More Info -Site Through Time

One solution to failing tombs has been to completely encase them in cement. Water will still enter the structure through rising damp and any small micro-cracks that develop, the internal porous materials will still respond to moisture movement and will try to move, creating stress within the system. The strength of the concrete shell will hold these stresses in check for some time until they become too great, when the pressure will be relieved through the development of a structural rupture.

In some tombs, rather than stabilize and restore, the worst areas of lost stucco were patched with modern cement. The moisture movement and strength properties of the patch are greatly different from the surrounding material. The older stucco is generally more absorptive and can wet out more, but has a much faster drying rate. At the interface, the cement patch inhibits the evaporative process of drying, keeping the seam area wetter and the materials beneath the patch damp. Expansive salts from the damage products of cement develop at the seam.

Also at this point stresses due to expansion, hygric movement and dissolution transfer to the weaker material, causing the most damage to the historic material. Removal of bad repairs often causes even greater mechanical damage. The high adhesive strength of the repair would bond tightly to the wet brick or stucco substrate with compromised cohesive strength, thus resulting is further destruction of the historic material as the repair is removed. This creates a situation in which the cement repairs cannot be considered reversible, repairable or sacrificial because they cannot be removed from the brick without causing greater damage. The incompatible repair ultimately requires total replacement.

Incompatible surface finishes fail because of failed adhesion. Adhesion relies on mechanical means to lock into a porous surface or a chemical attraction between surface and finish, or on both mechanisms working together. Finish to finish and finish to substrate incompatibility are due to mismatched mechanical properties, or poor surface preparation. When either or both of these conditions exist, the bond between surface and finish, or finish and older finish, is not great enough for adhesion and the finish will soon peel or flake off. In the interface, shear tension is created and the materials pull apart.

Many of the more elastic modern finishes used on tombs in the past were not compatible with the brittle lime washes originally on the surface. These modern organic finishes are also less environmentally stable and have yellowed and failed due to sunlight and UV degradation.

The high heat, humidity and rainfall in New Orleans create a long growing season. A solid stucco skin is the best defense against the invasion of higher vegetation and the structural damage that plants and root systems create. Once cracks are allowed to develop, growth and destruction will begin. Root systems can progress deep into a tomb seeking nutrients from the clay-lime rich mortar, resulting in broken mortar to brick adhesive bonds and more disruption of the brick structural wall.

When plants are killed with chemicals after root systems have already burrowed into the masonry, the removal of the dead plant leaves new channels for water and more biological growth. The chemicals can also be harmful to the masonry elements or add new soluble salts into the groundwater.

All built structures require maintenance. If that maintenance is constantly deferred, opportunities are missed to fix small problems before they grow into larger problems, creating damage that compromises the tomb structure. Cracks allow moisture an uneven access to the tomb materials. This leads to broken adhesive bonds between stucco, brick and mortar, all of which can create more cracking and detachment. Once water is directed through a crack into a mortar joint, the mortar starts to dissolve, loosening the brick structure.

Typically, damage is first evident at the top of the tomb, where falling rain has the greatest impact and the bricks have the least weight above to hold them in place. Movements of brick lead to wall instability and more structural cracking and the deterioration cycles out of control until the tomb becomes a ruin.

The application of lime washes served to reduce the surface area of the stucco and thus reduce initial water absorption, particularly in conditions of falling damp. The surface finish also provided a smoother surface less inviting to biological growth and was temporarily biocidal, as well. When surface finishes were allowed to deteriorate, breaches would develop in the layer, allowing water entry, dirt accumulation and biological growth. Such breaches became weak points when a later application of surface finish was made, leading to thick, uneven build-up of poorly attached material on the stucco surface.

Over time, micro-cracks developed in these areas. The micro-cracks were of a size that enhanced capillary absorption into the interior stucco material. The micro-cracks expanded to larger cracks where biological growth took root. With time, neglected surface finishes resulted in a dirty tomb with uneven remnants of finish and aggressive biological growth and set up the conditions for further deterioration through moisture driven cracking mechanisms.

In the well-maintained tomb, the tomb owners regularly applied lime wash to protect the stucco skin. When small cracks began to develop, they were noticed during the frequent attention and were repaired. Eventually, as cracks began to grow larger, the decision would have been made to repair or re-stucco areas of the tomb. The family caretakers would notice small changes in the tomb as moisture driven movement and weathering occurred.

These issues would be repaired or stabilized during the regular maintenance work before real problems threatened the tomb. Highly vulnerable building elements such as roofs may have been repaired more often. Roof stucco repairs over intact original brickwork is a common condition at the site.