Wax Setting Silicone: Use, Re-use and Replacement

Which silicone should I order?

If you run a Semsons setter and want the simplest answer, order the ready-to-use putty. Choose the two-part putty when you want the pad to set firm around an awkward shape.

Both hold a wax model through a full run. The difference is how you get there: one is ready in seconds, the other sets firm around the piece. Most floors running Semsons setters keep the ready-to-use tubs on the bench and reach for them all day.

Why does the pad matter so much?

An automatic setting machine works to a coordinate map. It cannot see the wax, so it cannot tell when the wax has moved.

If a model shifts by a fraction of a millimetre halfway through a run, nothing alarms and nothing stops. The machine keeps placing stones against positions that are no longer where it thinks they are. You find out after casting, when the stones come back out of line.

Silicone that grips over the whole contact area is what stops that happening. It is the cheapest part of the chain and the one most often treated as an afterthought.

This is the same argument behind the mounting base: the base gives every model the same starting position, and the silicone is what keeps it there. Neither works without the other.

How do I apply it?

Six steps, the same for both products. Step five is the one that matters most — if the model rocks, stop and re-bed it.

1. Soften the pad. Take a pad from the tub, or knead equal amounts of parts A and B until the colour is completely even. Work it until it is evenly soft.
2. Press it onto the base. Push it onto the mounting base so it keys to the disc and cannot rotate. The base is a 76 mm machined disc with a locating stud, which puts every model in the same position.
3. Bed the wax model in. Use steady, even pressure. Never force it down — heat and force are what distort wax.
4. Keep the stone-bearing surfaces clear. The nozzle needs a free approach to every place a stone goes.
5. Check the model does not rock. Do this before you start the run. This is the whole point of the pad.
6. Peel, do not scrape. When the run is finished, peel the pad off the wax and the base, then re-form it for the next model.

How much do I use, and when do I replace it?

Use enough to bed the model without swallowing it. Replace the pad when it stops taking a clean impression — not when it finally lets go of something.

• How much per model. Enough that the model cannot rock and the stone-bearing surfaces stay clear. Most operators settle on their own quantity within a few pieces. If in doubt, use a slightly larger pad and a shallower bed.
• The signal to replace it. Loss of clean impression. Once a pad no longer moulds crisply around a model, it is gripping on high spots instead of the whole contact area — and a model gripped on high spots can pivot.
• What wears it out. Wax crumb, workshop dust and stray stones picked up over many mounts. Contaminated putty grips unevenly, and uneven grip is model movement.
• How to store it. Keep the tub sealed, cool and dry, out of direct sun and away from any heat source. For the two-part putty, keep parts A and B sealed and separate until you mix them.

How much you get through in a month follows two things: how many models you mount, and how many times each pad is re-used. A floor running a machine all day keeps silicone as a stocked consumable, alongside trays and nozzles.

What does the pad sit on?

A 76 mm base with stud — a precision-machined disc with a perpendicular locating stud and a flat working face. It gives the machine a model position it can rely on, but it does not grip the wax, which is why you order a base and a fixing medium together.

• The stud is what makes it repeatable. It locates the base the same way in the holder every time, so the coordinate map does not have to be re-established for each model. A stud knocked out of square quietly puts every model after it at a slight angle, which is why a bent stud means a new base rather than a straightening job.
• Keep a stack of them. With several bases you bed the next model at the bench while the current one runs, and the machine only stops long enough to swap a base. That is the cheapest way to buy back cycle time on a setting machine.
• When to replace a base. The disc face wears, the stud shifts out of perpendicular, or corrosion pits the mounting surface. All three do the same thing: they let the model sit at a slightly different height or angle than the machine assumes.
• Looking after them. Peel silicone off the face rather than scraping it, keep solvents off the machined surfaces, dry them properly after cleaning, and store them so the studs are not taking the weight of the stack.

The base also accepts other fixing media — cyanoacrylate glue and thermoplastic beads are both used this way. Silicone is what we stock for it; ask the sales desk if you need one of the others.

What do I need to order?

A fixing medium and a base. Neither is usable on its own, and both are consumables — so most floors order them together and keep a month ahead.

Everything on this page is under Consumables and dispatches the same day from our Mumbai and Rajkot warehouses, across India and to the 34+ countries we export to. If you are stocking a machine from scratch, ask us for a consumables kit rather than assembling it item by item.

Read next: automatic versus manual stone setting explains why the coordinate map matters, single versus double station compares the two machines that use these pads, installation, training and spares covers setup and service, and the glossary explains the terms used here.

Frequently asked questions