Concrete brick slips: how to work out how many you need, with joints, corners and boxes

Brick slips are thin facing pieces that give a wall the look of brickwork without building a brick wall. Ristone makes them from pigmented concrete, in several sizes and colours. Ordering the right quantity comes down to three things: the size of the slip, the width of the joint, and how coverage per box is stated. This guide works through all three with real slip sizes, so that you can check a quotation line by line.

Step 1: measure the area

Measure each wall you want to clad, multiply width by height and add the walls together. Then subtract openings: doors, windows, vents. Write down the external corners separately, with their height, because they are handled with corner pieces or cut slips, not with flat slips alone.

Step 2: slips per square metre, with the joint

Each slip plus its share of joint occupies a small rectangle on the wall: (slip length + joint) × (slip height + joint). The number of slips per square metre is 1 divided by that rectangle.

slips per m² = 1 ÷ ((length + joint) × (height + joint)), all in metres

Ristone calculates brick slips with a joint of about 10 mm. With that joint, the four main slip sizes work out as follows:

Model	Slip size	Slips per m², 10 mm joint	Slips per m², no joint
Oxford	240 × 73 mm	about 48.2	about 57.1
Berlin	240 × 65 mm	about 53.3	about 64.1
Belgrad	245 × 65 mm	about 52.3	about 62.8
Ribe	285 × 60 mm	about 48.4	about 58.5

With a 10 mm joint, the joint takes up roughly 15.6 to 17.2 % of each repeating module of slip plus joint, depending on the slip size. That is why a count without the joint overstates the number of slips the wall takes.

Step 3: check how box coverage is stated

Manufacturers state how many square metres a box covers. The catch is that this figure can mean the net area of the slips, or the area they cover once laid with joints.

We checked the coverage figures published in the Ristone catalogue against the slip sizes and the number of slips per box. For Oxford, Berlin and Ribe, the stated coverage is close to the net area of the slips, without joints; for Belgrad, it is close to the area with a 10 mm joint. These are approximate matches from historical data, not confirmed conventions, and the Oxford box contents are still being confirmed. Dividing a wall area (which includes joints) by a net coverage figure gives more boxes than needed; dividing a net area by a coverage that includes joints gives too few. Until the current product sheets confirm each figure, the safe way is to count slips, not square metres:

flat slips needed = flat area × slips per m² (with joint) + an allowance for cuts, with corner pieces counted separately (see Step 4)

boxes = slips needed ÷ slips per box, rounded up

Then ask for the quotation to confirm the number of boxes for your joint width.

Worked example

A feature wall of 4.0 × 2.5 m with one door of 0.9 × 2.1 m, clad with Berlin slips and a 10 mm joint.

• Area: 4.0 × 2.5 = 10.0 m²; door: 0.9 × 2.1 = 1.89 m²; net area: 8.11 m².
• Slips: 8.11 × 53.333… ≈ 432.5, so allow at least 433 flat slips before cuts and waste.
• Add an allowance for cuts around the door and at the wall edges, agreed with the installer and confirmed in the quotation.

Step 4: corners

External corners are finished either with dedicated corner pieces or with another solution set out in the installation instructions for the model. In the Ristone range, Belgrad and Ribe, among others, have corner pieces. For a model without corner pieces, ask Ristone how corners are finished before ordering.

Measure the total height of external corners in linear metres. Where corner pieces are used, subtract the area their returns cover from the flat area before counting flat slips, so that nothing is counted twice. Corner pieces are packed separately from flat slips; the quotation confirms both.

Batches and shade

The colour of Ristone slips is in the concrete, not painted on the surface. As with any cement-based product, small differences in shade between production batches are possible. Order the whole quantity for one wall in one go, so that it comes from the same batch where possible, and ask Ristone how to combine slips from different boxes on site.

Tall residential buildings in England

If the building has a storey at least 18 m above ground and contains dwellings, an institution or a room for residential purposes, regulation 7(2) of the Building Regulations 2010 requires materials in its external walls to achieve European Class A2-s1, d0 or Class A1, subject to the exemptions in regulation 7(3) (The Building Regulations 2010, regulation 7). The definition of a relevant building, including how the 18 m is measured and which storeys are excluded, is in regulation 7(4). Before specifying any brick slip on such a building, ask for the product’s classification document. Ristone confirms which documents exist for each product; nothing is assumed from a photo or a catalogue line.

Delivery to the UK and Europe

Ristone manufactures in Romania and supplies the UK and the rest of Europe on a quotation basis, depending on product, quantity and destination. For the UK, transport, customs duties and import VAT are paid by the buyer.

What to send with your enquiry

1. the net area to clad, or the wall sizes and openings;
2. the total height of external corners;
3. model, colour and joint width;
4. the substrate (render, blockwork, concrete) and whether the wall is internal or external;
5. the delivery address or postcode and your timeline.

All figures here are indicative; quantities, coverage and delivery are confirmed by Ristone before an order is placed. See concrete brick slips or send your project enquiry.