The ratio is the proportion of powder to water in your mix. It is the single most important number in casting, because it decides how the material flows, how completely it fills fine detail, and how the finished surface reads.
FormCast+ is mixed by weight, not by volume. Grams on a set of scales, not lines on a jug.
The two ratios
Both are correct. They produce different results, and you choose between them based on the piece you are making.
| Ratio | What it means | What it gives you |
|---|---|---|
| 3:1 | 3 parts powder to 1 part water | The most fluid mix. It travels into fine detail and settles to a refined surface. |
| 4:1 | 4 parts powder to 1 part water | The strongest mix. Less fluid, so it holds together more firmly and moves less as it sets. |
Powder first, water second is how the numbers are written. Weigh the water into the container first, then add the powder to it.
Which one to use
Use 3:1 when the surface is the point: a shallow tray, a detailed relief, anything where you will be looking directly at a large flat face.
Use 4:1 when the object is the point: a thicker form, a piece with a narrow section, anything that needs to feel solid in the hand more than it needs a flawless face.
If you genuinely cannot decide, pour 3:1. A more fluid mix is more forgiving of a beginner’s pouring technique.
Weighing it accurately
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Work out your total mix
The total is the powder plus the water. If you need 500g of mix at 3:1, that is 375g of powder and 125g of water — the total splits into four parts, three of powder and one of water.
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Weigh the water into the container first
Zero the scales with the empty container on them, then add water to the target weight. Water is easier to correct than powder.
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Add the powder to the water
Zero the scales again and add powder to its target weight. Adding powder into water wets it through more evenly than pouring water onto a heap of powder.
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Mix until it is even
No dry pockets, no lumps at the base of the container. Scrape the sides and the bottom corner — that is where unmixed powder hides.
Things worth knowing
- Small mixes punish small errors
- Ten grams out of a 100g mix is a ten per cent error. The same ten grams in a 1kg mix is one per cent. Beginners often start with mixes so small that ordinary scale inaccuracy becomes the dominant variable.
- Changing ratio changes the colour slightly
- A wetter mix and a stiffer mix will not read identically once dry, even with the same pigment. Keep the ratio constant while you are testing colour.
- Do not adjust mid-mix
- Adding more water to loosen a stiff mix that has already begun to set gives you a weak piece. If it is wrong, start again — the material is the cheapest thing on the table.
Questions people ask
Can I measure by volume instead of weight?
No. A cup of powder varies with how it settled in the bag; a gram is always a gram. Volume measuring is the single most common reason two casts of the same recipe come out differently.
Can I adjust the ratio to make the mix thicker or thinner?
Within the two ratios, yes — 3:1 flows more, 4:1 flows less. We don’t recommend going outside that range: more water gives a weaker piece, and less water stops the mix flowing into detail.
Does water temperature matter?
Use water at room temperature for consistency. If you want to compare two pieces meaningfully, everything except the variable you are testing should stay the same — and temperature is part of that.
Can I re-mix material that has started to set?
No. Stirring a mix that has begun to stiffen, or loosening it with extra water, gives a weak piece. Start again.
