Interior and finishes · Flooring Materials
Terrazzo Flooring (In Situ and Precast)
Explains what terrazzo is made of and why the in situ and precast routes are effectively two different decisions, one governed by the substrate and its movement, the other by laying and jointing.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What terrazzo flooring is
Terrazzo is a composite. Chips of marble, granite, glass or other aggregate are set in a binder, allowed to cure, then ground back and polished so that the aggregate is cut through and exposed as a flat surface. The binder is either cementitious or a resin, and that choice affects the weight, the curing, the colour range available and how the finished floor behaves in use.
In situ terrazzo is placed wet on a prepared base and ground in position, producing a continuous surface interrupted only by divider strips. Those strips are not decoration alone: they define panels, they control where the material cracks, and they are set out to relate to the movement in the structure beneath. Whatever the substrate does, an in situ floor tends to follow it.
Precast terrazzo is made off site as tiles, slabs, stair treads or sills, cured and usually polished before delivery, then laid and jointed much like natural stone. It brings joints and a bedding decision that the in situ route avoids, but it removes the on-site grinding, the wet work and much of the dependence on whether the substrate cracks.
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.
- Terrazzo floor
- Poured terrazzo
- Precast terrazzo
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Halls, entrances and circulation spaces where a hard polished composite surface is wanted.
- Continuous floors where divider strips are used to set out panels and to control cracking.
- Stairs, treads, risers and sills produced as precast units to match a terrazzo floor.
- Interiors where the aggregate itself is being chosen as the visual character of the space.
- Refurbishments where precast units are laid over a base that could not take wet in situ work.
- Floors where a continuous appearance is wanted across a large area without a tile grid.
Consideration
Where it is commonly considered
- Where a hard, ground and polished surface is wanted and the aggregate is part of the design.
- Where the substrate is sound and stable enough to carry an in situ composite without moving under it.
- Where precast units allow the same appearance without wet work and grinding on site.
- Where divider strips can be set out to relate sensibly to the structure that lies beneath.
- Where the programme can accommodate curing and grinding, or the delivery of precast units.
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.
- Over a substrate that is cracking, moving or of unknown condition, since an in situ floor follows it.
- Where structural movement joints have not been identified and carried through the finished floor.
- Where the base cannot take the additional weight, which is an engineering matter for a qualified professional.
- Where the programme cannot accommodate wet work, curing and the disruption of on-site grinding.
- Where a continuous appearance is expected from a precast installation, which will always show joints.
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.
- Substrate dependency
- An in situ floor is bonded to or laid on the base and behaves as an extension of it. Cracks, movement and inadequate preparation in the substrate reappear in the finished surface, which is why the base governs the whole decision.
- Installation dependency
- The two routes are different trades. In situ means wet placement, curing, grinding, grouting of pinholes and polishing on site, while precast means laying, bedding and jointing units that arrive already finished.
- Appearance
- Aggregate type, size range and density in the mix determine the look, and grinding is what exposes it. Divider strips on an in situ floor, and joints on a precast one, are visible parts of the design rather than incidental.
- Maintenance
- Cementitious and resin binders are cleaned and protected differently, and many floors carry an applied sealer or protective treatment that has to be maintained on a defined regime set by the supplier.
- Repairability
- Local damage in an in situ floor can be cut out, refilled and reground, though matching the aggregate distribution is difficult. A precast unit can be lifted and replaced where matching stock still exists.
- Surface wear
- The surface is the same material all the way through the topping, so wear does not expose a different layer. Sheen changes along traffic routes long before any loss of material becomes noticeable.
- Moisture behaviour
- A cementitious binder and a damp base interact, and a resin binder placed over a damp base can lose its bond. The moisture condition of the substrate belongs in the discussion from the very start.
Exposure
Exposure and environmental conditions
- What is the condition of the substrate, including any existing cracking or movement?
- Where are the structural movement joints, and how will they be carried through the finished floor?
- Has the moisture condition of the base been established before any binder is chosen?
- What will be dragged, dropped or spilled on the surface in normal use?
- Does the space take strong sunlight that would show the sheen and any unevenness in it?
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.
- Structural movement has to be identified first, because divider strips and joints follow it rather than the reverse.
- The base needs assessing for soundness, cracking and moisture before an in situ topping is considered.
- Added weight from a topping or from precast units is a matter for a qualified professional to assess.
- Precast units need a bedding and jointing decision much like natural stone, including adhesive and grout.
- Finished floor height, thresholds and junctions with other coverings are set by the route that is chosen.
Appearance
Appearance and finish considerations
- Aggregate choice, size range and density change the character of the floor more than the binder colour does.
- Divider strips are visible, and their layout should be designed rather than derived from a convenient bay size.
- Precast units show a joint pattern that in situ work does not, and that is the visual difference between them.
- Grinding and polishing levels change the sheen, and a higher sheen shows unevenness more readily.
- Colour and aggregate distribution vary between batches, which matters for later repairs and additions.
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.
- Will the substrate move, and what would that do to a bonded in situ surface above it?
- How does the chosen binder respond to the substances that will reach this floor?
- How is the surface protected, and what happens as that protection wears along traffic routes?
- Can local damage be reground into the surrounding floor convincingly, and by whom?
- Service life depends on the base, the binder, the installation and the maintenance regime together.
Upkeep
Maintenance and repair considerations
- What sealer or protective treatment is specified, and how exactly is it renewed?
- Which cleaning products are excluded for this binder, and does that differ from natural stone?
- Who would carry out a local repair, and would the floor need regrinding across a wider area?
- Is spare aggregate or spare precast stock being retained for any future work?
- How often does the guidance suggest the protective treatment is reviewed?
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.
- Substrate preparation and any crack treatment come before the topping is placed.
- Divider strip layout is set out against the structure rather than against the room dimensions alone.
- Curing, grinding and polishing take the space out of use and generate slurry and dust.
- Grouting of pinholes between grinding passes is part of the process, not an optional refinement.
- For precast units, bedding, adhesive and grout are selected together with the unit and the base.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- Confirmation of the binder type and what the manufacturer says about the substrate it needs.
- Guidance on movement joint treatment and on how divider strips relate to the structure.
- The sealer or protective treatment specification and the regime for maintaining it.
- Cleaning guidance, including any products excluded for this particular binder.
- For precast work, the adhesive and grout recommendations for the units being supplied.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Are we discussing in situ or precast terrazzo, and what makes that the right route here?
- What is the condition of the substrate, and how exactly has it been assessed?
- Where are the structural movement joints, and how are they carried through the floor?
- Which binder is proposed, and what does that mean for weight, curing and cleaning?
- How are divider strips being set out, and is that a design decision or a convenience?
- What protective treatment is specified, and who maintains it once we are in?
- If the floor is damaged locally, how would it be repaired and how visible would that be?
- What does the added weight mean for the structure, and who has actually checked it?
- How long will the space be out of use for curing, grinding and polishing?
Blind spots
Commonly overlooked points
- Divider strips are read as decoration when their main job is deciding where the floor will crack.
- An in situ floor inherits the substrate's problems, so investigating the base is the real first step.
- Structural movement joints that stop at the topping reappear as cracks a short distance away.
- The weight of a terrazzo floor is easy to forget until someone asks about the structure beneath it.
- Grinding, grouting and polishing on site are disruptive in a way that photographs never suggest.
What this page does not do
- Where a terrazzo floor adds weight to an existing structure, the adequacy of that structure is an engineering matter for a qualified professional.
- This entry makes no assessment of how any polished surface behaves underfoot, which is outside what a reference page can determine.
- Binder systems, sealers and adhesives vary by manufacturer, and this page is not a specification for any of them.
- Build Design Hub publishes reference material only and does not test, approve or recommend flooring systems.
Related entries
Related materials
Materials from the same family, an adjacent role in the assembly, or a shared application.
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.
Flooring Materials
Reference entries for floor coverings and floor surface systems — wood and engineered wood, laminate, vinyl and LVT, linoleum, rubber, cork, bamboo, carpet, terrazzo and resin.
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