Machine Foundation Grouting and Anchoring: Cementitious, Epoxy or Chemical Anchor

Machine foundation grouting: check the load, the gap and the exposure

A machine, a steel column or a crane rail does not sit directly on concrete. It is levelled on packers or jack bolts, and the gap under the base plate is then filled with grout. The grout is the load path. If it shrinks away from the plate, leaves air pockets or breaks up under vibration, the bolts loosen, the alignment drifts and the foundation cracks. That is why a base plate is grouted with a non shrink grout and not with ordinary cement mortar, which shrinks as it dries. Armstrong makes cementitious precision grout, epoxy grout, grout additives and chemical anchor grouts for bolts and rebar. Three decisions pick the right one: the load, the gap and the exposure.

Find the right non shrink grout or anchor grout for the job

Match the job to one route. Each route names the Armstrong products made for it and takes you to its section. Where several products suit, all are listed, and an Armstrong expert helps you pick.

Prepare first, pour once, pour from one side. All loose concrete, laitance, old grout, oil and flaking material is removed before any grout is mixed.

Non shrink grout and anchor grout finder

Armstrong makes cementitious precision grout, epoxy grouts, grout additives and chemical anchor grouts. Every one is a sound choice for its job. Answer three questions for a starting recommendation, then confirm it with an Armstrong expert and the machine supplier.

How to grout a machine base plate: preparation and formwork

This sequence applies to a new installation, whichever grout is used. The work is done by the erection contractor or an Armstrong applicator. The steps show what a proper job looks like.

1. 1
   Clean the foundation

   The concrete must be sound and free of oil, grease, dust, laitance and loose particles. Remove weak surface concrete so the grout sits on sound material. Clean with air blowers and water jet.Why: Grout bonds to sound, clean concrete. Oil, laitance and dust leave a weak layer under the grout, and the plate then works loose.
2. 2
   Clean the plate and bolts

   The underside of the base plate must be free of oil, grease, rust and scale. For epoxy grout, Armstrong states that steel surfaces should be shot blasted free of rust.Why: Rust and oil under the plate stop the grout bonding to the steel, which is where load is transferred.
3. 3
   Fix the anchor bolts

   Bolts in drilled holes are fixed with a chemical anchor grout. See the anchoring section.Why: The bolts hold the machine down, so they are set and cured before the plate is levelled and grouted.
4. 4
   Level and align the machine

   Set the plate on its packers, shims or jack bolts and complete the alignment before grouting. The grout fills the gap. It does not level the machine.Why: Grout fills a gap; it does not correct alignment. Aligning first means the grout sets with the machine already in its final position.
5. 5
   Provide air vents

   Air trapped under a large plate leaves a void. The RAPIDSTRONG GROUT POWDER (GP2) data sheet asks for special care with air ventilation under base plates.Why: Trapped air leaves a void under the plate, and a void carries no load. Vents let the air escape as the grout rises.
6. 6
   Build leak-proof formwork

   The formwork must be watertight, sealed with rubber strips. Armstrong states that the gap between the formwork and the plate should not exceed 150 mm on the pouring side and 50 mm on the other sides, with no gap at the flanks if possible.Why: Grout that leaks from the formwork leaves the gap unfilled. Tight formwork and a limited gap also keep the head of grout needed to push air out.
7. 7
   Wet or dry the surface

   For cementitious grout, wash the concrete and keep it damp so it does not draw water out of the grout, with no standing water. For epoxy grout, the surface is dry.Why: Dry concrete pulls water out of cementitious grout and weakens it. Epoxy needs a dry surface to bond. The surface condition depends on the grout type.
8. 8
   Have everything ready

   Grouting must run without a break. Enough material, mixing capacity and labour are on hand before the first mix, and for large pours a holding tank that gently agitates the grout.Why: A break in the pour leaves a cold joint under the plate, and that joint is a weak plane.
9. 9
   Pour from one side

   Pour from one side only, so the grout pushes the air ahead of it and out at the far side. Keep a head of grout on the pouring side until it appears along the other side.Why: One-way flow pushes the air ahead of the grout and out the far side. Pouring from two sides traps air in the middle.
10. 10
    Cure and protect

    Cementitious grout shoulders are water-cured for at least 7 days after the formwork is removed, or sprayed with ROOFEXCURE WB, the Armstrong curing compound stated to take the place of water ponding and wet hessian, applied straight after the formwork is removed. Epoxy grout needs no water curing.Why: Cement grout gains its strength only while it is moist. Dried-out shoulders crack and let oil and water under the plate.

Non shrink cementitious grout for base plates and column bases

For static loads and general structural bedding, the standard choice is a bagged cementitious precision grout. RAPIDSTRONG GROUT POWDER (GP2) is a ready-to-use powder of Portland cement, bonding additives and inert fillers. Water is the only thing added at site, so there is no batching error. A gas-producing additive expands the grout slightly while it is still plastic, which makes up for shrinkage and settlement and keeps the grout tight under the plate. It contains no metallic iron and no added chlorides.

Non shrink grout mix ratio: how much water per bag

1. 1
   Measure the water

   Measure it. Extra water lowers strength and brings back shrinkage.Why: Extra water lowers strength and brings shrinkage back, which is exactly what a non-shrink grout is bought to avoid.
2. 2
   Add powder to water

   Put the water in the mixer and add the powder slowly. Mix with an electric paddle stirrer or grout mixer for at least 5 minutes, until smooth.Why: Adding powder slowly to the water gives a lump-free, uniform mix. Dumping water onto powder leaves dry pockets.
3. 3
   Place within 20 minutes

   At 30°C the grout is placed within 20 minutes of mixing, so the expansion takes place under the plate and not in the bucket.Why: The grout expands as it sets. Placed in time, the expansion happens under the plate where it holds the plate; placed late, it happens in the bucket.
4. 4
   Pour continuously from one side

   As in the preparation section. Air pockets are released by tapping the formwork or by light vibration.Why: Continuous pouring keeps the grout flowing as one mass. Tapping or light vibration lets the trapped air out.
5. 5
   Thick pours

   Under a plate, RAPIDSTRONG GROUT POWDER (GP2) goes in a single pour up to 100 mm. Above 100 mm, well-graded, silt-free 10 mm aggregate is added at 50 to 100% of the weight of the grout, to limit heat build-up. Armstrong also makes high strength, non-shrink cementitious micro concretes: ROOFCRETE MC 240, ROOFCRETE PFMC 122, which is fibre reinforced, and ROOFCRETE PMC 112, which is polymer modified and yields about 21.92 litres per 40 kg bag. An Armstrong expert advises where a micro concrete suits a deep section better than a grout.Why: Deep pours generate heat and shrink more. Adding graded aggregate above 100 mm controls both.
6. 6
   Cure

   Keep the exposed shoulders wet for at least 7 days.Why: Keeping the exposed grout wet for the first week gives it the strength the machine will load.

Grout additives for site-mixed non-shrink grout

Where grout is batched at site from cement, Armstrong additives make it free-flowing and non-shrink. These suit bolt pockets, bedding, duct grouting and void filling, and base plates where the engineer accepts a site mix.

Epoxy grout for machine foundations: vibration, impact and chemicals

An epoxy grout is used where a cementitious grout would be worked loose or eaten away: reciprocating machinery, mobile loads, testing equipment, heavy crane and transporter rails and high-speed turbines, and in steel works, refineries, electroplating shops and chemical plants where spillage reaches the base. RAPIDSTRONG GROUT EP 403 is a two-component, low-viscosity, free-flow epoxy grout conforming to ASTM C-881-78. It is non-shrink, has low creep under sustained load and resists repeated dynamic load.

Epoxy grout mix by gap thickness

1. 1
   Prepare dry and clean

   Concrete sound and free of dust, oil, grease and loose material. Steel shot blasted. The minimum hardening temperature is 10°C.Why: Epoxy bonds very strongly to clean, dry concrete and blasted steel, and not at all to dust or oil. Cold slows hardening below the stated minimum.
2. 2
   Mix resin and hardener

   Add 500 g of Part 2 slowly to each 1 kg of Part 1 and mix with a slow-speed power stirrer for 2 to 5 minutes, until the colour is uniform. Then add the filler, and the aggregate for deep pours. Aggregate must be even-sized, clean and dry.Why: The ratio and the mixing time set the cure. A wrong ratio leaves soft grout that never reaches its strength.
3. 3
   Have enough ready

   Continuous flow is essential, so sufficient grout is made available before the pour starts.Why: A break in the pour leaves a joint that cannot take load. All the grout must be ready before the first pour.
4. 4
   Pour from one side

   Pour or pump from one side until the grout shows on the other. For pressure grouting, inject from one side until grout flows from the other.Why: The grout pushes air out ahead of it so the whole gap fills without voids.
5. 5
   Leave it to harden

   No water curing. Keep the machine still until the grout has gained strength.Why: Epoxy does not need water curing, and moving the machine on soft grout breaks the bond.

Deep pours under heavy equipment and crane rails

ROOFCRETE EP is a three-part, solvent-free structural epoxy concrete and machine mortar. The kit holds the epoxy resin base, the amine hardener and graded quartz silica aggregate. It is made for deep pours with a gap of 10 to 75 mm under vibrating equipment, crane rails, bridge bearing seats and anchor blocks. It reaches 93 N/mm² in compression and 21 N/mm² in flexure at 7 days, with a tensile strength of 14 N/mm², bonds to concrete at above 4 N/mm² and has a pot life of 90 to 120 minutes. The foundation is primed with ROOFBOND EP, mixed base to hardener at 65:35 by volume and covering 2 to 2.5 sq.m per kg, and the epoxy concrete is placed while the primer is still tacky, within 30 to 50 minutes. Tools are cleaned with acetone only.

Chemical anchor grout for foundation bolts, anchor bolts and rebar

A chemical anchor fixes a bolt or a bar into hardened concrete or rock. A hole is drilled, a resin grout is poured in and the bolt is pressed into it. The resin fills the space around the bolt and bonds it to the concrete. It is used for foundation bolts and machinery base plates, crane rails, starter bars and extension bars for new concrete, load-bearing anchorages for equipment and structures, and rock bolts in tunnels and mines. Armstrong makes three anchor grouts. All three suit bolts and bars, so pick by the site conditions or ask an Armstrong expert.

How to fix a foundation bolt or rebar in existing concrete

1. 1
   Fix the depth and hole size

   The embedment depth and the annular gap depend on the bolt, the load and the concrete. Armstrong asks that they be fixed with its technical representative, and for structural anchors by the design engineer.Why: Embedment and hole size decide how much load the anchor can carry, so they are fixed with the supplier or the design engineer.
2. 2
   Drill and clean the hole

   Drill to depth. Blow out the dust with compressed air and brush the hole. It must be free of dust, grease, oil and loose material, or the resin bonds to the dust and not to the concrete.Why: Resin bonds to the dust, not to the concrete, if the hole is not cleaned. A clean hole is what gives the anchor its pull-out strength.
3. 3
   Clean the bolt

   The bolt or bar is free of oil, loose rust and scale.Why: Rust and oil on the bolt weaken the bond between steel and resin.
4. 4
   Mix the grout

   Mix the two parts thoroughly, preferably with a mechanical mixer, until uniform. Mix only what can be placed within the pot life.Why: Two parts mixed fully cure fully. Unmixed streaks stay soft and fail. Mixing only what the pot life allows avoids setting in the bucket.
5. 5
   Pour, then insert

   Pour the measured quantity into the hole. Press the bolt in gently until it touches the bottom, so the resin rises and fills the annular space. Move the bolt slightly once or twice to spread the resin evenly.Why: Pouring first and pressing the bolt in pushes the resin up the annular gap, so no void is left around the bolt.
6. 6
   Do not disturb

   Hold or support the bolt in position and leave it untouched until the grout has set.Why: A bolt moved while the resin sets breaks the bond and loses the strength.
7. 7
   Load after cure

   Tighten and load the anchor only after the grout has cured.Why: Loading early pulls the bolt out of uncured resin.

Bolts cast in pockets, and not in drilled holes, are grouted with a free-flowing non-shrink grout: RAPIDSTRONG GROUT POWDER (GP2), or cement grout made with RAPIDSTRONG GROUT ADMIX or RAPIDSTRONG GROUT PB 66. Starter bars for column jacketing and concrete extensions are covered on the structural concrete repair page. Exposed bolts and steelwork are protected as shown on the steel rust protection page.

Machine vibration and loose foundation bolts: regrouting an existing base

Rising vibration, bolts that will not stay tight, a hollow sound under the plate, cracked grout shoulders and oil seeping from under the base are signs that the grout has failed. The usual causes are a grout that shrank, voids left by trapped air, mortar used in place of grout, and oil or chemicals that broke down a cementitious grout. Repair is the first choice. Lifting the machine and rebuilding the foundation is the last resort.

1. 1
   Find the extent

   Tap the grout and the plate to map the hollow areas, and check the bolts. Have the machine supplier or a structural engineer review a foundation that has cracked.Why: Tapping maps the voids so only what is bad is repaired. A cracked foundation goes to the supplier or engineer first.
2. 2
   Inject voids and cracks

   Voids under the plate and dormant cracks in the foundation are injected with RAPIDSTRONG GROUT EP 403 as resin and hardener at 100:50, which enters gaps from 0.1 mm. The method is on the injection grouting page.Why: Very thin epoxy enters gaps from 0.1 mm, so hollows under a sound bed can be filled without lifting the machine.
3. 3
   Or remove the old grout

   Where the grout is broken or oil-soaked, support the machine and chip out all of it, back to sound, clean concrete. Oil-contaminated concrete is removed until clean concrete is reached.Why: Oil-soaked grout cannot bond to new grout. It has to come out back to clean concrete.
4. 4
   Re-fix loose bolts

   Bolts that have pulled loose are re-drilled and fixed with RAPIDSTRONG AG, RAPIDSTRONG GROUT AG PRIDE or ROOFBOND EPP 504.Why: A loose bolt cannot clamp the plate. Re-drilling and resin anchoring restores the hold-down.
5. 5
   Regrout with the right grout

   If the old grout failed under vibration or oil, change to epoxy: RAPIDSTRONG GROUT EP 403 or ROOFCRETE EP. If it failed from shrinkage or poor placing under a static load, RAPIDSTRONG GROUT POWDER (GP2) placed correctly is the answer.Why: If grout failed under vibration or oil, the same grout fails again. Epoxy resists both.
6. 6
   Realign, then return to service

   Check alignment after the grout has gained strength and before the machine runs.Why: The machine may have moved during the work. Alignment is checked once the grout has strength, and before the machine runs.

Epoxy grout vs cement grout: compare Armstrong grouts and anchor grouts

Every product below is a sound choice for the job it is made for. They differ in chemistry, in the gap they fill and in the loads and exposure they are made for. Figures are from Armstrong data sheets and brochures.

All Armstrong grouts and anchor grouts for machine foundations

Machine grouting and anchoring products by stage

How much non shrink grout for a base plate

Grout is ordered by volume: plate length multiplied by width multiplied by the gap. The example is a base plate 1.2 m long and 0.6 m wide with a 50 mm gap, which is 36 litres, and four 20 mm bolts in 32 mm holes drilled 200 mm deep. The hole size is an example for the arithmetic, not a recommendation. Add the grout shoulder outside the plate and an allowance for wastage. Figures are worked out from each product's stated yield or density. An Armstrong expert confirms the final quantity after seeing the site.

Standards and tests for non shrink grout and anchor grout

• RAPIDSTRONG GROUT POWDER (GP2) complies with BS 1881 Part 116:1983 and ASTM C1107. Flexural strength is tested to BS 4551 and strength with aggregate to IS 516:1959.
• RAPIDSTRONG GROUT EP 403 conforms to ASTM C-881-78. Its compressive strength is tested to BS 6319 Part 2.
• ROOFCRETE EP is listed as conforming to ASTM 827 SNF CROC 621.
• RAPIDSTRONG AG complies with ASTM-827 SNF CROC 621 and was pull-out tested to BS 5080 Part 1:1974, the British Standard for tensile tests on structural fixings.
• RAPIDSTRONG GROUT ADMIX is stated to give 1 to 4% expansion to ASTM C827, with nil chloride to BS 5075. It is listed as complying with BS 1881 Part 116:1983.
• Site checks: cube samples of the grout taken during the pour, a solid sound when the plate is tapped after hardening, and a pull-out test on sample anchors where the engineer asks for one.

Grout volume and anchor grout calculator

Enter the plate size and the gap to get the grout volume and the material for the grout you choose. Enter the bolts to get the anchor grout. Quantities only.

Eight mistakes that make machine base grouting fail

1. Using cement mortar. Ordinary mortar shrinks and leaves the plate bearing on a few high points.
2. Adding extra water. It lowers strength and brings back shrinkage. Measure the water for every bag.
3. Pouring from two sides. The two fronts trap air in the middle. Pour from one side only.
4. Stopping midway. A break leaves a cold joint under the plate. Have all material and labour ready.
5. Leaking formwork. The head of grout is lost and the far side never fills.
6. Grouting on oil, dust or laitance. The grout bonds to the dirt and not to the foundation.
7. Cementitious grout under a vibrating, oily machine. Dynamic load and oil need an epoxy grout.
8. Dusty anchor holes and early tightening. Clean the hole, and leave the bolt alone until the resin has cured.

Machine grouting and anchoring questions and answers