. Application of daub
Prior to daubing a historic building, it is advisable to form test panels to verify the performance of a daub. Application was either by throwing or by pressing the balls, or ‘cats’ of daub onto the wattle backing. From the evidence of large cracks in historic daub, throwing of a wetter mix may indeed have been a common technique but, for conservation work, it would be judicious to choose the dryer mix placed as cats, so as to minimise cracking and maximise strength.
The method by which daub cats are applied to a wattle or lath backing is as follows:9
1. Thoroughly dampen the withies or lath with a sprayer. They should not be dripping with excess water.
2. Form a cat of daub in the hand and kneed it to ‘knock it up’.
3. Working from the base of the panel, press the cat in and down into the wattle so as to ensure that the daub is well keyed into the backing.
4. Work along the panel, then upwards, merging each cat with adjacent ones so as to form a homogeneous mass.
5. Build up additional layers of cats to the thickness of the timber frame.
6. Roughly flatten the surface using a damp (but not wet) sponge wrapped in chamois leather.
7. Using the end of a piece of lath or a suitable small tool, compress the outer 20 mm of the panel against the timber frame.
8. Finish the panel to the local tradition before drying commences:
a. If panels are not to be plastered, add detail or decoration.
b. To accept a plaster, key the daub surface using a comb scratcher.
Cracking of new daub is not a sign of poor workmanship but is caused by the clay drying. Large cracks may be the result of a highly shrinkable clay, excessive fines in the soil or too much added water. Even so, lateral cracking does not necessarily mean poor bonding to the wattle: cracks are likely to be reinforced by the fibre and may therefore be considered as cosmetic. They may subsequently be filled either by reworking the redampened surface of the daub or by filling with fresh daub after rewetting of the cracked edges. Where panels are to be plastered, cracks in the daub will subsequently be filled and may be considered positively in that they provide an additional key.