This paper shares a testing program that incorporated the use of phosphate solutions to create a mineral coating (hydroxyapatite) on stone to impart strength and durability. The project goal was to consolidate the surface of weathered stones (primarily calcareous stones were tested) to prevent loss from dissolution. Naidu shared that the idea of this testing program came from natural patinas (phosphate and oxylate-based) that can be observed on stone surfaces. Calcium phosphate and hydroxyapatite (main inorganic component of teeth and bones) were analyzed.
Testing was conducted to react a phosphate source with calcite (carrara marble used), and diammonium hydrogen phosphate (DAP) was selected for further analysis through SEM/EDS and XRD. Variables of DAP concentrations (1m and 2m) and exposure times (12 hours and 24 hours) were analyzed. SEM images were used to evaluate film formation, and it was found that after 24 hours of 1M DAP concentration exposures that a dense film was created on the stone’s surface. Raising the concentration to 2M created a denser film, though spalling was evident. XRD confirmed the presence of apatite in the film.
Studies also found that during the process of converting minerals the porosity of the stone increased and further testing should consider adding calcium back into the stone. SEM analysis was used to evaluate the addition of calcium ions back into the samples, and the most coverage was seen with calcium chloride at a 1M concentration. Naidu also mentioned a study by Snethlage that reported success of converting minerals using ADP. This testing will continue and explore external ion additions and sequence transformation, control films, and comparison of effectiveness with calcium oxylate.
Naidu discussed the process of consolidation using silicate-based systems, pointing out that sometimes coupling agents such as tartaric acid are used to assist bonding. A comparison study was designed to evaluate Conservare OH100 and 1M DAP on artificially weathered limestone (heat was used to induce damage to samples). The consolidants were applied and the tensile strength (all samples) was tested at 2 days (DAP 25% increase) and 4 days (DAP 28% increase). The results indicated a greater improvement with DAP treated samples. This testing will continue and explore the effect of calcium ion additions, organic additives and extending samples to marble. Tracking the progress of this continued testing will be important, since there are relatively few stone consolidants on the market that meet current environmental and safety standards.
This talk presented an approach to fountain care that is preventative, focusing on maintaining an ideal water chemistry to prolong the life of fountains and associated mechanical systems, plumbing and artwork. Krueger presented a process for treatments to fountains, particularly when biogrowth is observed. Prior to treating water chemistry, Krueger recommended draining the water and mechanically cleaning the elements with a surfactant and clean water, taking care to rinse thoroughly.
Fountains must then be re-filled and if using a municipal water source it is likely that minerals and organic matter must be addressed, while a distilled water source may require addition of minerals. Krueger explained the concept of water saturation, and that unsaturated (soft) and supersaturated (hard) water both create problems either with leaching or precipitates. Water saturated of minerals is ideal, and pH and water temperature both affect saturation as well. Krueger recommended the Taylor Brand test kit, which is available at commercial pool/spa supply stores, to assist with balancing and monitoring water chemistry.
Regarding biogrowth, he explained that additives such as silver/copper, chlorine and quaternary ammonia all can effectively control growth but can cause issues such as staining, deterioration of mechanical systems and water foaming. Poly-quats act as blocking agents in swimming pools and ponds, and Krueger recommended its use for controlling bacteria and fungi. Filters help maintain water chemistry and control biogrowth by limiting nutrients available in water. Krueger explained that oligotropic water is ideal (trace amounts of minerals Ni, Zn and Cu), and that controlling phosphate levels is recommended to limit biogrowth.
A series of steps were presented for checking levels and making alterations to the water chemistry. 1- Make visual observations, as the presence of a slippery surface can indicate the beginning of growth. 2- Test water (phosphate levels, temperature, and level of polyquats which requires a special kit). If high levels of phosphates are found then it can be remedied by draining some water and refilling it (if under 125ppm) or using a chelating agent and then backwashing (if over 125ppm). To adjust alkalinity, sodium bicarbonate can be added in small quantities and checked every 24 hours. Then total dissolved solids (hardness) should be tested and followed by checking calcium carbonate hardness, keeping in mind that calcium hypochlorite should not be added to adjust, rather by draining some water and adding new. Finally the overall saturation should be checked. 3- Inspect mechanical equipment. Filters should be inspected per manufacturer’s instructions. Krueger shared that he is researching the practice of adding barley straw in water, as there is published data that supports or disputes its ability to eliminate algae by releasing peroxides in the water.
This talk focused on research studies of biodiversity and treatments to control biogrowth on fountains, thus slowing the deterioration of stone. Cuzman explained several factors that affect micro-environmental conditions including: water regime (continuous or sporadic), materials (intrinsic properties), location (colonizers) and treatments (to water or fountains). Four fountains were selected in this study – two in Florence, Italy and two in Grenada, Spain (Patio de la Sultana and Patio de la Lindaraja). Microbial diversity of the colonized surfaces (green algae, cyanobacteria, and diatoms) was identified on the surface, forming a complex structure (biofilm); DNA sequencing was used to characterize sampled biofilms, and similarities were found between the two different geographic areas.
Regarding removal of biofilms, mechanical removal or water treatments can be effective. For this experiment a chemical treatment was also explored by adding an antifouling agent to a commercial waterproof coating (Wacker Chemie AG, SILRES® BS 290). Antifouling agents considered include: poly-alkyl pryidium salts, zosteric acid, capsaicin, and algophase.
Two fountains were selected for treatment (Tacca’s fountain in Italy and Patio de la Lindaraja in Spain), and both fountains were drained and mechanically cleaned. Afterwards, the modified waterproof coating was applied and allowed to cure for two weeks before adding water back to the fountains. Both fountains were visually observed, and at four months slow growth was observed, while at six months significant green growth was observed. Sample analysis from both fountains found a decreasing number of colonizing organisms, so even though growth was observed the diversity of organisms in the biofilm was affected. Cuzman found that the treatment only affected specific colonizers and that the unaffected ones flourished with less competition. Research on this subject will continue, perhaps modifying the antifouling agents (amount or types) added to the coating.
Thomas J. Podnar opened with a picture of an anonymous fountain to illustrate the beauty of these structures and their ability to bring beasts together (displayed by horses drinking from the fountain). The talk consisted of three case studies which are summarized below.
The Probasco Fountain in Cincinnati, Ohio (c. 1887) was the subject of the first case. The fountain consists of Quincy granite with a polished bowl and a bronze top. The fountain was located precariously close to an existing roadway, and Podnar was hired to evaluate the condition of the fountain and explore the feasibility of moving it to a safer location. During an investigation of the interior cavity, he found a water main running through the chamber and an electrical box, which was added for display lights. Research of historic photographs revealed that the water display had been diminished and that it was missing elements such as drinking cups. In the end the city decided that it was cheaper to move the alignment of the road (slightly), and the fountain remains in the original location.
The second case study subject was the Athena Tacha in Cleveland, Ohio (c. 1985). The stepped granite fountain was designed to be ½ wet and ½ dry (the latter for students to perch upon). After running for eight years, the fountain was shut off due to issues with water leaks. A condition assessment found that the adhesive sealant, used to control water, had failed and resulted in water leaking to the dry side. Mineral deposits were also found on the stone’s surface, other conditions included broken pipes, corrosion, and inadequately sized equipment. The client also shared photos taken during the installation process, and Podnar noticed that it was the middle of winter. Low temperatures had also caused poor bonding of the stone to the continuous mortar bed. A full re-installation and equipment upgrade was recommended and subsequently executed. Stones were removed and labeled, and when re-installed provisions were made for water seepage to flow to the pool (at the base) and stainless steel clips were added to reinforce connections. Custom-fit pieces of sheet metal were installed to separate the wet and dry sides. The mechanical system was fully replaced (upgraded) and the access grate was designed to match the existing (granite) in galvanized metal, rather than stone, to facilitate maintenance with a lighter unit.
Voyage of Ulysses on Sixth Street in Philadelphia (c. 1977) was the subject of the final case study. The stainless steel fountain was fabricated by Lippincott and designed by David von Schlegell. During the condition assessment, Podnar found that the clear coating (applied to the metal’s surface) is failing and that the water display has been diminished (when compared with historic photographs). The fountain installation is located over a parking garage, and is leaking into it. The mechanical system consists of separated pumps for the two different display elements (high water throw on one side and a continuous waterfall on the other). Other findings include that the screen strainer has never been removed during maintenance and that over the years pumps were replaced with smaller ones. Podnar shared historic photographs taken during fabrication of the artist testing the water flow at Lippincott, emphasizing the importance of water flow in this fountain’s design. Conservation treatments are planned and have not yet been executed.