What Is Plaster?
Plaster is a building material, usually made from lime, gypsum, or cement that is mixed with water and applied to surfaces to create a smooth, slightly textured yet durable surface. Thicker than drywall, plaster creates a strong barrier for air and sound. It can also be moulded and cast to create trims and other decorative elements.
Lime Plaster vs. Gypsum Plaster
Lime plaster is probably what you think of when you think of traditional, original plaster. Lime plaster has been used for centuries and is made from a mixture of lime (crushed limestone or chalk), water, and sand. It’s incredibly durable and has the ability to “breathe”, which is great for avoiding moisture buildup and helping to maintain a healthy indoor air quality. Lime plaster was also a solid choice—literally—for older buildings, as its malleable quality allows it to shift and adapt to settling without cracking.
Where Lime plaster has its advantages in that it’s breathable and flexible, Gypsum plaster has the advantage of being fast to apply and dry. Gypsum plaster does not have the breathability of Lime plaster, so it should be used in dry spaces only. It creates a smooth, modern finish, and is usually more affordable than Lime plaster.
Types of Lime Plaster Finishes
Thanks to its health-conscious and environmentally friendly properties, lime plaster has regained popularity in the design and decorating world. Traditional lime plaster was and is used just like drywall: applied to coat and protect, but also in preparation to finish or decorate. However, there are several lime plaster varieties that are meant to act as the finish themselves, creating a different visual effect and texture. Here are the three most common Lime plaster finishes.
Venetian Plaster
Often associated with Italian architecture, Venetian plaster is a lime plaster made from slaked lime (calcium hydroxide) and marble dust or marble chips. The slaked lime creates a base for the plaster, while the marble dust and chips create a smooth yet textured surface with a slightly polished, luminous finish. Venetian plaster is applied in layers to create visual depth and movement. Installers have the ability to burnish (or polish) each layer to create more shine, so the overall finish is almost completely customizable. It’s also very durable and available in a variety of color finishes.
Marmorino
Marmorino is similar to Venetian plaster in that they both are made from lime and marble dust, but where Venetian plaster creates a more shiny, luxurious finish, Marmorino has a matte, natural stone-like finish. Marmorino can be applied in smooth or rough strokes to create the desired amount of texture, but each layer will remain low-sheen.
Tadelakt
The word “tadelakt” means “to rub in” or “massage” in Arabic. Tadelakt plaster originated in Morocco and is considered one of the oldest plaster finishes in the world. It gives walls a sumptuous, smooth texture with a good bit of sheen. It’s completely waterproof and has a high pH value which helps it resist bacteria and mold. Tadelakt is most commonly used in bathrooms and even in pools. It can also be used to create architectural details (that are, again, completely waterproof) like archways, shelves, and benches.
Lime Wash
Lime Wash isn't as much of a plaster as it is a paint, but it's a DIY-able, budget-friendly option worht mentioning. Lime wash is made from crushed burned limestone, natural pigments, and water and is zero-VOC. Due to the way light bounces off crystals that form when it cures, limewash seems to change color depending on the light.
Lime wash is a favorite among interior designers who want the look of plaster in a medium that’s easier to apply—it’s brushed on using quick cross sftrokes, as if you’re painting overlapping Xs. It shows where you stop and start, creating a mottled effect, so aim to do the whole wall in one shot. You can apply lime wash directly over surfaces like brick and stucco. On nonporous, painted surfaces or new drywall, apply a special lime prep coat. In high-traffic areas, a sealer is recommended. Portola Paints and JH Wall also offer a range of great lime wash options.
Types of Gypsum Plaster Finishes
Thanks to its affordability and ease of application, Gypsum plasters have become more attainable and common than others. Here's the one to know.
Roman Clay
Roman clay is similar to Venetian plaster but with a slightly more organic feel and soft, almost touchable effect. Roman Clay is an ultralow-VOC paste made from a gypsum plaster base that dries with a mottled finish and a stone-like texture. It gets applied in layers with a putty knife and sweeping motions, allowing the installer to vary the surface—smoother for more modern settings or textured stuccolike finishes in more traditional ones. (For lighter colors, it’s a good idea to use plastic joint knives rather than metal ones, which can sometimes leave gray marks on the surface.)
You can leave the final coat as is for a very slight sheen or finish with a special top coat for additional shine. (It is also recommended to seal it if using in a high-traffic area.) The walls should generally be prepared with a stain-blocking primer, although Roman clay can be applied directly over flat matte paint if it’s in good condition and not in a contrasting color.
