Incised pargeting relies on non-hydraulic fat lime putty (calcium hydroxide) mixed with coarse, sharp well-graded aggregate and reinforced with thoroughly teased ox or horse hair. The hair fibers distribute flexural stresses over moving timber frames while maintaining high breathability. While the finish coat remains green, plasterers drag hand-carved wooden or bone combs across the surface to produce historic repeating geometric patterns such as herringbone, fish scale, and guilloche.
At a Glance: Key Takeaways
- Aggregate Mix: 1 Part Lime : 2.5 Parts Sharp Washed Pit Sand (0.2–3.5mm)
- Comb Materials: Carved Oak, Boxwood, or Stiff Horn Combs
- Lime Putty Grade: CL90 Non-Hydraulic Chalk Lime Putty
- Working Window: 4 to 12 hours depending on humidity and suction
Chalk Lime Putty Slaking and Maturation Principles
The foundation of all successful pargeting is non-hydraulic fat lime putty. Produced by calcining pure calcium carbonate (chalk or high-calcium limestone) at 900°C to form quicklime (CaO), the quicklime is subsequently drowned in an excess of clean water in slaking pits, initiating an intensely exothermic hydration reaction.
As the slurry cools into a silky, cheese-like putty, calcium hydroxide micro-platelets continue to subdivide and disperse over months of wet maturation. Putty aged for at least six months develops exceptional plastic workability, allowing crisp comb lines that hold their sharp geometric edges without sagging or tearing.
Animal Fiber Selection, Scouring, and Homogeneous Chopping
Historically, plasterers harvested hair from local tanneries and abattoirs. Ox body hair, goat fleece, and horse mane provide different mechanical characteristics: coarse, stiff ox hair is ideal for locking the thick scratch coat between laths, while softer goat or calf hair is reserved for the finer combable top coat.
Hair must be scoured in alkaline water to strip natural grease and residual flesh, which otherwise ferment and foul the wet mortar. When compounding the mix, the hair is chopped into 25mm to 40mm bundles, teased apart with rakes or carding combs, and beaten into the lime-sand mortar using wooden beating sticks until every strand is coated and dispersed without fiber clusters.
Aggregate Sizing: Sharp Pit Sands and Crushed Chalk Fillers
Aggregate selection controls both shrinkage and tactile finish. Marine or beach sands containing soluble sodium chlorides are strictly avoided as they attract damp and cause efflorescence. Plasterers demand sharp, sub-angular inland pit sand graded continuously from fine 0.2mm quartz grains up to 3.5mm grits.
In East Anglia, ground soft chalk or crushed oolitic limestone is frequently incorporated (up to 15% of total aggregate volume) to replicate historical vernacular tonality and optimize workability under the plasterer's steel lay trowel.
Comb Tooling: Geometries, Rhythms, and Stickwork Patterns
Incised patterns are created using hand-carved wooden combs made of dense, close-grained hardwoods like boxwood, fruitwood, or English oak. The teeth are filed at 45-degree angles to produce crisp, clean grooves that cast defined shadows across the facade.
Classic East Anglian motifs include the herringbone, the scallop shell, the chevrons, and the basket-weave. Plasterers must coordinate tool passes while the mortar has set sufficiently to support tool pressure without slumping, but before carbonation hardens the surface into brittle stone.
East Anglian Comb Geometry & Pattern Catalog
Use this reference table to calculate exact physical dimensions, ratios, and specifications before purchasing:
| Motif Pattern | Comb Tooth Spacing | Tooth Depth | Stroke Technique | Historic County Origin |
|---|---|---|---|---|
| Fan / Scallop Scale | 6mm pitch (rounded tip) | 4mm deep | Rotational wrist pivot (180° swing) | Suffolk & North Essex |
| Herringbone Chevron | 8mm pitch (triangular notch) | 5mm deep | Alternating 45° diagonal drags | Cambridgeshire & Essex |
| Basket-Weave (Square) | 10mm pitch (square tooth) | 4mm deep | Interlocking 90° rectangular blocks | Hertfordshire & Kent |
| Guilloche Interlace | Specialty twin-arm compass | 3mm deep | Overlapping concentric circular sweeps | Bury St Edmunds (Suffolk) |
Practical Constraints
Every successful decoration project must account for physical and environmental constraints:
Direct Sun and Wind Desiccation on Scaffolding
Rapid surface drying prevents proper comb dragging and stops carbonation, requiring monarflex scaffold sheeting and heavy hessian shading.
Supply of Authentic Non-Dehaired Cattle Hair
Industrial modern tanneries use chemical dissolving agents that ruin hair; authentic fiber must be sourced from specialized historic restoration suppliers.
Execution Blueprint & Craftsmanship Sequence
Execute this professional sequence to achieve flawless results without backtracking:
Lime Putty Acclimatization and Slaking Check
Verify lime putty has reached a minimum maturity of 90 days, free from unslaked quicklime nodules and standing excess water.
Sand Grading and Sifting
Sift sharp inland pit sand through a 3mm mesh screen to eliminate oversize pebbles while retaining a continuous aggregate gradation curve.
Mortar Beating and Hair Dispersion
Combine 1 part lime putty to 2.5 parts sand in a wooden mixing trough; beat with wooden paddles while progressively teasing in scoured ox hair.
Application of the Finish Plaster Plane
Apply a uniform 5mm to 6mm finish coat across the dampened float coat, consolidating the surface with a timber float to bring lime cream to the face.
Pattern Layout and Comb Incising
Snap light chalk guide cords; draw the carved boxwood comb through the green plaster with smooth, steady pressure to engrave crisp geometric grooves.
Edge Cleaning and Hessian Mist-Curing
Dress panel perimeter margins with a small margin trowel, erect protective damp hessian burlap, and mist daily for two weeks.
Common Mistakes & Countermeasures
Avoid these costly errors that compromise aesthetics, ergonomics, and budget:
Using Unwashed Animal Hair Containing Tanner's Fats
Tooling the Comb Too Late After Plaster Has Stiffened
Project Execution Checklist
Track your physical progress. Checkboxes persist automatically on this device:
Frequently Asked Questions
Can polypropylene synthetic fibers replace animal hair in pargeting?
While synthetic fibers provide tensile resistance, they lack the porous microscopic surface texture of natural protein hair, which physically absorbs and binds calcium hydroxide crystals into an integrated composite matrix.
How soon after plastering can combs be drawn through the surface?
Depending on temperature and relative humidity, the optimal window is typically 1 to 3 hours after application, once the surface sheen dulls but thumb indentation leaves a clean imprint without slurry.
