Thursday, April 2, 2015

Venetian Plaster Looks Great Come Rain or Shine

The popularity of Venetian plasters has surged in the U.S. during the last decade. Driven by European design and architectural trends, typical Venetian plasters made from limestone are softer and create more natural variations than most Portland-based cement and acrylics. Whereas many modern building materials create a flat, synthetic look, limestone finishes have an iridescence and translucency that create a far richer aesthetic to any building project, whether old-world or contemporary.
Southern California-based Vero is the national distributor of Rialto’s high-end Venetian plasters based in Trieste, Italy. These products are suited for residential, commercial, hospitality, government, healthcare, and even historical restoration. Vero is unique because it is one of the few plaster companies to import genuine Italian limestone mixed with fine Carrara marble aggregate that, when light reflects on the finish, enriches the colors, giving organic warmth to the walls.

But looks aren’t everything.

The content of magnesium in the mineral is very important, because it gives the finish coat an immediate abrasion and weather resistance. Due to the seasoned slaked lime’s high pH levels, the river limestone used in Vero-Rialto plasters are considered natural biocides. Therefore, they do not promote the growth of mold. They have a high water vapor permeability, which helps the natural vapor-flow through the walls, reducing the risk of blistering and peeling in humid areas, making it an exceedingly durable and long-lasting plaster finish. Whether rain or shine, these finishes get richer and beautify with age, emphasizing the natural movement throughout its life on the wall!

Vero’s Venetian plaster production process originates in Italy and is produced in a manner steeped in tradition.

  • Lime rocks (limestones) are selected from a river in Italy, where they were formed in shallow, calm, and cool fresh waters. The smaller limestones are separated to obtain a load of similar size to create a homogenous cooking of the stones.
  • Limestones are then taken to a 100-year-old kiln, which is fired with sawdust from nearby furniture manufacturers. The heating is a very slow process, typically seven days at an average temperature of 1650°F. During the heating phase, the calcium carbonate and magnesium release the CO2, and the stones lose 1/3 of their original weight. The stones become calcium oxide, known as quick lime.
  • The lime rocks are sorted again from the overcooked stones, which are used in creating statues and mosaics. The quick limestones are slaked with water, and turn into a liquid slurry made up of water and fine lime particles, which eventually turns into slaked lime or lime milk. Once slaked, the lime is distributed to separate seasoning pools for two years or 24 months. This turns into Grassello di Calce, “grassello” meaning fat, a creamy like substance that is the Ferrari of building materials used to create Vero-Rialto plasters.
Vero’s plasters elevate the appearance of a building and allow designers, architects, and builders to differentiate their work and recapture the tradition of artisans from generations gone by.

Monday, June 24, 2013

Embracing The Old Ways In The New Age


Roman Seawater Concrete Holds the Secret to Cutting Carbon Emissions

Berkeley Lab scientists and their colleagues have discovered the properties that made ancient Roman concrete sustainable and durable
June 04, 2013

Paul Preuss 510-486-6249

News Release

The chemical secrets of a concrete Roman breakwater that has spent the last 2,000 years submerged in the Mediterranean Sea have been uncovered by an international team of researchers led by Paulo Monteiro of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), a professor of civil and environmental engineering at the University of California, Berkeley.

Drill core of volcanic ash-hydrated lime mortar from the ancient port of Baiae in Pozzuloi Bay. Yellowish inclusions are pumice, dark stony fragments are lava, gray areas consist of other volcanic crystalline materials, and white spots are lime. Inset is a scanning electron microscope image of the special Al-tobermorite crystals that are key to the superior quality of Roman seawater concrete. (Click on image for best resolution.)
Analysis of samples provided by team member Marie Jackson pinpointed why the best Roman concrete was superior to most modern concrete in durability, why its manufacture was less environmentally damaging – and how these improvements could be adopted in the modern world.

“It’s not that modern concrete isn’t good – it’s so good we use 19 billion tons of it a year,” says Monteiro. “The problem is that manufacturing Portland cement accounts for seven percent of the carbon dioxide that industry puts into the air.”

Portland cement is the source of the “glue” that holds most modern concrete together. But making it releases carbon from burning fuel, needed to heat a mix of limestone and clays to 1,450 degrees Celsius (2,642 degrees Fahrenheit) – and from the heated limestone (calcium carbonate) itself. Monteiro’s team found that the Romans, by contrast, used much less lime and made it from limestone baked at 900˚ C (1,652˚ F) or lower, requiring far less fuel than Portland cement.

Cutting greenhouse gas emissions is one powerful incentive for finding a better way to provide the concrete the world needs; another is the need for stronger, longer-lasting buildings, bridges, and other structures.

“In the middle 20th century, concrete structures were designed to last 50 years, and a lot of them are on borrowed time,” Monteiro says. “Now we design buildings to last 100 to 120 years.” Yet Roman harbor installations have survived 2,000 years of chemical attack and wave action underwater.

How the Romans did it
The Romans made concrete by mixing lime and volcanic rock. For underwater structures, lime and volcanic ash were mixed to form mortar, and this mortar and volcanic tuff were packed into wooden forms. The seawater instantly triggered a hot chemical reaction. The lime was hydrated – incorporating water molecules into its structure – and reacted with the ash to cement the whole mixture together.

Pozzuoli Bay defines the northwestern region of the Bay of Naples. The concrete sample examined at the Advanced Light Source by Berkeley researchers, BAI.06.03, is from the harbor of Baiae, one of many ancient underwater sites in the region. Black lines indicate caldera rims, and red areas are volcanic craters. (Click on image for best resolution.)
Descriptions of volcanic ash have survived from ancient times. First Vitruvius, an engineer for the Emperor Augustus, and later Pliny the Elder recorded that the best maritime concrete was made with ash from volcanic regions of the Gulf of Naples (Pliny died in the eruption of Mt. Vesuvius that buried Pompeii), especially from sites near today’s seaside town of Pozzuoli. Ash with similar mineral characteristics, called pozzolan, is found in many parts of the world.

Using beamlines,, 12.2.2 and 12.3.2 at Berkeley Lab’s Advanced Light Source (ALS), along with other experimental facilities at UC Berkeley, the King Abdullah University of Science and Technology in Saudi Arabia, and the BESSY synchrotron in Germany, Monteiro and his colleagues investigated maritime concrete from Pozzuoli Bay. They found that Roman concrete differs from the modern kind in several essential ways.
One is the kind of glue that binds the concrete’s components together. In concrete made with Portland cement this is a compound of calcium, silicates, and hydrates (C-S-H). Roman concrete produces a significantly different compound, with added aluminum and less silicon. The resulting calcium-aluminum-silicate-hydrate (C-A-S-H) is an exceptionally stable binder.
At ALS beamlines and, x-ray spectroscopy showed that the specific way the aluminum substitutes for silicon in the C-A-S-H may be the key to the cohesion and stability of the seawater concrete.
Another striking contribution of the Monteiro team concerns the hydration products in concrete. In theory, C-S-H in concrete made with Portland cement resembles a combination of naturally occurring layered minerals, called tobermorite and jennite. Unfortunately these ideal crystalline structures are nowhere to be found in conventional modern concrete.
Tobermorite does occur in the mortar of ancient seawater concrete, however. High-pressure x-ray diffraction experiments at ALS beamline 12.2.2 measured its mechanical properties and, for the first time, clarified the role of aluminum in its crystal lattice. Al-tobermorite (Al for aluminum) has a greater stiffness than poorly crystalline C-A-S-H and provides a model for concrete strength and durability in the future.
Finally, microscopic studies at ALS beamline 12.3.2 identified the other minerals in the Roman samples. Integration of the results from the various beamlines revealed the minerals’ potential applications for high-performance concretes, including the encapsulation of hazardous wastes.
Lessons for the future
Environmentally friendly modern concretes already include volcanic ash or fly ash from coal-burning power plants as partial substitutes for Portland cement, with good results. These blended cements also produce C-A-S-H, but their long-term performance could not be determined until the Monteiro team analyzed Roman concrete.
Their analyses showed that the Roman recipe needed less than 10 percent lime by weight, made at two-thirds or less the temperature required by Portland cement. Lime reacting with aluminum-rich pozzolan ash and seawater formed highly stable C‑A-S-H and Al-tobermorite, insuring strength and longevity. Both the materials and the way the Romans used them hold lessons for the future.
“For us, pozzolan is important for its practical applications,” says Monteiro. “It could replace 40 percent of the world’s demand for Portland cement. And there are sources of pozzolan all over the world. Saudi Arabia doesn’t have any fly ash, but it has mountains of pozzolan.”
Stronger, longer-lasting modern concrete, made with less fuel and less release of carbon into the atmosphere, may be the legacy of a deeper understanding of how the Romans made their incomparable concrete.
This work was supported by King Abdullah University of Science and Technology, the Loeb Classical Library Foundation at Harvard University, and DOE’s Office of Science, which also supports the Advanced Light Source. Samples of Roman maritime concrete were provided by Marie Jackson and by the ROMACONS drilling program, sponsored by CTG Italcementi of Bergamo, Italy.
Scientific contacts: Paulo Monteiro,, 510-643-8251; Marie Jackson,,  928-853-7967
For more information, read the UC Berkeley press release at
“Material and elastic properties of Al-tobermorite in ancient Roman seawater concrete,” by Marie D. Jackson, Juhyuk Moon, Emanuele Gotti, Rae Taylor, Abdul-Hamid Emwas, Cagla Meral, Peter Guttmann, Pierre Levitz, Hans-Rudolf Wenk, and Paulo J. M. Monteiro, appears in the Journal of the American Ceramic Society.
“Unlocking the secrets of Al-tobermorite in Roman seawater concrete,” by Marie D. Jackson, Sejung Rosie Chae, Sean R. Mulcahy, Cagla Meral, Rae Taylor, Penghui Li, Abdul-Hamid Emwas, Juhyuk Moon, Seyoon Yoon, Gabriele Vola, Hans-Rudolf Wenk, and Paulo J. M. Monteiro, will appear in American Mineralogist.
The Advanced Light Source is a third-generation synchrotron light source producing light in the x-ray region of the spectrum that is a billion times brighter than the sun. A DOE national user facility, the ALS attracts scientists from around the world and supports its users in doing outstanding science in a safe environment. For more information visit
Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at










Thursday, April 18, 2013


Merlex President Nick Brownrecently taught a class of Long Beach4th graders how the Missions were built. Using authentic materials and methods, Mrs.Ward’s class mixed up adobe using clay, sand, and straw, and then made bricks using a breakaway mold.

We found the optimal ratios to be 3:2:1 (sand:clay:straw) by volume. The mold can be removed the next day and the bricks will turn hard as they dry in the sun. They need to be rotated 90 degrees every so often to expose all surfaces to the sun, but the kids made authentic adobe bricks, the building blocks to make a Mission-style wall.

The kids will visit Mission San Juan Capistrano later this month and, as Nick put it, “be able to look inside the walls as if they had X-ray vision”, after this adobe lesson.

Using lime mortars made the traditional way in Italy, the kids then each took turns building a wall using the adobe bricks made ahead of time, cooking show style. They didn’t mind getting mud and mortar all over their hands, either!

Kate Brown learns that the builders of the California Missions could not just go down to their local “Mission Depot” to find building materials, but had to build with what they had on-site (hence adobe and some wood)

The last step was plastering the wall using the Italian lime mortar imported by Vero for use in traditional restoration projects, such as the California Missions. The children took turns trying their hand at spreading the lime mortar on the adobe brick wall with differing degree of success.

Nick told the class that “not only did you learn how the Missions were built today, but you also got a taste of two trades, masonry and plastering. If you like working outside, maybe you can get a summer job doing this and make some money for your family!” The kids did a fantastic job, and learned that building a Missionwould have been hard work. A good time was had by all.

Wednesday, August 1, 2012

Plaster And The California Missions: Traditional Construction and Restoration

As the most viewable buildings still standing, the 21 California Missions are California history.  They serve as the main inspiration for custom home architecture in Southern California, and provide every 4th grader in the State with a unique education.  Some would argue that the Missions in California represent a unique architectural style all their own.  Plaster products were widely used in the Missions, and provide the stucco industry with its most relevant historical reference point.

When people ask “Why is stucco so common in the Southwest?” my answer is “The Missions.”  Their building methods set a precedent that continues to today, rooted in Spanish, Moorish, and Mexican traditions.  From the first Mission begun in San Diego in 1769 to the final one begun in 1823 north of San Francisco, the network of Spanish Missions did more to create the stucco industry than any other single factor.

                             The Church at Mission Santa Ines

The Missions all started very humbly, as these were frontier outposts.  They worked with what was available, adobe, ladrillo bricks, and stone.  “The first temporary quarters, hastily built, were little better than brush huts with grass-thatched roofs… The second structure at most of the missions was of adobe…. As soon, however, as a mission was strong and prosperous, the pride of the padre usually extended to an ambition to build a church in more lasting material, hence stone or burned brick were employed.”[1]

The Church at Mission Santa Barbara, made of stone

As through the course of human history, once the Missions became prosperous, they were plastered.  “All mission churches had exterior plaster of lime-and-sand stucco, following the Roman formula of three parts clean washed sand to one part burned lime, slaked with water.”[2]  It seems hard to believe, but the Mission construction projects drew from Roman records of building techniques written 17 centuries earlier, notably Vitruvius’s De architectura, as evidenced by the books found in several Mission libraries.  So perhaps we have Vitruvius to thank for today’s stucco industry.

Mission Walls & Ceilings

Together with the clay roof tiles, the plaster served a vital function, protecting the underlying adobe blocks, ladrillo bricks, and stone units in the walls from moisture.  “When roofed, plastered, and protected from groundwater, adobe walls are enormously durable and provide effective insulation, although their soft surface does not lend itself to decorative relief.”[3]  A lime-based whitewash served as the final wall surface as additional protection from the weather and also to provide an attractive finish.

Mission compounds were mixes of adobe blocks with limewash, structures of adobe and kiln-fired ladrillo bricks, and stone.  The prosperity of the Mission at the time of construction and the function of the building determined the materials.  “For important buildings such as the church and the convento, the final plaster would be made of lime, producing a hard and durable finish.”[4]  Ladrillos provided improved weather resistance and sharper lines that were not possible with adobe, and are widely used at Mission San Luis Rey (Oceanside), Mission San Antonio (Monterey County) and Mission San Diego.  Prominent stone churches were built at Mission Santa Barbara, San Gabriel, and the now ruined San Juan Capistrano.  Nothing made a prouder padre than building a stone church clad in white plaster. 

The church at Mission San Luis Rey, built with adobe and kiln-fired clay ladrillo bricks

Interior Wall Decoration

While exterior walls were left simple and bare, interior walls were decorated extensively.  Where Mission jobsites couldn’t use expensive wood and stone features, they often painted them on the walls.  “Dado” wainscots were common, as were painted cornices at the tops of the walls.  “True fresco painting was rare in Alta California, identified only recently at the Royal Presidio Chapel in Monterey.  This technique is executed on wet plaster, allowing the paint to bond with the wall surface and resulting in a more durable finish.”[5]

                           This wall painting came from Mission San Fernando Rey

Visitors to today’s Mission museums might be surprised to learn of the colorful decorations used on the Mission interiors, because most have been covered up.  “…when the Catholic and Hispanic heritage of the missions was widely unpopular, some mission interiors were redecorated according to British Victorian taste or whitewashed to modernize and dim their Hispanic origins.”[6]  Many painted decorations were whitewashed over, covered in wood paneling, or damaged by years of neglect.  Many of these decorations only survive today because of a New Deal-era survey of American art called the Index of American Design.  Now housed at the National Gallery of Art in Washington, D.C., the Index contains the full spectrum of American art up to the 1930s, and included many California Mission wall decorations that would not have survived to this day, if it weren’t for the Index.  See to see some for yourself, listed under Folk Arts of the Spanish Southwest.  Mission San Miguel, just off the 101 freeway near Paso Robles, is the only surviving completely original interior.

The Hispanic builders and Native American workers were both experienced with paint materials.  “Red was made from hematite (red ochre) and cinnabar, white from diatomaceous earth (chalklike fossil rock), and black from charcoal, burned graphite, and asphaltum.  To these sources the Spanish added pigments imported from Mexico… and linseed oil, used as a binder.”[7]  One Chumash Indian artist was said to have used “meat of the red tuna, egg whites, and pitch to the pigments.  He also used urine, which he collected in clay pots, as a mordant for the paint.”[8]  Sometimes the old way is the best, as with lime plasters; other times the old way is best left buried, as with urine paints.

Restoration of California Missions

As the Missions faded from the public interest, they were neglected.  The fairly simple maintenance required to preserve adobe and stone buildings was not done, and in extreme cases, walls were dissolved back into the mud from which they were made.  Earthquakes accelerated the pace of deterioration of many of the mission buildings.

Concerned citizens groups got organized to save and restore the Missions, and thankfully many are now maintained and well financed.  The restoration work done on the missions has shown what works with these walls and what does not.  Portland cement repairs do not work.

Well-intentioned repair efforts used Portland cement in the 1940s, 1950s, and 1960s on walls that had lasted almost 200 years by then.  Portland cement was stronger than the original materials, cheap, and readily available.  So it was reasonable to believe that cement repair products would only strengthen the structures.  But, “when cement was applied to adobe walls, often over chicken wire, its hard, water-repellent surface proved so impermeable that when moisture did occur in the walls it remained trapped behind the cement veneer, slowly eroding the adobe wall from within… In other cases, a cement mortar was added to ladrillo constructions; over time, the stronger mortar pulled away the surface of the tiles.”[9]  The lime mortars and plasters, on the other hand, that had ably protected the walls for decades, when properly maintained, “are porous and “breathe”, allowing modest dampness to evaporate.  Traditional lime- or earth-based renders (exterior plaster) and finishes protected adobe bricks from direct contact with the weather, providing an easily replaceable sacrificial layer.”[10]

“Modern conservation practice recommends that cement coverings, including renders, plasters, and “aprons” (surface coverings placed along the lower portions of walls), be replaced with renders and mortars similar to the original material, allowing the walls to breathe… Now mission ladrillo arcades are remortared and restuccoed using soft lime mortars.” [11]  Lime is the right material for these structures, because of its breathability, durability, and ease of maintenance.  Plus, the hard feel of cured limestone hides an inner softness that gently coats and supports masonry units without breaking them (like Portland cement products will). 

Restoration at Mission San Juan Capistrano, for example, strives to reproduce as closely as possible the original construction of the walls.  “To reinstate the historic character of this area, removal of all inappropriate past repairs, mainly the use of cement, is a key element to the project.  Work on the masonry columns includes the removal of hard cement mortar at the joints between the bricks and repointing with a softer, more compatible lime mortar.”[12]

    Restoration work at Mission San Juan Capistrano using lime mortars to repoint bricks

Products Available for Mission Restoration Projects

Thanks to their softness, breathability, and protective qualities, lime mortars, lime plasters, and lime washes are ideally suited to restoration of Missions and other buildings of similar construction.  There are several products that have established themselves in this niche.  Headquartered in Orange, California, Vero imports Italian seasoned-slaked lime mortars, plasters, and lime washes, produced in much the same way as those used by Vitruvius in Ancient Rome.  Malta Grezza/Fine are ready-to-use lime mortars, and are made more weather-resistant through the addition of Cocciopesto (brick dust).  This technique is consistent with that used for reservoirs and fountains in the California Missions, which “were often rendered with water-resistant coccio pesto, hydraulic lime stucco made pink by the admixture of ground terracotta tiles, another Vitruvian formula.  Coccio pesto was also used on architectural elements, such as the ladrillo colonnade columns at Mission Santa Ines.”[13] 

Malta Grezza & Malta Fine produce this characteristic pink tone when Cocciopesto is used to provide added water-resistance and faster set.

Lime washes (such as VeroEpoca 800) are an ideal finish coat over a lime mortar, as they beautify, can add color, and cross-link with the lime mortar to provide a water-shedding topcoat.  “[Limewash] gives a smooth coating which, after an initial wetting, encourages an easy run-off of rainwater.  At the same time the nature of this surface allows good, all-over evaporation which helps the wall to dry out.  Limewash is unaffected by the ultra-violet rays in sunlight which destroy synthetic paints.”[14]

Vero lime plasters can also be used as topcoats over the lime mortars, when smooth textures and a more substantial color coat is desired.  “Lime plaster is extremely strong stuff that has withstood hundreds of years of weather.  Moreover, because it is pliant (somewhat flexible), lime plaster is not likely to crack very much as a building shifts or walls expand and contract in response to natural temperature fluctuations or as moisture levels rise and fall… In addition, lime plaster and earthen materials expand and contract similarly.  Consequently, when lime plaster is applied on an earthen wall or an earthen plaster, it is less likely to crack or peel off a wall.”[15]

Other manufacturers also carry lime mortars, including the bagged Natural Hydraulic Lime products imported from France by Transmineral USA out of Petaluma, California.  Their Ecomortar product is preblended with properly graded sand and ready to use.  Lime finishes are available from many companies in California and elsewhere in the U.S.


Next time you’re near a Mission, pay it a visit.  If you’re in the plastering business, you’ll pay extra attention to how the walls were built, and you should thank the Franciscan Padres for bringing plaster to California and planting the seeds for the architecture, materials, and techniques used today.  The same materials used in building the Missions are available today, and should be used exclusively in preserving these and other historic buildings.

[1] E. Engenhoff, Fabricas (Sacramento: California Division of Natural Resources, Division of Mines, 1952), 181, as observed by Eugene Duflot de Mofras during his visit in 1840-42.
[2] E. Kimbro & J. Costello, The California Missions, The Getty Conservation Institute, 2009.  p. 94
[3] Ibid., p. 96
[4] Ibid., p. 97
[5] Ibid., p. 135
[6] Ibid., p. 146
[7] Ibid., p. 134
[8] Ibid., p. 147
[9] Ibid., p. 156
[10] Ibid., p. 156
[11] Ibid., p. 156
[12] “South Wing Conservation”,, July 10, 2012.
[13] E. Kimbro & J. Costello, The California Missions, The Getty Conservation Institute, 2009.  Chapter 4 note 7
[14] Holmes & Wingate, Building with Lime, ITDG Publishing 2002, p. 49
[15] Guelberth & Chrias, The Natural Plaster Book, New Society Publishers, 2003, p.165