The Building Speaks - Project Blog
The Building Speaks - Project Blog
Spalling Pattern Question 1
All - we’ve got some very interesting Spalling on either side of the carving on the left pilaster. The same problem and pattern also appears on the right pilaster. I don’t understand what’s causing this. What can anyone tell me about the history of the building or prior damage, and repairs? (John Spalling, conservator)
1. John this could be related coal black or coal tar being used on new construction ca. 1910 in order to match air pollution blackening of 1989 Nave construction. Even though it was only 11 years apart, the pollution in Pittsburgh was so severe that the Nave was black from the coke ovens and steel mill pollution. Apparently a decision was made to paint the new building with coal tar at the time of construction so it would match. (Alan Jones, owner)
2. Alan, very interesting. They must have had to dilute the coal tar pitch significantly with large volumes of solvents in order to be able to paint it on. I’d say this is chemical spalling induced by the solvents and other pollutants in the coal tar. This explains the flaky nature of the surface of much of the stone on this building. The solvents must have penetrated the stone to 1/8 inch or so and permanently altered the physical composition so that what we are seeing now is spalling. We'll probably want to abrasion clean this building to remove all visible traces of the stain as well as loose flaking stone. This could create a situation after cleaning where we may need to re-dress the face of the stone in a few selected places. Fortunately the dressing of this stone is not flat so I don't think it will be generally visible or a problem. (John Spalling, conservator)
3. John,
Cleaning the stain and the flaking stone won't be a problem for the Joss cleaning system. We'll only take as much of the surface off as necessary to either remove the stain or flaking stone. This will probably leave some areas where the solvent absorption and flaking is deeper (uneven) due to the original physical variability in the stone or quantity of solvent used. We won't be able to determine how to address this or if necessary until we are into the cleaning process. It may be possible to crank up the pressure on the cleaning abrasion to selectively wear down the stone instead of dressing the face again. In any case this will require either more cleaning time or the additional task of dressing the stone. This should be a line item in the RFP as a time and materials item with an hourly rate. We should try to estimate the quantities involved so we can ask for the projected total extended costs to be included. (Corky Smith, mason)
4.Sally, here are my estimates for the Parish Hall on the cleaning and redressing issue.
2 Chimneys - 100% of surface area
South facing Ellsworth Avenue Entrance - 15%
West face 2nd floor stone portion only 10%
Rest of building, stone portions only - less than 5%
(John Spalling, conservator)
5.Completed 2009/06/04. Scope changes added to drawing pages, and specification change added to draft RFP. (Sally Brown, architect)
Comments Closed
Wednesday, December 1, 2010
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