Material failure
•
Use of new materials with unproven peliormance records·
Use of new materials without knowledge of best practice methods for use•
Use of traditional materials in new ways, or in combination with new materials•
Poor workmanship and quality control (new materials chosen for reasons of economy)Detailing failure
·
Lack of knowledge for best methods of detailing new materials to ensure long-term survival·
Adaptation of traditional materials to new detailing tQ achieve aesthetic Outmoded production•
Rapid development of materials and eqJally rapid supersession of materials·
Use of environmentally unfriendly materials now banned·
Lack of salvage industry yet established for modern buildings Maintenance failure·
Naivete regarding maintenance requirements for new materials andbuilding systems
·
Failure to implement maintenance recommendations Patina of age·
Comparative accelerated aging of modem architecture·
Short-term performance of modem materials·
Unrecognized nostalgia for aging modern buildings·
Material problems for deteriorating modern buildingsDesign and functionalism
•
Adaptation for new spatial and planning requirements (open plan and glazing expanses)•
Upgracfing for modern environmental performance requirements (energy conservation)·
Health and safety requirements·
Large scale of some modern buildingsLifespan
·
Throwaway architecture', intentionally designed for short lifespan•
Poor technical performance of materials and systems·
Economic viability•
Recording as a valid form of conservationCultural
·
Lack of recognition/appreciation for modern buildingscircumstances/position on
•
Poor understanding of 20th Century architecture (incomplete histories) the time line·
Lack of experience•
Lack of knowledge of modern materials and their performance over time·
Lack of knowledge of repair systems in the longer term•
Undeveloped repair methods to meet conservation aims·
Availability of resources (expertise, financial and salvage material)·
Presence of the original architect (wish to restore and improve)do_co,mo.mo_ 52 The Fair Face of Concrete
Table 2. Typical reinforced concrete decay problems for postwar buildings, current repair options, and conservatIon dilemmas
CAUSE OF OECAY MANIFESTAT10N REPAIR SOLunON" CONSERVATlON DILEMMA
1.0 Inherent material problems
1.1 Low cement content and Highly permeable concrete: Traditional repair and coating Loss of original material, chanpe In appearance Finely ground cement poor durability leading 10 (unless patches match orlglna cancrele), caatlng
reinforcement corrosion changes surface appearance
Realkallzation and coating Some physical damage from application 01 process, coating changes appearance Cathodic protection Potentially none
Corrosion inhibitor Potentially none Sprayed cementitious over New surface to building coating/render
1.2 Hfgh alumina cement Gradual loss of SlrBnp,th
leadIng to structural ailure No cure
1.3 Poor·quallty aggregates: Poor du rabillty
· Impure aggregates Chloride anack Desalination Some physlcaf damage from process (unwashed sea sands)
Poor workability, high As 1.1 As 1.1
• Poorly graded/shaped
aggregates water/cement ratios leadIng to poor durability and reInforcement corrosion
1.4 Alkali aggregate reaction Concrete breakdown No cure
1.5 Presence 01 calcium chloride Chloride attack Cathodic protection or Potenllally none
addliives In mIx Desallnallon Some physical damage from process
1.6 Creep Structural failure No cure
Surface cracking Crack filling Aesthatically Intrusive unless fillings match origInal concrete
1.7 Decorallve linishes: Reduced ~Ikallnlty of CathodiC protection or Potentfally none
• Acid etching concrete, .ncreaslng Realkalization Some physical damage from process suscepllblllty to
• Bush hammering /surface reinforcement corrOSion As 1.1 As 1.1
profiling Reduced cover to
relnlorcement
1.8 Poor quality/lack of Dllferent levels of cover As 1. t As 1.1 relnlorcement, scrap and Siructural failure No cure
Inconsistent type
2.0 Envlronmentallntluenc8a
2.1 Acid gases Poor durability leading to
relnlorcement corrosion
As 1.1 As 1.1
2.2 Air and mOisture Poor durability leading to relnlorcement corrosion
As 1.1 As 1.1
2.3 Freeze thaw Poor durability leading to Coating Coating changes a~earance
breakdown 01 concrete Sprayed cementitlous over New surface to bul Ing coating/render
2.4 Sea water Chloride attack Cathodic protection andlor Potentially none
Coating Change In appearance
2.5 Road salts Chloride attack Cathodic protection and/or As 2.4
Coating
2.6 Sulphate attack Concrete breakdown Coating Change in appearance
3.0 Poor deSign and workmanship
3.1 Lack 01 cover to Poor durability leading to As t. t As 1.1
relntorcemenVplacement reinforcement corrosion
3.2 Remote site batchlng • poor mix Poor durability leading to As 1.1 As 1. t
quality reinlorcement corrosion
3.3 Inadequate control of water Poor durability leading to As 1.1 As 1.1
content reinlorcement corrosion
3.4 Inadequate curing Cracking, loss of strength, Crack IlIIing and elastomeric Change in appearance and poor durability coating
3.5 Inadequate Cracking, loss of strength, As 3.4 As 3.4
compaction/vibration and poor durability 3.6 Plastic shrinkage Cracking, lass of strength,
and poor durability As 3.4 As 3.4
3.7 Accessibility tor maintenance Lack of maintenance Dependent on how manllested 3.8 Design laults Nater ponding. choice 01
'ixlngs at attached materials,
Neathering detailS, etc.
Inprovements to detailing May involve alteratton to building's appearance
clQ.<:"o,mo.mo_ 53 The Fair Face of Concrete
Heritage Convention, Nara, 1-6 November 1994 (UNESCO, ICCROM, ICOMOS, 1995); J. Jokihleto and H. Stovel, 'The Debate on Authenticity', ICCROM Newsletter, nQ. 21, July 1995, pp. 6-8; B. Feilden and J. Jokihleto, Management Guidelines for World Cultural Heritage Sites, Rome 1993, pp. 59-76.
5. See Thomas Jester and Susan Bronson, 'Mending the Modern: A Selected Bibliography', in APT Bulletin. The Journal of Preservation Technology, Vol. XXVIII, no 4, pp. 59, For more key references on the subject.
6. Table 1 is a summary of the issues as discussed in S.
Macdonald, 'Reconciling Authenticity and Repair in the Conservation of Modern Architecture', Modern Matters, pp. 87- 1 00.
7. The arrival of a number of architects From continental Europe (such as Berthold Lubetkin, Walter Gropius and Erne; Goldfinger), who had direct experience in the experimental use of reinforced concrete within the modernist oeuvre, helped stimulate this. Amyas Connell (later of Cannell Ward and Lucas) established his own architectural/building firm and went on to build a number of seminal modern concrete houses in England.
8. In Britain the modernists developed a monolithic poured-panel-and-slab method of construction, which enabled building joints to
be
reduced to a minimum and reduced wall thicknesses to as little as 2 inches in some cases.9. T-here are now reasonably well-established means of coping with the repair of interwar, typically rendered concrete buildings that do retain these smooth jointless Finishes and thus the aesthetic authenticity of the building relatively well, although often at the expense of the original material.
10. The two-man weight limit on lifting equipment restricted the use of large-scale prefabricated components until the 1960s in Britain. In addition, the association of precast concrete with the temporary housing of the immediate postwar period had established it as a low-status material, a perception which took some time to shift.
11. A paper discussing English Heritage's research into mosaic-clad concrete and the options for its repair will be published in English Heritage Research
Transactions, Volume III, in 1997. It will be available from: English Heritage, Architectural Conservation, 23 Savile Row, London, Wl X 2AB, United Kingdom.
12. For a general explanation of concrete decay phenomena and repair options see: J. Allan, 'The Conservation of Modern Buildings' in E. Mills, Building Maintenance and Preservation: A Guide to Design and Management, Oxford 1994; for more detailed information see: P. Pullar-Strecker, Corrosion Damaged Concrete: Assessment and Repair, London 1987.
13. For an explanation on corrosion inhibitors see: J.
Broomfield, Corrosion of Steel in Concrete:
Understanding Investigation and Repair, London 1997, pp. 104-106.
14. Grade I listed buildings are subject to listed building consent for any works deemed to alter the character of
the building including internal works.
15. Opaque coatings due to the presence of pigments offer better long-term protection against carbonation than clear versions.
16. The repairs to Falmer House were broken down into four phases of work, of which this is the first.
17. There are limitations associated with patch repairs, and there are instances where other repair methods for areas of latent damage will be more appropriate.
18. For an interesting discussion on the weathering of buildings see: D. Leatherbarrow and J. Mostafari, On Weathering: The Life of Buildings in Time, Cambridge 1993.
19. The methodology developed at English Heritage is outlined more fully in: S. Macdonald, 'Conservi,lg Carbuncles, the Dilemmas of Conservation in Practice:
an Overview of Current English Heritage Advice and Research for Twentieth-Century Buildings' in M. Stratton (ed.), Structure and Style, London 1997, pp. 207-224, and 'Technical esponses to Typical Conservation Problems For Postwar Architecture in England: Current Research and Case Studies from English Heritage' in Conference Proceedings, Fourth International DOCOMOMO Conference, Bratislava 1997.
20. This is not to say that coatings do not often play an important role in a repair strategy; however, the decision to use a coating and determine which coating is most appropriate should be made in response to a building's particular problems. There are other repair methods (such as cathodic protection), which may provide viable alternatives.
21. Most information to date is contained within conference proceedings and is often case-specific. See for instance the -990, 1992, 1994 and 1996 DOCOMOMO International Conference Proceedings, and various articles in the DOCOMOMO Journals since 1990. For lists
of
key texts see T. Jester and S. Bronson (note 5) and J. Allan (note 12).dCJc,mo.mo_ 54 The Fair Face of Concrete