Varietals
The French are renowned and appreciated the world over for their many traditions and a unique perspective on life that form the foundation of their culture and have contributed to our culture here in America. Who doesn’t love a French press coffee complimented with a buttery croissant on a lazy Saturday morning? A visit to the Metropolitan Museum of Art to see the impressionist works of Monet and Cézanne? Although we as Americans enjoy our own hustle and bustle way of life, I think we appreciate the fact that someone on the other side of the pond has taken a little more time to perfect a few of the finer things and are willing to share. Vive la différence!
Two of those traditions mean a lot to my family personally and professionally: Wine and Plaster. My wife Angela is a professional chef trained in classical French cuisine and a wine consultant specialized in wine and food pairing. I am a plasterer who has made numerous visits to France to improve my skills in moulding and ornament. Angela and I talk a lot about our respective interests and have perceived a philosophical constant, a sophisticated approach to product development that these completely different industries appear to share. We got excited about the opportunity to do a project together comparing the common themes we see and sharing them with others.
This essay is the first of a five part series on French traditions of wine and plaster making framed in a very wine oriented vocabulary:
- Varietals
- Terroir
- Viticulture
- Viniculture
- Pairing
Varietals in Wine
As you may know, a varietal is a wine made from a single grape variety. Varietals are very popular in the United States, especially where we live in California. I think we like the simplicity of having a wine from a single grape variety that we can learn about and expect to have certain characteristics. By contrast the French generally prefer wines that are blends. For example, the prized and often very pricey Châteauneuf-du-Pape may contain up to eighteen distinct grape varieties!
Throughout our wine and plaster comparison we are going to concentrate on the popular and much simpler Bordeaux blend. A Bordeaux blend can have up to six grape varieties. Typically though, the following three grapes dominate most Bordeaux wines: Cabernet Sauvignon, Merlot & Cabernet Franc. Interestingly, in the United States we grow and blend these grapes in a similar way. More about that later! For now let’s take a closer look with Angela at a couple of the varietals that she and I love to drink, Cabernet Sauvignon & Merlot.
Native to Bordeaux, the Cabernet Sauvignon grape is the love child of the Cabernet Franc and Sauvignon Blanc grapes. You can recognize the Cabernet Sauvignon grapes because they are quite small, their skins are very thick and are dark blue in color. They cling to each other in very tight clusters and bond tightly to the vine with their strong stems. Many of these physical characteristics express themselves by producing a powerful, complex and masculine wine. The skins, large seeds and stems give the Cabernet Sauvignon wine a dark, almost inky color and strong tannins which can be overwhelming in a young wine, but mellow beautifully with age. With regard to aroma and taste, the flavor profile will vary greatly depending on where the grapes are grown. In new world production, cabernet sauvignon is typified by bold, jammy mouth-filling flavor. Up front you may taste over-ripe blackberries and plums or dried currants gently blended with notes of chocolate or coffee. By contrast, old world productions, particularly French, are lower in alcohol and much less fruit-forward. As a result, earthier and more complex notes of mushroom, leather and tobacco are given their chance to shine.
Merlot, sometimes called “cabernet without the pain” is a perfect foil for its partner. Where Cabernet Sauvignon is bold, powerful and angular, Merlot is round, soft and voluptuous. Merlot grapes are larger than cabernet sauvignon and their skins thinner and almost violet in color. These characteristics produce medium-bodied wine with lower tannins. Although, Merlot is an integral part of the orchestra that is Bordeaux wine, it does quite well on its own with a remarkable range of aromas. In the new world merlot shows notes of plump and perfectly ripened dark-skinned fruit while old world merlot displays deep notes of vanilla or coffee beans and earthy aromas of damp grass and leaves.
Varietals in Plaster
Plaster has its varietals as well. Whereas varietals with wines start with a single grape variety, varietals in plaster begin with a single mineral. A few of the popular minerals that historically have been used to make plaster are: gypsum, clay, limestone, marl and silica. Paralleling our tastes in wine, plasters made from a single mineral are very popular in the United States. We generally manufacture and use clay, lime and gypsum plasters mixed only with sand. I think the American approach to plaster manufacture resembles our wine production. We like the simplicity of having a plaster from a single mineral that we can completely understand and expect to have certain characteristics. It probably comes as no surprise that the French have a long history of developing plasters that are blends of many minerals.
During our wine and plaster comparison we are going to examine parallels with the aforementioned Bordeaux blend with a historic French plaster blend, Terre de Séléné. As with our Bordeaux blend three minerals dominate this plaster blend: gypsum, limestone and clay. In the United States we have deposits of these minerals and mine them aplenty. Now it’s my turn to take a closer look at a couple of these minerals.
Pure limestone is a carbonate of calcium or calcite having the chemical formula CaCO3. Lime is the main component of many materials familiar from everyday life: teeth and bones, chalk and marble are common examples. It is this type of limestone that is used to make the lime for Terre de Séléné. Plasters made exclusively from pure limestone always have certain characteristics. For example, lime is a very white, reflective material which makes it a great base for creating colored plasters. Lime is highly alkali and inhibits mold growth. Lime plasters such as Venetian plaster, Tadelakt and marmorino are very popular in the United States.
Gypsum and limestone are geologically related. Whereas limestone is a carbonate, gypsum is a sulphate of calcium having the chemical formula CaSO4. Like its cousin, pure gypsum is a very white, reflective material that is easily tinted with mineral colorants. At the same time it has some properties that are unique. Gypsum plaster can be manufactured at a very low temperature (and corresponding low environmental impact), starting at about 150 °C or 300 °F. It also has a fast set with no shrinkage which makes it very useful for moulding and casting.
As with all grapes, including our Bordeaux varietals Cabernet Sauvignon and Merlot, geology makes a considerable contribution to the qualities of a wine. Geology makes an even bigger impact in the world of limestone and gypsum. Next blog it’s time to go full French and talk Terroir!
Terroir
In our previous essay we familiarized ourselves with the concept of varietals and how they exist in wine and plaster. For wine we learned that each variety of grape possesses unique characteristics and that a few of these grapes varieties actually produce a good wine without blending, known as a varietal.
Nature. Culture. Perhaps these seemingly disparate aesthetics were no better reconciled than by the French Renaissance tradition of the formal garden.
As we have seen so far, wine making is truly a partnership between the wine maker and nature, with majority control vacillating between one and the other depending on the process underway. Nature dictates the terroir and the varietals she will support while the wine maker plants and prunes according to those dictates. The partnership story continues now with a look at viniculture, the creative part of wine making; namely hand harvesting, oak barreling and blending as they are practiced by small scale, world-class Bordeaux wineries.
No doubt we’ve seen old photographs of workers manually harvesting grapes from vines and placing them in the small woven baskets on their backs for transport to the winery. We may look at these photos with a sense of romanticized nostalgia but within them are important, time-tested instructions for the best way to harvest grapes. Here’s why.
Viniculture in Plaster
Not unlike American choices in wine, "varietal" plasters made from either gypsum, lime or occasionally clay are the norm in the United States. These are largely supplied by industrial manufacturers who modify properties such as the set time, hardness, plasticity of plasters by means of synthetic chemical additives, often with unpredictable and undesirable long term effects. Europeans in general and the French in particular have a long, continuous tradition of blending the mineral binders themselves to adapt the properties of a resulting plaster to a given use. Fortunately, many of the heritage mineral binders or "varietals" are highly compatible with each other, offering plasters with a wide range of applications, adaptable to almost any specification. Let’s now take a closer look at how this "made to measure" approach of the French utilizes clay, gypsum and lime to prepare the traditional blended plaster, Terre de Séléné.
Ecology. Clay is the primary mineral used for Terre de Séléné plaster. It is a very sustainable choice as suitable clays are widely available and require very little energy to produce. Clay is harvested, left to dry by the sun and goes through a crushing and screening process to make ready for plaster. Like clay, gypsum is also a material that requires little embodied energy to manufacture. Lime requires substantially more energy to produce but fortunately only a small percentage is needed for Terre de Séléné. All three mineral binders are free of volatile organic compounds and completely non-toxic.
Breathability. Although shared by all three heritage mineral binders, clay has the highest capacity to absorb and release water vapour which can be attributed to its platelet structure, composed of tetrahedral sheets.This property contributes significantly to interior air quality by allowing vapour to migrate naturally through the wall assembly.
Permeability. Gypsum and limes have a loose crystalline structure that allows for the absorption of liquid water. This is a characteristic that all but eliminates condensation inside the wall assembly and absorbs water infiltration from small structural cracks. Yet, permeability can also draw standing water via capillary water rise. However, the aforementioned platelet structure of clay swells as moisture content increases, eventually creating a self sealing effect.
Durability. All three binders imbue Terre de Séléné with high flexural strength, providing incomparable crack resistance, eliminating the need for control joints. Gypsum and lime acts as stabilizers for clay reducing vulnerability to erosion from streaming water. Together with good flashing, water table and eave desgin there are many extant examples of Terre de Séléné that have served their sacrificial function of protecting the substrate for many decades, even centuries.
Efficiency and Frost Resistance. Gypsum has a rapid set, controllable from mere minutes to several hours. Rapid setting permits subsequent coats to be applied in successive days allowing application to proceed efficiently. This property also becomes very useful for plastering in climates that may undergo freeze thaw cycles within days of application.
Workability and Mold Resistance. Lime has a lower viscosity than clay or gypsum which eases application of the plaster, particularly by trowel. Although mineral binders are inorganic, sometimes organic matter will contaminate the aggregates or water used to make the plaster, providing a food source for molds. The high alkalinity of lime combats the growth of mold during the drying process.
Beauty. Due to the self-binding nature of gypsum, there is a far wider range of flexibility in the selection of aggregates and natural fiber additions than would be available for a clay or lime based plaster varietal. Size, concentration, colour, softness and shape can all be controlled to create a plaster that has a very specific aesthetic. A Terre de Séléné version of "Stuc Pierre", a plaster resembling a limestone or brownstone, is a common composition that reflects the authenticity of traditional, artesanal plasters.
This essay was coauthored by Angela and Patrick Webb
Terroir
In our previous essay we familiarized ourselves with the concept of varietals and how they exist in wine and plaster. For wine we learned that each variety of grape possesses unique characteristics and that a few of these grapes varieties actually produce a good wine without blending, known as a varietal.
Varietals are important; however, for the French there is one contributing factor in making a truly great wine or plaster that is absolutely fundamental. That essential component is the one we have little to no control of. It is summed up in a small yet tricky to pronounce word called terroir (ter-whah).
This blog post is the second of a five part series on French traditions of wine and plaster making framed in a very wine oriented vocabulary:
- · Varietals
- · Terroir
- · Viticulture
- · Viniculture
- · Pairing
Terroir in Wine
Terroir comprises all the geologic, atmospheric and climactic conditions found within a wine-making region that give grapes the foundation they need to develop the characteristics we enjoy in our favorite wines. Just like it sounds, terroir is an extensive topic. For our glimpse into this world; however, the following overview addresses three key aspects of terroir: temperature, moisture and soil composition.
All of the world’s major wine growing regions are situated between 30˚ and 50˚ latitude in both the northern and southern hemispheres meaning that cool to moderate temperatures are optimal for wine grape growing. In cooler climates with less sun exposure (think Washington State or Germany) ripe grapes retain enough “greenness” to produce wonderfully crisp, herbaceous wines like sauvignon blanc which pairs nicely with a green salad topped with goat cheese, green beans and basil pesto. In warmer climates (California and Bordeaux) grapes remain on the vine longer sunning themselves and developing more color, sugar and complexity in the process. The resulting big, bold, fruit is why cabernet sauvignon is known as King Cab.
California and Bordeaux are world-class wine producing regions with oceans bordering both regions providing a moderate and stable climate with minimal risk of damaging frosts. Rainfall in both regions averages a healthy 29 to 34 inches annually. In general, when grapes receive less than optimal rainfall, the vines will produce fewer grapes, though often of superior flavor. In contrast, if heavy downpours occur, particularly close to the harvest time, the grapes absorb too much water, which dilutes the flavors and produces low quality wine. So balance in moisture be it rain, fog or dew is crucial to superior grape production. However, while moisture is important for the vineyard, of equal importance is the vineyard’s drainage system. This leads to our third topic of terroir: soil composition.
As a rule the best wines come from grapes that have suffered a bit; where nutrients are available, but the vine must work for them. According to The World Atlas of Wine writers Hugh Johnson and Jancis Robinson state that best soil (for vineyards) is not particularly fertile, it drains quickly thus forcing the roots downward in search of a water supply. Vineyards in the Medoc region of Bordeaux produces some of the most notable wines because beneath the gravelly topsoils are alternating layers of hard compacted sand and clay. These quickly draining surfaces force the roots to dive deeper until they reach a moist layer of sand and clay near the water table. When nutrients are too easily accessible, vines become complacent and results are one dimensional grapes with underdeveloped structure and complexity.
Terroir in Plaster
For plaster, terroir means geology. It is what nature has provided us. You can’t make something from nothing and you can’t produce a great plaster if the geology is poor. Let’s again take a closer look at the terroir of two of the minerals used to make the plaster blend Terre de Séléné: lime and gypsum.
Lime typically is derived from limestone. Limestone is sedimentary rock formed from the skeletal remains of marine creatures that accumulated on the sea floor millions of years in the past. With time and pressure these skeletons are pressed together in beds of stone.
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 mixed with water. However, many limestone deposits found in both France and the United States are relatively pure with little contamination from clay or other materials. This type of pure limestone produces a lime that blends well with other plasters. It is the very terroir needed for the lime in Terre de Séléné.
I mentioned in the previous post that gypsum and limestone are geologically related. While limestone was forming on ancient sea beds another phenomenon was occurring in salt marsh lagoons along the shore. Through repeated cycles of seawater infiltration and evaporation gypsum, salts and other compounds precipitated and formed large masses.
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 mixed with water. However, many limestone deposits found in both France and the United States are relatively pure with little contamination from clay or other materials. This type of pure limestone produces a lime that blends well with other plasters. It is the very terroir needed for the lime in Terre de Séléné.
I mentioned in the previous post that gypsum and limestone are geologically related. While limestone was forming on ancient sea beds another phenomenon was occurring in salt marsh lagoons along the shore. Through repeated cycles of seawater infiltration and evaporation gypsum, salts and other compounds precipitated and formed large masses.
Many of these masses have been preserved relatively unchanged, covered by layers of clays that protected them from erosion. In these one can find gypsum rock with many of the original impurities that give the gypsum very interesting properties often useful for construction. In many instances though the original gypsum, being more soluble in water than other precipitates, would be carried off with underground water to recrystallize in successively purer forms in subsequent locations. Many distinct forms of gypsum with diverse crystalline, chemical structures and levels of purity formed. There are gypsum crystals found in underground caves in Mexico for instance that measure over 30 feet long and weigh several tons each, the largest crystals in the world!
Grapes, gypsum and limestone were here a long time before we arrived on the scene. Terroir is the result of millions of years of geology and current climate conditions we study and benefit from but can’t imagine to control. That being said good wines and beautiful plasters don’t make themselves. Next blog we’ll consider the human touch, Viticulture.
Viticulture
Viticulture
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| Château de Chambert |
“In the Renaissance taste the garden was an extension of the main design. It was a middle term between architecture and Nature. The transition from house to landscape was logically effected by combining at this point formality of design with naturalness of material.” – Geoffrey Scott, The Architecture of Humanism
To this point we have considered Varietals and Terroir…learning about grapes and minerals…exploring soils, weather and geology…recognizing all of nature’s generous contributions. All that we have hitherto discussed is most fundamental; however, wine and plaster are uniquely products of culture. The balance of our five part series will consider the human touch.
Viticulture in Wine
Although located in what is considered the “old world” of wine production, Bordeaux is squarely in the forefront with regard to wine-making technology. So in this segment we are going to discuss an aspect of the Bordeaux wine industry that receives nowhere near the attention it deserves. We are talking about viticulture. Viti is latin for vine therefore viticulture roughly translates to vine cultivation. In this article, we will examine two methods of viticulture that are essential to making a great wine; vine manipulation and pest control.
Vine leaves contain chlorophyll cells that absorb sunlight enabling the plant to extract carbon dioxide from the air and convert it to sugar. The nutrients imparted by the sugar feeds the vine roots, grape clusters and leaves ensuring the entire plant receives exactly what it needs, when it is needed.
Allowing too much foliage shields the grapes from the sunlight they need for the last stage of their healthy development, so pruning is crucial to producing a quality wine. However caution must be exercised with cutting, because every cut is an entry point for pests to enter and attack the vine. On the other hand, if too many leaves are pruned, the plant does not have the means to absorb sufficient sunlight to sustain the entire vine.
Wine grapes emerge at the end of the growing season so the plant’s nutrients must further be shared with the new grape clusters. If there are too many clusters, the sugar and acid levels will likely be undeveloped and/or unbalanced resulting in a poor showing as a wine. Too few clusters negatively affects potential profits from wine sales.
Pest control is another very important aspect of viticulture. In the 1870s a small, deadly phylloxera louse made it’s way to Europe and all but wiped out all wine production. Phylloxera destroys the grapes, rots the vines and often leaves its larvae in the root, eventually killing the vine completely. Although Bordeaux and Europe at large have regained their wine producing capabilities, phylloxera and other lice, along with viruses, bacteria, fungi, mites and insects are still among the many threats to healthy vines.
In an effort to eliminate ongoing threats to their vineyards and livelihoods, many late 20th century wine growers often used chemical fertilizers and pesticides indiscriminately. Thankfully much has changed since then with most of the region’s winegrowers using more environmentally conscious, natural pest control methods. For example, Bordeaux wine growers are currently and constantly experimenting with root grafting in order to find the genetic combination that is naturally resistant to harmful bacteria and viruses. Scientists and wine growers are also experimenting with sea algae as a natural deterrent to gray rot.
There is no doubt that viticulture is both science and art. Winemakers must have intimate knowledge of their vineyard’s terroir as well as which viticulture methods will work best within its parameters. It is with this intricate knowledge and dedication to quality that winemakers are able to extract the best wines from the best grapes.
Viticulture in Plaster
France is a geologically, minerally rich country. Correspondingly rich in culture, the French have been very successful in exercising their influence over a number of raw mineral materials to produce some of the finest plasters in the world. The plaster equivalent to Viticulture is baking. Let’s now take a closer look at how 3 minerals are prepared for our blended plaster, Terre de Séléné.
Clay is the primary mineral used for plaster in Terre de Séléné. It is an abundant mineral worldwide, the result of millions of years of erosion. In parts of France a relatively pure form is available just under the topsoil, just a few feet below ground. It is easy to excavate and is still traditionally dried by the sun. Later, with minimal effort, it is ground into a powder ready to be used for plaster. While there are a variety of clays in France, clay with a low shrink-swell capacity such as Kaolinite is desirable for Terre de Séléné.
Historically, the French were enamored with this type of clay for additional uses. The word “Kaolin” comes to us directly from French. They in turn inherited the term from China. In the early 18th century the French were obtaining an extremely pure form of clay useful for porcelain, “China”, from a deposit near a mountain the Chinese called Kao “high”, Ling “hill”.
Gypsum is the secondary mineral used in Terre de Séléné plaster. Gypsum is plentiful in France and particularly so in Paris. Gypsum plaster is almost synonymous with the expression “Plaster of Paris”. Paris in fact sits on a “massif” or deposit of mineral gypsum that is among the largest and finest in quality on earth. Naturally occurring gypsum is a type of salt that precipitates through cycles of evaporation from lime or other calcium compounds, typically in lagoons or inland seas.
Preparing gypsum plaster requires a little more effort and energy than clay. It is usually mined from underground deposits. Relatively soft as a stone, it is easily pulverized to a coarse sand ideal for baking. Most of the gypsum plaster useful for Terre de Séléné only needs to be baked at under 350° F for less than an hour. In general, considerable influence can be exercised in the baking process. Adjustments to the grind, temperature, length of baking and even barometric pressure can produce an amazing range of properties in gypsum plaster such as fast setting plasters good for casting or extremely dense, hard plasters appropriate for floors or countertops.
Limestone is the third mineral used for our plaster blend. In abundance in the South of France, limestone is a sedimentary stone, the result of millions of years of marine skeletons accumulating on ancient sea beds. The lime most useful for Terre de Séléné plaster is very pure, having little contamination from magnesium or silicates. By itself, limestone is very useful as a building material; however, to produce a plaster requires considerable fuel and labor.
Limestone is found underground but is plentiful and easier to extract from surface mines. Much harder than gypsum or clay, extraction is laborious. For baking limestone is broken into golf ball size pieces. Traditionally, it was baked for 24 hours in vertical kilns at an extremely high temperature of 1500° F. Modern production methods utilizing crushers and horizontal kilns have reduced the time considerably.
The resulting “quick” lime is highly caustic, potentially hazardous to handle. At this point of production enough water is introduced to cause a partial reaction that reduces reactivity and danger. The slaked lime, also known as dry hydrate, is now ready to be blended with the clay and gypsum plaster to make Terre de Séléné.
As you have read, the French traditions of Viticulture and plaster preparation are very sophisticated. The usefulness of our modern scientific, chemical understanding still lags behind the practical experience gained through centuries of empirical observation and practice. This is especially evident in our subsequent, fourth segment considering the art of the blend, Viniculture.
Viniculture
Viniculture
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| Bacchus, circa 1497, Caravaggio |
Previously considered was "Viticulture", the cultivation of the grape on the vine itself and its equivalent in plaster manufacture, the careful selection and baking of the various mineral binders. We now progress to our fourth step in the process, "Viniculture", the art of the blend.
At this point, man must utilize his intelligence, engage all of his senses to influence nature. Man as creator of the "Artificial" in the original Latin sense of the word, that which is "made by craft".
Viniculture in Wine
No doubt we’ve seen old photographs of workers manually harvesting grapes from vines and placing them in the small woven baskets on their backs for transport to the winery. We may look at these photos with a sense of romanticized nostalgia but within them are important, time-tested instructions for the best way to harvest grapes. Here’s why.
Harvesting begins when the grapes have reached their appropriate sugar to acid balance. Hand harvesting ensures only the best quality grapes are picked and are not damaged in the process. The grapes are then transported in small batches to reduce the risk of being crushed under their own weight. By using vented baskets, juice from any grapes that are crushed can drain away before it oxidizes and affects the other grapes in the bushel. Once the delicate bundles of juice have been delivered to the winery they are meticulously sorted of any remaining unacceptable grapes and then pressed for fermenting.
What emerges is a wine that is full of promise but whose initial characteristics are often brash and a bit rough around the edges. Centuries of wine making have proven that grapes need time to adjust to their new role as wine and that barrels provide the ideal location for such quiet contemplation.
Through the years various types of wood have been used in barrel making, but oak remains the wood of choice primarily because it contributes the most interesting characteristics. Oak barrels have their own tannins and are rich in aromatic compounds, which are imparted to the wine. Over time, this interaction tempers the aggressiveness of the new wine while enhancing its flavor subtleties.
Wine blending is another way an artistic wine maker can enhance wine’s subtleties. Contrary to some opinions, wine blends are not inherently inferior to varietal wines. To this point, Bordeaux wines, arguably among the most prestigious wines in the world are blends of several varietals. In fact, the mighty Cabernet Sauvignon grape itself is a blend of mixed heritage.
So while less reputable wine makers have been known to blend wines in a “hail-Mary” effort to make drinkable the undrinkable, quality wine makers understand that there is an art to blending and do so only to make minor tweaks to what is already fundamentally good wine.
For instance, a wine maker may decide his Cabernet Sauvignon wine is a bit cloying and bordering on flabby. To provide balance and structure he may blend in a Cabernet Franc wine, which is lighter bodied and higher in acid. Or perhaps a wine perceived to be too crisp, tart and sour, can be muted through blending with earthier, more rounded wines. Or a wine maker in the enviable position of having several outstanding varietals may select some for blending into an extraordinary and wholly unique wine.
Thanks to high-yielding varietals, fertile soil and industrialized processing, today almost anyone can afford to buy wine; which bottle to bottle, year to year, maintains a standardized flavor profile. Many see this example of technological advancement as a profitable and efficient way for large producers to bring affordable wine to the mass market. However, quality wine making requires full cooperation of all of our senses; touch, taste, smell, sight, hearing and intuition. For this reason technology, advanced as it may be, will never match the wine maker’s innate human ability to harness, nurture and coax into each glass the sensual essence found in each bottle of wine.
Not unlike American choices in wine, "varietal" plasters made from either gypsum, lime or occasionally clay are the norm in the United States. These are largely supplied by industrial manufacturers who modify properties such as the set time, hardness, plasticity of plasters by means of synthetic chemical additives, often with unpredictable and undesirable long term effects. Europeans in general and the French in particular have a long, continuous tradition of blending the mineral binders themselves to adapt the properties of a resulting plaster to a given use. Fortunately, many of the heritage mineral binders or "varietals" are highly compatible with each other, offering plasters with a wide range of applications, adaptable to almost any specification. Let’s now take a closer look at how this "made to measure" approach of the French utilizes clay, gypsum and lime to prepare the traditional blended plaster, Terre de Séléné.
Ecology. Clay is the primary mineral used for Terre de Séléné plaster. It is a very sustainable choice as suitable clays are widely available and require very little energy to produce. Clay is harvested, left to dry by the sun and goes through a crushing and screening process to make ready for plaster. Like clay, gypsum is also a material that requires little embodied energy to manufacture. Lime requires substantially more energy to produce but fortunately only a small percentage is needed for Terre de Séléné. All three mineral binders are free of volatile organic compounds and completely non-toxic.
Breathability. Although shared by all three heritage mineral binders, clay has the highest capacity to absorb and release water vapour which can be attributed to its platelet structure, composed of tetrahedral sheets.This property contributes significantly to interior air quality by allowing vapour to migrate naturally through the wall assembly.
Permeability. Gypsum and limes have a loose crystalline structure that allows for the absorption of liquid water. This is a characteristic that all but eliminates condensation inside the wall assembly and absorbs water infiltration from small structural cracks. Yet, permeability can also draw standing water via capillary water rise. However, the aforementioned platelet structure of clay swells as moisture content increases, eventually creating a self sealing effect.
Durability. All three binders imbue Terre de Séléné with high flexural strength, providing incomparable crack resistance, eliminating the need for control joints. Gypsum and lime acts as stabilizers for clay reducing vulnerability to erosion from streaming water. Together with good flashing, water table and eave desgin there are many extant examples of Terre de Séléné that have served their sacrificial function of protecting the substrate for many decades, even centuries.
Efficiency and Frost Resistance. Gypsum has a rapid set, controllable from mere minutes to several hours. Rapid setting permits subsequent coats to be applied in successive days allowing application to proceed efficiently. This property also becomes very useful for plastering in climates that may undergo freeze thaw cycles within days of application.
Workability and Mold Resistance. Lime has a lower viscosity than clay or gypsum which eases application of the plaster, particularly by trowel. Although mineral binders are inorganic, sometimes organic matter will contaminate the aggregates or water used to make the plaster, providing a food source for molds. The high alkalinity of lime combats the growth of mold during the drying process.
Beauty. Due to the self-binding nature of gypsum, there is a far wider range of flexibility in the selection of aggregates and natural fiber additions than would be available for a clay or lime based plaster varietal. Size, concentration, colour, softness and shape can all be controlled to create a plaster that has a very specific aesthetic. A Terre de Séléné version of "Stuc Pierre", a plaster resembling a limestone or brownstone, is a common composition that reflects the authenticity of traditional, artesanal plasters.
We've spent a good bit of time learning about the Bordeaux wine and Terre de Séléné plaster. Now its time to set the table! The motivation of countless generations of artisans developing these French wines and plasters will next be fully revealed in the upcoming fifth and final segment, the perfect: Pairing.
This essay was coauthored by Angela and Patrick Webb
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