Is there a standardized methodoly for attaching EPS foam trims to an exterior 3 coat cement plaster building?
I have searched a number of places, including this forum, and haven’t found much. Something more definitive would be helpful.
usually there are embeds that are attached to the metal mesh behind the cement plaster. They are either welded to the stud backup or to some other piece of structure; the plaster is done over and around them. you should have a neoprene or other non-staining, resilient spacer/washer at each embed to keep the plaster from adhering to and cracking with the building movement. a good plasterer will know how to do that… a bad one will really make a mess of it.
Nathan,
The following is the recommendations from the Northwest Wall and Ceiling Bureau (NWCB).
“EPS foam shapes (ornamental) are attached to the stucco base coat with EIFS base coat material or other material manufactured specifically for this purpose.”
“The EIFS foam shapes are finished as in a standard EIFS assembly (reinforcing mesh, basecoat, and acrylic finish coat).”
“Reinforcing mesh from EPS foam shape should extend a minimum of 6 inches onto stucco basecoat. EIFS basecoat should be applied over extended mesh and feathered out onto stucco base coat. Stucco base coat and EPS foam shape finished with the acrylic finish coat.”
The following is an excerpt from my most recent portland cement plaster (stucco) spec that utilized preformed EPS foam shapes.
2.4 PREFORMED EPS FOAM SHAPES
A. Molded-Polystyrene Board Insulation (EPS): ASTM C 578, of type and density indicated below, with maximum flame-spread and smoke-developed indexes of 75 and 450, respectively:
- Type I, 0.90 lb/cu. ft.
B. Cut aesthetic reveals in outside face of insulation with high-speed router and bit configured to produce grooves, rabbets, and other features that comply with profiles and locations indicated. Do not reduce insulation thickness at aesthetic reveals to less than 3/4 inch.
C. Reinforcing Mesh: Balanced, alkali-resistant, open-weave glass-fiber mesh, made from continuous multiend strands with retained mesh tensile strength of not less than 120 lbf/in. per EIMA 105.01, complying with ASTM D 578 and the following requirements for minimum weight: - Standard-Impact Reinforcing Mesh: Not less than 4.0 oz./sq. yd.
D. Waterproof Adhesive/Base-Coat Materials: EIFS manufacturer’s standard waterproof mixture complying with one of the following requirements for material composition and method of combining materials: - Job-mixed formulation of portland cement complying with ASTM C 150, Type I, white or natural color; and manufacturer’s standard polymer-emulsion adhesive designed for use indicated.
- Job-combined formulation of manufacturer’s standard polymer-emulsion adhesive and manufacturer’s standard dry mix containing portland cement.
E. Primer: EIFS manufacturer’s standard factory-mixed elastomeric-polymer primer for preparing base-coat surface for application of finish coat.
F. Finish-Coat Materials: EIFS manufacturer’s standard acrylic-based coating with enhanced mildew resistance complying with the following requirements for material composition and method of combining materials: - Factory-mixed formulation of polymer-emulsion binder, colorfast mineral pigments, sound stone particles, and fillers.
- Sealer: Manufacturer’s waterproof, clear acrylic-based sealer for protecting finish coat.
3.7 PREFORMED EPS FOAM SHAPES
A. Shapes: Adhesively attach shapes to substrate in compliance with ASTM C 1397, EIFS manufacturer’s written requirements, and the following:
- Apply adhesive to insulation by notched-trowel method in a manner that results in coating the entire surface of basecoat with adhesive once insulation is adhered to basecoat unless EIFS manufacturer’s written instructions specify using primer/sealer with ribbon-and-dab method. Apply adhesive to a thickness of not less than 1/4 inch for factory mixed and not less than 3/8 inch for field mixed, measured from surface of insulation before placement.
- Abut shapes tightly at joints to produce flush, continuously even surfaces without gaps or raised edges between boards. If gaps greater than 1/16 inch occur, fill with insulation cut to fit gaps exactly; insert insulation without using adhesive or other material.
- Cut insulation to fit openings, corners, and projections precisely and to produce edges and shapes complying with details indicated.
- Rasp or sand flush entire surface of insulation to remove irregularities projecting more than 1/16 inch from surface of insulation and to remove yellowed areas due to sun exposure; do not create depressions deeper than 1/16 inch.
B. Base Coat: Apply to exposed surfaces of insulation shapes in minimum thickness recommended in writing by EIFS manufacturer, but not less than 1/16-inch dry-coat thickness.
C. Reinforcing Mesh: Embed in wet base coat to produce wrinkle-free installation with mesh continuous at corners and overlapped not less than 2-1/2 inches or otherwise treated at joints to comply with ASTM C 1397 and EIFS manufacturer’s written requirements. Do not lap reinforcing mesh within 8 inches of corners. Completely embed mesh, applying additional base-coat material if necessary, so reinforcing-mesh color and pattern are not visible.
D. Extend reinforcing mesh minimum 6 inches onto stucco base coat. Apply EIFS basecoat over extended mesh and feather out onto stucco base coat.
E. Finish Coat: Apply over dry base coat, maintaining a wet edge at all times for uniform appearance, in thickness required by EIFS manufacturer to produce a uniform finish of color and texture matching approved sample and free of cold joints, shadow lines, and texture variations.
Wayne, thanks very much. Was able to track down a 3rd edition of the NWCB reference manual. I also called them this morning, and their 4th edition is nearing completion soon.
You have a very robust spec there!
Regards,
NW
Nathan - make sure you specify silicone sealant, like Dow 790 applied around the perimeter of all foam profiles - this is extremely important to keep moisture from getting behind the foam.
Wayne, I’m a little confused by your post, when is the foam profile installed in relation to the stucco? We specify a foamboard adhesive, like PL300 manufactured by OSI for adhering the foam profile to the scratch coat, along with mechanical fasteners that typically are supplied by the profile manufacturer.
Jerome,
Foam shape is applied to the portland cement base coat (brown/scratch coats) followed by an acrylic finish coat over both foam shape base coat and portland cement plaster base coat.
Installation method uses EIFS base coat material for adhesive or other material made specifically for this purpose.
Wayne
Wayne,
Attaching the foam shape (which by the way comes prewrapped in our area SO Cal), is only one of the issue.
I am concerned with details showing foam projections of more than 4 inches simply glued to the brown coat - I have seen 14 inches on a project this year.
We advise our clients, and we specify it as design/build, that anything projecting more than 4 inches must have an independent support that can safely carry the same loads as other exterior wall elements. This assumes that a steel angle or other structural support will be embedded in the foam.
Gerard,
The foam shapes I have used were under the 4" rule of thumb. NWCB does not discuss deeper projections nor mechanical attachment.
For projections greater than 4" we would detail the bulk of the projection profile with light gage steel framing or wood framing.
The custom foam shapes we detailed did not come prewrapped or back-wrapped. Please forward a link to the SO Cal supplier(s) that furnishes prewrapped or back-wrapped shapes (stock or othwersise. e-mail wyancey@weberthompson.com
Thanks
Wayne
Here is one: http://www.foamvisionsinc.com/
Thanks Nathan.