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How-To Info:
Keys to a Great Stucco Finish

“Stucco” finishes are probably the easiest and most popular method to finish exterior ICF walls.  They are fast and cost-effective to apply, and are readily available in an amazing array of colors, textures, and patterns.

Most “stucco” finishes applied to ICF walls are more correctly described as Exterior Insulation and Finish Systems (EIFS) or Textured Acrylic Finish Systems (TAFS).   This type of finish is already used on more than 30 percent of all commercial construction, and is becoming increasingly popular in residential work as well.

When applied to traditional frame construction, a “stucco” look requires extensive preparation with rigid foam boards or felt paper and lath.  With ICFs, though, the process is much simpler.  Because the exterior insulation is already in place, they are among the simplest to apply.

Most major manufacturers, including PermaCrete, Degussa, Dryvit, and GrailCoat, offer specially formulated products for ICFs.   While the application process is similar regardless of brand, methods do vary, so be sure to consult the manufacturer prior to starting work. 

ICF Builder recently visited a jobsite just south of Salt Lake City, Utah to see just how easy the process is.

Preparation

Workers from Elite Exteriors started by going over all the ICF walls with a large rasp.  This may be the most time-intensive part of the process.  “Rasping does take time,” says Ruben Bojorquez, head of the Elite Exteriors crew, “everything else is the same.”

The idea is to roughen the block and remove oxidation, dirt, and other small particles from the foam to ensure the base coat adheres firmly to the foam.   

Any large gouges or gaps should be filled with aerosol foam and trimmed flush.  Exterior framing—such as roof gables and porch columns—need to be covered with rigid foam board. 

Trim, usually built up from strips of EPS foam, is fastened into place with drywall screws and large nylon washers. Be careful that the fasteners and washers do not protrude past the surface of the foam.

Fiberglass mesh just large enough to cover the trimwork should be cut to size and fastened between the ICF wall and the trim at this stage.  Then, carefully mask all windows, doors, and vents prior to mixing up the mud.

Base Coat

Once the prep work is done, fill any large depressions—such as screws driven too deeply—with slivers of EPS or an approved aerosol spray foam.  “You need a flat surface for the finish coat,” explains Bojorquez, “If you applied the color coat directly over the ICF block, the gaps between blocks would still be visible.”

Methods for applying the base coat varies from manufacturer to manufacturer.  Some, such as GrailCoat, recommend mechanically fastening fiberglass mesh to the wall, then applying the base coat.  Most others apply the basecoat first, then trowel the mesh into place.  Mesh is required to give the finish tensile and flexural strength.

On this job, the base coat was troweled on first.  “The idea is to get the mesh into the middle of the base coat, so it has to go on fairly thick,” says Luis Bojorquez.

Bojorquez and his crew troweled the fiberglass mesh into the wet base immediately after finishing a section.  Special care is required around windows and doors to trowel in the pre-attached strips of mesh.  Sometimes, a second coat of base is required to get a smooth finish, but on this job, the block was in good shape and a single coat was all that was needed.

When the base coat is dry, inspect it for any imperfections and repair those imperfections before applying the finish.  Many contractors rasp the base coat to remove any lumps and ensure good adhesion between the base and color coats.  

If labor costs are high in your area, or if your projects are quite large, PermaCrete makes a spray-applied base coat that could save time and money.  It goes on in two steps, one under the mesh, and one over the top of it.

Finish Coat

Nearly all EIFS and TAF systems feature integral color, which means the final product never requires painting.  It also means that two or more colors have to be mixed and applied at most jobs.  The trim color is usually applied, textured, and allowed to dry before the crew applies the main color coat.  If the trim is a different color than the rest of the building, carefully mask the trim prior to applying the main color.

On the Salt Lake job, the crew working quickly, one team troweling on the acrylic color coat while another team followed just a few minutes behind to add texture. 

The Elite Exteriors crew carefully timed their work so that they were always on the shady side of the building.  Finishes applied in the sun dry faster, and probably need to be textured only once, while walls worked in the shade may need two passes for consistent texturing. But don’t be fooled into thinking faster is better.  The difference in dry times can affect the finish color, and shadows from scaffolding and planks have been known to leave permanent marks on walls worked in direct sun. 

Unlimited Possibilities

The creative uses of EIFS are not limited to a few simple textures or colors.  When applied by trained contractors, they can acquire the look of limestone block, antique brick, or even granite.

“This commercial building with a combination of real brick and limestone block would have several expansion joints between the dissimilar materials to seal," notes J.W. Mollohan, Central Regional Sales Manager for Dryvit Systems, Inc., referring to the Volvo dealership pictured above.  “But as these custom brick and limestone surfaces are in fact both a single cladding of Dryvit EIFS, expansion joints are unnecessary.   It's a single weather-tight exterior finish.”

Fossilcrete has gone a step further and made it possible to create cobblestone, flagstone, and even rustic log finishes on ICF structures.  The secret is a low slump mix that can be applied up to an inch and a half thick, and can then be stamped, stained, or even hand-carved to achieve the desired finish. 

Exterior finishes are the most visible part of any building, residential or commercial.  It’s only logical to choose a finish that will compliment the style, quality, and durability of your ICF project.

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