A GRP walkway and an aluminium one look similar on a drawing, cost roughly the same order of money, and behave very differently once installed. The comparison is usually made on corrosion resistance, where both perform well, and that is why so many specifications end up choosing on price.
Four properties actually separate them, and each material wins two of them outright. Knowing which four apply to your site settles the question in about ten minutes.
What the two materials are
GRP, also called FRP, is glass fibre in a cured resin, usually pultruded into profiles or moulded into grating panels. The glass carries the load and the resin holds it together and decides the chemical and temperature behaviour. Aluminium walkways are extruded or welded structural sections, typically in the 6xxx series, with grating or plank decking of the same metal.
| Property | GRP | Aliuminis |
|---|---|---|
| Electrical conduction | Insulator | Conductor |
| Stiffness | Low, directional | Moderate, uniform |
| Fire | Combustible | Non-combustible |
| Strong alkalis | Resists | Attacked |
| End of life | Landfill | Scrap value |
Where GRP wins
The first case is electrical. GRP does not conduct, which makes it the right answer for platforms around live equipment, substations, electrified rail environments and anywhere an earthing regime would be complicated by a conductive walkway. No amount of detailing makes aluminium non-conductive.
The second is chemical exposure of a particular kind. Aluminium is attacked by strong alkalis, and contact with fresh concrete, some cleaning chemicals and certain process streams is a genuine limitation. GRP with an appropriately selected resin will sit in environments that would consume a metal walkway, and in chemical plant that is frequently the deciding argument.
Two secondary advantages follow: GRP is non-magnetic, which matters in a small number of installations, and it has low thermal conductivity, so the surface is less unpleasant to touch in extreme heat or cold.
Where aluminium wins
The first case is span. GRP is strong in the fibre direction and not stiff, and its properties are strongly directional, so deflection rather than strength sets the design and sections either get deeper or supports get closer together. On a long run of elevated walkway that translates directly into more supporting steelwork, which is a cost that appears in the substructure rather than in the walkway quotation.
The second is fire. GRP is an organic composite; flame-retardant grades exist and perform respectably, but the material burns and contributes smoke. Aluminium does not burn at all. It should be said plainly that aluminium is not a fire-resistant material either, since it loses strength well before it melts, but it does not add fuel to a fire, and in an escape route that distinction can be the whole argument.
Two further points favour the metal. Aluminium tolerates ultraviolet indefinitely, while GRP needs stabilisers, surface veils or a coating and will still chalk over decades of direct sun. And aluminium has a genuine scrap value at end of life, whereas a GRP structure is a disposal cost, which increasingly appears in whole-life assessments and in public procurement scoring.
The practical differences on site
Cutting GRP produces glass dust that requires respiratory protection, and every cut edge has to be sealed to stop moisture wicking into the laminate. Cutting aluminium produces swarf and a clean edge, and the metal can be welded, drilled and modified indefinitely without a sealing operation.
That makes a difference over the life of an installation rather than during construction. Plant changes, new penetrations and added handrails are ordinary events, and a structure that can be modified with a saw and a drill stays serviceable in a way a laminate does not.
Where the choice is genuinely close
For a short-span platform in a wet but chemically ordinary environment, with no electrical constraint and no fire route, both materials will do the job for thirty years and the decision comes down to price, availability and what the maintenance team is used to. That covers a fair share of industrial access, and there is no point manufacturing a distinction.
What is worth resisting is the assumption that the two are interchangeable across a whole site. Mixed specification by area is usually the correct answer: GRP where the electrical or chemical case applies, metal everywhere else, and a clear note about where the boundary sits.
Corrosion is not the deciding factor people expect
Both materials handle ordinary industrial atmospheres, wash-down and salt spray without a coating system, which is the main reason either is chosen over galvanised steel. The failures that do occur are specific rather than general: for GRP it is resin attack and UV degradation, for aluminium it is contact with other metals and with alkaline materials, and both are design problems rather than material problems.
That is why a specification asking for corrosion resistance and nothing else has not narrowed the field at all. Naming the chemicals present, the temperature range and the electrical situation narrows it immediately.
What to put in the enquiry
State whether electrical isolation is required. List the chemicals the walkway will be exposed to, including cleaning agents. State whether the route forms part of an escape route. Give the span between available supports, because that is what decides the section depth. State the design life and whether end-of-life recovery is scored.
Five lines, and they usually produce a single obvious answer rather than two comparable offers.
Before the material is fixed
The most expensive version of this decision is choosing one material for a whole site because it suited one area. The properties diverge sharply in four places and are near-identical everywhere else, which argues for deciding area by area rather than globally.
Our engineers will go through a plant layout and mark where each material belongs, and the aluminium industrial walkways and access bridges we supply are quoted against the span and the support positions that already exist rather than assuming a new support grid.