Hanging by a Hair — Techniques for Reattaching Plaster Ceilings

Most of us with an older home have experienced sagging and cracking plaster in our ceilings. While ceilings are affected by all the normal wear and tear that goes on within our houses - structural shifting, leaks and temperature shifts, traffic and vibrations - they have the addition stress of being at the mercy of gravity! Because ceiling surfaces tend to be some of the largest, unsupported surfaces in the house, older plaster systems applied over wooden lath have a limited life span before they begin to break and pull away. The good new is, they can be repaired and saved from further damage.

We have successfully reattached many old ceilings using a reattachment process which involves injecting glue to create a new bond between the plaster and lath where the keys have been damaged and broken away over time. This technique uses modern adhesive materials that are easy to handle and cause minimal damage to savable plaster, and will restore the old plaster's integrity for many more years.

After correcting whatever problem made the ceiling loose in the first place (leaky roof, structural problems), the first step is to assess how far the ceiling has pulled away from the lath - the extent of the delamination. Gently push on the plaster and judge the amount of play between plaster and lath, and listening for clues to what you will be dealing with. Hopefully, you will feel it going back into place, like a puzzle piece sliding into it's own unique spot. If there are broken keys or debris in the way, it will resist going back into place, and will feel and sound "crunchy." Peter refers to this crunchiness as the sound of breaking eggshells or crushing popcorn. Do not force the plaster back into place or more may break, just gently encourage it with the flat of your hand.

Reattachment can occur from the front- or back-side of the plaster. If you have access to the ceiling from an above attic or removed floor, some or all of this process can take place from behind. There are advantages and frustrations with either method. Doing reattachment from the plaster side leaves you will holes to fill and further disturbs the plaster. From the back, or lath side, you must deal with a cramped, dark, and uncomfortable space to work in, but this method is particularly useful when working with ornate plaster, a hand painted ceiling, or when minimal disturbance to the plaster is important. We prefer approaching reattachment from the plaster side if possible because visibility is better, it can be completed by one person, and you can tell at any time how the plaster is reacting and holding up to the reattachment process.

Drilling injection holes with a 1/4" drill bit. Holding the vacuum nozzle to the hole removes dust as you go along.

If the separation is slight - ¼" to ½"- reattachment success is likely because the plaster will usually push back into place and feel solid and flat against the ceiling surface. If the plaster is sagging ½" to 1" from the lath surface there is often too much debris from broken keys or years of silt in between the plaster and lath. With these materials in the way, the reattachment process is not an option unless you can access the ceiling from an above to vacuum out all this debris. Often the worst part of the ceiling has too much debris, and we need to remove this section entirely for infill and reattach the edges to further secure the ceiling. Plaster that is too soft will not hold up during the pushing and drilling and should be removed as well.

Removing areas of damaged plaster, especially in a ceiling, will encourage more plaster to come down. Using a chisel-type tool will encourage the plaster to keep going - we call this the "domino delamination effect." We recommend controlling this tendency by carefully marking out your repair plan, then removing any areas with a sharp utility knife. Using the hand-pushing method, we will determine at what points the area seems to become solid again, mark any complete removal area, crack repair areas, and the spots for reattachment drilling. Do this marking with a lumber crayon or pencil, as a pen will bleed through your paint later on.

The holes you will drill to inject the adhesive must be placed directly beneath the wood lath - not the spaces between the lath - so that the glue has a solid bonding area. If you have removed any plaster, or dug out a crack for repair, then you have the advantage of seeing the lath and you can go by that. If this is a reattachment-only repair, it's basically hunting and pecking. The best approach is to first stand back and look for the shadows or images of the lath showing through the plaster in the ceiling. If the plaster is thicker and the lath "ghosts" cannot be seen, then you have to wing it. Once you have found a solid lath spot, assume that most lath is 1 ½"-2" wide and runs with approximately ¼" to ½" gaps in between the slats. If you have an infill area or crack that needs reattachment to the edges, go 1 ½" to 2" back from the edges to mark the injection sites. If you are doing only reattachment, injection holes should be every 3"-4", no more than 6"apart.

We drill the holes with a ¼" carbide drill bit. If you are a less experienced driller, this presents your second challenge because you must drill through the plaster completely, stopping before drilling into the wood. If reattaching from above, you need to drill through the lath stopping before the plaster. By paying attention to the changing resistance of the materials on the drill, you can develop a feel for the different layers of materials. We can best describe it as a change from drilling through sand to hitting a solid mass (or vise versa). It is very important to drill only through your injection surface, or you will jeopardize the integrity of the bonding surface and cause further structural damage.

Wire lath inserted over the wood lath provides a solid infill substrate for this repair. Reattachment has occured around the patch area.
Damaged plaster has been removed for later infill. Injection holes have been drilled every 2"-4" and vaccumed out, area is ready for glue injection.

Once you have drilled your holes, you want to vacuum out the debris and drilling dust. Older plaster is soft so be careful not to suck it off the ceiling with the vacuum! Place your hand near the hole to gently support the plaster while you vacuum using the other hand. Do not push the plaster back up into place, however, because leaving that void will allow the vacuum to pull out some of the debris through the hole. If you have access from above, the vacuuming can be done from this perspective, accessing more of the silt and debris. The keys that are visibly loose or broken should be removed also. If you are reattaching from above (behind) the plaster, drill holes through the lath every 4" - 5", now stopping before you get to the plaster. Vacuum the holes out again once drilling is completed. A shop vacuum designed to handle the fine dust of plaster is best for this practice.

Next, wet the injection holes either by spraying down the lath with a squirt bottle, or squirting up into the drilled holes from the plaster surface. Wetting encourages the adhesive to travel further when it is compressed, and will also slow the drying time down slightly for a stronger bond.

Here a caulking gun is used to inject the acrylic adhesive into the drilled and vacuumed holes.

Finally it's glue injection time! We use a water-based, latex glue that is actually a vinyl floor adhesive. Any good-quality latex or acrylic glue adhesive can work (Liquid Nails, floor or foam adhesive). These products are available at construction supply houses and hardware stores, and can be purchased in caulking tubes for smaller projects or bulk in 5-gallon pails for larger jobs. We use a caulking gun with the tip cut to fit snuggly in our ¼" drilled holes, and inject the glue until you feel the plaster move away just slightly (one squeeze of the average caulking gun is usually enough). If you inject too much glue you will push the plaster too far away, and leave too much glue - which will actually push the plaster off the ceiling further. Wipe the excess glue that will travel out the hole when you remove the nozzle with a damp sponge as you go along. Complete your entire series of holes and go back over the plaster with a clean, damp sponge to remove further glue residue. You would follow the same process if reattaching from the lath side, but not need to wipe off excess glue.

Once the glue has been injected to the repair area, we push the plaster back into place against the lath, and secure it in place with forms. This will spread the glue out so that it is attaching a greater surface area - our technical term for this is "smooging" the glue around. We use flexible, ¼" - 3/8" plywood forms covered with a layer of poly. Do not underestimate the importance of this layer of poly, if you forget it the form will be permanently glued to the plaster and take all the plaster off with it when removed (sound like first hand experience?)! These forms are then secured in place using screws or wood strapping supports from the floor so that they remain pressing the plaster firmly against the lath to set-up for 24 hours. Screwing saves the time of fitting wooden supports and keeps the work area clear, but can damage the plaster and leaves you with more holes to fill. For more fragile, decorative, or museum-quality plaster wooden supports would be more appropriate. Supports are used for both plaster- and lath-side reattachment.

Left: Floor to ceiling braces hold poly layered forms tightly against the reattachment areas.

Use a putty knife to remove the dried glue residue that will escape out the injection holes when forms are "smooged" into place.

The next day you can remove the forms. Some of the plastic will stick if you injected from the plaster side, simply scrape it off with a putty knife. The glue is still soft around the drilled holes at this point, but has set up enough to remove the forms and allow for full set up. For plaster side reattachment, use a joint or putty knife to scrape the dried glue reside off, then use the corner of a putty knife to pull (gently!) the excess glue showing from the hole. As it dries fully (another day or so depending on heat and humidity) it will further retreat into the hole leaving a clear space to fill.

We usually fill the glue and screw holes with Durabond (mixed to the consistency of peanut butter) because this product has a quick set up time and dries very hard with minimal shrinkage. Any vinyl paste filler, plaster or joint compound can be used for this step. Usually, it takes two to three coats to fill the holes flush with the ceiling, depending on the product used. These are just holes, but Peter's favorite approach is Durabond 45-Unsandable for the first coat, then Durabond 45-Sandable for the second final coat. The unsandable is stronger and more like plaster so he prefers it for the first coat, then the easy-to-work-with sandable for the finish coat. The inexperienced should stick with joint compound or Durabond Sandable.

Voila! Your ceiling is now reattached and ready for a skim-coat of plaster, or a fresh coat of paint!


This article is also available in print in the January/February 2001 issue of Old House Journal.

©Copyright 2004 Peter Lord Plaster & Paint, Inc. 24 Moody Road, Limington, Maine 04049 (207) 793-2957