Metallic Plaster

Following up on my previous plaster article, I wanted to dive in with more detail regarding some of the more trendy or fashionable plaster finishes that are currently being applied in the U.S. and abroad.

For quite some time now, metallic plasters have been in style, and they continue to be “riding high” in terms of popularity. Let’s try to explain the current trend a bit more: what is metallic plaster?

A metallic plaster finish will have a shiny metallic, pearlescent or iridescent look when viewed from a side angle. The material is called “metallic,” but, in fact, there is not much metal in the mixture at all. Instead, there are metallic additives, such as copper, aluminum, iron and rust that are dyed to appear as gold. Actual metal grinds, like brass, bronze, zinc and tin, are fairly expensive, so the plaster industry uses cheaper solutions of dyed metallic additives that are mixed into the pre-mixed plasters.

The majority of the metallic effect comes from mica powders or iridescent powders, with the exception of a few actual metal applications, such as cold metallization. Cold metallization is made from actual metal grinds and has a more involved application and polishing process to reveal the metal finish. To learn more about this process, refer to our future article on cold metallization. Most of the pre-mixed metallic plaster finishes start with the same type of acrylic-based plaster that is then loaded with iridescent or mica powders to give them the metallic effect.

To learn about how to apply the many plaster kinds, visit the earlier article in Walls & Ceilings on plaster finishes and applications. Overall, whether metallic or not, the general process and procedure for application remain somewhat similar, if not the same, so I will concentrate on the actual metallic effect than the plaster application.

Types of Metallic Plaster

The easiest option for most applicators is to buy ready-made metallic plaster finishes, as the formulation for metallic plasters can be quite complex and may require machinery to mix the mica powder evenly throughout the plaster. The challenge in the application is getting an even coat of the iridescent mixture without too many trowel marks. Highly loaded metallic plasters have a tendency to behave like velvet, pushing the iridescent in one direction when you trowel in that direction.

There is quite a variety of metallic plasters available that can be bought from economical, big-box stores, as well as from more high-end retailers for the more refined finishes. In general, metallic plaster will always be more expensive than your run-of-the-mill plaster, as it requires ingredients that are more expensive. Since there is such a variety, one should shop around and practice with different manufacturers before settling on a preferred material.

One of the challenging issues that we often encounter is trying to find a plaster that is well-loaded with mica pigments but also workable with a decent open time and strap time.* The best option is to use a well-known brand, as they have a good track record and longevity in their plaster finishes. The great majority of metallic plasters are acrylic-based, tend to feel a little like plastic under the trowel, have a short strap and become sticky quite quickly. So before tackling a large wall, start practicing on small elements, such as columns and smaller rooms, in order to get the technique right.

Creating a Metallic Effect

Besides ready-made metallic plasters, there are other solutions to achieve a metallic effect. One can create a metallic effect with regular plaster or marmorino, which do not have any metallic particles in them. Personally, I am not a big fan of the highly loaded metallic finishes, which tend to look more like bronze paint and are too contrived for my taste. I prefer the subtler look of Mother of Pearl or lightly reflective finishes that are subtler and more delicate visually.

One material that I use to create a metallic effect is mica powder. Mica comes in a great variety of hues, from blue-green to orange-red, as well as several different tonalities of pearls, gold and copper. This offers a vast array of tones to choose from and allows you to modify the overall appearance of the plaster and create finishes that are more refined.

Recommended Application Methods

Using wax and mica powder:

To achieve a subtle metallic effect, I will add mica-loaded wax to my favorite plaster finish. After applying the preferred plaster or marmorino finish, add a mica-mixed wax mixture to the last two coats of plaster. Adding the mica-loaded wax to the mixture will create a more subtle finish. Purchase mica powder in bulk and then thoroughly add it to the wax, mixing it firmly and grinding as much as possible to disperse the mica evenly throughout the wax. Mica is extremely fine, light and hard to mix into a paste, such as a wax (even a waterborne wax), so it requires a little bit of whisking in order to create a paste. Note that you can also mix mica powder in every stage of your plaster application, but they tend to be fully absorbed by the acrylic binder or lime binder, which renders them somewhat flat. Therefore, the wax finish made with powder seems to be the best way to create those subtler finishes.

I found the greatest success in the metallic effect by creating a texture (whether striae, stippled, troweled or knocked down) in order to create “cavities.” These recessed areas will catch the mica wax or the metallic plaster in a final coat, thus creating highs and lows in the metallic effect. This final coat is the decorative painter’s equivalent to glazing, however, with metallic pigments over plaster.

Using a Metallic-looking Aggregate:

Another way to go about it is by adding an aggregate, such as mica flakes, glass beads or quartz flakes, to your non-metallic plaster. Any source of aggregate that will be thicker than 1/64-inch and be able to be troweled will work. Then, when you sand the top layer, you will expose the metallic aggregate below to create a very unique finish.

That being said, there are many great manufacturers who have created good metallic finishes. They are not over the top, and the final wax, tinted with mica powder, can give you the extra shimmering effect that you would want to complement that.

Bronze Effect:

To achieve this effect, I will start with a dark brown plaster and create a knocked-down texture on the surface. For the final filler coat, I will use a gold metallic plaster, applying it over my fully dried brown undercoats. I ensure to trowel tightly so there is more of a deposit of gold inside the crevices, almost creating a dry brush effect on the flat sections. Then, I burnish it and, finally, seal it by rubbing it with a wax loaded with gold mica powder all over the surface, creating an aged bronze finish. I often use Mixol tints to modify the intensity of the gold filler coats so they’re less yellow and more bronze-toned. I do this by adding a few drops of black or raw umber.

You can also create your own metallic plaster using MIXOL metallic tints. They are fairly expensive but worth their weight in gold, no pun intended. The MIXOL Metallic also mixes very well with the wax to ultra-saturate it.

In conclusion, there is no shortage of manufacturers of ready-made metallic plasters, and I would encourage you to experiment with different products in order to find the “sweet spot” for your desired effect. Another thing to add is that many of the pre-mixed metallic finishes are harder to polish because of the excessive amount of mica and aluminum grind that is required to achieve a metallic effect. It makes the surface more porous and less slick, which makes it more difficult to polish. This is why the tinted wax method, which gives an extra little glow, is preferred.

*Strap time is the elapsed time from the initial open time until it starts to set and develops a skin or film.