Writing a rendering specification for industrial premises

What an industrial render specification states

A product sheet describes a material; a specification says where it goes and how. For an industrial commission, the specification for each elevation should name the background, the preparation and any bonding primer, the base coat and its thickness, where mesh goes, the finish and its texture or grain, the beads at the damp-proof course, corners, openings and stop ends, the movement joints, and the weather limits and curing times that apply.

Manufacturers’ data sheets provide the numbers. K Rend’s HP14 base coat, for example, is a nominal 4 to 6 mm, its Silicone TC topcoat goes on to the thickness of its grain after at least 14 days’ curing of the base and 24 hours’ drying of the primer, and its K Mono monocouche is sprayed to 17 to 18 mm and scraped to at least 15 mm. Writing those into the specification, product by product, is what lets two tenders be compared.

If a contractor proposes an alternative product, it should be reviewed as a change to the package, with its own thicknesses and limits, rather than slipped in as like for like.

Commercial & new build ↗

Backgrounds on industrial buildings

Industrial walls are rarely one material. A unit may have blockwork below and steel cladding above, concrete columns, brick infill from an earlier phase and render boards on a later extension. Older Bradford industrial buildings add stone; the council’s Little Germany assessment notes that brick was used extensively in industrial buildings, especially for internal walls, alongside the dominant sandstone of the frontages.

Each background has its own preparation. Dense block and concrete get a bonding primer or stipple coat; lightweight block gets suction control; render boards get the board manufacturer’s base coat and mesh. Where one background changes to another, the render either has mesh across the line or a bead and joint, depending on whether movement is expected.

Keep the reason for any change with its approval, so the final records describe what was actually built.

Checking the existing construction

Drawings of an older industrial building rarely match it exactly. Panels get replaced, openings are cut and filled, and extensions are added in different materials. Before the render is specified, the walls are checked on site: tapping existing render, looking for changes of material at openings and joints, and opening small areas where the background is unknown.

The checks matter because preparation depends on the background. Hollow render is removed; painted block may need the paint taken off or a bonding coat; a panel of render board needs its own system. Where access is not possible before tender, the area is named as unchecked so it is inspected before rendering.

Structural questions, such as cracked lintels, corroded steel or bowing walls, are for an engineer, and the render follows their repairs rather than covering them.

Details at openings, cladding and fittings

Industrial walls have more interruptions than houses: roller-shutter guides, loading doors, personnel doors, service penetrations, plant supports, signs and rainwater pipes. Each needs a defined detail. The render normally stops on a bead short of a shutter guide or frame with a sealed joint between, pipes passing through are sleeved and sealed, and brackets fixed after rendering need sealed fixings so water cannot track behind.

Where render meets profiled cladding above, a flashing over the top of the render throws water clear. At the base, a bell-cast bead above the DPC forms the bottom edge, and along vehicle routes it may be better to stop it higher above a harder plinth, because render at bumper height is easily damaged.

External insulation moves the face outward, so every one of those details changes and has to be redrawn for the insulated wall.

Weather, curing and acceptance

Write the weather and curing limits into the programme, because they decide what can happen when. For K Mono that means nothing under 5°C or over 30°C, nothing with frost due in the next day, nothing in the wet and nothing on a wall in full sun, and every area scraped at an equal stage of set. Silicone TC wants 5°C or more, shelter from strong sun and wind, and cover against rain and rapid drying.

For appearance, agree a sample panel on site in the specified product, texture and colour; K Rend advises one because its through-coloured renders can vary slightly in shade. Inspect each stage before it is covered: background preparation, base coat and mesh at openings, beads and joints. Photographs of those stages are useful for maintenance later.

Record any accepted variation as a change to the package and keep the final record clear enough for maintenance staff who were not involved in the original meetings.

For example, on a hypothetical 60-metre blockwork wall with three roller-shutter openings, the specification might split the elevation into bays at the shutter heads and at a structural movement joint, with each bay sprayed and scraped as one, a sample panel beside the office entrance, and the base detail raised above a concrete plinth along the yard.

Maintaining a large industrial render

Big rendered walls need regular attention. Algae and dirt collect on north faces and below ledges and are cleaned with a biocidal wash and a soft brush, not a high-pressure jet. Sealant round shutters and windows hardens and splits over time and is replaced. Impact damage at low level is repaired promptly before water gets behind it.

Most damage comes from later work: new signs, cameras, cable runs and plant brackets fixed through the render without sealing. A simple rule for site staff, that nothing is fixed to the render without a sealed fixing suited to the system, saves repeated repairs.

Records for the building

The building manager needs to know, for each elevation, what the background is, which system was used, its colour reference and texture, where the movement joints are, and the manufacturer’s cleaning and repair advice. Photographs of the stripped and prepared walls show where the hidden repairs and changes of background are.

The Bradford rendering service overview links to the commercial, insulation and repair pages where a building needs more than one kind of work.