Your bath bombs are swelling because the mixture contains too much moisture, causing them to start fizzing prematurely and expand.
This happens when the ingredients, specifically the baking soda (sodium bicarbonate) and citric acid, react with water or excess moisture. Normally, this reaction is supposed to occur only when the bath bomb is dropped into bathwater. However, if the mixture is too wet during the making or drying process, the reaction begins prematurely, leading to swelling or even crumbling as carbon dioxide gas is produced and expands within the formed shape.
Based on the provided reference, the primary reason for expansion out of the mold is simply that the mixture is so wet that it's fizzing, which causes it to expand.
Preventing Bath Bomb Swelling
To prevent your bath bombs from swelling and losing their shape before use, consider these solutions based on the reference:
- Control Moisture Content: The most critical factor is the amount of liquid binder you use.
- Choose the Right Liquid: Use witch hazel instead of water as your primary liquid binder. Witch hazel evaporates more slowly and is less likely to trigger the fizzing reaction prematurely compared to plain water.
- Avoid Water-Based Ingredients: Avoid any colors or fragrances with water bases, as these can also introduce enough moisture to start the reaction. Opt for anhydrous (water-free) alternatives like mica powders, oil-soluble dyes, or pure essential oils/fragrance oils.
- Manage Humidity: If you live in a really humid area, we recommend investing in a dehumidifier to keep things dry while you work. High environmental humidity can introduce unwanted moisture into your mixture and finished bath bombs, even if your recipe and technique are perfect.
By carefully controlling the moisture content during mixing, choosing appropriate ingredients, and managing your environment, you can significantly reduce or eliminate the issue of swelling bath bombs.
Here's a quick summary of the cause and solutions:
| Problem | Cause Identified | Solutions |
|---|---|---|
| Bath Bomb Swelling | Mixture is too wet, causing premature fizzing & expansion. | Use witch hazel instead of water. Avoid water-based colors/fragrances. Use a dehumidifier in humid environments. |
Following these steps can help you create solid, perfectly formed bath bombs that only fizz when they are supposed to!
