Make hypertufa from 1-2 parts sifted peat substitute or sphagnum peat, 1 part coarse sand or fine grit and 1 part cement. Add sufficient water to form a thick paste. After the bonding agent or the outdoor adhesive is dry, apply the hypertufa paste to the outside of the sink and also inside, down to well below the final level of compost. Put the hypertufa on your sink by hand, wearing rubber gloves, to leave a craggy finish. The paste on your sink should be 1-2 cm thick. Roughen the surface so that it resembles stone.
When the hypertufa is fully dry, after about a week, use a wire brush to scrub the surface, then coat your sink with a weak solution of permanganate of potash – about 3 teaspoons to a liter of water – or liquid manure to discourage algae and encourage moss and lichen to grow on the surface of your sink.
Troughs may be made entirely from hypertufa. You will use the same mixture that you used for coating your sink but increase the proportion of sand and grit to 3 parts to make a stiffer mix. You will need two wooden boxes that fit inside one another, with a cavity of 5-7 cm between them, to make your trough. Coat the surface of the boxes, the bigger one inside and the smaller one outside, with oil to prevent the hypertufa mixture sticking.
Place a 2,5 cm layer of hypertufa mix on the base of the bigger box, put a wire netting on top of this layer and around the sides to reinforce the trough, then add a second layer of hypertufa. To make drainage holes into the bottom of your trough, press severals thick, wooden dowels into the wire and hypertufa base.
Put the smaller box centrally on top of the hypertufa base, making sure that the vertical netting is between the two boxes. Fill the space between the boxes with the hypertufa mix, tamping down well as you fill. When the cavity is full, cover the trough with a sheet of plastic for at least a week, until the mix sets and protect from frost if necessary.
When the mix has set, remove the wooden shuttering from the outside of the trough. If the box does not slide off easily and the hypertufa has stuck to the box, carefully dismantle the box with a hammer and chisel. The surface of the hypertufa will be smooth and straight. For a more natural-looking appearance, scrub the outside of the trough with a wire brush or coarse-grained sandpaper to roughen the surface.
Remove the smaller box from inside the trough. To encourage moss and lichen to grow on your trough, paint the outside surface with liquid manure or with a weak solution of permanganate of potash. All you have to do now is set your alpines.