About Master Builders Solutions MasterRoc TSG (TBM tail sealants)

Shielded TBM tunnelling has moved from a rarity to routine practice on Indian infrastructure over the last decade — Delhi, Mumbai, Chennai and Bengaluru metro corridors, Himalayan hydropower headrace tunnels, and large-diameter water and sewage tunnels under our cities are all being driven by EPB or slurry shields rather than blasted open. Every one of those machines has the same vulnerable point: the tail shield, where a ring of overlapping wire brushes rides against the newly erected concrete segments while grout is pumped into the annulus behind them at pressure. If that gap isn’t packed with a grease tough enough to resist the grout and groundwater pressure pushing back at it, the brushes wear, the seal fails, and water or grout finds its way into the machine and the finished ring — a problem that is far cheaper to prevent with the right grease than to fix underground. MasterRoc TSG is Master Builders Solutions’ answer to exactly that problem: a family of homogeneous paste greases, sold under names like TSG 6, TSG 7, TSG 16, TSG 800 and the fire-resistant TSG 870, each tuned to a different combination of sealing pressure, pumpability and, where needed, fire performance.

What sets a proper tail sealant apart from a generic industrial grease is that it has to do several contradictory things at once — pump easily through long feed lines to the brush chambers, then stiffen enough in place to resist bar-scale water and grout pressure without washing out, stay non-miscible with the annulus grout so the two don’t intermix and lose their separate properties, and remain stable through months of continuous TBM operation without breaking down under the constant mechanical working of the brush rings. That’s a narrow, project-specific specification, which is why tail seal grease is chosen on the strength of test data — sealing-pressure resistance, consistency, washout resistance — rather than on brand familiarity, and why the grade used at shield assembly (the heavier “first-fill” charge) is often different from the grade used to top up during boring. For contractors and TBM operators working Indian metro and hydro projects, getting this specification right is a procurement decision as much as a technical one, since the product has to be sourced, tested against project ground-water data and scheduled well before the machine is launched.

The technical insight

MasterRoc TSG’s performance is reported against test methods that are specific to the tail-seal application rather than general grease standards, and it’s worth knowing what they actually measure. The Matsumura sealing test simulates the brush-and-grease seal under rising water/grout pressure in a rig and reports the pressure at which it holds — reference grades in the range are documented passing at 34 bar (493 psi), which gives a specifier a direct pressure rating to compare against the project’s anticipated hydrostatic head plus grout injection pressure. Consistency is measured by cone penetration to ASTM D217 (reported in tenths of a millimetre) — a lower number means a stiffer, less flowable paste, which affects both pumpability through the feed lines and how well the grease stays put under mechanical working of the brushes. Washout or water spray-off resistance (tested to ASTM D4049) reports the mass percentage lost when the grease is subjected to a water jet, which is the lab proxy for how well it will resist being flushed out by groundwater ingress at the shield gap; documented reference values sit under 5-7% mass loss, and the grease itself is reported as insoluble in water. Together these numbers are what a tunnelling engineer actually uses to size the grade to the ground conditions, rather than relying on a general safety-data description of “grease.”

Where it is used

• First-fill charge of tail brush seal chambers before TBM launch and shield assembly
• Continuous running/top-up dosing into the tail brush rings during EPB and slurry-shield tunnel drives
• Headrace and pressure tunnels for hydropower schemes bored through water-bearing rock with shielded TBMs
• Large-diameter water transmission and sewage/interceptor tunnels driven under rivers and cities
• Mountain highway and rail tunnels excavated with shielded machines through wet or fractured strata
• High water-table or sub-riverbed reaches that need an elevated sealing-pressure grade
• Confined or methane-risk tail-shield compartments where a fire-resistant grade is specified
• Mid-drive top-up or grade change when brush wear or early grout/water seepage is detected

Key advantages

• Engineered specifically for TBM tail-brush geometry and pressure conditions, not a repurposed industrial grease
• Documented sealing-pressure resistance (Matsumura test) gives specifiers a hard number to match against ground-water head
• Non-miscible with annulus backfill grout, so the seal grease and the grout don’t intermix and weaken each other at the interface
• Strong adhesion to both the steel tail shield and the concrete segment face it rides against
• Good pumpability through long feed lines from the grease skid to each brush row, even in a stiff, high-consistency grade
• Range spans standard, high-sealing-pressure and fire-resistant grades so the product can be matched to the actual risk on site rather than over- or under-specifying
• Reported biodegradable leachate profile, a genuine consideration on urban and river-crossing drives with tight environmental clearances
• Backed by Master Builders Solutions’ global tunnelling technical service, with documented TDS/SDS for each grade

Limitations & considerations

• Not a shelf-stocked commodity in India — supply is project-specific import, so lead time has to be built into TBM mobilisation planning well ahead of shield launch
• Requires a dedicated grease pump/skid and a trained tunnelling crew; it is not something a mason or general waterproofing applicator handles
• Grade selection is critical — the wrong TSG variant for the actual hydrostatic head and grout pressure can under-perform, so ground-water data needs to go to MBS technical service before ordering, not after
• Lab test values (Matsumura pressure, consistency, washout) describe the grease in isolation; actual sealing performance on site still depends on brush condition, ring-build tolerance and grout pressure control, none of which the grease itself can compensate for
• Narrow storage window for site logistics — 5 to 35°C with a 12-month shelf life in sealed drums, which needs a proper store on sites without climate control
• High per-kg cost relative to bulk construction chemicals, so consumption (kg per metre of tunnel or per metre of shield circumference) needs to be estimated and budgeted at tender stage, not treated as an afterthought

Selection & best practice

Specifications

Industry use cases

How we position Master Builders Solutions MasterRoc TSG (TBM tail sealants)

MasterRoc TSG sits inside a wider MasterRoc TBM consumables range from the same manufacturer — soil-conditioning foams and polymers used for face support on EPB machines, and annulus backfill grout systems used behind the segments — and specifiers already running MasterRoc on a drive will typically source tail sealant, soil conditioner and backfill grout from the same technical support line for consistency across the machine. Fosroc, despite being a strong alternative across most of Space Arc’s construction-chemicals range, does not manufacture a comparable TBM tail-seal grease — this is a narrow, mechanised-tunnelling niche that Fosroc’s product line doesn’t cover, so specifiers evaluating alternatives to MasterRoc TSG generally look to other specialist tunnelling-consumables suppliers such as Sika or Condat rather than to Fosroc. For Delhi NCR and pan-India metro, hydro and tunnelling contractors, Space Arc’s role is less about stocking this item and more about the sourcing and technical coordination around it — getting ground-water and pressure data to Master Builders Solutions’ tunnelling technical service, confirming the right grade, and managing import lead time into the project’s TBM mobilisation schedule.

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