Terrazzo specification: cement or resin, tiles or in situ, strips and joints

At a glance

Approximate. The US National Terrazzo & Mosaic Association's nominal thicknesses and weights (2023), converted; system names are theirs. Cement thicknesses include a 13 mm topping. Resin is outside BS 8204-4 and BS EN 13748. UK build-ups may differ: the partner terrazzo supplier confirms them. Terrazzo is heavy: have the structure checked.

Cement or resin, tile or in situ

Four questions settle most of the choice: how much build-up height the floor has, how much weight the structure can take, how long a wet trade can run on site, and how the floor will be cleaned and repaired.

Cement or resin. Our terrazzo page describes cement-bound terrazzo as valued for its weight, depth and long working life. It is porous, so it is sealed and kept with a neutral-pH cleaner, because acidic cleaners can etch the cement and any marble in the aggregate. It is heavy, and the structure, the handling and the build-up height need planning early. Resin-bound terrazzo uses an epoxy or polyester matrix, which allows thinner sections, brighter pigments and a non-porous surface. On the US figures in the table it is roughly a seventh of the thickness of a sand cushion floor and an eighth of the weight.

In situ or tiles.

• In situ terrazzo is mixed and laid on the floor, cured, then ground and polished there. It gives a continuous floor with few joints and room for inlaid patterns, but it is a long wet trade, and the grinding slurry has to be controlled around drains and joinery.
• Tiles are made in a factory (BS EN 13748-1 for inside, -2 for outside) and sold ready to place. They are laid on a bed like stone, so the bedding, joints and movement joints follow natural stone flooring specification. BS 5385-3:2024 lists terrazzo tile in its scope.
• Repair. Our terrazzo page says both cement and resin surfaces can be reground and repolished in place if scratched or dulled.

The standards cover cement. BS 8204-4 is the code of practice for in situ cementitious terrazzo as a wearing surface on a concrete base or screed, and BS EN 13748-1 covers factory-made cement-bound tiles. Resin terrazzo falls outside both, so its specification rests on the resin maker's system data.

Aggregate: chip sizes and thickness

Terrazzo is chips of marble, granite, glass or other hard material set in a matrix. Chip size and topping thickness go together, because a topping has to be thick enough to hold its biggest chip. Our terrazzo page notes that chip scale runs from a fine, almost speckled grain to pieces several centimetres across.

The US National Terrazzo & Mosaic Association grades chips by number, 0 to 5, from about 1.6 mm to about 19 mm (drawing below). Its customary pairings: a 13 mm cement topping takes No. 1 and 2; a 10 mm resin topping takes No. 0, 1 and 2 (6 mm with No. 0 and 1); and Venetian work, with larger chips, sits in a topping of about 16 mm using No. 1 to 5.

For a UK floor, suppliers grade their own way and often describe chips in millimetres. Specify the chip range in millimetres, the material and the colour, and approve a ground sample panel, not an adjective such as ‘fine’ or ‘large’.

Divider strips: what they do and where they go

Divider strips are thin metal strips set on edge in the topping and ground flush with it. They divide the floor into panels, separate colours and draw pattern lines. The US guide lists zinc and brass for cement terrazzo, and zinc, brass, plastic and aluminium for resin, in widths from 18 gauge up to about 13 mm, with 16 gauge or about 3 mm the standard. A brass strip is the same metal as our brass inlay, and the questions about its finish and how it ages in a floor are in lacquered vs unlacquered brass and copper.

What a strip does not do. The US guide is plain about it. For the systems that bond to the slab, strips set over a joint in the concrete do the work of a joint, and strips not over a joint are decorative: they do not level the floor and they do not prevent cracks. So the strip layout cannot be left to the pattern alone. It starts from the joints in the base, and the pattern is drawn around them.

Panel size. For sand cushion terrazzo the guide asks for the strips to make squares of about 1.2 m or less, or rectangles of no more than about 2.3 m² and a proportion of 1.5 to 1 at most. That is US practice. UK panel sizes and joint spacing come from BS 8204-4 and the terrazzo contractor; we have not read the standard, so none is given here.

Movement joints, edges and the slab

Terrazzo that is bonded to the slab follows it: cracks and movement in the slab can show through, so the base decides the joints. Carry every structural and screed joint through the terrazzo in the same place, with a strip over each, and add joints at perimeters and at columns. The UK specification guidance we found says the same, but it is secondary, and the BS 8204-4 clauses were not read.

A movement joint in terrazzo is often drawn as two strips back to back with a flexible gap between them. For sand cushion terrazzo the US bulletin says double strips handle practically any slab movement, advises against pre-formed neoprene filler between them, and says the gap is often held with a temporary filler that is removed several weeks later, once most of the shrinkage has happened, and replaced with a pourable flexible sealant. Where the slab carries a metal expansion plate, the terrazzo butts it with a metal strip between the two.

Where terrazzo meets timber, carpet or stone, see floor transitions and movement joints.

Grinding, slip, sealing and care

• Grinding and finish. After curing, terrazzo is ground in stages with finer abrasives to expose the chips, voids are filled, and it is reground. A honed finish is matt and low-glare and suits floors, while polished lifts the colour and is common on tops. Our terrazzo page says lightly textured or anti-slip finishes are available where a floor requires them.
• Slip. Grinding and sealing change the surface, so ask for a wet pendulum test on the finished floor, or on a ground and sealed sample, not on the raw material. HSE's pendulum bands are on our natural stone finishes sheet. We found no slip value for a terrazzo finish.
• Sealing and cleaning. Cement-bound terrazzo is sealed and kept with a neutral-pH cleaner; resin is effectively non-porous and needs little more than routine cleaning (our terrazzo page).
• Dust and slurry. Grinding on site makes wet slurry and dust. Ask the terrazzo contractor how it controls both; see engineered stone and silica guidance for HSE's approach to stone dust.

Terrazzo flooring: [cementitious in situ, bonded / cementitious in situ, sand cushion / resin in situ / cement-bound tiles to BS EN 13748-1:2004+A1:2005]. In situ cementitious work to BS 8204-4:2004+A1:2011 [confirm current edition] on [concrete base / screed to BS 8204-1], accepted in writing by the terrazzo contractor. Total thickness [ ] mm including [ ] mm topping, confirmed by the contractor for the base and use. Resin systems: the resin maker's system data, with base moisture and flatness requirements in writing.

Matrix [cement and pigment / resin], colour [ref]. Aggregate [marble / granite / glass], colour [ref], chip range [ ] to [ ] mm. Approved sample panel [ref], [ ] x [ ] mm, ground and sealed as the works, signed, dated and kept on site as the reference. Trial area [ ] before the main floor.

Divider strips [brass / zinc / aluminium / plastic], [ ] mm thick and [ ] mm deep, in the layout on drawing [ref], with a strip over every joint in the base in the same position. Movement joints [two strips back to back with flexible sealant] at [ ] and at all perimeters and columns. Strips are not levelling devices and do not replace base joints.

Ground to [honed / polished] finish in [ ] stages. Sealer [penetrating, as the contractor recommends]. Wet pendulum test value not less than [36] on the finished floor, [Slider 96], reported before handover. Slurry and dust controlled; method statement before work starts. Cleaner [neutral-pH]; care instructions at handover.

Standards and sources

• BS 8204-4:2004+A1:2011 and BS 8204-1:2003+A1:2009: in situ cementitious terrazzo; concrete bases and screeds. Listings read 5 Nov 2026; texts not read.
• BS EN 13748-1:2004+A1:2005 and BS EN 13748-2: cement-bound terrazzo tiles. Part 1 listing read; texts not read.
• BS 5385-3:2024: floor tiling code, lists terrazzo tile. Listing read; text not read.
• US National Terrazzo & Mosaic Association: Terrazzo Systems Reference Guide (2023); bulletins S-6 and S-8 (8/13): read in full; imperial figures converted.
• Our terrazzo page: the live description, which this sheet follows.

Questions we are asked

What is the difference between cement and resin terrazzo?

Cement terrazzo has a cement matrix: it is heavy, porous and sealed, and is valued for its depth and long working life. Resin terrazzo has an epoxy or polyester matrix, so it can be thinner, lighter, brighter in colour and non-porous. On a US trade body's figures a resin topping is about 10 mm against about 64 to 76 mm for a sand cushion cement floor.

Is terrazzo laid in situ or as tiles?

Both. In situ terrazzo is poured, cured, then ground and polished on site, and gives a continuous floor. Tiles are made in a factory and laid on a bed like stone. In situ cementitious terrazzo is covered by BS 8204-4 and factory-made cement-bound tiles by BS EN 13748-1.

How thick is terrazzo?

It depends on the system. A US trade body's nominal figures are about 64 to 76 mm for cement on a sand cushion, 44 to 57 mm for bonded cement, 13 mm for a monolithic cement topping and about 10 mm for resin. UK build-ups may differ, so ask the terrazzo supplier for the build-up for your base.

What are divider strips for in terrazzo?

They divide the floor into panels, separate colours and draw pattern lines, and strips placed over joints in the base do the work of those joints. They are set on edge and ground flush with the topping, in brass, zinc, aluminium or plastic.

Do divider strips stop terrazzo cracking?

Only where they sit over a joint in the base. The US guide says strips that are not over a slab joint are decorative and are not crack preventers or levelling devices. The strip layout should start from the joints in the base.

What British Standard covers terrazzo?

BS 8204-4 is the code of practice for in situ cementitious terrazzo, read with BS 8204-1 for the base. BS EN 13748-1 covers factory-made cement-bound tiles for inside use and part 2 for outside. BS 5385-3:2024 covers floor tiling including terrazzo tile. Resin terrazzo falls outside these, so use the resin maker's data.

What size are terrazzo chips?

A US grading scheme runs from No. 0, about 1.6 to 3.2 mm, to No. 5, about 16 to 19 mm, with larger Venetian pieces beyond. UK suppliers may grade differently, so specify the chip range in millimetres and approve a ground sample panel.