{"id":32441,"date":"2017-10-23T09:00:37","date_gmt":"2017-10-23T09:00:37","guid":{"rendered":"http:\/\/architizer.wpengine.com\/?p=32441"},"modified":"2022-01-14T09:24:20","modified_gmt":"2022-01-14T14:24:20","slug":"how-to-specify-stucco","status":"publish","type":"post","link":"https:\/\/staging.arc.ht\/blog\/practice\/details\/how-to-specify-stucco\/","title":{"rendered":"How to Specify: Stucco"},"content":{"rendered":"

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Stucco is a funny material. On one extreme, it\u2019s the stuff of pure material abstraction. When finished at its smoothest and whitest, it\u2019s the face of modernist simplicity. It\u2019s barely there. On the other extreme, it\u2019s intensely tactile. Rough and grainy, it calls to mind the windblasted deserts of the American Southwest. It\u2019s physical; elemental, even. And it can be a lot of stuff in between.<\/p>\n

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Le Corbusier\u2019s Ville Savoye has a white stucco exterior; image via Medium<\/a>.<\/i><\/p>\n

One of the major appeals of stucco is its versatility. It can take any color and adapt to any shape, from flat boxes to doubly curved fantasias.<\/p>\n

What makes stucco a little tricky is that it is mixed and installed on-site. It\u2019s not produced in a factory under carefully controlled settings; it\u2019s made in the field where anything can happen, and architects have to rely on trusted contractors. Contractors will have their own preferences and experience working with various mixes and finishes that depend on local conditions and availability.<\/p>\n

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\u00a9 Diego Opazo<\/p>\n\t<\/div>\n\n

Casa Balint<\/a> designed by Fran Silvestre Arquitectos<\/a><\/i><\/p>\n

We talked to Mark Fowler, Executive Director of the Stucco Manufacturers Association (SMA), about what architects need to know when specifying stucco.<\/p>\n

His advice was to \u201cstay with established standards. Many architects make the mistake to add items that are either not appropriate or incompatible, which adds costs by wasting time on RFIs or worse, systems that fail.\u201d Contractors and manufacturers can talk you through what is necessary for the specific approach you are taking.<\/p>\n

Fowler\u2019s advice was clear: \u201cListen to the pros and find someone you can trust. Stucco has more variables than almost any other assembly.\u201d<\/p>\n

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Maggie\u2019s West London Centre by Rogers Stirk Harbour + Partners<\/a>; image via ArchDaily<\/a><\/i><\/p>\n

So what is stucco, anyway? Historically, it was the same material as plaster. In some languages, there is still only one word that covers both materials. Today, plaster is mainly used inside, and stucco out.<\/p>\n

Stucco siding is a mixture of Portland cement, sand and water. It\u2019s not radically different from concrete. It is applied in a combination of layers with a standard base coat and a refined finish coat. Finish coats can include small pebbles to add texture or be made with acrylic for more color options. Additional coatings can be added to protect or restore the surface.<\/p>\n

We\u2019re going to break down the basics below, but Fowler advised reaching out to the SMA or an experienced contractor for more information on what would be appropriate for your area and installation. \u201cThe SMA is here to help architects,\u201d he said. \u201cSpecifying an SMA-registered contractor is a good start to a quality stucco job.\u201d Although stucco can be used anywhere, its installation can be a specialty skill, and it is best to get someone who knows what they\u2019re doing.<\/p>\n

Contractors will be used to working with certain mixtures and products, so if you are tied to a certain finish or appearance, make sure that your contractor is experienced with it. If you are flexible, follow an experienced contractor\u2019s lead. Fowler put it this way:<\/p>\n

\u201cI always tell architects to think of a race car driver. If a driver has won many races with a Porsche, why would you force him to drive the next race with a Ferrari? He does not know or understand this car. The best chance to win is let him drive what he knows. Of course, it must be ASTM- or ICC-approved. Do not let them make their car.\u201d<\/p>\n

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VitraHaus<\/a> by Herzog & de Meuron<\/a><\/i><\/p>\n

Read on to get a good base:<\/p>\n

One, Two or Three Coats?<\/h2>\n

Stucco can be applied in one, two or three coats. Which one you choose largely depends on your wall construction, but one- and three-coat systems are the most common.<\/p>\n

One Coat<\/b><\/p>\n

One of the main trade-offs to one-coat assemblies is that one-coat stucco systems are proprietary. Special products must be used, and installation must follow the manufacturers\u2019 instructions. Two- and three-coat stucco systems are generic assemblies, meaning that contractors and designers can use, mix and apply their own products how they like.<\/span><\/p>\n

One-coat stucco has been applied over rigid foam backing for decades, but this is not exactly the same as EIFS (Exterior Insulation and Finish System), a product that is popular and will be discussed in another article.<\/p>\n

Two Coats<\/b><\/p>\n

Two-coat assemblies are applied on masonry or concrete walls. This application is most common in Europe, where it has been used for centuries. The stucco should be applied directly to the masonry surface without any vapor barrier in between. \u201cToday, too many think we need to add a building paper between masonry and stucco. It generally turns out a disaster,\u201d Fowler said.<\/p>\n

The two coats are the base coat that adheres to the masonry wall and the finish coat that faces the exterior.<\/p>\n

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Two-coat assembly diagram; image via <\/i>International Masonry Institute<\/i><\/a><\/p>\n

Hairline cracks will generally develop at some point over the lifetime of a two-coat stucco system, but because of excess calcium and hydroxide in the mixture, these cracks can self-heal. Water mixes with those chemicals to patch minor flaws. Even with the threat of small cracks, the water that could pass through is not enough to threaten the concrete base.<\/p>\n

The thickness of two-coat assemblies can vary. According to the SMA:<\/p>\n

\u201cThe thickness of the cement depends greatly on the substrate\u2019s porosity and flatness. Thickness of application can range from an 1\/8-inch skim coat to a 5\/8-inch-thick cement base. Any applications exceeding 5\/8 inch would generally require a lath be installed to carrier the weight.\u201d<\/p>\n

A lath is a wood or metal mesh backing that adds support to stucco.<\/p>\n

The SMA added the following tips:<\/p>\n