Wonderful clay

The grey, chalky pond clay makes a great building material
Pond cleaning in 2011: the pale grey, chalky pond clay makes a great building material. (The darker areas are pond mud on top of the clay).

Postscript on wattle and daub – 2013

We have a great resource in the pond, which we knew about from when we drained it in 2011, but we had not appreciated until this year its amazing building material potential: pale blue-grey boulder clay, which underlies much of Suffolk.

It seems to be made up largely of fine chalk interspersed with chalk pieces of varying sizes. When wet at the bottom of the pond it is extremely sticky but remains firm enough to walk on without sinking in. When dry, it is as hard as a lump of chalk. We were told by an engineer that in our part of Suffolk the boulder clay would typically be 25 metres thick. We are lucky, in that it comes almost to the surface in the garden, and its impermeability is the reason why we have an ancient pond. We had already found a lot of it used in the old wattle and daub panels.

We discovered its quality when making minor repairs  this summer to the other walls (not the one from which the cement render was stripped).  Some of the boulder clay was put aside when the pond was cleaned in 2011. We pounded it in a bucket for 20 minutes (for larger quantities it would be a builder’s bath) until it became plastic. Then it was mixed two to one with sand and lots of chopped straw added (in fact dried wild barley stalks, growing in the meadow).

This shrank much less when it dried than the yellow Essex clay daub we bought in 2009 and 2010 (for some major repairs to one of the walls and for filling gaps in the panels inside). Our pond clay is a much better repair material for damaged wall areas, including  holes and cracks, and it may also make a good clay-based render – to be tested. Memo to self: when the new foundations are piled, keep any boulder clay that comes up with the augur.

Instead of rendering or plastering, this time we just limewashed the clay. We had noticed areas of clay in the walls that showed no signs of old render; instead, there seemed to be many layers of old limewash flaking off. Perhaps we  will carry on repairing the other walls with just clay and limewash, and skip the plaster stage.

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