Renovating

renovation home
our projects
attics
bathrooms
books
brick houses
general
insurance
links
organizations
plaster
research
schedules
styles
suppliers
getting on TOH
tin ceilings
tools
water problems
old house worries
Phouka Home

"An architect's most useful tools are an eraser at the drafting board, and a wrecking bar on the site" - Frank Lloyd Wright

Plaster Walls
Old plaster should be cherished - it is stronger and more soundproof than current walls made of gypsum board or sheetrock. It can often be saved with no damage to the trim pieces. Even cracking or crumbling plaster walls should be repaired, not replaced, even though every contractor will assure you that the only solution is to laminate the existing walls with drywall. The difference between old plaster (or new plaster, for that matter) and wallboard is noticeable. Even with texturing, plaster has a very different feel to it than gypsum board.
Even the preparation and maintenance of plaster hint at its lifespan. Wallboard can be painted in 30 minutes, while a 3-coat plaster job must cure for 30 days or more. In fact, homeowners used to be warned to wait an entire year before painting plaster walls. The year wait allowed the plaster to cure completely. Plaster walls over a hundred years old are still as solid and smooth as the day they were finished, if they are well cared for. Other than a few minor cracks, and some dings left by inattentive prior owners, the walls of our house are in very good shape.
Plaster of some sort has been used for hundreds of years. Before 1900, Lime-based plaster was used. This was mixed with animal hair and sand to give it stability and strength. After 1900, a gypsum based plaster was used. A three-coat system was used in either case:

Scratch Coat, which was pressed into the lathe to form the plaster "keys" to hold it in place.
Brown Coat
Finish Coat, applied to make the entire assembly about 1/2" thick. The finish coat of lime plaster had to be "packed" - trowelled under pressure until it was mirror smooth. Textured walls are a fairly recent invention, as far as I can tell.

Plaster Damage
In most cases, if the plaster in your house is covered (by wallboard, paneling, or canvas) assume that is is damaged. Most people won't go to the expense or hassle of covering all the wallspace with something else if it's in good shape. Some will decide that he look of cheap luan panelling is just what they want and will put it up over anything. Unfortunately, the installation of wallboard veneer or panelling can damage the underlying plaster. Removing the covering is occassionally impossible.
Plaster is pretty tough stuff, but like any wall, it's going to get banged or gouged, and age will take it's toll.

Impact Damage can be serious problem in an old house. Over the years, the walls are going to get banged and dented. Remember that when a piece of plaster breaks, it usually loosens the surrounding plaster from the lath. Generally you have to replace th plaster 6-12" from the visible hole to reach plaster that is still keyed to the lath tightly.
Nearly every wall has a few (always oddly placed -- what on earth did people hang there?) nail holes. These can usually be fixed with a tiny bit of spackle applied with your finger. Not perfect, but they will be unnoticeable when the wall is painted. I've even heard that some people will use a bit of toothpaste when they just want to fill the hole but aren't planning on repainting the entire wall. NOTE: When you want to hang a picture, never use nails in furring strips! Pounding a nail into the wooden furring lathe can loosen the keys of the plaster and cause sagging or bowing of the wall. For that reason, always use screws in plaster walls, predrilling each hole. A piece of cellophane tape over the spot you want to drill can keep the surface of the plaster from spalling.
Water is the enemy of of plaster. Look for brownish stains on the walls or ceiling, or evidence that the plaster is bowing out. Make sure that all sources of water are completely corrected before replacing the plaster in the damaged area. Water-damanged plasted can be very friable, so if you have plaster that has been wet, it likely will be necessary to replace it.
Brown spots are usually caused by dampness or continuous leaks. This is bad. If there is a single brown-edged spot, the problem may have been previously corrected, or may have been a single occurrence. A spreading set of rings indicates continued and serious water seepage from somewhere. Find the source of the water and repair it. The plaster that was damaged by water is usually crumbly and should be replaced, or you risk whole hunks of plaster raining down the next time someone jostles the wall or ceiling.
Plaster that was wet at any time can be crumbly and will disintigrate with the smallest touch. The plaster walls in our basement were under water for about a day several years ago and the plaster is crumbled and falls apart when touched. The same wall, farther up where the water didn't touch, is solid and rock-hard
Old walls and old houses often have cracks. Stress cracks are a sign of possible structural shifting, extreme temperature changes, incorrect plaster mix, improper curing or leaks. Don't panic if your walls have small cracks, just keep an eye on them and determine if they are actively widening or stable. We have a few cracks in the walls that have been absolutely stable -- widening slightly in cold, dry weather, closing when the humidity rises. We don't patch them.
In most old houses, cracks mean that the keys of plaster that hold it securely to the lathe have broken (from one of the possible causes above). If the crack is old, and does not have any loose material, it probably is not anything to worry about.
Diagonal cracks over doorways signal settlement, or a nearby source of vibration, such as a highway or railroad. Again, new cracks are worrisome, older ones are often not so serious.
Peeling paint and plaster can be indications of water damage, or they can indicate problems with paint. Both of these symptoms can occur when too many paint layers build up, or when calcimine paint is panted over with latex or oil based paints. Occasionally the paint pulls the top layer of plaster off as well. It may also be the result of an overzealous wallpaper remover, who gouged layers of plaster from the walls underneath the wallpaper.
Bulging plaster is an indication that the plaster keys have broken off and allowed the plaster layers to separate from the lathe behind them. Bulging can be repaired with plaster washers.
I've received so many emails about plaster washers that I tracked them down:

Charles St. Supply Co
54 Charles Street
Boston, MA 02114
800-382-4360

Should you repair or replace?
I'm usually all in favor of repairing plaster walls, regardless of what they look like. But honestly, this is not always possible.
Basically, if:

there is more than 1 large hole per 4 x 8 area, or
there are more than 3-4 cracks in 100ft², or
the cracks are more than 1/4" wide
then replace the section of wall. You're going to spend more time (and failed attempts) to repair this wall than it is worth. Now, if you have an irreplaceable mural or original stenciling, it might be worth it, but you'll probably hire a professional restoration expert to deal with it.
Repairs and Options

For repair of minor cracks, use fiberglass mesh tape then go over with a wide trowel and joint compound. There are also plaster patch compounds available that are excellent.
For larger cracks and holes, you need to remove all the debris and enlarge the crack until you reach solid plaster. Remember that in the case of impact damage, the damaged area can extend 6-12" from the actal hole. Make sure that you clean out the lathe as well. Then, back-cut the hole and fit a piece of drywall into the void. (in our house, we were able to use drywall screws to hold it to the lathe), then use mesh tape over the edges and fill the hole with several thin layers of joint compound or plaster patch.
You also have the option of actually putting down plaster (scratch coat, brown coat, and finish coat) if the hole is large enough. It is a tough skill to learn, and even harder to finish properly (there is a reason that plasterers are so expensive!). Try it in a closet or something first. They make it look so easy on This Old House, but it's really hard to do. I have a few wavy walls in my stairwell to prove it. Really wavy. I tell people it was on purpose. (Hmmm. Maybe I'd be better off with Lincrusta...).
If the walls are simply slighly wavy or oddly textured, you may want to apply a highly textured wallcovering, such as Lincrusta or Anaglypta. The busy pattern and deep texture can hide many imperfections. Another option is to apply canvas or a product called NuWall to crumbling plaster to smooth out the walls for further wallcoverings or paint effects.
If the problem really is too bad to possibly salvage, you can resort to the suggestion of the contractor: laminate drywall over crumbling plaster. Use 3/5" drywall over plaster, screwed through the studs. Often the lower part of the wall (which suffers the most damage from kicks, furniture, and movers) can be covered and the top edge masked with chair rail molding to save the appearance of the old walls. This faux wainscotting effect is very believable and quite appropriate in many houses.
If you choose to put wallboard over the plaster, use the following tips:

Apply wallboard horizontally
Use the largest boards available. Yes, it's difficult to bring 4x12 sheets up the stairs, but it's worth it.
Use screws, not nails, 12" apart in ceilings, 16" on walls
Use a floating joint - the wall holds up the ceiling sheets
Use corner clips at all corners
Use fiberglass mesh tape, not paper, and special compound that is available for plaster walls.
Caulk interior corners with acrylic latex caulk. I know, not historically correct, but the effect is smooth and unnoticeable.