Drying Cakes

Part of Adhesives

Forming and drying adhesive into storable cakes for later use.

Why This Matters

Freshly prepared liquid glue spoils within days. Bacteria consume the protein, mold colonizes the surface, and the adhesive breaks down into a foul-smelling sludge that cannot bond anything. In a post-collapse scenario where you cannot produce adhesive on demand — because fuel is scarce, raw materials are seasonal, or your workshop has other priorities — the ability to store adhesive for months or years is essential.

Drying glue into solid cakes solves this completely. Dried adhesive cakes resist bacterial decomposition because bacteria need moisture to function. A properly dried hide glue cake stored in a dry location remains usable for years, possibly decades. Historical examples of animal glue found in Egyptian tombs — over 3,000 years old — still dissolved and bonded when reconstituted with warm water.

The technique is straightforward but demands patience and attention to detail. Rushing the drying process with excessive heat destroys the adhesive properties. Inadequate drying leaves moisture pockets that breed mold internally, hidden until you crack the cake open months later to find it rotten inside. Getting it right means your community always has adhesive available regardless of season, weather, or supply conditions.

Preparing Glue for Drying

Before forming cakes, your liquid glue must be at the correct concentration. Thin, watery glue produces cakes that take forever to dry and tend to crack badly. Overly thick glue is difficult to pour and forms uneven cakes.

Concentrating the Glue

1. Heat your liquid glue in a double pot to 70-75°C.
2. Allow water to evaporate slowly with the pot uncovered. Stir occasionally to prevent surface skin formation.
3. Test concentration by lifting your stirring stick and watching the drip. The glue is ready for cake-forming when it:
   • Drips slowly in thick, honey-like ribbons
   • Forms a skin on the stick within 20-30 seconds at room temperature
   • Coats the stick without running off
4. The target is roughly 40-50% solids content. Professional glue makers called this “strong liquor.”

Do Not Boil

Resist the urge to speed evaporation by increasing heat. Boiling breaks protein chains and weakens the final adhesive. Slow evaporation at 70-75°C preserves full bonding strength.

Straining

Before pouring into molds, strain the concentrated glue through cloth to remove:

• Undissolved hide or bone fragments
• Sediment and impurities
• Fat globules that weaken bonds

Use a coarse-woven cloth stretched over a frame or vessel. The glue should be hot enough to flow through the weave — if it gels during straining, rewarm it.

Forming the Cakes

Mold Options

You need flat, shallow molds that produce cakes no thicker than 1-2 cm. Thicker cakes dry unevenly — the surface hardens while the interior stays wet, trapping moisture that causes internal decay.

Mold Type	Pros	Cons
Flat stone slabs	Durable, reusable, naturally smooth	Heavy, glue may stick without oiling
Wooden trays	Easy to make, lightweight	Glue bonds to wood unless oiled
Clay tiles	Cheap, disposable	Can crack during drying if thin
Greased cloth on frames	Easy release, thin cakes	Needs sturdy frame to prevent sagging
Leaf-lined baskets	No preparation needed	Limited to small, irregular shapes

Preparing Molds

Coat mold surfaces lightly with a release agent so dried cakes pop out cleanly:

• Vegetable oil applied with a cloth — thin coat, not pooling
• Animal fat (tallow) — works well but can transfer rancid smell
• Wet clay slip — traditional method, leaves a slight powdery surface on the cake
• Dampened parchment — if you have access to prepared skins

Pouring

1. Pour hot, concentrated glue into prepared molds to a depth of 8-15 mm. Thinner is better for drying speed, but cakes under 5 mm are fragile and hard to handle.
2. Allow the glue to cool and gel in the mold. This takes 1-4 hours depending on ambient temperature and glue concentration.
3. Once fully gelled (firm to touch, no liquid movement), the cake is ready for the drying stage.

The Drying Process

This is where patience determines success. Drying too fast causes surface crusting that traps interior moisture. Drying too slow in humid conditions allows mold growth before the cake stabilizes.

Ideal Drying Conditions

• Temperature: 15-25°C (cool room temperature). Warmer is faster but riskier.
• Humidity: Below 60% relative humidity. In humid climates, dry indoors near a fire (but not directly over it).
• Airflow: Gentle, consistent air movement. A well-ventilated room or covered outdoor area with cross-breezes is ideal.
• Light: Indirect. Direct sunlight heats the surface unevenly and can cause warping.

Drying Procedure

1. Day 1-2: Once gelled, carefully unmold the cakes. They will be flexible, like firm gelatin. Handle them gently to avoid tearing or fingerprint dents.

2. Day 2-5: Place cakes on drying racks — screens, nets, or slatted wooden frames that allow air circulation on all sides, including the bottom. If you lay cakes flat on a solid surface, flip them every 12 hours to prevent the bottom from staying wet while the top dries.

3. Day 5-10: Cakes shrink noticeably as moisture leaves. They become translucent at the edges and darken in color. Surface may develop a slight tackiness in humid weather — this is normal and resolves as drying continues.

4. Day 10-21: Final drying phase. Cakes become hard, brittle, and fully translucent (for hide glue) or opaque yellowish (for fish glue and casein). They should sound hollow when tapped and snap cleanly when bent rather than flexing.

The Snap Test

Break a small corner off a test cake. It should snap like hard candy with a clean, glassy fracture surface. If it bends, flexes, or shows a wet interior, continue drying. If it crumbles to powder, it may have been exposed to excessive heat during concentration.

Dealing with Humid Climates

In tropical or coastal environments where humidity rarely drops below 70%, standard air drying may not work. Alternatives:

• Smoke drying: Suspend cakes above a low, smoky fire (fruit wood or hardwood — not resinous softwood). The smoke deposits a thin antimicrobial layer while warm, dry air pulls moisture out. Keep cakes at least 1 meter above the fire to avoid heat damage.
• Salt assist: Sprinkle a thin layer of fine salt on drying racks beneath the cakes. Salt absorbs ambient moisture, creating a local dry microclimate.
• Lime drying room: Place open containers of quicklime in a closed room with the drying cakes. Quicklime aggressively absorbs humidity from the air. Replace lime when it crumbles to powder (slaked).

Storage

Properly dried glue cakes store for years if kept dry. Moisture is the only real enemy.

Storage Methods

• Wrapped in cloth, in a dry container: Wrap individual cakes in linen or cotton, place in a wooden box or ceramic jar with a tight lid. Add a small cloth pouch of wood ash or charcoal as a desiccant.
• In sealed ceramic jars: Stack cakes with cloth separators. Seal the jar with wax or pitch. This provides the longest storage life.
• Hanging in mesh bags: In dry climates, simply hang bags of glue cakes from rafters in a dry room. Good air circulation prevents any condensation.

Storage Conditions

• Keep away from direct moisture — no damp cellars, no outdoor sheds with leaking roofs.
• Avoid extreme heat — storage above 40°C for prolonged periods can partially denature the protein.
• Protect from insects and rodents. Dried glue is essentially pure protein, and pests will eat it. The sealed container approach is best.
• Label or sort by type and date. Hide glue, fish glue, and casein cakes look similar when dried but behave differently when reconstituted.

Reconstituting Dried Cakes

To use stored glue cakes:

1. Break into small pieces. Use a hammer or the back of a hatchet. Smaller pieces dissolve faster. Aim for roughly 1 cm fragments.
2. Soak in cool water for 4-12 hours (overnight is convenient). The glue absorbs water and swells into a soft, rubbery mass. Use just enough water to cover the pieces.
3. Heat in a double pot to 65-75°C. Stir as the softened pieces dissolve into liquid glue. Add small amounts of water if the consistency is too thick for your application.
4. Use while hot. Reconstituted glue gels as it cools, so keep it in the double pot during application.

The ratio of glue to water depends on intended use:

• Strong structural joints: 1 part glue to 1.5 parts water (thick, syrupy)
• General woodworking: 1 part glue to 2 parts water (honey consistency)
• Paper and fabric bonding: 1 part glue to 3 parts water (thin, brushable)

Reusability

Reconstituted glue that gels before you finish using it can be reheated and used again. Each reheating cycle slightly reduces strength, but glue can be reheated 4-5 times before noticeable degradation. After that, add it to a fresh batch rather than using it alone for structural work.