Structural and base materials · Concrete & Cement
Non-shrink Cementitious Grout
Explains the load-transferring bedding material poured or packed into a confined gap, and why it is not a tiling grout, a screed or a floor levelling compound.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What non-shrink grout is
Non-shrink cementitious grout is a factory-blended powder mixed with water and placed into a confined gap between two elements so that load passes from one to the other through it. It is supplied in flowable grades that are poured or pumped, and in drier grades that are packed or rammed into place by hand. The word grout is doing double duty in construction, and this is not the material that fills the joints between tiles.
The name states the property that gives it its purpose. An ordinary cementitious mix shrinks a little as it sets and dries. In a floor screed that is managed with joints and it matters mainly to cracking; under a loaded steel base plate it means the bed pulls away from the underside of the plate and leaves a void, so the load arrives on the edges of whatever contact remains instead of being spread across the bearing. Non-shrink grades are formulated to hold their volume, or to expand slightly while they are still plastic, so the bearing surface stays in contact.
The situations are all the same shape: a gap that has to be filled completely, is confined on several sides, and is carrying something. A steel column base plate over a holding-down bolt arrangement. A precast unit bearing on another. A starter bar or an anchor inside a drilled or cast socket. The annulus around a soil nail or ground anchor. A machine base being levelled onto a plinth. In each case the tolerance between two manufactured or cast items has to be resolved by something poured in afterwards.
That confinement is what separates it from its neighbours. A floor levelling compound is poured onto an open floor to find its own level under nothing but its own weight. A screed is a layer over a structural floor. A repair mortar is built onto an open, prepared face. A tiling grout fills a decorative joint. None of them is being asked to carry a bearing, and a grout used as a levelling pour, or a levelling compound used as a bedding grout, is a substitution the products were not made for.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- Structural grout
- Bedding grout
- Base plate grout
- Expanding grout
- Precision grout
- Cementitious anchor grout
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Bedding beneath steel column base plates over a holding-down bolt arrangement.
- Horizontal joints and bearings between precast concrete units.
- Filling sockets, pockets and sleeves around starter bars, dowels and cast-in items.
- The annulus around ground anchors, soil nails and similar ground-engineering elements.
- Levelling and bedding machine bases, plant plinths and bearing plates.
- Filling the gap at a pinning joint where new work is brought up tight against existing construction.
Consideration
Where it is commonly considered
- Where a manufactured item has to bear on a cast one and the tolerance between them has to be taken up.
- Where a gap beneath a bearing has to be completely filled with no void left behind.
- Where the designer has specified that load passes through a bedding layer rather than through direct contact.
- Where an element is set into a socket and has to be fixed and stabilised within it.
- Where an existing structure is being pinned and the final gap has to be closed tightly.
- Where a bedding material needs to be flowable enough to travel under a plate without leaving air behind.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- Where the gap is open on the top surface and what is really wanted is a levelling pour or a screed.
- Where the material would be applied to an exposed face rather than into a confined gap — a repair mortar situation.
- Where the element is structural and the designer has not stated what the bedding is required to do.
- Where the joint has to accommodate movement rather than transfer load.
- Where temperature during placing falls outside what the product information covers.
- Where the gap is too tight or too wide for the grade being used and no check has been made against the product information.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Installation dependency
- Filling completely is the whole job. Grout is normally introduced from one side so air is pushed out ahead of it, with a head of material maintained, and a gap that looks full from the outside can still contain a void.
- Substrate dependency
- Both faces of the gap matter: the cast surface below is cleaned and usually saturated, and the underside of the plate or unit above is clean and free of anything that stops contact. Loose material in the gap stays there.
- Documentation
- Grades differ by flow, by gap size and by placing method, and the manufacturer's information is the only source for which grade suits a given gap. The designer's specification says what the grout is required to do.
- Repairability
- A void discovered under a bearing is difficult to deal with after the element is loaded, which is why the placing operation is the point at which it can be got right.
- Moisture behaviour
- The material contains water and gains its properties by hydrating, so pre-wetting the substrate, protecting the exposed edge and curing all affect what happens in the gap.
- Weathering and exposure
- Where the grouted joint is exposed, the visible edge weathers like any cementitious material, and external bedding may be detailed with a formed or dressed edge for that reason.
- Maintenance
- The material is buried inside a joint and cannot be inspected. What can be inspected is the visible edge and the behaviour of the elements it beds.
Exposure
Exposure and environmental conditions
- Is the joint internal, external, below ground or in water?
- What is the temperature during placing, and is the gap in direct sun or exposed to frost?
- Is the grouted edge exposed to view or to weather once the work is complete?
- Is the location subject to salts, ground chemistry or repeated wetting?
- Will the joint be loaded soon after placing, and has that been allowed for?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- The gap is cleaned out completely before placing, since debris in it becomes a permanent void.
- Holding-down bolts, sleeves, packs and shims are positioned and fixed before the grout goes in.
- Temporary formwork or damming around the gap keeps the material in and allows a head to be maintained.
- Levelling packs or wedges under a plate are part of the arrangement and their removal, or otherwise, is a design decision.
- Adjacent elements have to be stable and supported while the grout is placed and until it has set.
- Access to introduce the material from one side determines how the pour is organised.
Appearance
Appearance and finish considerations
- Most of the material is invisible; only the edge of the joint is seen.
- The exposed edge can be dressed, chamfered or formed, and that is decided before placing rather than afterwards.
- Colour rarely matches surrounding concrete and is generally accepted as a different material at the joint.
- Spillage and staining on adjacent faces is easier to prevent than to remove, particularly on visible concrete.
- Where the joint is visible in a finished space, the line and neatness of the edge is what will be judged.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- What is this bedding required to do, and who specified it?
- How will it be confirmed that the gap has actually filled?
- Is the grade being used appropriate to the size of this gap, according to the product information?
- How long before the joint can take load, and who confirms that?
- Is the grouted edge protected from weather or exposed?
- Has curing been planned, or is it assumed the material will look after itself?
Upkeep
Maintenance and repair considerations
- What record exists of the product, the grade and the date for each grouted joint?
- If a void were suspected under a bearing, who would assess it and how?
- What visible changes at the joint edge would be worth reporting?
- Can a grouted joint be re-made, and what would that involve for the elements it beds?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- Mixing follows the product information exactly, since extra water to improve flow removes the property being bought.
- The material is placed continuously from one side so that air is displaced rather than trapped.
- Formwork or damming has to be tight, as a leaking dam loses the head that drives the fill.
- Working time after mixing is limited and governs how the operation is staged.
- Temperature and the condition of the substrate influence both flow and set.
- Curing and protection of the exposed edge follow placing rather than being left to chance.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The manufacturer's technical information for the specific grade supplied.
- The designer's specification stating what the bedding is required to do at this joint.
- A record of which grade was used at which joint, and when.
- Any placing method the designer or manufacturer has set out for the gap in question.
- Confirmation from the contractor of how complete filling was checked.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- What is passing through this joint, and what is the grout there to do?
- Which grade is being used, and does it suit the size and shape of this gap?
- How will the grout be introduced so that air is not trapped under the bearing?
- Are packs or shims staying in place, and does that affect the bedding?
- When can this joint be loaded, and who decides that?
- How will complete filling be confirmed, and is that recorded?
- Is the exposed edge to be formed or dressed in any particular way?
- Does anything about the location — weather, water, ground chemistry — change the product choice?
Blind spots
Commonly overlooked points
- Two unrelated products share the word grout, and a tiling grout has nothing to do with this one.
- A floor levelling compound is not a bedding grout, even though both are poured cementitious materials.
- Adding water to improve flow removes the non-shrink property that was the reason for buying the product.
- A gap that looks full from the outside can contain a void under the middle of a plate.
- The material is invisible once placed, so the placing operation is the only chance to get it right.
- Grades differ by gap width and placing method, and picking one by name alone skips the actual selection.
What this page does not do
- This page does not state that any grout suits any bearing, joint or load; bedding arrangements at structural connections are engineering decisions for a qualified professional.
- No strength, load-transfer or expansion value is given here; those belong to the manufacturer's documentation for the specific product.
- Placing procedures, temporary works and stability of elements during grouting are contractor matters outside this reference.
- Build Design Hub does not supply, test, approve or endorse grouts or any supplier of them.
Component forms
Building components commonly formed from this material
Elements this material is commonly used to make, named by the position they occupy in an assembly rather than by what they are bought as. This states common practice only — it is not a statement that this material suits any of these components in a particular building.
Related entries
Common comparisons
Entries met at the same decision but which behave differently, so the comparison is about the difference rather than a swap.
Related entries
Often used alongside
Entries commonly encountered together with this one. Co-occurrence only — never a claim that any combination is compatible or suitable.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Concrete & Cement Materials
Reference entries for cement-based materials — ready-mixed and precast concrete, screeds, levelling compounds, renders of the cementitious family and the admixtures that modify them.
Browse all concrete & cement entries →