Wattle & Daub: Craft, Conservation & Wiltshire Case Study
Contents 2 History
3 Craft
3.3 Panel Types
3.4 Staves
3.6 Daub
3.7 Decoration
4.1 Soils
4.1.1 Constituents
4.1.2 Plasticity
4.1.3 Strength
4.1.4 Field Testing
4.1.5 Selection
4.2 Dung
4.2.2 Lignin
4.2.3 Urine
4.2.4 Microbial Debris
4.2.5 The Role of Dung
4.3 Fibre
5.2.3 Maintenance
5.3 Repair
5.3.1 Partial Renewal
5.4 Replacement
5.4.1 Brick Infill
5.4.2 Renewal
6.3 Fieldwork
6.5 Evaluation
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4.1.4 Field TestingSamples of dry historic daubs need to be removed from the
site in sample bags and analysed in the
laboratory.[58]
However, a reasonable characterisation of a soil can be readily performed
on-site where a quick assessment is required or where laboratory tests are not
justified.
Coarse and fine soils can be distinguished by whether a damp
soil sticks together. The sample may require drying in the palm of the hand or
wetting in order to perform this test.
The sand/silt boundary can be judged by comparing the
particles that are visible with the naked eye versus the proportion that become
visible only with a loupe
magnifier.[59]
Gravels and sands are distinguishable visually, since
particles sizes of 2mm can be roughly judged by eye. The critical dimension of
an elongated particle is its smallest diameter, which determines whether is may
pass through a 2mm sieve.
The proportion of fines can be judged by spreading a sample and inspecting with a loupe magnifier. A more detailed field test can be done using a set of ‘pocket sieves’. Similar to their larger counterparts used in the laboratory, they can quickly grade the gravels, sands and silts of a small soil sample on-site [Figure 28]. A sand can be identified by attempting to roll a thread in the hands. Since sand is not cohesive, it will not be able to form a thread with any residual strength. A cohesive soil can be identified by squeezing a damp sample in the palm of a hand. If it forms a firm mass with residual strength then it is cohesive. It is the requirement of firmness that is important here since the ability to hold a shape (without strength) is a test of coarseness, as described above. Plasticity of a soil is demonstrated by its ability to deform to some extent without cracking. Both silts and clays may act plastically. The presence of clay can be determined by smearing a damp sample with the finger. Clays tend to bind to the skin and leave a stain. A further test that distinguishes a mainly silt/sand soil is its ‘dilatancy’. This is performed by taking a moist flattened sample in the palm of the hand and jarring it against a wall or other hand until water forms a film on the top. If the sample dulls again when pressed with a finger, followed by stiffening and eventual crumbling, then this indicates the predominance of silt/sand rather than clay.[60] The approximate strength of fine soils can be determined on site using Table 1.
[58]
The ethics of conservation must be considered. Historic fabric should not be
removed unnecessarily or where it affects the character of the building. Removal
might be justified only after careful consideration to the objectives of the
investigation.
[59]
An eye lens.
[60]
BS 5930:1999, p.116.
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