Stucco Color & Texture/Q and A’s
Stucco, the common term for portland cement plaster, is a popular exterior finish for buildings. It provides an economical hard surface that is rot, rust, and fire resistant, which can be colored and finished in a wide range of textures to adorn any architectural style.
Stucco for Building Color and Texture
Traditional portland cement plaster is an extremely versatile, time-tested exterior finish, frequently referred to as “stucco.” It consists of portland cement-based materials and sand, mixed with water to form a workable plaster. The key ingredient, portland cement—the same material that is the basis for the hardened properties of concrete used to build super-highways, bridges, and skyscrapers—provides strength, durability, and toughness in portland cement plaster.
As an exterior cladding, stucco is cost-effective and tough enough to resist damage. That inherent toughness is beautifully complemented by the variety of colors and textures available. Color is determined by selecting cement and aggregate color, and quite often modified by adding mineral oxide pigments to the plaster mix. White portland cement makes it possible to achieve the widest range of colors for the stucco finish, including bright white. Factory prepared finish coat products, which are available in many areas, often contain white cement. These pre-pigmented, packaged cements offer ease of use for achieving the desired stucco color, but it’s also possible to add pre weighed mineral oxide pigments to the finish coat stucco during mixing.
Texture gives substance and character to the plaster surface. It can be used to provide highlights, depth, continuity, segmentation, and even achieve the look of a completely different construction material such as wood timbers, brick, or stone masonry construction. Texture is achieved by selecting aggregate size, controlling finish mix consistency, and using special treatment techniques during and after application of the finish coat plaster.
Color and texture add dimensions to your projects. To confirm the suitability of a desired color and texture, be sure to ask your plasterer to provide a sample panel for evaluation prior to starting work.
Q n A:
Can stucco (portland cement plaster) be applied directly over painted brick?
This is a common question that often arises when people are rehabbing or updating older construction. Plaster is a cost effective finish, relatively easily installed, that improves the appearance and creates a water resistant wall surface.
A painted surface will not typically absorb water and, as such, is a substrate to which stucco will not readily bond—at least not uniformly. There are two basic alternatives to covering a painted brick surface with a new coating of portland cement plaster.
Sand blast or water blast to remove the paint in its entirety, then direct apply a two coat system. It is essential to have a surface that is uniformly absorptive to accept the plaster coating. In addition, it may be beneficial to use a bonding agent or dash bond coat with this approach.
Attach paper backed lath or install appropriate building paper between wall and attached metal lath to provide a moisture barrier and to serve as a bond breaker. Apply traditional three coat stucco to metal lath and accessories. In this approach, the idea is to treat the plaster like a sheathed system, using metal lath to support the plaster on the substrate, while completely isolating the plaster layer from the backup with building paper. This prevents a partial bonding situation, which could set up undesirable stresses in the plaster and lead to cracking.
Please call a professional if you have never used this kind of equipment before.
What is the correct weight of Portland cement plaster?
This question comes up in both new and repair construction. Designers need to know how much weight the stucco adds to the wall so that they can be sure the structural system provides adequate support.
In new construction, the structural system usually has more than enough strength to support installed plaster. In buildings that are being updated or retrofitted, however, stucco may be placed over existing construction. Especially in this case, designers should verify that the added weight of the new stucco will not exceed the structure’s ability to support it along with whatever other materials remain in place.
Concrete or masonry walls generally have sufficient structural strength to support the additional weight. In wood frame construction, support members (studs) should be checked to ensure they can carry the extra load.
On wood framing, three coat plaster is typically installed over metal lath to a 7/8 inch nominal thickness. A typical plaster mixture weighs about 142 pounds per cubic foot, roughly the same as mortar, and this amount of material would cover about 13.7 square feet at 7/8 inch thick. The metal lath may add a small additional amount of weight, so the end result is that three coat stucco weighs about 10.4 pounds per square foot (psf) installed.