Architects & interior designers
Technical guide for specifiers
Which metal and grade for which place, typical thicknesses, how PVD and patina finishes behave, the rules for outdoors and near the sea, and how the work is fixed. A starting point: every project is confirmed on its own shop drawing.
Before you specify the metalwork
This guide collects the questions architects and designers ask us most often before they specify metalwork. The figures are typical starting points, not a specification: each project is engineered on its own shop drawing, and we are glad to check a detail at the design stage.
Stainless steel
Grade 304 or 316?
304 for interiors
The standard grade for interiors and sheltered exteriors: lift cladding, lobbies, furniture, railings under cover.
316 near water and salt
With molybdenum for better resistance to chlorides: for sites near the sea, swimming pools, spas, wet areas and exposed facades.
The surface counts too
A smooth finish (mirror, satin) sheds dirt and salt better than a coarse brush. Outdoors, choose the finer finish and let rain or washing reach it.
Typical thicknesses
Where we usually start.
Confirmed on the shop drawing for each piece: the size of the panel, the span and the fixing decide the final figure.
- Wall and lift cladding on a backing board: thin sheet, about 0.8 to 1.2 mm.
- Self-supporting panels and door facings: about 1.5 to 2 mm, or thicker with stiffeners on large panels.
- Laser-cut screens and jaalis: 2 to 6 mm by pattern and span; our laser cuts up to 20 mm.
- Railings and balustrades: sections sized for the loads the building code sets for the place.
PVD colours
How a PVD finish behaves.
PVD (physical vapour deposition) bonds a thin, hard coating to stainless steel in a vacuum chamber. The colour is in the coating, not in a paint: it does not peel, and it stays even in sunlight.
The coating follows the surface beneath it, so a mirror base gives a mirror colour and a hairline base a hairline colour. Clean it with water, mild soap and a soft cloth; never with abrasives or scouring pads, which cut through it. On door pulls and handrails, ask for an anti-fingerprint layer on top.
Patina and living finishes
A finish that keeps changing, on purpose.
The patinas on brass, bronze and copper are grown on the metal with chemistry and heat, then sealed with lacquer or wax. A sealed patina changes slowly; where hands touch it, it polishes and warms, and that is part of its character.
Outdoors, a living finish keeps moving with the weather unless it is lacquered and looked after. Agree the sample as the standard, and agree the care, before you specify it.
Outdoors and near the sea
Five rules for metal outside.
- Choose 316 stainless for coastal sites, pools and exposed facades.
- Keep stainless away from carbon steel and its grinding dust: the particles rust and stain the surface.
- Separate different metals (aluminium and copper, steel and brass) with isolating washers, so they do not corrode each other.
- Mild steel goes outside only galvanised and painted or powder coated, never bare.
- Let water drain: no channels or ledges where it can stand, and exterior-grade coatings on patinated metal.
Fixing and tolerances
How the work meets the building.
Measured as built
We measure on site once the walls and floors are finished, so the work fits the building as it was built, not only as it was drawn.
Fixings out of sight
Panels are held by cleats, channels or bonding to a backing frame, so no screw heads show. Every fixing is shown on the shop drawing.
Room to move
Joints allow for movement and expansion, more outdoors than in. The shop drawing shows each gap and how it is closed.
What we need from you
Drawings in DWG or PDF, the finish references, where the work goes (inside, outside or a wet area), quantities and the programme.
Start a project
Check a detail with the workshop.
Send the drawing or the detail you are working on. We reply within one working day.