Surface preparation Your wall needs to be very flat. This plaster mix won't fill gaps, so make sure the wall is at a finish quality of level 4 or 5 as understood by drywall and plaster contractors. If you try to level an area by applying a thick coat of this mix, you will spend the rest of the evening babysitting the area, frequently recompressing it to prevent cracking.
Mist the wall with water before applying the plaster. If you don't, the water will immediately be wicked out of the wet plaster, causing it to stick to the trowel on the smoothing pass seconds later. The moisture in the wall also aids adhesion.
Don't apply the lime plaster directly over gypsum drywall. It will crack and chip off in a few days. You will need to apply a quartz primer first, and ideally a skim coat of gauged lime plaster over the whole wall. I know this because I tried various types of wall board as test panels.
Application technique Basically the plaster is troweled on in very thin coats. Think heavy-paint thin. It is the variation in trowel techniques and aggregates that produces the varied finish effects. Since the permutations of techniques are endless, consider the mechanics of the process to guide you to your desired finish. Ultimately, though, this is an art that requires practice. If you are easily discouraged, spend the money on an experienced professional applying a proven product.
My observation is that controlling the finish is all about controlling imperfections. When you trowel on the plaster, the resulting surface has minor imperfections in the surface height. Subsequent applications of plaster will fill in the low areas and may even leave high areas exposed. The variation of exposed layers and tapering of thicknesses creates variation in tone in the finished surface. Burnishing creates the variation because higher burnishing pressure deepens the tone. Higher points in the fluctuating surface get more burnishing pressure and deeper color, even if you used only one tint in a perfectly mixed plaster for all the layers.
We can affect the imperfections by controlling how we use the trowel, and also by the aggregate in the plaster. The length of trowel passes changes the size of the area of similar imperfections, so it changes the density of tonal variation. The angle of the trowel changes the pressure at the working edge - higher angles have higher pressure thereby exposing more of the underlying layers. A flatter trowel will float more wet material aver the surface. The stiffness and size of the trowel used controls pressure as well. The direction of the trowel pass will affect how that layer reflects light - almost as if it changes the orientation of the marble particles. Larger aggregate creates larger variations in the finished surface, and also increases the abruptness of those variations. Abrupt variations lead to more contrast and even the illusion of lines and hard edges.
Use short, crossing strokes with a fine aggregate plaster, and the result will be a dense but subtle variation in tone. From a distance the color will look uniform, but will come alive like paint cannot. Use fine aggregate layers over a course aggregate base coat along with pigment changes, and you can achieve high contrast like that from the exposed sedimentary layers in a slate or shale.
Do be careful to not overwork the underlying layers. As the moisture evaporates and wicks out of the plaster, it will begin to burnish with the trowel. That will adversely affect adhesion of subsequent layers.
Burnishing This is when the surface comes to life. Referring to the photos in my previous post, that wall was a pretty uniform light drab brown before burnishing. Almost all of the tonal variation appeared during burnishing. Regarding pressure, one pass with a few pounds of force on the trowel results in 50%-75% of the surface taking on a sheen. The task is tedious, not strenuous.
I use a flexible pool trowel that allows me to work in a circular motion. A stiffer trowel dictates that it be dragged in one direction per pass, otherwise it digs into the plaster. Either way, I start with a very light pressure to knock down the high spots, then increase pressure until I get the desired depth. If the surface has a low spot that defies burnishing, use a little 600 grit paper to level the area first.
Perhaps it is the type of lime, use of sharp sand, or lack of finesse, but I have a little difficulty burnishing before the surface is completely dry. Most of an area will burnish fine, but then the trowel will stick or catch, pulling off a small area of plaster. Patching is easy, but I prefer to burnish the dry plaster. The main drawback to burnishing dry is that the high spots are much harder to work down, so sanding will occasionally be required to get a uniform burnish.
One more note about materials - did you know that the marking "chalk" used on sports fields is many times actually marble dust. I've found 50 lb bags of Imery's marking powder (marble) for under $10.
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( 0 / 0 )Well, bummer. I had a long post typed in but when I hit submit, my session had expired. DoOver.
Here is a picture of the results from my homemade venetian plaster:
The base layer uses 1/2 part masons sand in place of 1/2 part of the marble dust. In retrospect, course marble dust would probably work better if I'd had it. The sharp silica sand tends to get grabbed by the burnishing trowel, and can "pop" or scratch the surface if too much pressure is applied while burnishing. You can also see the vertical lines caused by the wet trowel chattering over the sand grains. The lines are coloration only, and can't be felt by touch. We like the effect.
The color is "BROWN" liquid integral concrete pigment from Menards. I added the pigment last after everything else was well mixed. I did not fully mix in the pigment, but left a little variation in the bucket. The base layer was textured slightly with a natural sponge roller.
The second and third layers used all marble dust for the aggregate. I tweaked the pigment levels about 50% up and down in the top layers to get contrasting shades. I mixed the pigment well for these layers.
As the following picture shows, the homemade VP burnishes easily. I used a thin stainless steel pool trowel for burnishing. This trowel is very flexible, and does a better job of burnishing low areas. I only spent a minute to work this 2'x2' area into a nice shine. As you can see, some areas are a touch low, and don't get burnished right away. A few passes with 600 grit sandpaper will smooth things out enough so burnishing has better coverage.
Enough with that, here is the recipe:
Lime Putty (1 part) Make this by sifting hydrated lime powder into distilled water until it won't accept any more (dry powder floats on the surface for more than a minute). Cover the container and leave it sit overnight. The next day, the lime will have settled, so add more dry powder to refusal. Repeat until a rest overnight no longer results in appreciable water on the surface (maybe 3-4 repetitions). Now let it sit for a few weeks covered airtight in a cool place. Water and a thin floating crust will form on top of the putty. Pour this off and mix the putty well. Either use the putty immediately, or replace the 1" of water on top of the putty and reseal the container for long term storage. It only improves with age. (Basic method described to me by The Plasterers Arms over at FauxForum)
I used Western Miracle Lime. Yes, it is high magnesium dolomitic lime. No, it doesn't appear to detrimentally affect the plaster.
Marble Dust (1 part) I use Imery's, which is available from various distributors nationwide (they make cultured marble sinks with it). It is also sold as pool aggregate. Get a variety of gradations from medium sand (0.5 mm or so) down to the finest sold. $50 should get you several 50-100 lb bags.
Linseed Oil (~1/10th part) Just plain old boiled linseed oil from the paint store will do fine.
Olive Oil Soap (a smidge) I use Kiss My Face brand from the local natural foods store. Prepare the soap by shaving it and combining with an equal part of distilled water. Melt over a double boiler. The consistency after cooling should be like grease. A smidge is two tablespoons per gallon of plaster. (Method described by Eli Lucero at FauxForum)
Lime-safe Pigment I use the liquid integral concrete pigments. These won't fade in the presence of lime. You can add up to 15% by weight of lime, or 5% of the overall plaster batch weight. Fresco pigments should work as well.
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( 0 / 0 )One thing I've spent a lot of time researching is plaster and mortar. As I mentioned before, the mortar for old brick needs to be right. If you use the modern hard mortars, the softer brick will be destroyed. Modern mortar traps moisture within the brick and is less accommodating of the small movements a house makes.
Plaster and mortar from the late 1800's was lime based. This is softer than the premixed stuff you get at the local builders supply. You are lucky if you live in an area with many historic homes. This creates a market for contractors and suppliers experienced in these original building materials.
We aren't so lucky here. Type N mortar is as soft as you can find. If you ask for plaster you get taken to the section of the store with pre-mixed joint compound for drywall. Neither of these are suitable for restoration in my opinion. Fortunately, I have been able to locate sources for materials locally after considerable research.
When trying to get mix designs for plaster, most of the information I had spoke of lime putty. Much of that information came from Europe, and that is the material of choice over there. Quicklime is carefully slaked in water then left to age for a long period of time - up to several years. Quicklime isn't available in quantity around here, nor do I have several years to wait for it to slake properly. Lime putty is only available shipped, and it is rather expensive.
What we do have is hydrated "Type S" bagged lime known as Miracle Lime. This is fine, white, powdered lime that has already reacted with water. Mix it with the right amount of additional water (to a peanut butter or yogurt consistency), let it sit for a few days to a week, and you have lime putty suitable for all the mortar and plaster work on an older house. I mix it and store it in a plastic tote with a tight fitting lid. I can mix a 50 pound bag of lime easily in it, and the tight fitting lid prevents the lime from completing the carbonation reaction.
Reading the information out there, I get the feeling that many are under the impression that high calcite limes are superior. I think this has to do with magnesium affecting the creation or durability of frescos. It may also be due to the fact that magnesium oxide takes longer to hydrate. If it isn't hydrated by the time it's on the wall, it could hydrate there, expanding and destroying the finish. The lime I am using probably has 35% or greater magnesium content. It is pressure hydrated in an autoclave, ensuring the MgO is hydrated properly. Given that:
a) I won't likely have a fresco (although maybe polished plaster)
b) Properly made dolomitic lime is cures harder, is more plastic, and has better water retention than alternatives
c) The house was probably built using the readily available dolomitic lime
I have decided that the Miracle Lime will do just fine. It is very plastic and workable, and is surprisingly easy to finish. It quickly mixes with water to form a smooth paste. Best yet, it is $6 for a 50 lb bag at the local contractor supply company.
I've also read conflicting data on whether simply adding water to Miracle Lime really makes lime putty. So long as the bagged lime hasn't reacted with atmospheric CO2, I don't see how there could be a difference. I sure can't feel a difference, and the lime mortar gets hard as stone after a few weeks. The people claiming that there is a difference are usually selling the more expensive putty in a bucket, so I'm not inclined to believe there really is a difference.
I'm using 1 part lime putty with three parts sand for the scratch and brown coats. Sometimes I add one-third part of gauging plaster (see below) if I want the plaster to firm up quicker. The same mix ratio works out pretty well for the repointing mortar as well (sans gauging plaster).
I made a few other material substitutions. The scratch coat of plaster on our walls contained animal hair - presumably horse. I'm using polypropylene fibers instead, FiberMesh brand available at your local concrete supplier. It doesn't take much. I've gotten very solid keying into the lathe and no cracking when using a small handful of fibers in an ice cream pail of plaster.
For the surface coats of plaster, I am "gauging" the lime putty with a small amount of Durabond 90. I know what I said about joint compound above, but read the MSDS sheets. Durabond is almost all Plaster of Paris and powdered limestone - very close to gauging plaster. The Durabond 90 gives me plenty of working time to get the plaster on the walls and finished. Once Durabond is set, it does not soften when wet like premixed joint compound will. To make finish plaster, I take 1 part lime putty and form it into a dish on a scrap piece of countertop. Within that dish mix 1/3 to 1/2 part Durabond with water to a workable consistency. Once the Durabond is blended smooth, work the lime putty into the mix to make a nice finish plaster.
After much searching, I did find a supply company in Saint Paul, MN that sells fine marble dust in 50 lb bags. I will use this in the surface finish for the bathroom walls. I am experimenting with a Venetian Plaster recipe that is 1:1 lime putty to marble dust, with a small amount of olive oil soap (Kiss My Face) and linseed oil. Formulations will follow once I have some test panels made up.
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( 2.7 / 145 )We purchased our home in the spring of 2007. It is a nice sized brick house with a footing plan like a Greek cross. It was constructed in 1896, according to the county records and the date scratched in the mortar in the foundation. The architecture is Victorian - perhaps more accurately Folk Victorian. The style is not as ornate as Queen Anne. Turnings and scroll work make up the trim around the porches, and arch-top windows have brick dentil cornices.
;)
Given the age of the home, it is in very good shape. The foundation shows almost no evidence of settling. The brickwork is largely in good shape. The timber structure only has a few places where moisture damage is evident.
That's not to say that there is nothing to be done. Although the home has a new roof now, leaking and subsequent staining led the prior owners to cover portions of the plaster with drywall. We are taking a room at a time approach to restoring the original plaster.
Most of the original storm windows are gone. These were arch topped just like the primary windows and have a seamless look. Most were replaced with cheap aluminum storm windows. These really destroy the look of the home, and I seriously doubt that they perform as well as the original storms. I am making new storm windows to match the originals, and will be doing away with the aluminum units. The main windows will be treated with weatherstrip kits from Advanced Repair Technologies. The combination of original storm windows and tightly sealed main windows should perform nearly as well as new triple-pane windows, but for a fifth of the cost.
The sills of some of the windows have rotted or shrunk enough to allow moisture to enter the top of the brick. This has led to deterioration of the mortar under the windows (old lime mortars were responsible for wicking moisture from the surrounding brick and dissipating it into the air). We plan to repoint these areas as soon as possible.
A previous owner tried repointing the brick in one area at the back of the house. Unfortunately, they used modern portland cement based mortar, which caused the brick faces to spall off. Our repointing project will also involve replacing these bricks with ones from the stockpile that came with the house.
That's it for now. More as we dig into the restoration.
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