Why this calc exists
Grouting a base plate looks like a small job — a 600 × 600 mm plate with a 50 mm gap is only 18 L of grout. But the engineering stakes are high: a poorly-grouted plate transfers uneven load to the concrete below, the equipment above vibrates, and the joint fails within months. Procurement-wise, ordering the wrong quantity means either halting erection while emergency bags are sourced, or returning 25-kg bags that have been sitting open in monsoon humidity.
The arithmetic is gap volume × density × bag yield, with two field additions: (a) head-box / formwork extension to the gap volume (typically 20–50 % extra for flow-out and air relief), and (b) anchor-pocket grout as a separate line if the base plate has levelling bolts. The Grout Quantity calculator handles all three in one screen.
Code references (with provenance)
- IS 456 Cl 13.5 — Curing for grouted joints.
- IS 516 (Part 5/Sec 4):2020 — Rebound hammer for verifying base plate grout integrity.
- ASTM C1107 — Standard specification for non-shrink grout (international, product-spec basis).
- Manufacturer TDS — bag yield, flow, working time, post-cure strength. Always the binding document.
Worked: 600 × 600 base plate, 50 mm gap, with head box
Gap volume: 0.6 × 0.6 × 0.05 = 0.018 m³ = 18 L.
Head-box extension: +30 % to allow grout to flow 200 mm beyond the plate edge (typical head box) → 23.4 L.
Wet density: 2,200 kg/m³ (cementitious non-shrink). Mass = 23.4 × 2.2 = 51.5 kg.
Bag yield: 25 kg bag → 2.06 bags nominal · 5 % wastage → 3 bags.
Anchor pockets: 4 × 0.05 × 0.05 × 0.10 = 1 L each → 4 L total → ~0.4 bag.
Total: ~3.5 bags for one plate.
Field notes (what trips people up)
- Gap depth is not bolt pocket depth. The bolt pockets go through the plate into the foundation; the gap is the space between plate bottom and foundation top. Don't mix them up.
- Head box forms extend ~150–250 mm beyond the plate edge to give the grout a reservoir and let air escape. Multiply the gap volume by 1.2–1.5 for this.
- Epoxy vs cementitious. Epoxy grout has higher strength and chemical resistance but no water of convenience; needs precise mixing. Cementitious is forgiving and cheaper, with similar compressive strength (60–80 MPa).
- Wet density varies 20 %. Cementitious non-shrink 2,100–2,250 kg/m³; epoxy 1,950–2,100; high-precision metallic-aggregate 2,400+. Always confirm against the TDS.
Worked example
Site: 8 base plates for an industrial compressor foundation, 600 × 600 mm, 50 mm gap, 4 bolts each.
Output: 3 bags/plate × 8 = 24 bags grout · 8 × 4 = 32 anchor pockets × 0.4 bag = 13 bags · total 37 bags.
Cost: 37 × ₹600 = ₹22,200.
FAQ
What's the difference between non-shrink and regular cement grout?
Non-shrink grout uses an expansive additive (calcium sulfoaluminate, metallic aggregate, or gas-forming agent) that offsets the plastic and drying shrinkage of plain cement. Critical for tight-tolerance equipment bases.
Can I use OPC + sand instead?
For non-critical equipment bases (less vibration, looser alignment tolerance), OPC + sand + water-reducer is acceptable. For precision-aligned machinery, use the manufacturer's non-shrink grout.
How long before the equipment can be aligned and tightened?
Cementitious non-shrink grout: 24 h for bolt tensioning, 7 days for full design load. Epoxy: 8–24 h. Confirm TDS for the specific product.