14 areas were identified as “emergency conditions” requiring limited but immediate interventions to mitigate loss and damage to the remaining original historic fabric and insure visitor safety. “Emergency” in this case is defined as those conditions which will most likely lead to loss and damage of historic fabric and public risk within the next period of extreme weather (i.e. monsoon season of late summer). Identified conditions included incipient detachment of original masonry or repairs and loss of historic fabric in the case of original masonry.

Injection Grouting

Detached areas and associated voids greater than ¼” were grouted in place with a natural hydraulic lime, fine sand, and microsphere grout using low pressure hand injection. The formula was developed by the ACL in 1990s and has been used extensively since then in the Southwest region with good results.

Edging and fills

Open edges and voids were filled with a NHL and local grey sand mortar to protect from water intrusion and secure these elements to the façade.

Repair Removal

Previous repairs that were already partially detached and in danger of failing were carefully removed and the areas stabilized.

Facings

Areas considered too fragile for mortar repair were temporarily faced with cotton gauze and a soluble adhesive to allow the fragments to remain in place until permanent treatment can be implemented during the full preservation program.

During the January 2017 investigation of the east nave wall, areas of the lime plaster showed various conditions, such as voids, gapping, cracks, and the disintegration of the plaster. The weathering of the façade plaster is due to high diurnal temperature and heavy rainfall during the monsoon seasons; whereas the inside of the mission church has a relatively controlled environment. 

Plaster disaggregation is being test treated with a nanolime consolidant. Nanolime is very fine particles of Calcium Hydroxide(CaOH) dispersed in alcohol solvents. Using the same carbonation process as the calcareous building materials such as lime plasters, nanolime replaces the lost binding medium in the substrate. Thus, physically and chemically compatible consolidating effects can be expected. 

The performance of nanolime consolidant on replica plaster at the mission was investigated at the University of Pennsylvania and the in-situ experiment generally followed the same methodology.