From a Building Biology standpoint, clay – based plasters provide a superior wall finish because of the remarkable hygroscopic prop­erties of clay. For more information about mixing your own plasters, we recommend The Natural Plaster Book (listed at the end of this chapter). Resources for commercially pre­pared clay-based plaster are:

• American Clay Enterprises: A variety of clay-based plasters for interior finish­ing, including three texture styles and 42 colors.

• Japanese Wall: Several lines of interior and exterior natural plasters imported from Japan. All-natural, nontoxic plasters contain sand, diatomite earth, clay, natural stone chips, and straw.

Plaster Finish

Because of the porous nature of plaster, it will stain and show fingerprints if left unfinished. Plaster walls, which were the norm before the advent of gypsum board or Sheetrock, were commonly painted or covered with wallpaper. Today, homeowners enjoy the organic feel of the color variations in natural plaster and it is fashionable to leave it unpainted. Most people prefer to apply a clear finish over it to protect and enhance its natural beauty, or to leave the plaster unsealed.

Natural beeswax finishes will protect the wall while maintaining its permeability. Tra­ditionally, beeswax was applied with a hot knife and troweled on the wall. There are very few craftsmen who know this art form today. However, we have found that a natural bees­wax furniture polish can be applied with a cloth and buffed. As with all plant chemis­try products, chemically sensitive individuals may find the scent objectionable and should test a small sample first.

Some synthetic finishes will create a more impervious seal and are less expensive, easier to apply, and more enduring. Synthetic finishes should be carefully evaluated for chemical content and outgassing. Some maybe toxic or increase problems with static electricity. Since most make the surface nonporous, they may encourage mold growth on the paper back­ing of the gypsum lathing behind the plaster if moisture becomes trapped. So, as with gyp­sum board, if a water accident occurs it should be quickly dried. We have successfully used the following finishes:

• American Clay Black Soap Finish: A

gelatinous castile soap infused with potash

to enrich color and create a soft patina

This Santa Fe Style interior combines hard trowelled plaster wall finishes with brick flooring and stone de­tailing to create a healthy interior. Architect: Baker-Laporte and Associates; Builder: Prull and Associates. Photo: List Dennis.

• American Clay Gloss Sealer: Low-VOC product used for high-traffic areas, pro­viding water resistance to walls; easy to clean

• American Clay Penetrating Sealer: A

low-VOC soy resin/acrylic spray-on sealer that increases durability and water resis­tance

• Livos Glievo Liquid Wax: Apply a thin coat and hand buff

• Окоп Seal and Finish: For satin gloss

P. F. is a 54-year-old woman who was in good health until 1981 when she moved into a new mobile home. Shortly thereafter she developed a digestive disorder with gas and bloating, severe insomnia, and a chronic cough with frequent epi­sodes of bronchitis. By the following year she was suffering from persistent fatigue and frequent respiratory infections, including her first case of pneumonia. She became sensitive to most prod­ucts containing formaldehyde, especially press – board. She noted that she experienced "brain fog" while shopping at the local mall. Her symptoms continued to worsen, and now included allergies, hypoglycemia, and lethargy.

P. F. consulted with several healthcare practi­tioners, including a pulmonary specialist, psychia­trist, hypnotist, nutritionist, and acupuncturist. None of them ever questioned her about the air quality in her home. Eventually she received the diagnosis of multiple chemical sensitivity from a physician with similar symptoms, and was fi­nally educated about the underlying cause of her health problems. In 1992, P. F. moved into a house that contained low formaldehyde levels, alleviat­ing some of her symptoms. Her house contained several healthful features such as radiant heat in concrete floors and the absence of pressboard and particleboard in its construction.

However, further modifications were neces­sary before her health could be stabilized and im­proved. All gas appliances were removed; filtration was installed for both air and water; and the me­chanical room was vented to the outside. By 1996, P. F. had regained her health. However, as is typi­cal in such cases, she still becomes symptomatic on reexposure to toxic fumes and must diligently maintain a"safe"environment for herself.

Discussion

Indoor formaldehyde is gaining recognition as a severe health hazard for occupants of homes and office buildings where chronic exposure occurs. Several organizations, such as the American Lung Association, have recommended that formalde­hyde levels not exceed 0.1 part per million. People who have already become sensitized to formal-

minor cracks. To maintain a good barrier, these gaps should be filled with an acceptable sealant. Since most of the initial cracking will take place during the first 18 months while the house is settling, it makes sense to wait and do all of these minor repairs at once. In pumice – crete, clay/straw, and adobe construction, the plaster may be applied directly to the wall ma­terial (see Division 4).

Although most plasters are inert, some contain polyvinyl additives that are subject to outgassing and should be avoided. Verify the presence of additives with the manufacturer prior to purchase.

One potential health hazard associated with plaster lies in the method by which it is dried. Because new plaster releases a signifi­cant amount of moisture, it is necessary to dry it out quickly so that other building ma­terials are not adversely affected. This is espe­cially problematic in the winter months, when cold temperatures and lack of ventilation slow down the rate of evaporation. The standard solution is to use gasoline or kerosene heaters, dehyde will have reactions at levels as low as 0.02 part per million. Approximately 50 percent of the population is exposed on a daily basis in the work­place to levels that exceed the 0.1 part per million limit. Mobile homes are notorious for causing health problems because of the extremely high levels of formaldehyde emitted from the plywood and particleboard used in their construction.3

Individuals who develop permanent health problems associated with formaldehyde exposure often relate the onset of their symptoms to a flu­like illness, which is diagnosed as a viral infection. However, the affected individual usually does not totally recover from this so-called flu and is left with general malaise, fatigue, and depression. Other symptoms can include rashes, eye irritation, frequent sore throats, hoarse voice, repeated sinus infections, nasal congestion, chronic cough, chest pains, palpitations, muscle spasms, joint pains, numbness and tingling of the extremities, colitis and other digestive disorders, severe headaches, dizziness, loss of memory, inability to recall words and names, and disorientation. Formaldehyde is an immune system sensitizer, which means that chronic exposure can lead to multiple allergies and sensitivities to substances that are entirely unrelated to formaldehyde. This is known as the "spreading phenomenon."

P. F. was typical of people whose multiple chemical sensitivities stem from formaldehyde ex­posure in that she consulted numerous physicians and specialists in an attempt to obtain a diagnosis. Physical examinations and standard testing usu­ally fail to identify the cause of such health prob­lems. Sometimes it is suggested that the patient is a hypochondriac or in need of psychiatric evalu­ation. When asked if there might be a connection between the symptoms and formaldehyde, most physicians either do not know or believe that formaldehyde merely causes irritation. As a result, the patient’s health continues to deteriorate from continued exposure.

a. Jack Thrasher and Alan Broughton. The Poison­ing of Our Homes and Workplaces: The Indoor Form­aldehyde Crisis. Seadora. 1989, pp. 50-72.

but we do not recommend this practice. The byproducts of combustion generated by this machinery are readily absorbed into the plas­ter and other building materials. The heaters also create an unhealthy environment for the workers exposed to their fumes. Electric heat­ers tend to be more expensive to run, with far less BTU output. We recommend a combi­nation of dehumidifiers when necessary and careful scheduling so that the plasterwork is done during a warm, dry period. Although heat may be required for the comfort of the construction team, it is far less significant than dehumidification to the proper drying of wet building materials. In summary, we suggest that the following instructions be included in your specifications:

• Plaster shall be free of additives.

• The use of gas – or kerosene-generated heaters within the building envelope is prohibited.

• Turbo high-velocity heaters, other elec­tric heaters, and blow-in heaters with combustion sources outside the building envelope are acceptable for adding heat to a building during cold-weather con­struction.

• If plaster is applied when weather condi­tions do not permit the building to re­main open and well-ventilated, electric dehumidification should be used. At tem­peratures under 70 degrees Fahrenheit, moisture levels should be maintained at approximately 45 percent relative air hu­midity using electric dehumidification until the building is dry enough to consis­tently maintain this range without the use of this equipment. Interior surface tem­peratures shall remain above 50 degrees. Refrigerant dehumidifiers may not work well when temperatures drop below 65 de­grees Fahrenheit.