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Davenport Restoration Update - Interior Plaster

 
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pharding



Joined: 25 Jun 2005
Posts: 2213
Location: River Forest, Illinois

PostPosted: Tue Oct 17, 2006 8:05 pm    Post subject: Davenport Restoration Update - Interior Plaster Reply with quote

Today we reached another milestone with the completion of the brown coat on all of the interior plaster. All that remains to be completed on interior plastering is the 1/8" thick finish coat. We had the original 1901 plaster tested so that we could replicate the finish. Tomorrow the plasters will do the sixth and hopefully final mock-up / test of the finish system. We are using lime plaster which will match the original 1901 plaster. We retained all original plaster except where it fell off the wall when the wall coverings were removed or we had to remove it for structural repairs. Existing plaster to remain was generally 3/8" thick and finished with a distemper paint system. According to the close-out documents for the 1901 project the original plaster subcontractor did not complete his contract and "FLW repaired plaster". Two panels of the original plaster with distemper paint above the sideboard will remain as is with minor touch-up. The balance of the original plaster was re-anchored to the wall with injection gluing. Our mock-ups showed issues with the suction of the finish coat to the original plaster and the plaster patches. This created an inconsistent finish. Basically the plaster patches telegraphed through the finish coat. We had to apply a thin brown coat over the 1901 original plaster and the plaster patches. Then we applied the finish coat. We tried to use off the shelf mason and plaster sand in the finish coat in the mock-ups. This did not yield a finish that matched the existing. We had a custom mix of sand created which matched the sizes of the original sand granule mix. We also tried the Robie House sand mix which did not work. Tomorrow morning I will pick up the custom sand mix. I am confident that this will replicate the original. We will test different types of floats, plaster tools, with this sand in tomorrows mock-up. One of these will be a cork float that FLW specified for the Robie House plaster finish. Once we achieve a perfect match to the 1901 lime plaster finish, we will have the custom order for the sand filled. On Thursday the plasters will start on the finish coat. Two architects from my office spent the day checking the second floor plaster for flaws. They used a laser leveling device, and a six foot level to identify problem areas. In general the plasters did a fine job, but they have some remedial work to do.



In this process I learned "everything about nothing". That is everything about sand. I worked with two plaster consultants, quality control engineers at sand and gravel companies and vendors of custom mixed sand products, i.e. sand for PGA golf courses, in order to replicate the original sand. Using samples of the sand which was distilled by a lab from the 1901 plaster and the lab reports which graded out the size of the original sand, I was able to track down the original sand and replicate the original mix. I learned about the geology of sand and what gives it its size and color. The original 1901 sand was tightly graded and appeared to be from a quality source. The sand, the matrix which in our case is lime, and the float are all critical determinants of the finished appearance of the plaster. Then one needs to work with the plasterer to replicate the technique and the stroke of the 1901 plasterer. With that, one can match the original 1901 historic plaster.
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Paul Harding FAIA Owner and Restoration Architect for FLW's 1901 E. Arthur Davenport House, the First Prairie School House in Chicago | www.harding.com | LinkedIn
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