These finishes are thin, lightweight, and tough. Although the thinner exterior insulation and finish system materials can be direct-applied, moisture management then becomes even more critical.
If an EIFS coating is chosen, openings windows, doors, etc. Stucco is known to be a weather resistant building finish, but it is part of a system. In order for the wall to resist water penetration effectively, the system must be properly designed and detailed, then built according to plans.
The main purpose of building paper is to keep water from contacting the substrate and structural support members—very commonly sheathing like plywood or oriented strand board OSB and wood or metal studs—so that these materials stay dry. Metal can rust and wood can rot. Minimizing the changes in moisture minimizes the stresses that might be placed on plaster from behind.
In addition to structural considerations, excess moisture within a wall creates a potential for mold or mildew inside buildings.
Building paper prevents moisture-related problems in stucco walls. During construction, paper can be damaged. Paper should be lapped like siding, meaning that upper layers are placed over lower layers. This facilitates drainage toward the outside. Where the edges of paper-backed lath meet, connections should be lath-to-lath and paper-to-paper. This specification differentiates weather resistive Kraft papers by types, grades, and styles.
Grade D is a water-vapor permeable paper. Grade D paper with a water resistance of 60 minutes or more works well for stucco applications, and is often preferred to Grade D paper having the minimum minute resistance required by UU-Ba. Some specifiers are turning to house wraps for stucco underlayment.
While these materials may be more rugged than paper—and therefore less prone to damage during installation—a single layer is still not adequate according to many industry professionals. At best, a hybrid system, with the house wrap closest to the sheathing and covered with the paper, seems to be an acceptable alternative.
For best performance, the temperature of newly applied stucco should be maintained at a minimum of 40 degrees Fahrenheit. In many cases, this can be achieved by heating the structure and covering the exterior surfaces.
As temperatures drop lower, plaster ingredients can be heated before mixing the stucco. Both water and sand have enough mass to hold heat well, though it is often easiest to heat water. However, either one, or both, materials can be heated to give plaster added protection in cold weather.
To prevent problems like flash set of plaster, fresh mixtures should not be heated to temperatures exceeding degrees Fahrenheit. Most importantly, the stucco should not be allowed to freeze during the first 48 hours after placement. Excess water in the fresh stucco mixture expands as it freezes, thereby compromising the strength and durability of the finished product.
Sand can be heated over fire in a pipe, and water can be heated in metal drums. Portland cement-based plaster, commonly called stucco, has long been and continues to be a popular choice for finishes on buildings.
It allows for a wide expression of aesthetics, is a cost effective finish, is durable in all types of climates especially wet ones , and offers fire resistance. Fire resistance is typically classified by a fire rating, but what kind of fire rating does plaster provide?
The type of member—wall, partition, ceiling, or other, and member classification load bearing LB or non-load bearing NLB also influences the rating. Designers, specifiers, building code officials, contractors, and general public are the intended audience. For example, a typical residential application might be a three-coat system of plaster over 2-byinch wood studs using metal lath attached to the studs, either with or without a layer of sheathing, like plywood.
On the interior side would be a layer of gypsum board. The detail for a system made with these components is assigned a one-hour fire rating based on Uniform Building Code information.
Association of the Wall and Ceiling Industry. Its mission is to be an active, unbiased source of information and education to support the wall and ceiling industry. The association is is located at W. 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. 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. 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. Stucco finishes are popular across North America. They lend themselves to nearly every type of architectural style. Certain styles can be enhanced with built-out shapes, such as cornices, quoins, or decorative tiles. An expanded polystyrene foam section is bonded to the basecoat with a material made specifically for that purpose. Some people use an EIFS basecoat material as the glue.
This is attached to a portland cement plaster base, typically the brown and scratch coats, before final finishing. The shape is then finished like EIFS: covered with a basecoat and mesh, then a finish coat. The shapes must be securely attached to the wall. The basecoat material acts like a glue to hold the backside, then also embeds the mesh that goes over the top of the shape. As the foam itself has no structural strength, the mesh and basecoat together provide an impact-resistant surface to the shape, protecting it in service.
The Stucco Resource Guide from the Northwest Wall and Ceiling Bureau is one source of design and installation information for ornamental plaster shapes. It provides sample details of walls sections for creating architectural details on stucco walls.
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. Prewetting 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. To clean stains other than simple soiled surfaces refer to the reference documents for additional recommendations. The Technical Service Information Bureau TSIB is a trade group in southern California serving the needs of the wall and ceiling industry regarding lath, plaster, and drywall.
They have an excellent online resource depicting plaster textures. The 30 textures shown on the site are accompanied by suggested application procedures. This gives material ingredient advice, where appropriate, and methods of applying or finishing the plaster to achieve specific appearances.
For instance, the sand float finishes are described as light, medium, or heavy, and the grain size of aggregate helps achieve the desired texture. All of the textures can be made with gray or white cement, with or without pigments.
It is important to be aware of regional differences in naming finishes. Certain parts of the country may call a specific texture by another name than described by the TSIB.
That is why this site is so beneficial: it provides visual depictions of each finish to prevent misinterpretations that might occur with verbal descriptions. Joshua Gilman, P. Cement Industry Annual Yearbook U. Stucco Frequently Asked Questions.
Expand all Collapse all. Rigid sheathing materials are commonly used behind plaster finishes. They are directly attached to support studs then covered with building paper or other weather resistant barrier WRB. Metal lath attached over the sheathing and into the supports carries the plaster. The weather resistant barrier is intended to resist water penetration, so the sheathing is protected from moisture.
That means that many materials are suitable for this application, but the common ones remain plywood, oriented strand board OSB , cement board, and exterior grade gypsum sheathing.
In the early s, basic research on stucco systems looked at the then-current practice of using board lumber not panels as sheathing. These were commonly 6- to 8-inch wide boards attached to support studs at 45 degree angles. During that period, diagonal placement of the boards transitioned to horizontal placement, and was followed by a move to 4-byfoot panels.
Both wood and metal lath were common substrates for plaster at least through the teen years of the s. It should also be noted that it is possible to place stucco over open frame construction.
TIP: trim accessories can be cut to size using metal snips but are often very sharp, so always wear gloves when working with these materials. NOTE: galvanized nails or staples should be used every 6 inches both vertically and horizontally and should penetrate the studs a minimum of 1 inch. Step 5 Place control joints to create wall panels no larger than square feet. Keep the panels as square as possible. Step 6 Place expansion joints anywhere there exists wall expansion joints.
Step 7 Install corner trim on all outside edges to protect the exposed stucco and to provide clean finished lines. Step 8 Mix the base coat stucco to a workable consistency. Put up sheathing materials. You may stucco over any rigid material attached to your support studs. The most common surfaces for stucco are plywood, oriented strand board OSB , cement board, and exterior grade gypsum sheathing.
It is possible to stucco over an open frame, but this results in a less even and less structurally secure wall. If you plan to go this route, drive nails halfway into the studs, spaced out vertically in inch cm intervals. String line wire horizontally along the protruding nails. Cover the plywood with building paper and come back over that with a dimple screen or other rain screen. You may also use a draining house wrap such as Tyvek drainwrap.
Most building codes require at least 2 layers of "Grade D" building paper or an equivalent water-resistant barrier. You may also use 15 lb per square foot roofing felt 6. While not required by most codes, an air gap between the 2 layers is highly recommended to prevent wall rot. A 3D plastic drainage mat between the 2 barriers is one way to accomplish this. Install weep screeds and casing bead. Install casing bead as a plaster stop at the corners of doors and windows.
Attach metal lath. Selecting the correct lath and installing it properly is one of the more difficult parts of this project. Consulting a local contractor is recommended.
In most cases, you should nail or staple the lath to the studs not the sheathing at no less than 7-inch 18 cm intervals. Otherwise, your nails or staples will rust and pull loose. In all exterior stucco applications, you must use G hot-dipped galvanized lath. Install control joints. To reduce cracking, divide the wall into rectangular panels using control joints, spacing them no more than 18 ft 5. Also install control joints wherever 2 dissimilar walls meet.
Make the panels as close to square as possible, and no larger than ft 2 13 m 2. Mix the scratch coat. If you are using Type I Portland cement instead of plastic cement, you'll need to add your own hydrated lime; count the final cement and lime mixture as the "1 part cement.
Make sure to use cool water when mixing your stucco, especially if your hose has been sitting in the sun. If the water is hot or warm, it will cause your stucco to dry too quickly. The aggregate in the cement should be clean and well graded.
Trowel the scratch coat into the lath. You may find it easier to use a hawk for some portions of the application. Score the scratch coat lightly. The first coat is called the "scratch coat" because of the shallow, horizontal lines scored into it by a notched trowel. This will ensure a good bond with the next coat.
Wet cure the scratch coat. When stuccoing over stud construction, the thick scratch coat must be allowed to cure for 48 hours. During this time, it is critical to protect the stucco from drying out. Protect the wall with a windscreen or sunshade if necessary. You can also use a rotating lawn sprinkler to keep the stucco damp. Keep the sprinkler turned down to a low setting and pull it away from the house enough so that it keeps the surface damp without soaking it.
Mix and apply the brown coat. Mix another batch using 1 part cement and 3 to 5 parts sand. Wet cure for at least 7 days. Wet cure as you did the scratch coat, but this time allow at least 7 days. The first 48 hours are the most important, but you should continue to mist or fog it for this whole period, whenever it looks like it's about to dry. Cover with the finish coat.
You may purchase a finish which already contains pigment, or trowel on a plain finish and paint over it once it has had at least a week to cure. Colored stucco finishes work best in pastel shades. If the finish is colored, wetting the surface during floating may cause mottling. A fog coat may make the color more even.
Many decorative textures are possible when applying this final layer. Judge the appearance from at least 30 feet 9m back before settling on a look.
Method 2.
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