Pyrate Whilst I have no doubt that you'll find some of the steel corroding, I'd be wanting to make sure that the structural engineer was looking out for other mechanisms acting on the terracotta. Although the terracotta is connected by steel hangers, it is my understanding of the historic record and the practicalities of construction that the original terracotta masons actually 'stacked' the terracotta units into place, and fixed the hangers afterwards. When all was done, they removed their temporary falsework or supports. This is key to understanding the potential for other mechanisms to act on the terracotta. If the building is 14 stories high, and the terracotta was all stacked into place, this means that there is nowhere for any stress relief. If there is any form of differential stress develop between the terracotta units and the structure behind, then it will be locked into the terracotta. The problem is that whilst the material is strong in compression, it is extremely weak in tension. And if there is the potential for splitting tensile stresses to develop, then cracking of the face of the terracotta units (or shearing) can easily develop at changes in profile in the terracotta (e.g. projecting string course or column capitals). And there were a few of those in buildings of 1907, generally speaking! So, what I'm saying, is that the structural engineer needs to be on the look out for sources of stress in the terracotta. This might be differential thermal movement between the terracotta and the structure, although I doubt it in a building this old. This might be creep (or shortening) of the reinforced concrete structure - which although a big proportion of this occurs in the first few months after construction, it does continue for a long time (albeit at a very much reduced rate). I'd suspect that this is contributing to the problems with deterioration at the eyebrows and shelf angles, because they will act as a stress 'concentrator'. Have a good time. Cheers David West Executive Director internationalconservationservices T: +61 (2) 9417 3311 M: +61 (411) 692 696 sustaining your heritage <http://www.icssydney.com/> ________________________________ From: The listserv where the buildings do the talking [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: Monday, 21 December 2009 1:41 AM To: [log in to unmask] Subject: [BP] eyebrows have it I got the pictures in on fri I go for a "look see "Monday This is an academic discussion based on early 20th cent masonry engineering Subj: 1907 skyscrapper of 14 stories Poured in place re-enforced concrete hung with decorative terra cotta tile Conditions: Terra cotta bulging and popping off at mid and different pocket sections in elevation and pilasters Observations /poor roof for years now replaced with new roof and new flashing 1907 engineering Last time I took one of these apart the basic engineering was that an "Eyebrow" or poured in place shelf angle are supposed to pick up the "thrust and weight " of the hanging terra cotta at every floor....... and that the steel lintel at every window assists in this function as well . The terra cotta usually is supposed to be anchored into a back up terra cotta tile or brick substrate but at this writing I won't know until I ride the swing stage next week with the engineer Failure / opinions / repairs (for discussion purposes only ) What usually happens is that water errodes and makes failure of sections of the poured in place eyebrows ; shelf angle or brick back up ,this coupled with rusting anchors the terra cotta then bulges under its own weight sections of steel lintels are also prone to rust Note: all shelf angles are supposed to have weep holes Nes pas? sample repair In the past we have made repairs on the eyebrow with high strength mortars ;followed spray on by rust inhibitors To do this all the terracotta in that section (which could be the entire floor level ) has to come down Mission : To aid the engineer in the evaluation I am recomending to Inspect all areas of the shelf angle ; the good ones the 'bad ones and the ugly ones to get overall picture of conditions this goes for anchors and any and all rusting steel lintels . If all goes well I will be back in time to set out the cookies and milk /Py -- **Please remember to trim posts, as requested in the Terms of Service** To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: http://listserv.icors.org/archives/bullamanka-pinheads.html -- **Please remember to trim posts, as requested in the Terms of Service** To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: <http://listserv.icors.org/archives/bullamanka-pinheads.html>