Fulling Mill

Part of Mill Construction

Building and operating a fulling mill to mechanically finish woven wool cloth.

Why This Matters

Raw woven wool cloth is loose, rough, and open in texture — threads show individually and the cloth offers poor wind and water resistance. Fulling (also called waulking in Scotland) transforms this raw cloth by compressing and matting the wool fibers, making the cloth denser, warmer, more weather-resistant, and much stronger. Before fulling mills, this was done by human feet — people literally trampling the cloth in troughs for hours. It was exhausting, time-consuming work.

The fulling mill, powered by water, replaced foot-fulling and was one of the first industrial textile processes. Historical records show fulling mills appearing across Europe by the 11th century — among the earliest applications of waterpower to textile production. In a rebuilding scenario, once wool weaving is established, a fulling mill dramatically increases the quality and quantity of cloth that can be produced.

The Fulling Process

Fulling works by mechanical agitation of wet wool in an alkaline solution. Wool fibers have microscopic scales on their surface; when agitated in warm water with a mild alkali (fulling earth, urine, or wood ash lye), these scales interlock and mat together. The cloth shrinks (typically 20-30% in each dimension) and becomes felted — a solid, integrated fabric rather than a loose weave.

The degree of fulling is controlled by time and temperature. Light fulling (30-60 minutes at moderate agitation) produces a visible texture while keeping the weave pattern legible — good for coats, hats, and blankets. Heavy fulling (several hours, vigorous agitation) produces a dense, smooth felt-like surface — good for coats in wet climates and hats.

After fulling, the cloth is rinsed thoroughly, stretched on a tenter frame (a wooden frame with hooks called tenters — the origin of “on tenterhooks”) to restore dimensions while still wet, and allowed to dry under tension.

Stamp Mill Design for Fulling

The most common fulling mill mechanism is the stamp mill: a series of heavy wooden stamps (hammers) lifted by cams and allowed to fall on the cloth in a trough below.

The fulling stocks (trough): A V-shaped or U-shaped wooden trough, typically 1-1.5m long and 0.5m wide, made of dense hardwood (oak is traditional). The bottom and sides must be smooth — any rough surfaces catch the cloth and tear it. Line the bottom with a smooth hardwood plank, replaceable when worn.

The stamps (hammers): Typically two or three stamps per trough, each weighing 30-60 kg. Made of heavy hardwood — full tree sections or large squared timber. The striking face is broad and slightly convex (not sharp) to avoid cutting the cloth. Iron straps reinforce the sides and the striking face.

The cams and shaft: The rotating cam shaft lifts each stamp via a notch or projection on the stamp body engaging a cam projection on the shaft. The cams are offset so stamps fall in sequence — first one, then the next — rather than all simultaneously. This gives more continuous action and distributes power draw more evenly.

Cam angle and lift: The cam height determines how far the stamp rises before releasing — typically 200-400mm of lift. Higher lifts produce more violent action (better for heavy fulling) but require more power. The cam releases the stamp when the cam nose passes the engagement point on the stamp, allowing the stamp to fall freely.

Water and Alkali Management

The fulling trough requires hot or warm water — at least 40 degrees C, ideally 50-60 degrees C. Cold water fulls very slowly and produces inferior results. A small firebox or boiler adjacent to the mill can heat water for charging the trough. Alternatively, fulling in summer (using water warmed in the sun) is more efficient than in winter.

Fulling liquor (the alkaline solution) was traditionally made from:

• Stale urine: Rich in ammonia from bacterial decomposition, mild alkali. Collected and aged for weeks. Perfectly effective but odorous.
• Fuller’s earth: A clay mineral (montmorillonite) that absorbs grease from the wool while providing mild abrasion. Best combined with water but no added alkali.
• Wood ash lye: Potassium hydroxide solution from ash leaching. Effective but must be diluted to avoid damaging the wool.

After fulling, rinse the cloth in clean water, then rinse in diluted vinegar or sour whey to neutralize any remaining alkali. Residual alkali weakens wool fibers over time.

Tenter Frame Construction

After fulling and rinsing, the cloth must be stretched to its final dimensions and dried under tension. The tenter frame is a rectangular timber frame, set outdoors in a windy location, with rows of hooks (tenters) along the top and bottom rails.

Attach the cloth wet by hooking its selvedge edges to the tenter hooks, stretching it to the pre-shrunk dimensions. The cloth dries taut, retaining a smooth, even surface and consistent dimensions. Without a tenter, dried cloth wrinkles and distorts.

Scale the frame to the cloth width: a standard loom produces cloth 1.2-1.5m wide, which shrinks to 0.9-1.1m after fulling. The tenter frame should accommodate the stretched cloth at the pre-shrunk width. Tenters should be spaced 50-75mm apart for close support.