Recording the Evidence:

Condition and Measured Surveys.

Single or Dual methods of approach.
As previously mentioned the method and approach of recording the on site  evidence
will be determined by the aim and  purpose of the survey and inspection. It is possible to divide  the  main elements of the survey and inspection into two separate functions ,as  single methods of approach if so required , but it is more common to carry out the full survey and inspection as one complete task as a dual method approach.
On account of the above options and for the purposes of simplicity in this paper I have separated the survey and inspection phase into its two main functions and will deal with each of  these independently.

Condition Survey:
Having already visited the building  previously you will have already acquired some broad idea of its condition as seen from its general appearance. From this initial observation  combined with a knowledge and understanding of the building  type eg; its design and construction. You should  have also been able to identify some of the more obvious defects and problems evident as well as highlight common areas of concern , such as parapet gutters and rainwater systems.
After this it is now time to carry out a more detailed investigation of the external fabric of the building . Assuming  suitably adequate  access provisions  have already been organised as discussed previously. You  must now decide upon which system and sequence of investigation you propose to use. Where will you start , on which elevation and whether you proceed from  left to right and top to bottom. It is also important for you to correctly and consistently identify and label the areas physically examined when transferring their details to your site notes and records [.This will  prevent any later confusion or misunderstanding]. This is generally a matter of personal choice and preference but may well be dictated by the type and size of the building .What ever option you choose you should always incorporate an element of  common sense based upon your own or others previous experience. 

First Contact.
Now that you can get direct actual contact with  all the buildings surfaces and fabric you will be able add to your initial visual inspection with a close up view of things , while also introducing where necessary an acceptable level of  physical examination . This physical examination can take various forms, from the very simple hand testing to highly  technical analysis by sensitive electronic equipment.

The following list provides a selection of useful tests which can be used to assist in identifying certain conditions and problems. In all cases no examination should be carried out which is both detrimental to the building and its fabric or contravenes  the Conservation Policy Statement  previously discussed .Where ever possible the philosophy of minimal intervention and where realistic reversibility should be practised.

1.Close up visual inspection: 
From this position you should make close visual examination of the surface condition of the plasterwork, identifying any evidence of  :- cracking , loose or blown flat plasterwork , damp staining , surface erosion and deterioration, delamination , scaling , fabric / material loss  and other forms of movement .You should also identify any obvious signs of previous repair or making good .Always ensure you follow all the trails of  evidence available to you , other wise if you stop short or miss any signs it may well lead to an inaccurate diagnosis .

2.Low impact physical examination.
In addition to your close up visual inspection . The additional introduction of very simplephysical examination, such as surface tapping can also assist visual evidence and interpretation. Such  tapping either by hand or a soft tool will identify hollow areas of plasterwork suggesting delamination or adhesion loss between plaster coats ,etc .Simple physical examination will also allow hands on testing to areas of plaster detail , ornamentation and relief establishing how sound and secure it is and whether in a loose and defective condition.
           
3.Non destructive methods of investigation.
To aid the surveyor when inspecting the exterior fabric of a historic  building a selection of non- destructive instruments are now readily available for use .These instruments are generally non intrusive to the both the building and its fabric and therefore cause little or no damage .In most cases the equipment used provides access to information which would usually require physical intervention into the fabric and structure of the building .Most of these systems are financially expensive to purchase or hire, but can be extremely economic and beneficial in other more positive ways such as  causing minimal or no damage, nor loss to  historic fabric , limited making good to physical interventions, etc.
Examples of non-destructive techniques ;

• Radiography; penetrating X or gamma rays used to see inside elements of construction, detecting variations in density , hidden details ,cracks or voids and changes caused by  deterioration .Useful to identify  embedded fixings in plasterwork or wall structure, cracking in base materials and voids within plasterwork.
• Thermography; infrared energy waves useful in detecting subsurface details such as voids , inconsistencies and variations between materials.
• Infrared photography; similar in technology to thermography , using infrared film together with appropriate filters will indicate subtle variations in building surface colour which may be the result of increased moisture content or subsurface deterioration.
• Ultra sonic testing; high frequency sound waves directed into or through material can detect and  locate hidden details , voids , cracks and cavities. It can also be used to measure thickness and density in homogeneous materials.
• Magnetometer; metal detectors are extremely useful for identifying and locating metallic fixings or armatures within  plasterwork and wall structures.
• Fibre optic probe; enables direct penetration through small holes by flexible tube formed of optical fibres, connected to an eye piece or camera . Illuminates and views remote objects in inaccessible locations.   

4.High impact physical intervention.
There are only certain ways of acquiring specific information relating to a material  or components composition and construction and that is to physically remove a small section or layers of the plasterwork for laboratory analysis and report. If such intervention is essential then it should be kept to a minimum and carried out in the most appropriate position . Again  close observation and adherence to the projects Conservation policy statement must remain at all times.

When dealing with ornamentally decorated external plasterwork it is a possibility that a variety of different forms of construction, manufacture and material were used in the original design and site application [ also later repairs may also be foreign to original materials ] . This realistically means that if no documentary evidence is available to substantiate such data , then the intervention of specific areas of the plasterwork will be necessary to allow for small samples or sections to be removed for off site analysis and profile replication .
 
Where the condition of the plasterwork is poor and  structurally defective. Removal of such defective areas of  detail and decoration is more appropriate , particularly if it were requiring repair or replacement anyway. In the case of high detail decoration , statues or models which are either missing  in total or part. It may be considered  acceptable to carefully dismantle such pieces for off site replication ,remodelling  or repair. If the section of plasterwork in question was originally prefabricated  in a workshop , it may now require similar attention off site if accurate replication is to achieved. 

 One of the most difficult factors to ascertain without considerable intervention or opening up of  works is to establish the exact way in which each portion of the decoration , etc. was originally attached to the building . A lot is known of traditional plasterwork techniques and practice but it is extremely difficult to be exact as to the particular methods actually used without some physical or documentary evidence available .Therefore when attempting to replace missing portions of plasterwork you may have to decide to use a known traditional technique of attachment which is a realistic possible option used but which  cannot be definitely verified.  

Recording Data; 
Although this section of the paper is dealing specifically with the condition survey it is useful to mention that having some level of drawings of the buildings elevations and details may make the transferring of the site evidence as it is recorded much easier and accurate. Therefore outline sketches to some scale should be prepared if they donít already exist.[ another  reason why the dual approach is more commonly adopted.] If  using a CAD system  of production for your drawings such considerations are easily implemented.

Measured Survey:
The measured survey of the building will usually be carried out for the purpose of generating  scaled working drawings by either traditional draughting techniques or a CAD system.

General note.
There are a number of ways for which the information necessary to prepare suitable drawings can be acquired . The most traditional and still commonly used method is by hand measurement with or without the aid of electronic measurement equipment .Although in many cases this is the most time consuming and labour intensive method it is also probably the most financially economic .It will not be my intention to set about here trying to explain in any great depth these various methods of measuring buildings. In stead I intend to briefly outline the methods and systems available for this purpose. If you require more information on the detailed process of measuring buildings you should refer to the numerous texts available on this subject . One such good example is The Guide to Recording Historic Buildings  produced by ICOMOS United Kingdom.

Hand Measurement.
Until recently this was the only method of accurately measuring buildings and preparing scaled drawings .This system requires the direct measurement of the structure on site  and because of its considerable labour intensity should really now only be used on buildings of a modest size and complexity .The main advantage of this method is that it can be carried out by those who understand the building and the purpose of the exercise and not by a team of specialists with expensive equipment but no building knowledge. 

Photography.
Conventional photography is very quick and versatile but realistically will only provide a good visual record with no dimensional accuracy , even if combined with static scale or measuring rods positioned within the picture.

Rectified Photography.
This system involves the making of a true ­ to ­scale photographic print . Dimensions can be scaled off this photograph with reasonable accuracy. The advantages of this process is that it is quick and with the right  quality of equipment quite easy to produce. This disadvantages are the limitations on accuracy which are difficult to adjust for.

Photogrammetry.
Photogrammetry is a method of producing scaled drawings by measurement from photography. Used very successfully in the production of line drawings of facades. The image is produced by stereoscopic photography from which accurate measurement can be made. It requires a two step process both on and off site and necessitates specialist camera  and photogrammetric plotting equipment .The advantage of this system over rectified photography is that it is generally very accurate and will provide good value for money if its full potential is exploited otherwise it can equate very expensive.

It is quite common for a selection of these techniques to be used together successfully , but you most always ensure that the use and recording methods are kept separate so as to prevent a mix up of data introducing inaccuracy and mistakes.

The majority of the  systems shown above provide very useful tools in the production of  visual  records of elevations  at any scale . Where the need for large profile details of plaster ornamentation occurs you are best to revert back to simplistic hands on measurement techniques and investigations .

Measuring Plaster Ornamentation and Relief.
When required to measure and record raised plaster ornamentation , as with most surfaces, measuring along two plains is not difficult as the area can be divided into grid lines and the information transposed within the boxes formed by the grid as in the standard archaeological  manner of recording. Where the difficulty occurs is when having to add in the third dimension and therefore form the plaster features profile as well its plan form.

In these circumstances it is useful to look else where for inspiration. To acquire the size , profile and form of the raised plaster feature there are a number of ways in which to achieve this.

Paper profile:
The most simple method of achieving this is to insert a piece of stiff paper or card into an open joint and tracing around the edge of the mouldings  profile . Then remove the paper and transfer the traced shape onto drawing paper .Where no open joints can be found it may be necessary to mechanically open up one , or in the worst scenario actually cut a slice into the full depth of the moulding to form  a joint which can be filled later.

Another similar method is to look for a damaged section of moulding where the edge is exposed and again using a stiff paper sheet trace around the profile . You may be lucky and find a section of moulding loose or already fallen down .In this case the profile can be traced back in the office or alternatively a squeeze taken .This method is seldom available except in ruinous buildings .It is also only useful where the moulding profile remains the same throughout the feature, otherwise a selection of profiles will need to be taken.

Adjustable Profile Template;
This is a small tool made of steel or brass and looks a little like a double sided hair comb with adjustable teeth. The template can be pushed up against the moulding or feature requiring copying  allowing the adjustable teeth to form around its profile . On the opposite side of the adjustable teeth a reverse shape has been formed of the profile taken. This tool is very useful to get a rough idea of the shape and size of the profile which can then be adjusted more accurately on the drawing board. To get as accurate a shape as possible the moulding should be cleaned of all paint covering so as to expose the plaster lines of its profile.

Squeezing;
Traditionally this system of copying a mouldings profile was carried out by pressing either a thick layer of moist clay or squeezing wax onto the cleaned off profile after it has been dusted with French chalk and when set carefully removed. This then forms a reverse copy of the profile and if used as a mould by pouring plaster into it , it will yield an exact replica of the original plaster detail.

More recently the copying matrix has changed using either a hard plaster built up in layers, or more recently a rubber based liquid solution which can be painted onto the cleaned surface and when set carefully removed. The rubber based option is considerably more expensive then a plaster based equivalent, but is reusable.It is also a more simplified process and one commonly preferred by plasterers.

This process of replication can be easily preformed on site by most operatives , though  more commonly will be  carried out as part of the specialist plasterers duties.

Once the required information has been obtained you will be able to both specify the correct moulding patterns needed and decide which approach to adopt as your repairing regime. This will obviously be dependent upon the extent of replacement and repairs thought necessary after the survey and inspection has taken place contrasted with  what is thought to be economically and philosophically acceptable.
 

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