Machine Base Plate Grouting: Why Epoxy Grout Was the Right Choice for a Forging Press

What a machine base plate grout actually has to do

A base plate does not sit directly on concrete. The foundation is never perfectly flat, so the plate is levelled on packers or jacking bolts, which leaves a gap. The grout fills that gap and does four jobs at the same time:

• It transfers the load. Every kilogram of the machine, and every impact or vibration it produces, must pass through the grout into the foundation. Any void means the load travels through a smaller area and concentrates on the points still in contact.
• It locks the alignment. The grout holds the plate where it was levelled. If it shrinks or creeps, the plate settles and the machine drifts out of alignment.
• It damps vibration. A fully bonded, rigid grout layer stops the plate from working against the concrete.
• It survives the shop floor. Under a working machine the grout meets lubricating oil, coolant, grease and wash-down water. A grout that absorbs these breaks down from the edges inward.

Five failure modes account for most grout problems on site: shrinkage, which leaves voids; creep under sustained load; fatigue under repeated impact; chemical attack from oil and spillage; and incomplete filling, when the grout cannot flow all the way under the plate. Choosing a grout is really choosing which of these five risks the foundation can afford to carry.

The project: a forging plant and a confined 30 mm gap

The job was the grouting of a heavy machine's base plate at a forging plant. Harikarthika Engineering, Armstrong's main applicator and distributor, carried out the work with Armstrong Chemicals' materials. Three conditions defined the specification:

Those three conditions point to one family of materials, and within that family, to one mix.

Why epoxy, and not cement-based grout, for this foundation

Cement-based non-shrink grouts have a long record in general machine bedding. Armstrong's RAPIDSTRONG GROUT POWDER (GP2) is a non-shrink cementitious precision grout (BS 1881 Part 116, ASTM C1107) rated for 5–25 N/mm² of cyclic load over 2 million cycles. For the everyday machine base it is a proven choice.

The question is always the fit to the site. Where a foundation carries constant vibration, impact and repeated oil or chemical exposure, a cement grout has two characteristics that work against it: it is porous, so it takes up oil and aggressive liquids, and it is stiff under constant dynamic stress. An epoxy grout resists oil, grease and fats, bonds to both steel and concrete, and RAPIDSTRONG GROUT EP 403 is made for low creep under sustained load.

That is why Armstrong recommends RAPIDSTRONG GROUT EP 403 where the base plate faces constant vibration or chemical exposure: forging shops, steel works, refineries, electroplating works, chemical plants, turbine halls and crane-rail foundations.

What RAPIDSTRONG GROUT EP 403 is

RAPIDSTRONG GROUT EP 403 is a two-component, low-viscosity, free-flow epoxy grout conforming to ASTM C-881. It is made to fill the gap between the base plates of industrial installations and their foundations, under moving and dynamic loads, where spillage of chemicals, acids and alkalis is a real possibility.

Its defining feature is that it is one system with three mixes, chosen by the thickness of the gap:

This is a real practical advantage. The engineer does not switch product families as the gap changes: the same resin, the same supplier, the same technical support and the same bond to steel and concrete, scaled to the job.

Why the 1 : 3 mix was the right match at 30 mm

A 30 mm average gap sits in the middle of the 10–70 mm band, which is the 1 : 3 mix. Its figures (BS 6319 Part 2) show why it suits a plant that cannot afford long downtime:

Two things stand out. First, 72 N/mm² within a single day: the foundation reaches high working strength almost at once, which shortens the wait between grouting and commissioning. Second, the strength curve is almost flat from the third day: the grout reaches nearly its full strength early and keeps it, rather than relying on a slow cure.

For comparison, the over-70 mm mix (1 : 2 : 1.5) reaches 91 N/mm² at 7 days, the highest figure in the system.

Seven reasons it was the right choice

1. Non-shrink, so contact is complete. Shrinkage under a base plate creates voids, and voids concentrate load. RAPIDSTRONG GROUT EP 403 is non-shrink, so it keeps full contact and bond across the whole plate.
2. Free-flow, so it fills the gap instead of bridging it. Low viscosity lets the grout run into every corner of a confined gap, including under large plates where a stiffer material would leave air pockets.
3. Made for dynamic loads. Resistance to repeated dynamic load and low creep under sustained load are core properties of the product: the combination a forging press, a reciprocating compressor or a high-speed turbine needs.
4. Resists what plants spill. Oil, grease, fats, most chemicals, mild acids and alkalis, and fresh and sea water. For solvents or concentrated chemicals, ask Armstrong's technical team before specifying.
5. High strength early. 72 N/mm² at one day in the 1 : 3 mix shortens the time between grouting and starting the machine.
6. Bonds to both steel and concrete. The plate and the foundation become one bearing surface, with no gap left for oil or water to work into.
7. One system, three gap ranges, one supplier. The same product covers hairline gaps of 0.1 mm through to pours beyond 70 mm, with fillers and aggregates supplied by Armstrong and technical support from its team.

How the work is done

A high-performance grout still fails if the preparation or the placing is wrong. This is the sequence, from bolts to commissioning.

1. Fix the anchor bolts

   Set the foundation bolts in drilled holes with RAPIDSTRONG AG, a polyester chemical anchor grout. The anchor grout holds the bolt; the base plate grout supports the plate around it, and on the same installation they often work side by side. The chemical anchoring procedure gives the steps.

2. Level and align the machine

   Level and align the machine on its packers or jacking bolts before any grout goes in. The grout fills the gap; it does not level the machine.

3. Prepare the surfaces

   All contact surfaces must be free of dust, oil, grease, laitance and loose material, and the concrete must be sound. Clean the concrete with air blowers and a water jet, then let it dry for epoxy grout. Shot-blast the steel free of rust: wire brushing does not reach the same standard, and the underside of the plate matters as much as the top of the foundation.

4. Build tight formwork

   Seal the formwork with rubber strips so no grout escapes. Keep it no more than 150 mm from the plate on the pouring side, with a head box, and about 50 mm from the plate on the other sides, with air vents on the far side (Figure 1).

5. Choose the mix by the measured gap

   Measure the actual gap after levelling, not the figure on the drawing, and match it to the table above. A 30 mm average gap means the 1 : 3 mix.

6. Mix properly

   Pour Part 2 (500 g) slowly into Part 1 (1 kg) and mix with a slow-speed stirrer for 2 to 5 minutes, until the colour is even. Add the Armstrong filler for the mix you chose and mix until uniform. Mix only what can be placed within the pot life, 20 minutes at 30 °C for the 1 : 3 mix. In summer heat that means disciplined batching, with one crew mixing and a separate crew pouring.

7. Pour from one side, without stopping

   Pour into the head box only, so the grout flows under the plate and pushes the air out through the vents ahead of it. Pouring from two sides traps air in the middle. Have enough material and mixed batches ready before the first pour: a break leaves a cold joint, which is exactly the weakness the grout is there to remove.

8. Let it cure

   The minimum hardening temperature is 10 °C. Leave the grout undisturbed and dry while it gains strength; epoxy grout needs no water curing. Release the machine for commissioning on the engineer's instruction.

Packing. RAPIDSTRONG GROUT EP 403 comes in 1.5 kg, 15 kg and 30 kg packs. Graded silica filler and coarse aggregate come in 5 kg and 25 kg bags.

Using cement grout instead? Mix RAPIDSTRONG GROUT POWDER (GP2) with 3.76 litres of water per 20 kg bag for a flowable mix, or 3.36 litres for a pourable mix, for at least 5 minutes. Keep the concrete damp with no standing water, place within 20 minutes of mixing, and water-cure for at least 7 days. GP2 goes in one pour up to 100 mm deep; deeper than that, add 10 mm aggregate at 50 to 100% of the grout weight. The full steps for both grouts are in the machine base plate grouting procedure.

Six mistakes that undo a good grout

1. Using the grout to level the machine. Level first, then grout.
2. Choosing the mix from the drawing. Measure the real gap after levelling.
3. Wire-brushing the plate for epoxy. Shot-blast it.
4. Pouring from two sides. Air is trapped in the middle.
5. Mixing more than the crew can place. A half-set batch does not flow.
6. Stopping halfway, or loose formwork. Either leaves the gap part-filled.

Where else this grout is used

The same product and the same reasoning apply wherever a heavy installation needs a permanent, load-bearing, chemical-resistant bed:

• Reciprocating machinery and compressors
• High-speed turbines and generator sets
• Heavy crane and transporter rails
• Testing equipment and press foundations
• Steel works, refineries, electroplating works and chemical plants

Choosing between grouts: a quick guide

Armstrong's range covers the full spread of grouting work. The right product is a matter of fit, not rank:

• General machine base, moderate vibration, dry setting: RAPIDSTRONG GROUT POWDER (GP2), the non-shrink cement precision grout.
• Constant vibration, impact, or oil and chemicals under the plate: RAPIDSTRONG GROUT EP 403, the free-flow epoxy grout, from 0.1 mm to beyond 70 mm.
• A trowelled epoxy machine mortar bed, or a spalled foundation: ROOFCRETE EP, a three-component, solvent-free epoxy mortar and concrete reaching 93 N/mm² at 7 days, laid over a ROOFBOND EP bond coat. See epoxy mortar repairs.
• Anchor bolts and dowels: RAPIDSTRONG AG or RAPIDSTRONG GROUT AG PRIDE, polyester resin anchor grouts.
• Site-mixed cement grout: RAPIDSTRONG GROUT ADMIX at 250 g per 50 kg of cement, or RAPIDSTRONG GROUT PB 66.

If the foundation itself is cracked, repair it before grouting: see the concrete crack repair guide. The machine grouting and anchoring guide covers the whole job from foundation to commissioning.

Specification checklist for engineers

Before you issue a base plate grouting specification, confirm each of these:

1. The measured gap after levelling, and so the mix.
2. What reaches the base: oil, coolant, acids, wash-down water.
3. The load: static, cyclic, impact or reciprocating.
4. How soon the machine is needed, which sets the strength needed at that age.
5. The temperature at the time of pouring, which sets the batch size through pot life.
6. The steel surface standard: shot-blasted for epoxy, not wire-brushed.
7. Material, mixers and crew to pour without a break.
8. Armstrong's sign-off for any solvent or concentrated chemical exposure.

Questions and answers