Sufficient water is then added to the mixture to make a firm paste, which is plastered over the treated surface to a sufficient depth (say 2in[5cm]) to enable the surface to be patterned with a chisel to give a "natural" appearance. This should be done before the mixture is completely hard. Reverting now to our slab garden, the ideal base would be a slab of York stone (old tombstones are ideal) and surrounding walls of the same stone can gradually be built up using Hypertufa as the bonding material. Drainage, as always, is vital and if a single slab is used as a base, several drainage holes must be made on each side and a layer of gravel or chippings used to cover the base up to and slightly above the drainage holes. This layer should be covered with unsifted peat or coarse bark fibre, and the growing medium then placed on top. If necessity demands the use of a concrete slab as a base, the edge of the concrete should be treated with Hypertufa paste as in the case of a glazed sink. Modern stone-coloured artificial facing bricks can also be used. Whenever troughs, slab gardens or so on are used, they should be mounted on stone supports, for this helps to keep slugs and so on at bay; such supports can also be prefabricated easily and effectively from Hypertufa, using simple shuttering. Mounting troughs in this way in a paved section of the garden is also invaluable in that the shadow cast by the troughs can be used for shade-loving paving plants, and such planting spaces should always be prepared with the utmost care when paved areas are laid down. The making of troughs of all shapes and sizes out of Hypertufa can be a fascinating occupation, and the illustrations (Figs.95 and 96) give a clear idea of how the simplest trough can be made. There are those who favour elaborate wooden shuttering for the inside and outside of the trough, but the writer prefers to use boxes made out of really stout cardboard because these tend to get slightly out of shape under the weight and pressures of the Hypertufa and so avoid the rather formal outlines given by wooden shuttering. The essential (and a visit to the grocer or local wine merchant will help here) is to find two strong cartons which, when placed one inside the other, will leave a cavity of about 3in(8cm) between the two. Drainage holes are important, so stand the inner carton upon four supports (згп[8ст] sawn-off pieces of broom handle will do). Cut some wire netting to reinforce the trough, especially round the corners, and bind some wire tightly round, and over, the outer carton to prevent excessive "bellying". For the same reason, it is important to fit a few wooden struts end to end and side to side across the inner carton. Finally, remember that Hypertufa sets slowly. After 24 to 48 hours the outer carton, now soft and soggy, may be tentatively removed in order that corners may be rounded off and a pattern (shades of the stonemason's chisel!) made into the surface before it fully hardens.