Former Dip vs Mould Cast vs Flat Spread
Safety. Liquid latex concentrates carry ammonia and metal-hygiene rules (no copper/brass in dip/leach contact). Coagulant salts and heat sensitizers are plant chemicals. See Allergy and Skin Contact.
Executive summary
Liquid latex does not have one casting method. Former dipping builds film on a withdrawn shape. Mould casting gels inside a cavity (plaster or heat-sensitive metal; slush or rotational). Spreading is industrial textile proofing, not a tabletop puddle. Straight dips are thin per pass; coagulant and heat-sensitized branches build thicker walls.
Use this after Sheet vs Liquid Film Pathways confirms liquid latex work. The five-question decision tree routes geometry, thickness, mould type, metal hygiene, and spread equipment — with do-not-mix callouts for common cross-path mistakes.
Forming map
Dipping deposits on a former (positive shape you withdraw from the bath). Moulding replicates a cavity interior. Spreading coats fabric with doctor blades — aqueous latex dries slower than solvent doughs, so production lines run fabric slower.
What is a former vs a mould?
A former is the positive shape you dip into latex — like a glove form or mannequin arm. A mould is a cavity you pour or rotate latex inside — like a plaster body cast or a closed metal slush mould. Dipping builds film on the outside of the shape; casting builds film on the inside wall of the cavity.
Spreading, dipping, and fabric impregnation were distinct industrial routes historically — not interchangeable hobby shortcuts.
Former dipping branch
Straight dip: roughly 0.01–0.05 mm dry rubber per pass — multi-dip for gauge. Coagulant dip: coagulant bath + dwell time gels a shell on contact; above ~8 mil dry thickness, coagulant is usually the economical branch. Warm leach and staged cure follow. Rotate formers between dips; exclude copper and brass from dip and leach contact.
What does coagulant mean in dipping?
In dipping, a coagulant is a chemical bath (often a salt solution) applied to the mould before latex. It makes the liquid rubber gel on contact so each coat builds thickness faster instead of running off the form. Coagulant is a liquid-latex film-building step — not the same as coalescence, which is how rubber particles in water-based glue merge into a solid film after application.
Mould casting branch
Plaster: absorption plus calcium ions gel the latex; dry completely before cure. Heat-sensitized (Kaysam): closed mould, rotation, heat triggers gel — handbook example ~4 min at 82°C; sensitizer mixed just before use. Slush vs rotational: pour-out excess vs metered rotation — stability vs wall uniformity trade-offs.
What is slush vs rotational casting?
Slush casting pours latex into a mould, lets it gel on the walls, then pours out the excess — good for hollow parts with controlled wall thickness. Rotational casting spins a closed mould so latex coats the interior evenly — better wall uniformity on complex shapes but needs dedicated equipment and timing discipline.
Flat spread branch
Industrial blade angles control strike-through on fabric. Aqueous latex dries slower than solvent doughs — run the fabric line slower. This is textile proofing equipment, not a documented hobby flat-bed pour without plant controls.
What does calendered mean here?
Calendered sheet (see Calendered Sheet vs Home-Cast Film) is pressed smooth between heated rollers at the factory. Spreading in this article means coating fabric on a production line with doctor blades — a different industrial route from buying finished roll goods or dipping a former.
Decision tree (five questions)
Q1 — Geometry
Positive withdrawable shape → former dip. Enclosed cavity → mould cast. Continuous fabric width → spread line. If you are buying finished sheet and gluing seams, you are on sheet-based work — not this article.
Q2 — Thickness
Thin per-pass straight dip (~0.01–0.05 mm dry) → multi-dip. Target above ~8 mil dry → coagulant branch. Very thick hollow walls → slush or rotational inside a closed mould.
Q3 — Mould material
Plaster or porous positive → dry completely before cure. Heat-sensitive metal closed mould → heat-sensitized gel cycle. Do not run Kaysam-style rotation on an open tray.
Q4 — Metal hygiene
No copper or brass in dip tanks, leach water, or mould hardware contact. Metal catalysis accelerates aging — see Aging, Storage and Care.
Q5 — Spread equipment
Doctor-blade textile line with speed matched to aqueous dry time → spread branch. Tabletop puddle without plant blade geometry → not documented as equivalent to industrial spread.
Do-not-mix callouts
- Coagulant dipping logic on sheet-based work — coagulant is liquid-latex film formation, not a sheet seam prep step.
- Kaysam-style rotation on an open tray — heat-sensitized gel needs a closed mould discipline.
- Spread-blade production cards on plaster slush without dry-before-cure — plaster must dry completely before cure.
- Straight-dip pinhole logic on thick plaster cast without dry-before-cure discipline — wet plaster and premature cure are different failure modes.
Pair with Reinforcement & Laminate Zones for multi-dip builds and Home Shop Ventilation for ammonia during compound and dip work.
Deep dives (optional)
Deep dive: Straight dip thickness vs viscosity
Handbook band: log-viscosity scaling; single straight dip roughly 0.01–0.05 mm dry per pass. Multi-dip schedules build gauge — thickness is not one coat.
Deep dive: Tie-coat sequences
On smooth formers, coagulant-first vs latex-first tie-coat order changes gel shell behavior. Plant recipes differ by former finish — not a one-size hobby default.
Deep dive: Kaysam cycle
Heat-sensitizer rotation, leach, supported dry, and cure windows on closed metal moulds. Sensitizer mixed just before use; example gel time ~4 min at 82°C in handbook literature.
Deep dive: Slush vs rotational
Slush pour-out gives hollow parts with operator-controlled dwell; rotational metering improves wall uniformity on complex cavities at the cost of equipment and cycle discipline.
Deep dive: Spreading blade geometry
Knife-over-roll and diaphragm blade arrangements control strike-through on fabric. Aqueous latex dry rate sets line speed — slower than solvent dough spreading.