Gunning, Casting, or Shotcreting: Four Ways to Place a Monolithic
The same bag of castable can go in four different ways, and each one trades density and strength for speed. The datasheet numbers only apply to one of them.
Pick up a bag of castable and you have not yet decided how it goes into the furnace. Cast, self-flow, gun, or shotcrete: the method changes the water content, the density, the strength, the speed, and the price. It also changes which column of the datasheet actually applies.
Casting and self-flow: density first
Conventional casting means mixing with water, pouring into formwork, and vibrating to release air and consolidate. It gives the highest density, the highest strength, and the lowest porosity, which is to say it gives you the published datasheet properties. The cost is formwork, anchors, cure time, and a slower pace. It is the method for precast shapes and for new linings where quality leads.
Self-flow casting uses a castable formulated to flow and de-air under gravity with little or no vibration. Same density benefits, faster placement, and it reaches into congested anchor fields and thin sections a poker vibrator cannot. The water window is narrow, so mixing discipline matters.
Gunning: speed first, and the rebound tax
Gunning blows dry or damp material through a hose and adds water at the nozzle. No formwork, fast, and it handles awkward and overhead geometry, which makes it the standard for repairs and patches.
The costs are real. Rebound loss throws away a chunk of every bag as material bounces off the surface. The nozzle adds more water than a cast mix, so the in-place density is lower and the porosity higher, and the strength lands a step below the cast version of the same product. It is also dusty and depends heavily on the nozzle operator. Read the product's gunning-grade properties, not its casting-grade properties, because they are different numbers.
Shotcreting: the middle path
Shotcreting mixes the material wet, pumps it, and adds a setting accelerator and air at the nozzle. Rebound drops to a fraction of dry gunning, dust falls, and the density and strength come back close to cast, at a placement rate faster than casting. It needs a pump and a wet-mix crew, which is why it belongs on large new linings and relines where speed pays.
Which method for which job
- New lining, quality first, time available: cast or self-flow.
- Large new lining or reline, speed matters: shotcrete.
- Repair, patch, overhead, no formwork: gun.
- Shapes made off site: cast and vibrate.
Whatever the method, the dry-out schedule still applies, and the denser placements are less permeable, so they need the slower schedules and the fibres that come with low-cement material.
Every method that adds water at a nozzle is trading density for speed. That trade is often the right call for a repair and the wrong call for a slag line. Match the method to what the zone has to survive.
The short version
Gunning is the fast food of refractory installation: quick, convenient, and not quite what the menu photo promised. It has its place, and so do the other three. Our castables are supplied in casting and gunning grades with the properties stated for each: see the range, or tell us the job and we will suggest the method.