We learnt the basics of wattle and daub on an Essex County Council course at Onchors Farm near Braintree. The course tutors were Lydia Bucknell and Peter Roe of Traditionally Plastered. This was a prelude to a long term programme of repairs to the daub, inside and outside.
The first thing to think about is a supply of clay daub. On the course, we learnt to make it ourselves. The basic ingredient in that part of Essex was a pale yellow clay, containing small chalk pebbles, from a pit on the farm, which was quite similar in texture to the material in the walls of our cottage.
At Onchors farm, the clay was mixed with sand, chopped straw and cow manure and then trodden (literally) until the texture changed to plastic and doughy, not unlike plasticine. It took 3 people 30-40 minutes to tread one large wheelbarrow load into the right condition. Traditional builders used to short circuit this laborious process by leaving cows tethered in the clay pits to tread the mixture. Modern machinery can be used to make daub in quantity, but do not use cement mixers, because the material is too glutinous. Onchors farm has a machine very like a large bread doughmaker, with rotating arms. Given our experience of DIY daub making, we decided to buy ready made daub from the farm in tubs.
There are many recipes and much variation in advice on this subject. We used a straight daub mix of clay, sand, manure and chopped straw for filling deep holes or complete panel replacement. For shallow repairs and a base coat for render on top of the daub, we used a mix of 2 buckets of daub to one of lime mortar. The mortar was mixed from 3 buckets of sharp sand to one of mature lime putty.
The lime putty can be made up from slaked lime, but this is a messy process and the putty should also be stored for some months and preferably a year or more to mature it, which improves the consistency. Matured lime putty can be bought nowadays from ordinary builders merchants as well as specialist suppliers of building materials for old houses. Our supplies came from Travis Perkins.
The tools required are basic: for the daub, a plastering trowel, preferably one with a rounded end, a bucket and mixing spade, rubber gloves, and a hose with a fine nozzle or – preferably – a hand-held spray gun for dampening the old materials before applying new; for the wattles, a half inch or three quarter inch chisel and a mallet or hammer. We were taught how to split the hazel sticks with a frame and a special tool, but when investigating our house we found the builders had used unsplit sticks, so we did the same.
Old clothes or overalls are of course vital, because daub gets everywhere. Where the daub is being applied mixed with lime mortar as a first render coat, then a plasterers hawk is very useful for holding lumps of material while holding the trowel in the other hand.
And so to work: the wall on the west side of the kitchen was very badly damaged. A lean-to had protected it but had disappeared. There were large holes in the clay dug by woodpeckers seeking the insects that lived in the fabric. It was far from watertight, and beginning to dissolve. Early on, we had covered it in a plastic sheet to slow the deterioration.
From June to September 2009, the exposed clay daub, which was most of it in this area, was repaired. New hazel supports were made where the holes were particularly large. The method taught at Onchors farm did not, strictly speaking, use wattles, which are woven lattices, but instead vertical sticks tied to horizontal ‘ledgers.’
The ledgers were wedged horizontally into notches on the oak studs and the vertical sticks were tied to the ledgers with simple knots. There were already notches on the oak studs, but in one of two places where the ledgers had disappeared we had to make new notches, because the old ones weren’t usable.
We found a child’s stitched leather shoe sticking out of the crumbling daub above the west window to the kitchen, looking rather like a moccasin. We were superstitious enough to leave it where it was, because we suspected it was part of some mediaeval building ritual. It was eventually covered with new clay daub.
The original hazel sticks supporting the daub panels were tied together with brambles rather than twine. Some of the sticks that were visible were surprisingly big. They were not split, unlike the technique of using large split sticks that we were shown on the Essex course. We did not split our hazel, and instead used rather smaller diameter complete sticks from the coppiced hazel at the end of the meadow.
There was some very firmly fixed cement render left in places on the wall, and this was left for later removal while the urgent repairs were done.
The deep holes, some of which went right through the wall, were filled mainly with clay daub, after soaking the wall repeatedly with a fine hand spray gun at intervals for 24 hours beforehand. This was necessary to have any hope of getting new material to stick to the ancient daub. Aftyer this experience, I started soaking the wall a couple of days beforehand in other parts of the building.
After the major clay repairs, the whole surface, including minor holes, was thickly plastered – as advised on the course – with a clay-based render made up from two parts daub to one of a lime and sand render (by volume). The lime made the clay stickier and also harder, though it was difficult to work into the surface enough to stick properly, even after a prolonged soaking. The surface was then striated with a diamond pattern using a sharp stick to make a key for a final coat of a conventional lime and sand render
The clay and daub mix was left to dry for as long as possible – six weeks to three months, depending when it was done . The first week or so it was left covered with the plastic sheet and repeatedly sprayed to reduce the cracking. (In future, we will use hessian instead of plastic, because it will keep the atmosphere damper). Though we started in early summer, the work went through July and August, which is not ideal, because the heat caused the materials to dry too fast.
The final coat was three sand to one lime putty in a thickness of one to two centimetres. The daub and lime mix of the first coat seemed to have done all the cracking for us, and most of the lime render showed very few fissures. However, it was done in four separate panels, using different thicknesses of daub and render to test adhesion and cracking. One area of render did crack quite badly. This was where the first coat was thin and the top coat thick – so best to have a thick first coat and thin top layer. It is also important to keep render damp for several days, to slow the drying and minimise cracks.