FAQs

Can I paint stucco to get the color I want?

 

Stucco can be painted. Portland cement-based paints are very compatible with stucco because they are made of the same material. These paints should be scrubbed into the surface and fully cured. Alternatively, you could consider a colored stucco finish. These finish coats are often made with white cement and pigments, providing the widest range of colors. Premixed materials are color matched from batch to batch and are most consistent.

 

Additionally, the fact that you are placing a finish coat with a nominal thickness of 1/8 inch instead of a paint layer usually gives more assurance of complete coverage. It is possible to paint with other types of paint, though these are usually not as long lasting as cement-based paint. Acrylic paints are long lasting and durable but change the permeability of the stucco (make it non-breathable) which in some climates may have adverse effects on the long-term performance of the system.

 

What is a fog coat?

 

A fog coat is a light application of a cement-based slurry, the same proportions of cement, lime (if any), and water as used in the original application minus the sand, used to even out a surface’s appearance. It is typically sprayed or rolled onto the surface, similar to painting with a cement-based paint. Fog coating improves the look of stucco without changing its ability to transmit moisture vapor.

 

Can stucco, portland cement plaster, be cleaned, and if so, what methods should be used?

 

Whether you have some type of atmospheric contamination, biological growth, or staining from another construction process, stucco can be cleaned effectively. Because it is important to choose an appropriate cleaning method based on what actually created the stain, there is no single best process for cleaning stucco surfaces. To clean a dirt-contaminated surface, the following advice is useful: 

 

  • Stucco can be cleaned with a garden hose.
     

  • Like concrete and masonry, stucco is porous. Cleaning methods are similar. It is recommended to wet the substrate starting from the bottom and working toward the top. Pre-wetting the surface helps the wall shed water, preventing dirty water from being drawn into dry pores. It also begins to loosen soil so that it can be rinsed away. A garden hose may be effective. Special fan-type sprayers are available for increased cleaning power. Whenever using water on a cement-based material like stucco, the substrate should have set and hardened. Water under pressure can etch the surface and at higher pressures can even cut through hardened stucco. To prevent this, the water spray should be moved over the surface uniformly.
     

  • Most dirt is removed fairly easily. Cleaning power is increased by doing one or more of the following: increasing water temperature, scrubbing with a brush, or using some type of chemical detergent.
     

  •  You should always test the method on an inconspicuous area to first demonstrate its effectiveness and to assure that it won’t damage the plaster.

 

Are plaster, stucco, and EIFS the same?

 

While there are several parts of the North America where stucco always has a strong presence, there appears to be a general renewed interest in portland cement plaster for building finishes everywhere. We are often asked if stucco and plaster are the same thing, and if plaster and exterior insulation finishing systems (EIFS) are the same thing.

 

The answer requires a thorough explanation. Plaster is the general term for material that is applied to a wall surface in a thin layer. Portland cement-based plaster is such a material that uses portland cement as the binder. It is sometimes called “traditional stucco.” Stucco is a somewhat colloquial term for portland cement plaster, and some people consider it to refer to an exterior, not interior, finish. Exterior insulation and finish system is sometimes (incorrectly) called “synthetic” stucco. To complicate matters, “plastering” is the verb that describes the action of applying any of these various materials to a wall surface.

 

Portland cement plaster is applied either by hand or machine to exterior and interior wall surfaces in two or three coats. It may be applied directly to a solid base such as masonry or concrete walls, or it can be applied to metal lath attached to frame construction, solid masonry, or concrete construction. Applied directly to concrete masonry, portland cement plaster provides a tough ½-inch thick facing that is integrally bonded to the masonry substrate. When applied to metal lath, three coats of plaster form a 7/8-inch total thickness. A vapor permeable, water-resistant building paper separates the plaster and lath from water-sensitive sheathing or framing. Portland cement plaster has high impact resistance and sheds water, but breathes, allowing water vapor to escape. It’s a proven system that works in all climates.

 

Exterior insulation finishing systems (EIFS) consist of a polymer-based laminate that is wet applied, usually in two coats, to rigid insulation board that is fastened to the wall with adhesive, mechanical fasteners, or both. Polymer based (PB) systems, sometimes known as thin coat, soft coat, or flexible finishes, are the most common. The basecoat for polymer based systems is usually 1/16-inch thick and finish coat thickness is typically no thicker than the maximum sand particle size in the finish coat.

Exterior insulation finishing systems experienced performance problems in the 1990s, including water leakage and low impact resistance. While the polymer based skin repels water very effectively, problems arise when moisture gets behind the skin—typically via window, door, or other penetrations—and is trapped inside the wall. Trapped moisture eventually rots insulation, sheathing, and wood framing. It also corrodes metal framing and metal attachments. There have been fewer problems with EIFS used over solid bases such as concrete or masonry because these substrates are very stable and are not subject to rot or corrosion.

 

Clearly, portland cement plaster should not be confused with the exterior insulation and finish systems. The systems may share similarities in application techniques or final appearance, but the systems perform differently in resisting weather, especially wet conditions.

 

What type of cements can be used to make stucco?

 

There are many types of hydraulic cements that can be used as a binder for stucco, or portland cement plaster. The cement standards used in the United States most often are from the American Society for Testing and Materials (ASTM).

 

A hydraulic cement is one that sets and hardens when mixed with water. Cement, along with sand and water, are the basic ingredients of a plaster mix. The following materials are candidate binders for stucco:

 

  • Portland Cement, ASTM C150
     

  • Blended Cement, ASTM C595
     

  • Hydraulic Cement, ASTM C1157
     

  • Masonry Cement, ASTM C91
     

  • Plastic Cement/Stucco Cement, ASTM C1328 (primarily available in the west and southwest United States

 

Hydrated limes, either ASTM C206 Finishing Hydrated Lime or C207 Hydrated Lime for Masonry Purposes, are also used with portland cement to provide workability. Hydrated lime may be used with blended cement or hydraulic cement, too, but is not used with masonry cement, mortar cement, plastic, or stucco cement. Those materials already contain workability agents and the addition of lime is neither necessary nor allowed. If used with those materials, lime poses potential problems such as reduced strength or durability.

 

White cements are also available for use in stucco. They are generally specified under C150, C91, or C1328. More on specifying white cement.

 

Sometimes they are blended with pigment in the factory or on the job to create colored mixes. Where white or colored plaster mixes are used, they often are applied only as the finish coat.

 

How long does stucco last on a building?

 

While the service life of stucco can’t be quantified as a specific number of years, properly applied and maintained portland cement plaster, or stucco, is as durable as any commonly used cladding material. Its hard surface resists abrasion and can take a lot of physical abuse. It stands up to all sorts of climates, from cold to hot and wet to dry. Many homes built in the early 1900s have had very little maintenance and remain in good shape today.