Fired clay pipe is made in sections 30-60 cm long with a wider socket at one end, fired hard in a kiln and joined with clay or lime mortar, and it lasts for centuries when buried. It suits low-pressure gravity lines only, because it cracks under real pressure and water hammer, and a line of it has 167 to 333 joints per 100 m, each a possible leak; never use a lead glaze on the inside.
Clay pipe is fired ceramic tube laid end to end, bell into spigot. It resists corrosion and rot, which is why Roman clay pipes still survive, but it is brittle, heavy and weak against internal pressure.
What The Parent Page Specifies
Roll clay around a wooden form to make sections 30-60 cm long. Make bell-and-spigot joints, one end wider than the other. Fire in a kiln to vitrify the clay. Join the sections with clay or lime mortar. It is best for permanent buried installations where the pipe will not be disturbed.
The detailed making of the pipe is on Clay Pipes, which gives coil and hump-mould forming, wall thicknesses (at least 15 mm for a 50 mm bore) and joints. Kiln Building covers the firing.
Clay Is For Gravity, Not Pressure
The clay-pipes page states that clay pipes crack under significant internal pressure and do not handle water hammer. So:
- Use clay on low-head sections, or where the pipe runs partly full, not on steep, high-pressure lines.
- Put a break pressure tank above any steeper part.
- Never put a fast-closing valve on a clay line (Tap Types).
I give no head limit for clay, because none is sourced here; the safe rule is low head and no surge.
Worked Example: How Many Joints?
Joints per 100 m = 100 m ÷ section length.
- 60 cm sections: 100 ÷ 0.6 = 167 joints.
- 30 cm sections: 100 ÷ 0.3 = 333 joints.
By comparison, bored logs of 1-2 m (Wooden Pipes) give 50 to 100. Every joint is a place for a leak, a root or a contaminated inflow when the pipe runs under low or negative pressure. This is why careful jointing and a well-bedded trench matter more for clay than for any other pipe. One person can make 50-100 m of pipe per week (Clay Pipes), so a 100 m line is one to two weeks of potting before firing and laying.
What You Need
- Pipe clay tested for shrinkage and fired porosity
- A wooden form and a smooth working surface
- A kiln reaching the temperature that vitrifies the clay
- Clay or lime mortar for the joints, sand or fine gravel for the bed
- A trench with an even bottom, sloped steadily
Method: Make, Fire, Lay
Step 1: Form the sections with a wider socket at one end, so each spigot fits into the next socket with a small even gap for mortar.
Step 2: Dry slowly, then fire until hard, ringing and dense. A pipe that soaks water or shatters when tapped is under-fired.
Step 3: Choose the inside surface. Leave the interior unglazed, or use a salt glaze; avoid slip glazes unless you know they contain no lead. Never use a lead glaze: lead leaches into drinking water.
Step 4: Prepare the bed. Lay the trench to a steady fall on a bed of sand or fine gravel, below frost depth.
Step 5: Lay socket upslope, so the flow moves from spigot into socket without catching on the lip. Seal each joint with mortar, working it tight into the gap without letting it protrude into the bore.
Step 6: Backfill gently, in layers, without stones that can crack the pipe, and test with water before covering the joints fully.
Common Mistakes
- Pressurising the line.
- Lead glaze inside the pipe.
- A poor bed, which lets the pipe settle and crack at joints.
- Mortar protruding into the bore, catching silt.
- Backfilling with large stones.
Safety
Lead glaze, kiln heat and clay dust are hazards
Lead glazes dissolve into water and poison, especially children; never use salvaged glaze, old pottery glaze or a glaze you cannot identify on the inside of a drinking water pipe. Kilns burn and release smoke and carbon monoxide: fire outdoors or well ventilated. Dry clay dust can scar the lungs over time: wet-clean and wear a cloth over the face. A trench over about a metre deep can collapse; slope or shore the sides.
What’s Next
- Learn next: Salvaged Modern Pipe — the pipe to use for the pressured sections
- Combine with: Clay Pipes — wall thickness, clay testing and forming in detail