Alga-Cast Slow is a natural-origin alginate, completely safe for human skin, specifically designed for body casting: faces, hands, feet and other body parts. Its slow-cure formulation (9-11 minutes) gives you the working time needed to apply the material correctly and achieve exceptional detail. It is the go-to option for Life Casting, creative workshops and FX when you need a fast, clean and safe mould.
Technical specifications
| Parameter |
Value |
| Material type |
Alginate powder (body use) |
| Mixing ratio |
1 to 3 parts water : 1 part powder (by volume) |
| Cure time |
9-11 minutes |
| Mould uses |
1-2 castings (temporary non-reusable mould) |
| Safe for human skin |
Yes |
| Presentation |
Powder |
Quantity guide by body area
| Anatomical area |
Approximate alginate quantity |
| Baby foot or hand |
300 g |
| Adult foot or hand |
500 g |
| Face without ears |
500 g |
| Full head to shoulders |
1.5 kg |
| Front torso |
750 g |
| Full torso |
1.5 kg |
| Arm to the elbow |
750 g |
| Buttocks |
500 g |
| Intimate parts |
300 g |
| Full body |
7 kg |
Approximate quantities. The final result may vary depending on each person's body shape and the application technique. Responsibility for the amount of material required lies with the end user.
What it is used for
Alga-Cast Slow is designed for any process where you need to capture the detail of a body surface quickly and safely. As it is a single-use mould (it accepts 1-2 castings before degrading), it is ideal when the goal is to obtain one or several high-fidelity pieces without the need for a durable mould. For production work with multiple castings, it is recommended to opt for a platinum silicone suitable for skin.
- Hand and foot moulds for keepsakes (babies, weddings, couples)
- Life Casting of faces for special effects and character work
- Torso and limb moulds for prosthetics and models
- Educational art and sculpture workshops
- Mould-making for decorative figures and figurative sculptures
- Quick anatomical prototypes in design studios or medical settings
How to use it
- Prepare the body area: if there is significant body hair, apply a thin layer of vegetable oil or petroleum jelly to ease demoulding afterwards without damaging the skin.
- Measure the alginate and water: use a ratio of 1 to 3 parts water per 1 part powder by volume. For small areas (adult hand), start with 500 g of powder and adjust the water to achieve the right consistency.
- Mix quickly: add the powder to the water (not the other way around) and stir vigorously for 30-45 seconds until you obtain a smooth, lump-free paste. Working time is limited — do not delay.
- Apply the alginate: pour or apply the mixture directly onto the area to be moulded. For faces, work from the outside towards the more delicate areas (nose, eyes), always keeping the nostrils clear.
- Reinforce with a mother mould: before the alginate is fully cured, apply several layers of plaster bandages over the outer surface to give rigidity and support to the mould.
- Wait for full cure: in 9-11 minutes the alginate will have cured. Check that the outer surface is no longer tacky.
- Demould carefully: remove the assembly (mother mould + alginate) with gentle movements. The alginate is flexible and will release without damaging the skin.
- Cast immediately: alginate dehydrates quickly. Cast the final piece (plaster, resin or other materials) as soon as possible, ideally within the first 30-60 minutes after demoulding.
Usage tips
Control water temperature to adjust working time
Water temperature directly affects the alginate's cure speed. Cold water (15-18 °C) slows the process and gives you more application time, especially useful for large areas or when working alone. Warmer water (25-28 °C) accelerates the cure, which can be convenient for small pieces or in cold environments. Alga-Cast Slow is already formulated with a generous working time; in summer or at high ambient temperatures, use cold water as a general rule.
A plaster mother mould is essential
Alginate alone does not hold its shape once removed from the body: it is soft and flexible. To achieve accurate results, always reinforce the mould with a rigid mother mould. Plaster bandages are the quickest and most convenient option: apply two or three overlapping layers over the still-fresh alginate and allow them to set before demoulding. If you then want to cast the piece in high-quality plaster, Exaduro or Arquero offer far superior strength to conventional plaster.
Act fast after demoulding
Alginate contains water in its structure and will inevitably dehydrate over time, causing shrinkage and loss of detail. Once demoulded, you have a window of 30 to 60 minutes to cast the final material. If you need to wait, wrap the mould in a damp cloth and store it in a sealed bag to slow evaporation, but do not store it for more than a few hours. If your project requires reusable moulds, consider a skin-safe silicone instead.
Frequently asked questions
How many times can I use the same alginate mould?
The Alga-Cast Slow mould accepts between 1 and 2 castings, depending on the material you pour. It is a temporary mould, not indefinitely reusable. After the second casting, detail quality deteriorates noticeably. If you need a mould for multiple reproductions, a skin-safe platinum silicone is the most suitable option.
Is it safe to use alginate directly on skin?
Yes. Alga-Cast Slow is specifically formulated for use on human skin: it is completely harmless, non-toxic and does not cause adverse reactions under normal conditions of use. It is the same type of material used in dentistry for dental impressions. Even so, if the person has particularly sensitive skin or known allergies to seaweed, carry out a patch test on a small area first.
How long does it take to set and when can I demould?
Alga-Cast Slow cures in 9-11 minutes from when you mix the powder with water. The exact time depends on the water and ambient temperature. You will know it is ready when the outer surface is no longer tacky to the touch and the whole piece has a rubbery, firm consistency. Do not demould early: even if the exterior appears cured, the interior may still be soft.
What is the difference between Alga-Cast Slow and Alga-Cast Fast?
The main difference is working time. Alga-Cast Fast cures more quickly, making it ideal for small areas or when you want to shorten the process. Alga-Cast Slow, with its 9-11 minute cure time, gives you more application time, which is essential for large areas (torso, full face) or when working alone without assistants. In terms of detail and safety, both are equivalent.
What materials can I cast into the alginate mould?
The most common materials for casting into alginate are plaster and gypsum, which work perfectly. You can use Exaduro or Arquero if you need greater strength in the final piece. Some users also cast polyurethane resins, although the moisture in the alginate can interfere with materials that are particularly sensitive to humidity. Plaster is always the most reliable and straightforward option.
Can I store mixed alginate to use later?
No. Once mixed with water, the alginate starts the curing process and cannot be stored. Always mix only the amount you are going to use immediately. Unmixed powder, however, has a long shelf life if stored in an airtight container, away from moisture and in a cool place.
What do I do if the alginate cures too quickly before I finish applying it?
Use colder water. Lowering the water temperature to 15-18 °C can give you an extra 2-3 minutes of working time. Also make sure you mix in a clean container with no residual cured alginate, as cured fragments accelerate the setting of the new mix. If the problem persists in your usual environment, consider switching to Alga-Cast Slow if you are not already using it, as it is the longer working-time version.
Do I need a release agent to prevent the alginate from sticking to skin?
In most cases, it is not necessary: alginate does not adhere to skin and releases easily. However, if the area has significant body hair, applying a thin layer of vegetable oil or petroleum jelly before moulding makes demoulding easier and avoids discomfort when removing the mould. On faces, pay particular attention to eyebrows and eyelashes.
