Adjusting Casting Slip Fact Sheet

It is common for casting slips to set firm as they age. Indeed, it is this setting-on-standing that allows the slip to cast in the first instance.

If your slip has become too stiff and gluggy to use then:

  1. Stir with a power mixer to see if it regains it’s desired fluidity.
  2. Measure the density or litre weight (weight of 1 litre of slip). We like to use a 500ml plastic measuring cylinder from a lab supplier. Ali-Express has them. The narrow tube and accurate markings minimise errors. Our V4 slip should have a weight of approx. 1750 grams per litre.
  3. The gluggy slip will either need an addition of water or deflocculant. We sell Sodium Silicate and a Dispex-style deflocculant in 100ml dropper bottles which simplify handling.
  4. Adding the wrong modifier can have a negative effect on casting properties so caution is required. Never guess and treat the entire batch.
  5. Our slip expert, Bruce, recommends part-filling two 1-litre jugs with the gluggy slip. Adjust one with cautious additions of water until it reaches the desired fluidity – we use a Wagner seconds cup to measure the running time, with a target of approx. 50 seconds.

  6. Adjust the second jug with cautious additions of a deflocculant and record your additions. The target weight and running time is again 1750g/L and 50 seconds.
  7. Pour test casts with both samples to determine which was the more effective modification.
  8. Remember, slips with more water will be more plastic. Slips with more deflocculant will be more brittle to trim and may take longer to cast.
  9. Keep good notes and re-balancing your slip will become routine.