There is a wide range of surfaces in a building that require a surface finish to protect the material and/or add an aesthetic dimension to the material. Even a small home may have thousands of square feet of surfaces that require treatment, and choices in finishes visually define the building as well as influence longevity. It is rare that one type or one colour of finish is chosen for the whole home, leading to multiple finishing decisions that must all work together, both aesthetically and practically.
In many cases, the surface finish is a key element in the durability of the material it is protecting. We ask a lot of our finishes, which take the brunt of exposure to the elements, wear and tear and cleaning. Modern science has succeeded in creating finishing products that offer excellent durability, color choice and fastness, ease of application and adhesion. Unfortunately, in the pursuit of such qualities these products have become proprietary chemical soups. Even the “greenest” petrochemical finishes rely on extraction and manufacture of chemical components that have a wide variety of problematic environmental impacts. There have been excellent developments in reducing the impacts on the end user of such products, but this does not take into account impacts that happen throughout the entire chain of production.
The majority of the finishes described in this chapter fit under the heading of “natural finishes.” They use naturally occurring and minimally processed ingredients that are entirely free of petrochemical products. They are viable on a wide range of surfaces and materials, and offer low impacts and low or no toxins from raw material acquisition through to final application. In some cases, the products may not offer quite the same degree of color choice and fastness, ease of application, durability and adhesion as their petrochemical counterparts; a small trade-off for vastly reduced environmental impacts. And in many cases, the natural finishes offer a beauty and richness that cannot be matched by petrochemical finishes.
The one exception to the focus on all-natural finishes is the section on nontoxic latex paints. While almost every paint company offers a low- or no-VOC version of their latex paint, this alone is not enough to warrant inclusion in this book. These paints may not emit volatile organic compounds, but they still include many dangerous substances, many of which are known carcinogens, endocrine disruptors or other health-adverse chemicals. These can include (but are not limited to): ethyl acrylate, zinc pyrithione, benzisothiazolin, triclosan, methylchloroisothiazolin, hexanoic acid, tetraethylene glycol, nepheline syenite, ethylene-vinyl acetate and an array of antimicrobials. There are a few paint companies making an attempt to create actual nontoxic latex paints, and while these are a vast improvement over petrochemical paints of the past, even they are not entirely clean and free of toxins, nor can the chain of production be guaranteed to be clean and nontoxic. However, in the hope of increasing interest in truly nontoxic latex paints, we include them as a category in this chapter. They will offer homeowners the same level of performance expected from commercial paints with greatly lowered impacts.
Building Science Basics for Finishes
Surface finishes can alter the moisture-handling characteristics of the materials to which they are applied, and this is an important building science consideration when selecting finishes.
We often desire a finish that is “waterproof,” and for good reason. If a finish can completely repel all liquid water from penetrating the material it is protecting, the lifespan of that material can theoretically be extended. However, a truly waterproof coating can often cause as many moisture problems as it alleviates. Moisture will inevitably penetrate building materials; even the best waterproof coating can only delay the process. Depending on the position of the material on the building, restricting the passage of water can also prevent the passage of vapor, robbing the material of the ability to dry out properly and perhaps causing moisture to accumulate in the material or in adjacent materials, causing more harm than a porous finish might suffer.
As an example, a coat of latex paint on the exterior plaster skin of a permeable natural wall system will cause moisture that would have harmlessly passed through the wall and been released to the atmosphere to be trapped in the wall, first saturating the plaster and then the material behind the plaster. Rot and mold will follow.
The most versatile coatings are those that discourage the entry of bulk water via a very tight pore structure, but that still have pores to allow vapor to pass through the finish. This ability to allow moisture to transpire is measured in “perms,” and many finishes have published perm ratings. Many natural finishes do not necessarily have quantified perm ratings, but we can extrapolate from successful applications in a wide variety of climates and over long periods of time that they have a range of permeability that is suitable for long-term durability.
It is never a good strategy to rely on a finish to do a job that the material it is covering cannot do, at least to some reasonable degree, on its own. Finishes should be an enhancement, but not an integral part of, a building science strategy. Paints should not be considered a primary air or vapor control layer, and should not be relied upon to make otherwise vulnerable materials “durable.”
Embodied energy and finishes
Accurate data for the embodied energy of finish materials is not widely available or consistent between sources. Gross quantities of finishing materials also tend to be small, and many are mixtures of numerous materials that are each difficult to quantify, making accurate embodied energy figures too uncertain to be valuable or meaningful — so they are not included.
Extrapolations for comparison purposes can be made by examining the harvesting and manufacturing impacts listed for each finish.
Code compliance and finishes
Building codes will rarely prescribe finishes for residential construction, except in rare cases in which a particular finish is required by a material in order to be successfully used in a building. For this reason, code compliance is not rated for the products in this chapter.