Week 11 – On the weathering of limewash, and canaries in the coal mine

In her bestseller Under the Tuscan Sun, the author and poet Frances Mayes describes how the various old, weathered, mottled shades of red and yellow wash on her stucco-clad country house (Bramasole) resemble the skin of a beautiful peach. She also describes how a contractor is eager to paint it for her and even it all out, which she thinks is crazy – she appreciates that her house has the patina of time, which faux painters all over the world are trying hard to imitate.

Limewashed stucco of San Giorgio in Velabro, Rome

Last week I discussed the beauty of traditional limewash on stucco, which I attribute in large part to the subtle variations in color of the surface, which add considerable richnesss and visual depth to the appearance. This subtle variation results from both:

• the initial installation (e.g., from vagaries in the absorption of the limewash into the stucco – heavier in some areas, lighter in others), and

• from weathering over time, as the limewash slowly weathers, wears, and washes off the surface

Close-up of weathered limewash on stucco on a building in Rome's Centro

Limewashing a previously limewashed building will, over time, add yet another layer of depth and richness as it weathers. As the most recent limewash ages and wears off, the underlying coat of limewash often becomes gradually revealed. Thus, a building that is repeatedly limewashed tends to become a palimpsest of all the colors it has been limewashed with. I took the photo above on a random building that I happened to pass in Centro (the center of Rome), not far from the Pantheon. The most recent coat of limewash is the Tuscan red, while the previous coat was the ochre yellow. From this close-up you can see how the old coat (yellow) gradually becomes present in some areas as the most recent coat (red) weathers and wears off. Thus the surface becomes not one simple uniform color, but a mottling of two or more colors, that give it added richness. Currently popular “sponge painting”, “rag painting” and other techniques are in large part efforts efforts to imitate this look that occurs naturally with the layering and weathering of traditional limewashes over time.

Aesthetics aside, because limewashes are relatively impermanent as compared with stucco, brick or stone, they also tend to allow us to see interesting patterns and differences in the exposure, shielding and run-off patterns, and weathering of facades, decades before we could see the same thing in the deterioration or durability of stucco, brick or stone. In that sense, they are also “canaries in the coalmine” showing us well in advance of the most severe consequences how buildings weather how sometimes simple details can make a big difference.

Close-up of weathering patterns on travertine trim and limeswashed stucco

For example, on the same building (as pictured in the photo immediately above), I noticed patterns of weathering at the juncture of the limewashed stucco with the Travertine trim.   The purplish-brown line on the stucco indicates the run-off of water along that line, and shows how effective even the small top molding in the travertine is at redirecting water outward as it flows down the facade.  Travertine is a sedimentary stone formed from carbonate minerals, quarried near Rome, that has been widely used for millennia for construction in Rome.  Travertine, like other stones that are composed largely of carbonate or calcareous minerals (e.g., many limestones and marbles), tends to remain very white where it is frequently washed by the rain, and it attracts and collect soot where shielded from the rain. On the two moldings on the travertine, the outer edges, where the water washes over the stone edge, are white, but the inner recesses of the lower toothed triangular molding are soot-covered, indicating the same thing as indicated by the purple-brown streak on the stucco at left – that the top molding is shedding water and shielding the inner portion of the toothed triangular molding from the run-off of rain. Though this detail is quite small – only a few inches across – it is a microcosm of larger weathering patterns and telltales we can see in the limewash at the larger scale of the building facade.

Severe weathering of limewash from the facade of an elementary school

This is a limewashed, severely weathered façade of an elementary school in the Trasevere section of Rome. The building has a severe exposure – it’s on a corner, taller than the surrounding buildings, and exposed to the elements. There’s very little limewash remaining on the façade, but you can see that most of the limewash that remains is where the façade is shielded from rain and run-off: primarily, beneath the deeply overhanging eave of the roof, and to a lesser extent, beneath the molding drip edge of the arched window hood. And by the amount of limewash remaining on the wall beneath the roof eave you can see how effective a deeply overhanging eave can be in protecting a wall from the weather.

Using a deep roof overhang to protect a wall, and particularly the wall-roof juncture, from the weather is a time-tested principle of durability, (particularly in snowy climates, as further described in this article),  but one that is often forgotten or neglected, to the detriment of the durability of the building.  It’s not terribly difficult to design a deeply overhanging roof, with a crisp sharp edge or undercut drip edge to prevent water from curling back around, but that doesn’t mean that everyone always got it right, every time, even on buildings that display alot of thought behind their design.

Santa Maria in Trastevere

The photo above shows Santa Maria in Trastevere, a beautiful 12th century medieval church in Rome renowned for its interior and exterior mosaics. The line of saints across the façade are mosaics (small tile impressed into the stucco), while the area in the pediment above the saints is a mural (a painting on stucco). Although the primary flow of water is not over the rake edge of the roof (the sloped roof edge along the top of the pediment), the mural on the pediment shows extensive erosion and loss of the mural from water curling over the roof edge, around the concave cornice, and flowing down over the mural. The roof overhang on the cornice is minimal, and it lacks an undercut drip edge to prevent water from curling around the concave cornice and flowing down over the mural.

Small shrine in Trastevere with ornamental yet functional canopy

Just a couple short blocks away in Trastevere is this small shrine. The difference in the condition of the upper part of the mural (mostly intact), and the lower part of the mural (mostly lost) reminds us of the protective value of an overhanging roof. Here, the roof has gone beyond the simple utilitarian function to suggest an ornamental canopy or umbrella over the shrine – symbols of importance, as they were held over an important person to protect him/her from sun and rain, much as they do this mural. Of course, the word umbrella comes from a lovely Italian word (ombrello meaning “little shadow”).

Line of erosion in the sidewalk paving directly beneath drip edge

This deeply overhanging roof eave is part of my familiar walk down the big hill from the Gianicolo to Trastevere (see Week 8 post).  Although severe wind-driven rain can drive roof run-off water back against a façade despite a deeply overhanging eave, even a cursory look at the paving below tells us that this roof eave edge is working very well in shielding the facade the vast majority of the time.  Down the center of the photo, we see what appears to be a dark line in the paving – it’s the shadow of the voids between the pietrini (paving stones), directly below the eave edge of the roof, where the roof run-off has eroded the fill from between the paving stones.  Thus, the wear patterns in the paving joints show us that the vast majority of the time, the roof run-off is staying clear of the facade, and coming straight down to the ground.

The week ahead here at the Academy promises to be a week of culinary delights and special events – a cheese tasting today prepared by the kitchen interns, Alice Waters arrival here today, a reception for the U.S. Ambassador to Italy tomorrow, and a big traditional American Thanksgiving dinner on Thursday.