Brick and tile

Dig the clay in autumn and spread it in heaps no more than about 1 m high over winter. Frost splits it, rain washes out soluble salts, and by spring it is far more workable. This costs nothing but planning.

Pick out stones, roots and especially limestone fragments — a piece of lime in a brick turns to quicklime in the kiln, swells with moisture, and blows a crater out of the brick weeks later. Test for shrinkage first, as for pottery.

Add sand to control shrinkage — often 20–30% by volume depending on the clay — and mix thoroughly by treading, pugging or with a wheel. Consistency matters more than composition: every brick from the same batch must shrink the same amount.

Mix to a stiff plastic state that holds a thumbprint without sticking to your thumb. Too wet and the bricks slump and crack; too dry and they will not fill the mould.

Pick one size and never change it. Every wall, arch and flue you ever build will assume it. A common standard is 215 × 102.5 × 65 mm fired — twice the width plus a mortar joint equals the length, which is what makes bonding work.

Make the mould larger by the measured shrinkage — often 8–10%. Sand or wet the mould, throw a clot of clay in hard so it fills the corners, strike off the top with a wire or straight stick, and turn it out onto a sanded board. Keep one master mould, and check every working mould against it weekly.

Rain on green bricks destroys them; sun dries them too fast and cracks them. Dry them flat for a few days, then stack on edge in open lattice stacks — hacks — under a roof, with air all round, for 2–6 weeks.

The bricks are ready when they are lighter in colour right through and, like pottery, feel room temperature, not cool, against the cheek. A brick cut in half should show no darker damp centre.

In a clamp or kiln: a long, slow warm-up — a day or more at low heat — to drive out the last water, then raise to around 900–1,100 °C, orange to yellow, and hold it. Cool slowly. Firing too fast seals the outside before the inside has dried, and the bricks burst.

Sort them: the outer bricks are under-fired, soft and pale, and the inner ones hard and dark. A sound brick rings clearly when two are knocked together; a dull clunk means under-fired or cracked. Use hard bricks outside and in foundations; soft ones inside.

Ordinary brick spalls apart at forge and furnace temperatures — this is why first furnace linings fail mid-smelt. Firebrick needs fireclay: pale, alumina-rich clay, often found under coal seams, that stays pale and does not melt or slump in a hot fire.

Temper it with crushed fired firebrick (grog) rather than sand, and fire it hotter than ordinary brick, above about 1,300 °C. Test a sample by holding it in the forge at welding heat for an hour and letting it cool: it must not slump, glaze or crack.

Fired tile does not burn, and roof fire is what destroys dense settlements. Make tiles from the same clay, thinner — around 12–15 mm — with a nib or peg hole to hang them on battens, and fire them hard, since a roof tile must survive frost.

Lay at a pitch of about 35° or more, each course overlapping the one below by a third or so, and nail or peg every few courses in exposed places. Test a batch for frost resistance by soaking tiles and freezing them repeatedly through a winter; soft ones flake.

An arch carries load in pure compression, which is exactly what brick is good at, and it gives kiln roofs, furnace chambers, bridges and doorways without a single beam.

Build it over timber centring — a curved former — with wedge-shaped joints or wedge-cut bricks so the mortar joints point at the centre. Lay from both sides toward the crown at the same time and drop in the keystone last. The walls or ground either side must resist the outward thrust — an arch pushes its supports apart. Leave the centring in until the mortar has set, then lower it gently.