Choosing a brick slip cladding system

Plenty of new buildings look as if they were built in brick.

On many of them, the brick is a thin slip fixed to a backing system. It gives the look of traditional brickwork on a lighter wall. These notes are for self-builders, architects and specifiers who want to choose one of those systems well.

What a brick slip is

A brick slip is a thin piece of clay brick. Makers cut slips from full bricks or produce them to size. The finished wall gives the look of traditional brickwork.

Slips first came into use in the UK for repair and refurbishment work. Designers now use them on new buildings too, often with framing systems, insulated panels or rainscreens. A slip wall behaves very differently from a brick wall, in its structure, its fire performance and how long it lasts.

Two ways of fixing slips

In a mechanically fixed system, metal rails or carriers hold each slip in place. The fixings carry the load. Water drains and air moves behind the slips, as in a rainscreen.

In a bonded system, adhesive holds the slips. Some slips are bonded to boards or insulated panels in a factory. Others are fixed one by one on site, much like tiling. A third kind uses slips on a mesh backing. How well a bonded system lasts depends on the adhesive, the workmanship and the weather it meets.

Slip sizes and the carrier rail

Bricks for slips are commonly made to the British Standard BS EN 771-1. That standard judges size by the average of a sample. A single slip can meet it and still sit at the edge of the allowed range.

In a mechanically fixed system, a slip at that edge may not engage properly with its rail. Designers should agree early with the brick supplier and the system maker which slip sizes the system can hold.

Testing a system for the long term

Most systems carry third-party certification. Designers are still responsible for choosing a system that suits the building.

Some project teams ask for tests that copy years on a wall. These can include wetting and drying, freeze and thaw, and repeated wind loads. Slips usually go up before the mortar pointing. Some teams therefore test how well unpointed slips stay in place, and how they stand up to knocks.

Fire rules on taller buildings

In England, stricter rules apply to the outside walls of some taller buildings. They cover buildings with a storey 18 metres or more above the ground that hold flats, residential rooms or institutions. On those buildings, any material that becomes part of the outside wall must reach class A2-s1, d0 or class A1. A few items, such as membranes, seals and fixings, are exempt.

A material of "limited combustibility" does not meet this rule. The CROSS reporter noted that adhesives are generally combustible. On lower buildings, the fire guidance in Approved Document B still applies. A building control body can say what a particular wall needs.

Lessons from reported failures

Engineers report safety concerns to a confidential scheme called CROSS-UK. In 2021 it published a report of brick slips falling from buildings over three storeys high, next to busy streets. The adhesive holding the slips to their boards had failed. One building was later reclad with a mechanically fixed system.

A second report described slips falling from several storeys on another building. Slips had been removed twice to stop falls, and more still fell. The local authority then sought removal of all the slips.

CROSS asks designers to think about the life-span of every material on a facade. It asks builders to follow the maker's instructions for adhesives. It also asks them never to swap a product without the designer's approval.