Friday, August 28, 2009

EIFS and Synthetic Stucco

The terms EIFS and synthetic stucco are synonymous to many. Why discuss a synthetic coating in a blog about Real Finishes? EIFS systems have come to occupy a significant percentage of exterior cladding systems specified by design/build professionals in the United States. It is important to understand the contemporary architectural approach in exterior building cladding design utilizing EIFS to effectively articulate how traditional finish systems perform and compare.

It should be noted that synthetic stucco is only the finish component of an External Insulated Finish System or EIFS cladding and can be used in certain other non-EIFS applications. There are some variations in design; nevertheless, EIFS systems typically are comprised of the following components over an acceptable substrate:
  1. A vapour/moisture barrier. This traditionally has been a commercial vinyl sheathing or felt paper. Some EIFS manufacturers are now producing a liquid barrier applied like wet paint that performs this function within hours of application.
  2. An insulation board typically made of expanded polystyrene. Boards are usually affixed with an acrylic fortified cementitious paste by notched trowel. The lines of the paste are usually vertical to allow water to drain downward should it get behind the foam.
  3. Another typically acrylic fortified cementitious paste is applied over the entire surface of the foam and a plastic mesh is embedded to give the coating strength.
  4. Finally an integrally colored synthetic stucco is applied in a thin layer as a finish coat.
  5. Many EIFS systems include a track running along the bottom with a weep screed (holes) that allow any water that were to get behind the coating to quickly pass out of the system.
Until the mid-20th century temperature and air quality in interiors were achieved by working in harmony with the surrounding environment. Orientation of the doors and windows, shading from trees and bushes, eaves and attic design were critical elements of construction. Inevitably moisture would make its way from outside and be generated from normal activities within the home. It was necessary to have breathable building systems that allowed moisture to find its way out.

With the industrialization that accompanied two world wars and the development of mechanical HVAC systems, building design changed rapidly. Now a building of virtually any shape could be placed on a cleared piece of land irrespective of shade or orientation. Electrically powered HVAC systems would guranantee a comfortable environment. The following two factors became of primary importance in modern building cladding design.

Most critical was waterproofing the building envelope. A cladding system that could effectively stop the passage of water and significantly restrict vapour flow was now favored over traditional coatings that "breathed", absorbing and releasing water and vapour. Advancements in synthetic material production resulted in highly effective water barriers for the market. HVAC would now regulate humidity and temperature.

A secondary concern was insulation. Mechanical systems were now the primary means to control temperature and they consumed electricity. Initially fossil fuel power plants could provide cheap electricity to meet the limited demand. But as more buildings were constructed with HVAC systems energy prices rose sharply.

EIFS, in continuous use since the 1960's, does a good job in addressing these two concerns of modern building design. When properly installed it provides a watertight wall system. The foam panels have significant insulative value and the membranes of vinyl sheathing or liquid applied coatings provide good barriers to the passage of vapour that would otherwise result in an adverse loss or gain of heat depending on the season.

Significantly because of these energy saving properties of EIFS it has been classified by some as a "green" building system. EIFS manufacturers have worked hard to reduce Volatile Organic Compound (VOC) content of their synthetic components, have localized manufacturing and use as much recycled content as possible to assure their products can contribute to Leadership in Energy and Environmental Design (LEED) accreditation for certain projects.

What makes a coating or building system "green" however? Energy savings? Sustainability of resources? Biodegradibility of materials? Environmental impact? Effects on indoor air quality and human health? That is the subject of a heated debate in the industry and will be repeatedly addressed in this series of articles as we compare coatings and systems.

Contributed by Patrick Webb

Thursday, August 27, 2009

Lime and Limestone

Lime is perhaps the most prized and exceedingly versatile building material of the modern world. Early civilizations such as the Egyptians, Greeks and Romans used lime extensively. Many of their works in lime have survived to the present day testifying to its durability and intrinsic beauty (an important factor in sustainability: we tend to preserve what is well designed and are eager to tear down what is not).

Lime is utilized to produce plasters, stucco coatings, paints, mortars and cements. It can be modified to form large, imposing structures such as the Hoover Dam, footings for the Golden Gate Bridge or the space shuttle blast pad at Cape Canaveral. Alternatively it can be prepared as a sophisticated finish material such as Venetian plaster applied with a trowel or as a paint delicately applied al fresco.

Lime prepared for plaster typically is derived from limestone. Limestone is a sedimentary rock that forms from skeletons of marine creatures that have accumulated on the sea floor. With time and pressure these skeletons are pressed together in beds of stone. The White Cliffs of Dover on Britain's southeast coast pictured above provides a stunning example of sedimentary limestone.

Chemically defined, pure limestone is a carbonate of calcium or calcite having the formula CaCO3. Limestone is chemically identical to many materials familiar from everyday life: teeth and bones, chalk, marble and alabaster are common examples.

Pure limestone can be baked and further treated to prepare lime putty, a material very useful as a base for mortars, plasters and paints. Many limestone deposits found in the United States are relatively pure with little contamination from clay or other materials. When exposed to air under normal conditions the processed lime will quickly return to its natural state of calcite, resembling the limestone from which it was derived.

Some limestone contains contaminants of clay or other materials that affect its chemical properties. When these "hydraulic limes" are baked they will readily react and harden when sufficiently hydrated, given enough water. People quickly learned to add certain clays and other materials to pure lime during the baking process to create this effect artificially. This is the basis for cement technology ancient and modern.

In upcoming articles we will consider the lime cycles: the simple non-hydraulic cycle and the somewhat more complicated cementitious or hydraulic cycle.

Contributed by Patrick Webb

Saturday, August 22, 2009

What are Real Finishes?

Of course that is a highly subjective question. If one were to restrict the meaning of a finish to wall and ceiling surfaces perhaps the only truly "real finish" may be the walls of a cave naturally formed.

Even simple structures of bamboo or mud i.e. are modified and formed by human hand. Mined and fired materials such as lime and gypsum, despite continuous use for thousands of years, require a higher level of modification and sophistication to produce a workable coating. Modern, 20th century coatings largely based on latex, acrylic and epoxies owe their existence to our modern day elevated scientific understanding necessary to create synthetic combinations of materials that would otherwise not naturally occur.

Therefore, for the purpose of this upcoming series of articles we presume to define "real finishes" as:
  • Plasters and stucco renders that are applied as a wet paste and achieve a hard set
  • Materials that are strictly mineral based. Neither exclusively composed of nor blends of synthetic materials
Upcoming posts will feature in depth articles including interviews and contributing articles from plasterers, authors, manufacturers, professors and engineers expert in the following respective fields:
  • Clay: clay plasters, cob, adobe, rammed earth
  • Gypsum: stuc pierre, plaster of paris, Keene's cement, joint compound, GRG and many more
  • Air lime plaster: lime putty, Venetian plaster, marmorino, cocciopesto
  • Hydraulic limes: Tadelakt, NHL's, traditional plaster, portland cement
  • Synthetic: EIFS, acrylic latex plasters
  • Primers & topcoats: sealers, waxes, soaps
  • Substrates and building systems: plasterboard, cement block, wire mesh etc.

What are the distinctive properties of these minerals?
Where do they come from?
How do they relate to our health and environment?
What makes them an appropriate specification for a given project?

These are some of the questions that this will be addressed. This blog is an educational resource that attempts to demystify and consolidate plaster and stucco coating information for craftsmen and artisans who utilize these finishes on interior and exterior walls and ceilings.

Collective knowledge is an advantage of the modern age. Please feel free to contribute your comments and experience.

Contributed by Patrick Webb