Traditional Plaster Stabilization

According to Brian Pfeiffer, architectural historian, “The prevalence of epoxy and other modern substitute materials used in building conservation is an American enthusiasm.  In Europe – especially in France, England and parts of Scandinavia – where craft traditions and training through apprenticeship have survived, modern synthetic materials have declined in popularity for historic building repair in favor of traditional materials that have withstood the test of time.  The USA has been slower to move in this direction because of our national predilection for whatever presents itself as 'new and improved', our predilection to believe in the results ‘accelerated weathering tests’ for new materials, and because we have suffered the nearly complete loss of traditionally trained craftsmen in the mid-20th century.  Nonetheless, there are now a small number of skilled craftsmen who can accomplish these repairs.”  

Pfeiffer goes on to explain his preference for traditional methods of plaster repair techniques. “Lime is an inexpensive material that is more environmentally benign than chemical consolidates – it requires less energy input to manufacture than do modern cements, it re-absorbs carbon dioxide as it cures and at the end of its life cycle, it breaks down into a beneficial compound – calcium carbonate; it does not contain or release toxic materials.  Second, lime has the desirable quality of binding to itself, so a new lime repair will bind into existing lime-based materials without the need of chemical binding agents.  Although nearly indistinguishable from the original material in porosity and texture, lime repairs remain visible as can be seen in old buildings where renovations carried out two centuries ago remain visible in the visually discernable differences in material color and in the different lath on which plasters have been installed. 

"Epoxy consolidation for plaster essentially impregnates the pores of the plaster interfering with porosity and glues old plaster to dry, dusty lath which does not provide as reliable a mechanical attachment as plaster keys that squeeze through the gaps in the lath to provide an even distribution of weight across the plaster.  Finally, epoxy and other consolidates interfere with the vapor permeability of plaster, wood, mortar and other materials to which they are applied.  By blocking the flow of water vapor, they direct it toward the nearest permeable surface increasing the concentration of moisture and the possibility of condensation in that area.”

One issue with the use of traditional methods on a wall mural is that it takes water to make the lime mixture and water will damage and dissolve the wall mural pigments, if applied from the finished surface.  Repairs for painted surfaces can more safely be accomplished from the back of the wall, if access is available.