Engineering tool
Castable Mixing Water Calculator
Work out the mixing water for a refractory castable from the dry mass and the recommended water percentage, including water per 25 kg bag and the final wet mix mass.
Water required — kg (L)
Water per 25 kg bag — L
Final wet mix mass — kg
Always stay inside the water range on the product datasheet — excess water is the commonest cause of low strength. 1 kg of water ≈ 1 litre.
Formulas used
- Water required (kg) = dry mass (kg) × water % ÷ 100
- Water per 25 kg bag (L) = 25 × water % ÷ 100
- Wet mix mass (kg) = dry mass + water
Practical notes
- Water above the datasheet range raises porosity and cuts strength permanently. It cannot be corrected later in the cure.
- Mix water is not the only variable — water temperature and mixing time change flow as well, particularly with low-cement castables.
Frequently asked questions
What happens if I add more water than specified?
Flow improves but the cured castable keeps the extra water as porosity. Strength, density and corrosion resistance all fall, and no curing regime recovers them.
Why is water given as a range rather than one figure?
Because the workable amount depends on placement method, ambient temperature and the mixer. Vibration-cast placement needs less water than hand placement of the same product.