The hydrostatic pressure is too high above 600mm to be contained by plastic or expanded polystyrene. The first layer must therefore set quite soon and the subsequent layers must be poured before the rapid advancing set and exotherm. The position of the set layer must be constantly monitored to ensure-

1. The set does not overtake the pour.

2. The hydrostatic pressure of the fluid layer does not exceed 600mm.

The material is introduced through a pipe into the fluid layer. This prevents “splash marks” which a structural defects, and eliminates layering and discontinuities.

Preparation

1. Place angle irons on the mold corners and strap them tight.

1. Make a funnel attached to a tube the length of the pipe.

2. Make a stand to raise the funnel.

3. Make a graduated dipstick to monitor set level and top of fluid level.

4. Graduate the funnel stand.

5. Make a “blou-draad” poker to unblock the funnel.

6. Weigh out at least ⅓ of your mass in 2kg bowls for hand mixing. The critical factor to prevent joints is a short interval between successive pours.

7. Make a casting record to get data on setting rate.

8. Get a ladder long enough to reach the funnel at maximum extension.

9. Get a torch.

10. Get rags and washing buckets for dipstick, poker etc.

11. The geometry makes sealing of the bottom too difficult. Use spacers to centre the core and weights to prevent penetration under the mould.

Operation

• One man must be solely monitoring; recording mix times, temperatures, water %, set level and fluid level.

• One man must be solely pouring and adjusting the funnel and pipe level.

• Two men must be weighing and mixing.

Lessons from Green – Iron Tech pipe

• Number the bowls, otherwise you lose track.

• Drag the dipstick against the less critical former.

• The full length filling tube gets unwieldy and unstable. Change to a half length one at half way up.

• Keep bottom of bowls clean, stuff can fall into mould. (It didn’t, but could have.)

• Once the bottom has set, you can make 20kg machine mixes, as long as you have short interval 2kg mixes to get the material flowing.

• The middle of the outside of the funnel sets hard!

• If bubbles come out of the funnel, the tube tip has reached the set layer.