The Art of Fresco: Choosing a Wall

by Sr. Lucia Wiley, CHS

Just as the longevity of an oil painting depends in part on the way one prepares the canvas, the wall on which the fresco will live effects the life of the fresco. Many frescoes have been lost or damaged because of the wall that holds them. On the other hand, a "healthy" wall will support a fresco for thousands of years. While Leonardo da Vinci's "Last Supper" is not a fresco, I like to use it as an example. It was the construction of the wall itself which has been largely responsible for the deterioration of the painting. The foundation wall upon which it is painted is rock, resting directly upon the ground. Moisture from the earth has crept up the wall, loosening the plaster and loosening the paint. Many frescoes have also been lost for this same reason.

Present day building methods and materials have made damp walls unnecessary. Below I have listed several types of walls which create suitable homes for frescoes.

• Brick walls are ideal for frescoes. Bricks must be of even red color - dark violet bricks don't absorb water, remove them; the new plaster will not bond to them. Bricks should be baked to a fresh red color and laid in lime-sand mortar. Bloom efflorescence on brick will destroy fresco. Places where it is evident must be removed; it must be chipped out, brushed with hot thinned hydrochloric acid and rinsed in great deal of water or tarred with coarse dry sand.
• Machine made bricks must be roughened. For newly erected walls, use no bricks which have lain directly on ground. They absorb salts on the ground and cause efflorescence.
  
• Hollowtile walls are the next best wall for a fresco. Tiles that are deeply grooved and set in a checkerboard pattern form the best bond for the lime plaster.
• "Furring Walls" entails setting a new wall in front of an already existing wall. The airspace in front of a waterproofed wall ensures against the destructive work of moisture seeping into the fresco from behind.
  
• Movable panels are a practical solution to creating a safe fresco wall. The limitation here being that movable panels work only up to a certain size.
  
• Freestone walls are the least desirable base for frescoes but if they are well waterproofed, they work well also.

• Efflorescence is the greatest enemy of fresco. It may occur for many reasons, one of which is that it may be occurring within the wall itself and will grow into the fresco if the interior of the wall contains moisture or there is gypsum in the mortar. Bloom efflorescence on brick must be removed.
• Ventilation is important, so moisture will not condense on the wall.
• Waterproofing the wall is the best safeguard.