The Finish Line: Foam Shapes Revisited
August 3, 2010
One of the most popular design features of EIFS is its ability to mimic other materials. This includes being a stone, concrete or stucco look-alike. This feature of EIFS is widely used for many reasons, including its attractive appearance, light weight and low cost.
To enhance the appearance of many wall materials, foam shapes are often added. They are usually made of EIFS, by laminating the basecoat and finish onto an EPS core. This is done on the job site or in a factory or warehouse. Foam shapes can also be made by spraying plastic coatings onto EPS or onto polyisocyanurate foam. Extruded shapes are made in a factory by running an EPS core through a die and depositing the coatings on the surface of the foam core.
Photo 1 shows an extruded foam shape. Note the thickness of the coatings and that only the exposed surface are coated; the uncoated inside surfaces are in contact with the supporting wall, and adhesives are used on this exposed foam to bond the shape to the wall. Note also how crisp the edges are. This feature is especially popular with architects.
The advent of extruded foam shapes changes the way foam shapes can be created and installed, and this month’s column explores this special type of foam shape.
EXTRUDED FOAM SHAPES
Making foam shapes using an extrusion process goes back several decades and in the last half-dozen years has become more common. Several sources for this type of foam shape are available in the United States and Canada.
One way to think of an extruded foam shape is as a piece of lumber that is ready to trim to fit in place. The foam shapes come to the job site as long pieces (8 to 10 feet long, or more) in cartons and are usually trimmed at the job site to fit their allotted space.
Extruded foam shapes usually come as straight pieces, in a wide variety of stock and custom profiles, and can be trimmed and mitered to fit openings and corners and to do attractive, symmetrical joint layouts that coincide with other wall elements. Factory-curved extruded foam shapes are also available for use as arches and more.
Extruded foam shapes can also be obtained as precut kits. These are used as frames around openings, such a heads, jambs and sills, Photo 2 shows an example of this. The keystone and the capitals on the columns are also foam shapes. In this photo, the upper flat wall areas adjacent to the extruded foam shapes are stucco but the lower wall panels are also coated foam.
Extruded shapes are made by forcing a profiled piece of EPS through a die in an extrusion process. The EPS profiled solid base material is first cut to high tolerances using a computer control hotwire machine, and the coatings are then applied. In other words, it is not a laminated process.
The coatings are several times thicker than EIFS basecoat plus the finish. The coatings are also harder and thus are much more impact resistant than EIFS coatings. The color of the coatings is integral throughout the coating, and the coatings are reinforced with glass mesh. Extruded shapes come in precut (ready to trim) stock lengths, and also lengths cut-to-order at the factory.
The dimensions are highly accurate-much closer than can easily be done with a trowel or spraying. The edges are crisp (sharp) like real stone. This is markedly different than trowel or spray coatings which tend to “round out” corners.
Joints between ends of extruded shapes are done with a textured sealant-like grout that looks just like fine mortar joints.
Like EIFS foam shapes, extruded shapes are nonstructural, and are a type of decorative trim. Although they do supply some energy savings, unless they are used on large wall areas, they do not contribute much to saving energy.
Extruded foam shapes are sometimes called profiles, as most extruded foam shapes have some sort of curved (profiled) exposed surface. Extruded foam shape manufacturers offer hundreds of readily available stock profiles, many of which are based on the common stone shapes used in buildings that have a classical architectural appearance, such as churches, government buildings, museums, and so on.
Extruded foam shapes with custom profiles are easy to make. The designer simply provides the manufacturer with a dimensioned drawing that shows the contours of the exposed surfaces. The manufacturer then works out the profile of the foam core, taking into account the thickness of the coatings.
Sizes of extruded foam shapes can range from small flat pieces the size of a 2x4 (used for bands and trims) to large pieces that would fit an extrusion die several feet in diameter.
Shapes made with EIFS look like they are made of EIFS when you get close. The extruded types of shapes look just like stone when viewed up close.
Extruded shapes are also available in a slick-smooth surface that can be painted at the job site. Thus, they can look like wood moldings.
Extruded shapes can be made into thick, flat slabs. When bonded to a supporting wall in a stack-like pattern, they look like cut stone-especially with their fine mortar-like joints, as shown in Photo 3.
CODE COMPLIANT SUPPORTING WALL
Extruded shapes are applied over a code-compliant, waterproof supporting wall. Thus, extruded shapes rely on the supporting wall to keep the water out of the wall system. This approach is different conceptually from EIFS walls, where often the EIFS foam shapes are integrated into the EIFS and become part of the code-required weather resistive barrier-the EIFS itself.
This also means that extruded shapes can be used over a variety of wall surfaces, including stucco, brick, block, concrete and EIFS.
ATTACHING EXTRUDED SHAPES
Extruded shapes are attached with adhesive. Different adhesives are used for different wall surfaces. For common wall surfaces, like stucco, concrete and block, a Portland cement-based adhesive, very similar to that used to attach EIFS foam boards to their substrate, is used. The adhesive is applied by using a vertical notched trowel pattern.
The top and side edges of extruded foam shapes are sealed with the same synthetic grout used where the ends of the foam shapes abut each other. The bottom edge of extruded foam shapes is left open. This allows water, if it does somehow get behind the foam shape, to drain out.
If extruded shapes are used on stucco, they are normally attached to the brown coat. This leaves the surrounding exposed area-without shapes-bare. To finish-off the adjacent wall areas, extruded shape manufacturers offer trowel grade coating to be used as the finish coat for the stucco, so the shapes and main wall will match. Or some other type of final finish coat can be used, such as a textured coating.
For large shapes or inverted positions, clips are available to hold the shape in place while the adhesive sets. The clips are bonded to the supporting wall and the foam shape is then impaled onto the clip. This surface-attached system therefore avoids any need to penetrate the waterproof envelope with screws or fasteners.
To ensure an exact fit, extruded shapes can be mitered to produce crisp corner joints. They can be cut down with a circular saw at the job site, or pre-mitered L-shaped corner assemblies are available from the factory.
The extruded foam shapes themselves are cost competitive with EIFS-based shapes. However, the fieldwork is considerably reduced since the shapes come ready to install.
Installing extruded shapes is somewhat like doing carpentry. In other words, refined plastering skills are not critical but likely would be used anyway for the inevitable touching up, fitting and finishing of the shapes and the adjacent wall, such as when stucco is used as the supporting wall. Plastering skills are also used when applying the attachment adhesive to the unexposed surfaces of the shape to bond it to the wall.
A NICE ADDITION
Since extruded foam shapes are normally used as decorative trim, they offer a nice addition to a wall that is otherwise all one material. A good example is using extruded shapes next to a completely different material, and giving the appearance of fine cut stone at a fraction of the weight and cost. W&C