceilings can be coated by applying the compound with a paint brush or taping knife.
I suggest using a heavy-weight all-purpose compound, rather than a lighter-weight compound, because of its greater strength and adhesion qualities.
The reinforcing mat I use, FibaFuse Wall Reinforcement, is a fiberglass mat (not a weave), and because the fibers are not particularly dense, it is quite porous. So it’s easy to embed in joint compound, which is the adhesive that holds the material in place.
You should span the entire ceiling with one length. (On a wall, the mat should be hung vertically as one length, as well.) Position the first piece of wall reinforcement along a straight corner or chalked line and press it into the compound with a wide taping knife, working from the center toward the edges.
Each adjacent piece of the fiberglass mat is butted to the prior piece. This method is preferred, and I do it by first snapping a series chalk lines at intervals the width of the FibaFuse roll. Because the mat is relatively thin, it can also be lapped and double-cut, as you might do with wallpaper. Double-cutting is when you cut through both layers with a utility knife and then remove the narrow strips, leaving tight-fitting butted edges.
Excess material along the edges and around cased openings gets cut off with a taping knife. The fiberglass mat cuts easily, so there’s no need to use a sharp knife. Continue to embed tightly with the taping knife until the mat is smooth and compound is forced through the face.
Work one length at a time. Within a few minutes of embedding one length of the fiberglass fabric into the compound, apply a second coat of the same joint compound, rolling it on and working it firmly into the surface. This process fills any voids in the surface and any dry areas behind the fiberglass mat. Immediately smooth and remove most of this layer of compound with a wide taping knife, leaving only a thin coat of compound over the surface.
Let the compound dry thoroughly—it will most likely take more than 24 hours. At that point, lightly sand with a fine, 220-grit sandpaper.
Coat again. After sanding the base coat, roll on more joint compound. (A lightweight compound can be used for this final application). Remove and smooth with a wide taping knife, leaving the surface smooth and tight. This process is similar to applying a Level 5 finish (see “Specifying Drywall Finishes,” Nov/09). In most cases, no additional sanding is needed.
Photos by Chris Ermides
