How to Make Casein Glue

Collection: Field Notes - Regenerative Materials

Series: Natural Marine Adhesives & Sealants Hub

Subject: How to Make Casein Glue — The VAKA Guide

Field Entry: April 12, 2026

The VAKA Guide: How to Make Casein Glue

Okay, there are two routes into making this glue. The first starts with fresh or powdered milk and a mild acid to precipitate the curd. The second starts with dry casein powder, which is available from cheesemaking suppliers, homebrew shops, and scientific suppliers... The powder route is much easier to be honest - it'ss more consistent, easier to measure, doesnt require drying out a solution to powder and is where most builders should start - I do (I'm all for natural, but don't make the perfect the enemy of the good!). The dairy route produces excellent results and costs almost nothing if you have access to raw farm milk — and I'm sure it gives a satisfying practical connection to a material that has been used by craftspeople for thousands of years. Both end up in the same place: a batch of activated bonding compound that will outperform PVA and can approach the strength and durability of even epoxy if properly made for most structural timber joints, cost pennies to make, and leave nothing toxic behind when it is done.

This guide covers the VAKA recipe in full — the ingredients and what each one does, the alternative alkali options of potassium hydroxide and its differences from sodium hydroxide, and the practical steps for getting a usable batch. For the background on properties, history, and comparison with synthetic alternatives, see the casein glue overview. The full natural marine adhesives guide covers the wider system of natural bonding and bedding compounds used in VAKA designs.

Ingredients and Alkali Options: Potassium Hydroxide, Sodium Hydroxide, and When to Use Each

The VAKA recipe derives from US Forest Products Laboratory Formula 11, without the sodium silicate which whilst increasing the glues open time, it increases the brittleness of the glue line. All quantities are by weight:

Casein (powder or fresh-precipitated) — 100 parts
Water for soaking casein— 150 parts
Potassium hydroxide — 11 parts, dissolved in 30 parts in water
Lime (calcium hydroxide) — 20 parts, slaked in 30 parts water
Copper sulfate — 3 parts, dissolved in 30 parts warm water
OPTIONAL Tannic acid or cutch — 3% in water, for pre-washing surfaces

KOH vs NaOH — which alkali to use

The recipe uses potassium hydroxide (KOH) as the primary alkali. Sodium hydroxide (NaOH, caustic soda) can be substituted, but requires adjustment: use approximately 8 parts instead of 11, since it is a stronger base per unit weight. Both activate the casein effectively, but there are meaningful differences in working behaviour.

Potassium hydroxide produces a slightly more flexible glue line and dissolves more readily in cool water, making it the better choice for structural timber joints and boat construction. Sodium hydroxide is more widely available — sold as drain cleaner — and produces a harder, faster-setting compound, which suits some workshop applications. For the VAKA recipe and structural marine work, potassium hydroxide is specified. If you are making a simpler batch for general woodworking, paper bonding, or experimental use, go to town with whichever you prefer.

Baking soda (sodium bicarbonate) is sometimes mentioned as a beginner-accessible alkali. It will activate the casein sufficiently for light work such as paper bonding and pigments in paint, but it's not as strong and is not suitable for load-bearing joints.

Borax (sodium borate) appears in various older recipes. It produces a usable compound but carries significant health risks — it is classified as a reproductive hazard and is restricted for consumer use in the EU. I do not use or recommend it. The hydroxide route is both safer and stronger, and the ingredients are more readily available to most builders.

On sourcing casein powder

Dry casein powder is the most convenient starting point and gives the most consistent results. It is sold by weight, dissolves predictably, and keeps indefinitely when stored dry. Scientific suppliers and homebrew retailers are the most reliable sources in the UK; it is also available from fitness nutrition suppliers under the name micellar casein (though costs more). For boat construction quantities, order from a food ingredient supplier — a kilogram will make many batches and costs a few pounds. Look for acid casein powder rather than rennet casein; it's easier to activate and makes a better structural glue.

On lime

The lime in this recipe is calcium hydroxide — slaked lime or hydrated lime. It is not quicklime (calcium oxide), which is a different and more reactive material. Builders' lime and horticultural lime are both calcium hydroxide and work well. Garden lime is sometimes calcium carbonate (chalk) rather than calcium hydroxide — check the label, as chalk will not activate the casein effectively and the batch will not develop full strength.

On Copper

The copper sulfate in this recipe acts as a primary biopreservative in the cured glue line. While casein is incredibly strong, it is an organic protein—meaning that in the damp, dark environments of a boat's bilge, it could theoretically become a snack for mold and bacteria. The copper ions effectively poison the environment for these microorganisms while simultaneously interacting with the protein chains to improve water resistance. Be careful not to add more than specified though as too much will embrittle the glueline

The cutch (an extract from the heartwood of the Acacia catechu tree, rich in tannins) works in tandem with the copper. When mixed, they form a metal-tannin complex that further "tans" the casein, cross-linking the proteins to make the glue more resistant to moisture and fungal decay, but also more ductile which is improtant in a flexing structure such as a catamaran aka.

Starting with Milk: Precipitation, Whey, and the Curdling Method

If you are working from fresh dairy rather than powder, begin here. Skimmed milk works best — the fat in full-fat varieties interferes with the bonding chemistry and reduces final strength. Raw milk gives the highest casein content and is worth using if you have access to it. Milk powder reconstituted in water is a convenient alternative that allows precise control over concentration, and has the advantage of being available in bulk at low cost.

Warm the skimmed dairy gently in a pan to around 50°C — warm to the touch but not approaching a simmer. Add white vinegar gradually, stirring as you go. As the vinegar contacts the warmed milk, curdling will begin immediately and visibly. Continue adding vinegar until there's no more separation and the remaining fluid runs clear. That clear runoff is the separated whey — the liquid fraction has been left behind, and the solid precipitate is the casein you need. Too much vinegar is not a problem; too little means incomplete precipitation and weaker final strength.

Strain through a cloth or fine mesh, squeezing out as much excess as possible. Rinse the precipitate briefly with clean water to remove residual acidity (which would interfere with the alkaline activation). What you have at this point is wet casein resin — soft, white, and slightly rubbery. This material is chemically identical to the dry powder form, just wetter.

Let it reach ambient temperature if it has cooled during rinsing, then weigh it. Fresh-precipitated material contains significant moisture — typically reduce the soaking water in the main recipe by around a third when using this form rather than dry powder. Press out as much moisture as you can through the cloth before weighing for the most reliable results.

If you want to make dry casein powder from freshmilk: press the precipitate as dry as possible, spread thinly, and dry at low temperature — under 50°C — until brittle, then grind fine. Store in a sealed container away from moisture. This is useful if you want to make glue casein in bulk from inexpensive farm dairy and store it for later use — the dried form keeps for months.

Mixing the VAKA Recipe: The Step-by-Step Process

Whether starting from dry powder or fresh material, the activation sequence is the same. Order matters — adding components out of sequence produces a weaker or lumpy result.

Step 1 — Soak. Weigh out 100 parts casein powder. Add 150 parts water, stir to combine, and leave to soak for 30 to 60 minutes, or overnight if you like. The casein will absorb the water and swell into a thick, soft paste. This is the point to prepare the other components.

Step 2 — Prepare the three component mixes. While the casein soaks, dissolve the potassium hydroxide in its 30 parts water. Separately, slake the lime in its 30 parts water to produce a smooth slurry. Dissolve the copper sulfate and cutch in its 30 parts water. All three should be at ambient temperature before use. Handle the potassium hydroxide mix with care — it is strongly alkaline and will irritate skin and eyes on contact. Gloves are sensible.Once the casein is dry the PH reduces and becomes safe, but until then it is caustic - treat it like you would cement.

Step 3 — Add the potassium hydroxide. Stir the soaked casein and add the potassium hydroxide mix. Combine well. The paste will begin to change texture and may lighten slightly as the chemistry activates. Leave for two minutes. I use a food hand stick blender mixer - the type with the little blade in a cowl on the end. once its all mixed, so long as its well cleaned its not killed me yet reusing it in the kitchen!

Step 4 — Add the lime. Add the lime slurry and mix thoroughly. The compound will thicken noticeably. Leave for five minutes — this waiting time is important because the lime needs to complete its reaction with the activated casein before the copper is introduced.

Step 5 — Add the copper sulfate . Add the copper sulfate and stir well. Continue mixing until fully incorporated and the batch is a thick, smooth cream — this is the target working consistency.

Adjusting

If the compound is too thin — running freely from the spatula — add a small amount of additional lime slurry and wait five minutes. If still too thin, add a little more pre-soaked casein. If too stiff to spread easily, add water by the teaspoon and mix thoroughly. The right consistency spreads like soft butter and holds its shape on a vertical surface.

Surface preparation

Optional step: Before applying the glue, wipe timber surfaces with a 3% tannic acid solution in water. This opens the grain slightly and improves adhesion as it forms tannin-caseinate complexes that increase anti microbial and tensile strength. Allow the surface to dry before slapping the glue else the glue to wood bond could weaken instead...

Application and clamping

Apply the compound to both faces of the joint with a stiff brush or spatula — a reasonable coating on each face, not a thick layer. Assemble the joint promptly after application and apply reasonable clamping pressure. This compound requires clamping to develop full strength: the clamping pressure brings the surfaces into firm contact and squeezes out excess material, which you will see emerging from the joint line as a thin bead. This is a good sign. Leave clamped for a minimum of four hours at ambient temperature, or overnight in cold conditions. The joint will continue to develop strength over the following 24 hours as the bond fully cures. Do not stress the joint during this period. Do not overclamp - there needs to be sufficient glue in the joint to work.

Pot life and storage

The batch will remain workable for two to four hours at ambient temperature before thickening makes spreading impractical. Do not make more than you can use in one session. There is no method for extending pot life — prepare it fresh each time, use what you need, and discard the rest (casein glues are harmless once cured, apart from the small amount of copper salts). The components keep indefinitely in their dry or dissolved forms; it is only the activated compound that degrades quickly.

For properties, science, and comparison with synthetic adhesives, see the casein glue overview. The wider system — including shellac as a sealant and reversible threadlock, and the traditional rubberised bedding compound for through-hull fittings, bedding and seam sealing — is covered in the full adhesives guide. The boat plans specify which adhesive for which joint, and the Field Notes covers the wider context of natural materials in small craft construction

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