This reference sheet outlines the critical elements required to insure a durable, weather-proof stucco wall and includes a list of all the applicable building codes and
sources to obtain them.
MVP's stucco system dubbed "Walcrete" complies with or exceeds all applicable standards for Portland Cement Based Plaster
(stucco) as defined by the American Society for Testing and Materials. We're not trying to redefine stucco, we've simply taken the best of what's been proven to work and made
it better. In fact - ours are the only walls available in the valley with a life-time warranty option…
All exterior sheathing shall be covered with a two (2) layer water-resistant barrier (Tyvek, tarred felt etc.)
This is a necessary quality control measure - it is not for increased material performance. It is impossible to apply just one layer with zero error. For example, inside
corners where two walls meet are often pre-wrapped with Tyvek with too little slack and must be sliced with a razor in order to accommodate the metal lathe for a proper fit.
The second layer accounts for this and other situations which are impossible to avoid.
All walls shall be a minimum of 5/8" thick and shall be enhanced with elastics and structural fibers according to the ASTM C 926 using Portland cement Type CM.
The Walcrete method used by the MVP professionals employs the proven ASTM 3-coat stucco procedures, including a keyed scratch-coat, with a finished thickness that actually
measures an average of 7/8". In addition, MVP modifies the standard Portland-cement stucco with approved performance enhancing additives such as acrylic and glass
fibers to greatly increase the overall strength. Experience has shown us that a combination of full-thickness walls and modified plastic cement is actually needed to account
for the lenient tolerances of typical rough framing.
Expansion and control joints are to be installed at all wall-to-floor joints and at the corners of all window and door openings.
This is also a vital quality control measure. Some companies will shrug off this expensive and time-consuming step at the whim of an uninformed homeowner who considers them
unsightly. At Missouri Valley Plaster we refuse to compromise. Window openings are particularly vulnerable to moisture problems. Joints that allow for movement and yet remain
water-proof are critical elements.
All roof slopes that adjoin a wall shall be flashed properly with "kick-outs."
In addition to the step flashing required for composition roofs and/or the pans laid for metal or tile, a special flashing is required at the lower edge of all roofs that
adjoin a wall: This type of flashing is commonly referred to as a "kick-out" in the stucco industry, although this rule applies to all types of walls: stucco, stone and brick
as well as wood, metal and vinyl. Please note: If these are omitted, you can count on dry-rot to happen eventually and roofing contractors typically do not install these.
All windows, doors wall penetrations and terminations shall be sealed with a 100% polyurethane sealant with a minimum
5/16" X 5/16" bead which shall include a bond-breaking closed cell foam backing rod.
Polyurethane has the best performance available for this application, and when it comes to stopping leaks this is the most important step so demand the best. The backing rod
should also be demanded here, as it allow the sealant bead to flex and stretch more freely between the two critical surfaces as it was designed to do.
All ground-floor walls must overlap foundation stem-walls at a minimum of 1.5 inches.
This step would seem to be rather obvious, but you might be surprised if you take the time to investigate for yourself, just how often this gets "fudged" due to variations in
All walls are to be finished coated with an 100% elastomeric masonry finish coat at a minimum thickness of 7 mils.
Although this step is not required by code, MVP highly recommends this type of finish which minimizes the amount of moisture absorbed and released during the wet seasons. This
is referred to as wet/dry cycling and is experienced more frequently here than in many other parts of the country where stucco is commonly used.
The following are the ASTM International standards regarding the preparation and installation of cementious plaster (stucco).
C1063-03 Standard Specification for Installation of Lathing and Furring to Receive Interior and exterior Portland
This specification covers the minimum requirements for lathing and furring for the application of exterior and interior Portland cement-based plaster as in Specification C 926
C926-98a Standard Specification for Application of Portland Cement-Based Plaster
This specification covers the requirements for the application of full-thickness Portland cement-based plaster for exterior (stucco) and interior work. This specification also
sets forth tables for proportioning of various plaster mixes and plaster thickness.
C932-03 Standard Specification for Surface-Applied bonding Compounds for Exterior Plastering
This specification covers minimum requirements for exterior surface-applied bonding compounds for improving the adhesion of cementious material to concrete or other masonry
surfaces or any structurally sound surfaces. This specification also coers test methods for determining performance requirements and physical properties.