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Drayton Hall Conservation

Design and Evaluation
A treatment testing program was developed to identify and select the most appropriate formulations for reattaching  the ceiling.
Morgan Phillip’s seminal article on the use of acrylic emulsions for flexible and non-flexible reattachment of plaster to its substrate (1980) was critical to the success of this project.

His mixes used variations of the same basic six ingredients including two acrylic emulsions as binders: Rhoplex MC-76 and Rhoplex LC-76. Rhoplex MC-76 is the stronger emulsion originally designed as a masonry bonding agent while Rhoplex 1950, the accepted replacement for LC-76, is the more flexible component originally designed as a binder for elastomeric sealants. In the case of all the flexible formulas, the mixtures were based on 3 parts Rhoplex MC-76 to 1 part Rhoplex 1950 while the non-flexible used only Rhoplex MC-76. Additionally a thickener Acrysol ASE-60 was used to control viscosity and flow. The unfilled formulations using only the emulsions and thickener were intended for very small gapping.

Filled formulations were also designed to provide for more significant gaps. For the filled formulations a mix of equal parts lime, glass microspheres, and fluid petroleum coke were independently incorporated together. For these filled formulations where the Acrysol thickener was included, all mixtures were first thickened with 20% by volume of the emulsion formulation prior to the addition of the premixed dry filler ingredients.

Mechanical Testing
All testing was carried out at the Mechanical Testing Center of the University of Pennsylvania under the guidance of the facility director Dr. Alex Radin. Tests were run on the Instron testing machine model 4206, an electro-mechanical system which uses a special digital data acquisition system called “Measure” developed by National Instruments. The data collection system was a Microsoft Excel add-in allowing for the collection of 2 independent channels of data to be recorded in a spreadsheet. Channel 1 recorded the displacement of the machine while channel 2 recorded the applied load. The software recorded 10 scans per second allowing for easy extrapolation for time in minutes. The test carried out on the samples was a standard tensile strength test which involved increasing the load applied to the sample by increasing displacement. All samples were run at the same speed of 0.03 inches per minute until the sample either failed completely in the case of the rigid samples or peak load had been surpassed in the case of the flexible samples.
The principle phase of treatment involved injection of the acrylic emulsion adhesive to reattach areas of the ceiling which had been identified as detached but which were still in place. Once areas had been identified for injection, holes were drilled at an interval of approximately ½ inch using a 3/32-inch drill bit. For each crack drilling was begun in the center of designated lengths instead of at the ends. The purpose for this was to ensure that only damaged areas were being drilled. As each consecutive hole was drilled in a given direction along a crack, the amount of space within the gap between the plaster and the lathing was monitored using a simple technique of intuitive sensing, when drilling through the plaster resistance was noted. Once the bit exited the top side of the plaster and entered the void, it would travel with no resistance until it came in contact with the lathing and previous plaster repair above. As the drilling progressed along the length of the crack' the distance the drill would travel unhindered in this gap would change, reflecting the size of the void between the finished plaster surface and the lathing. This gapping would continue to shrink until it would disappear completely. At the point where this gapping ended, the drilling was stopped and then reinitiated from the first hole drilled traveling in the opposite direction along the crack.
historic image
All formulations were first tested for bonding strength and flexibility in order to identify the best adhesive for the reattachment. 
ceilign repair
High speed mixing ensured good dispersion of the formulation.
lindsay mixing
Using veterinary syringes, the acrylic emulsion was injected into small holes drilled along the pathway of the cracks. After the emulsion was injected onto the voids, light pressure was applied to the ceiling surface using custom designed padded extension poles.

posting in place
At the end of each day, treated sections of the ceiling which had been treated, were left with light pressure over night.