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:
- Stir with a power mixer to see if it regains it’s desired fluidity.
- 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.
- 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.
- Adding the wrong modifier can have a negative effect on casting properties so caution is required. Never guess and treat the entire batch.
- 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.
- 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.
- Pour test casts with both samples to determine which was the more effective modification.
- 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.
- Keep good notes and re-balancing your slip will become routine.