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Lifecycle of Terracotta from manufacturing to ultimate repair or replacement, including production flaws and installation problems.
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ConSpec Associates, Inc.
ARCHITECTURAL TERRACOTTA
HISTORYMANUFACTURING
ATTRIBUTESFLAWS
DETERIORATIONINSTALLATIONANCHORING
REPAIR
REPLACEMENT ALTERNATIVES
Mission Statement
To combine technology with tradition in both methods and materials for innovative, cost
effective, engineered solutions to the repair segment of the built
environment.
WHAT IS TERRACOTTA?
Terra-Cotta refers to a high grade of weathered or aged clay which,
when mixed with sand or with pulverized fired clay (GROG),
can be molded and fired at high temperatures to a hardness and compactness not obtainable with brick. Simply put, terra-cotta is
an enriched molded clay brick or block.
HOW IS IT MADE?
Hand Pressed Units: Clay is rolled out in order to remove the air from the raw clay material. The clay is then applied into high-grade gypsum plaster mold. When applying the clay into the mold, workers meticulously hammer and beat the clay, by hand, into all corners, reliefs and profiles of the mold.
HOW IS IT MADE?
Extruded Units: The raw clay materials are mixed into a plastic state and sent through a vacuum chamber to remove the air within the clay. Then the plastic clay material is pushed through a steel die and the terra cotta units are cut to length. This method is the least labor intensive and is most cost effective.
HOW IS IT MADE?
Ram Pressed Units: Ram pressing terra cotta units is very similar to the traditional hand pressing; however, a hydraulic ram presses the clay into a mold in lieu of a workers hand. This method of production is less labor intensive and is cost effective with medium to large quantities of repetitive units.
HOW IS IT MADE?
Slip Casting: Slip casting terra cotta units is also similar to the traditional hand pressing, except that the chemistry of the raw clay material is modified to create slip or clay slurry that is poured into a fully enclosed plaster mold.
How Long Does It Really Take
to Get Terracotta on a
Project?
PROCESS CYCLE
Contract Date 05/10/13 Receive Color Sample 05/17/13 Receive Survey Info 05/13/13 Receive Fragments 05/17/13 Initial Color Submittal 07/16/13 Arch Review 1st Color 07/26/13 12X12 Color sample 08/15/13
PROCESS CYCLE
Arch Approval 12X12 08/25/13 Shop Drawing Sub 06/14/13 Approved Shops 06/24/13 App Shops Received 06/26/13 105 Day Init Ship 10/09/13 Final Ship 134 Units 11/24/13
ATTRIBUTES
Shapes and designs, limited only to the imagination of the designer
This glass like glaze is durable and impervious to moisture penetration
Glazed surfaces are very dense and do not attract dirt and/or atmospheric deposits, resulting in a nearly self-cleaning surface
ATTRIBUTES
Fired clay material is fireproof Maintenance of the fired and
glazed surface is easy; it never needed paint and periodic washings restored its original appearance.
Durability and permanence – 100+ year life cycle
Manufacturing Defects
Air in material Poor Body Mix – Clay vs. Grog Delamination in Hand Pressed Warping – Aesthetic Only Improper Drying Inadequate Firing Improper Cooling – Body
Cracks Glaze Application
DETERIORATION
“The root of deterioration in glazed architectural terra-cotta systems often lies in a misapplication of the material”
PRESERVATION BRIEFS #7National Park Service
The Preservation of Historic Glazed Architectural Terra-
Cotta
DETERIORATION
Moisture Penetration Associated Material
Deterioration Corrosion of Underlying Steel Moisture Expansion Thermal Movements
DETERIORATION
Deterioration of Mortar Joints Cracking Spalling
– Glaze spalls – Freezing and thawing of entrapped
moisture Question – Grout fill or leave
terracotta empty?
DETERIORATION
Crazing - stresses caused by moisture expansion of the clay body exceed the tensile capacity of the glaze
Glaze shivering: glaze formulation not compatible or “fit” with the clay body shrinkage ratio during firing. glaze will be in tension without complete adhesion of glaze to the clay body. This can result in glaze peeling
DETERIORATION
Improper repair techniques typically cause the most severe deterioration to a terra cotta facade (cladding material and underlying structure).
Note: As Arch Terracotta is considered impermeable it was once thought that no weep system was needed! WRONG!
INSPECTION
Visual Inspection Sounding – Wood – Acrylic –
Rubber - Metal Tests for Impurities Borescope
– Filled or not filled– Anchor & Steel Condition
INSPECTION
Probe Holes Metal Detection Infrared Scanning Sonic Testing Crack Monitors Rhylem Tests
INSTALLATION
Question? – Match TC pieces line for line, cure for curve?
OR True lines that “should” be
straight – sills, watertables, etc?
INSTALLATION
Questions? What Happens When Anchor
Holes Don’t Align? Mockup for complicated
sections? If so how does it impact
schedule as produced units are 3-4 months out?
Albany Capitol Mock-up
MAIN CAUSES FOR FAILURE
Use of Tanking or Backfill in the Units
Type of Mortar Used Inconsistent or Sloppy
Workmanship– Missing Ties– Mortar allows water ingress– Flashing, Caulking, Support, etc
Anchor Types
Mechanical - Off The Shelf Mechanical - Custom Chemical Cementious
Materials
Anchor Types
Impediment– Split Tail– Undercut– Pin– Swelling Sock
Adhesive– Epoxy– Resin
Mechanisms
Support– Angle/Channel– J Hook– Clamp– Clip– Bracket– Rod
Manufacturers
Mechanical
Holman & Barnard
Dur-O-Wall Heckmann Helifix
Cementitious
Ambex Cintec
Manufacturers
Epoxy
Hilti Powers Rawl Sika ITW Red Head
Resin
Hilti Celtite
Anchor Details Supplied at Bid By
Structural Engineer of Record - Sub Consultant to SE of R - Terracotta Manufacturer - Contractor - Anchor Supplier - Terra Cotta Standard
Construction 1927Typical or Detail?
40%40%
10%
0%
10%
Design Process
New Construction– Control
conditions for assembly design for both terracotta and substrate
– Set the needs for the anchoring system
Restoration– Discover
conditions for assembly design
– Examine existing conditions through visual inspection of in-place materials
Anchor Type & Source Percentage
TYPE
Catalog – Custom -
DETAIL
Structural Eng -
Architect -
Manufacturer -
Contractor -
70%
30%
10%
30%30%
30%
Contributors
Engineers Robert Silman SGH RRJ Thornton
Tomasetti WJE
Architects WASA Vitetta
Contributors
Manufacturers Gladding
McBean Cintec Helifix
Contractors Union Stone
Comments
1. Specify as much as we can to take it out of the contractors hands.
2. We are typically cleaning up messes.
3. Have to take it building by building.
1st Engineer
Comments
1. Tough to get beyond what contractors want to use.
2. You can provide complete specs but will it get done?
3. Spec doesn’t matter as you must find an anchor that fits in the field.
4. Danger is if specified and can’t be used contractor will ask for more money.
5. Mention anchor but hold pricing as pricing seems to override engineering.
2nd Engineer
Comments
1. Terracotta Standards circa 1927 ok for massive masonry structures.
2. Transitional steel frame construction, details are inadequate and must be redesigned upon restoration
3nd Engineer
Review Process
The choice of fixing details for terracotta depends on many things – not simply on whose specifying it:
Type of terracotta construction eg. load bearing mass masonry; transitional steel frame/load bearing masonry or reinforced concrete or steel and terracotta cladding
Forms of deterioration i.e. structural cracking; cracking of face of blocks alone; spalling etc
Type of remediation – wholesale replacement; partial replacement; patch repair
Exposure of the repair i.e. in seismic or high wind areas; marine climate; desert climate etc
Logistics i.e. high rise and forms of access Costs of repair In response to these factors, fixing details have to provide structural
support and/or restraint, and yet account for movement (terracotta being notoriously poor in shear and tension). There are no standard details for all of this.
4th Engineer
Systematic Approach1. Anchor system is designed and included on the contract
drawings2. Contractor is required to coordinate with the terracotta
manufacturer to provide pieces for mockups3. Typically an engineered system4. Mockups and shop drawing details required on all
anchoring5. Number and location of all anchors detailed6. Main problem is contractor doesn’t see how tight
schedule is as mockups of production pieces of terracotta are required and this time element must be taken into account.
7. Manufactured terracotta may have holes or slots in the wrong location for the infield condition necessitating additional holes or slots drilled into the production pieces.
8. Complete process is quite rigorous.9. Mockups in many cases being done during actual
fabrication of the terracotta10. Contractor produced anchors are open for review but
typically only engineered systems are acceptable
PHOTOS
PHOTOS – Goodwin Hotel
PHOTOS – Goodwin Hotel
PHOTOS – PS 238
DETAILS
DETAILS
DETAILS
DETAILS
DETAILS
DETAILS
DETAILS
APPLICATION
Concrete Backup
Custom Fabrication Process
Custom Fabrication Process
Custom Fabrication Process
Custom Fabrication Process
Custom Fabrication Process
Photos courtesy of John Lindner of Union Stone – Hoboken NJ
REPAIR
Crazing - stresses caused by moisture expansion of the clay body exceed the tensile capacity of the glaze
Glaze shivering: glaze formulation not compatible or “fit” with the clay body shrinkage ratio during firing. glaze will be in tension without complete adhesion of glaze to the clay body. This can result in glaze peeling
2003Ritz Carlton HotelSan Francisco
20095 Years After Repair
Concerns
New Construction– Longevity of System Performance– Match Anchor to both Substrate and
Unit Capacity
Concerns
New Construction“Structural steel when erected
frequently varies from the exact figured dimensions, for this reason all supports for terracotta including angles, rods anchors, etc. should be designed so as to permit easy adjustment to the reasonable requirements of construction when the materials are being set” – Terra Cotta Standard Construction 1927
Concerns Restoration
– Longevity of System Performance 25 – 50 – 100 years
– Match Anchor to both Substrate and Unit Capacity
What is Substrate? Is Capacity of Substrate Diminished? Is Substate
– Solid or Hollow– Strong or Weak
“Anchors don’t fail substrates fail”
– Are Anchors Fire Rated?
Concerns Restoration
– Need for Replacement Units Deterioration Unstable Anchorage - Sometimes Rust Jacking due to Steel Corrosion
– Replace Steel– Apply Cathodic Protection to Steel
Concerns Restoration
– Replacement in kind may negate need for new anchorage design
– Replacement Material Durability Anchorage Requirements Aesthetic & Color Retention
– How do you inset single unit into existing structure?
– New codes may require Seismic upgrade
Replacement Materials
In Kind Stone Fiberglass Cast Stone Other
Longevity – Color - Cost
What Now?
Terra Cotta Standard Construction 1927– Covers Massive Masonry
Applications– Not as good for Transitional
Buildings More Standard Details for
Transitional Buildings?From Where?
Where?
– The Masonry Society– ICRI
Masonry Strengthening & Stabilization Committee
– APTI– SEAoNY– National Parks Service– Manufacturers, Engineers,
Contractors and Conservators
Preservation Engineering Who Restoration
Engineers What Master’s Degree When 4th Semester in
Progress Where Manhattan College Why Less than 5% of
Civil/Structural Engineers understand existing structures for restoration not Rip-Out-And-Replace
THANK YOU
Remember
“Combine Tradition with Technology”