Six materials keep turning up on the same drawing: GRP composite profiles, painted steel, galvanised steel, stainless steel, aluminium and wood. None of them wins on every line, and any comparison that says otherwise is selling rather than engineering. This page puts all six side by side against the ten criteria that usually decide a specification, gives a first and second choice for five common environments, and then says plainly where a GRP profile is the wrong answer.
NA-ME has been pultruding composite profiles in Ankara since 1982, and roughly half of what we make leaves the country. So we have an obvious interest in the answer. The way to keep that interest honest is to compare on criteria you can check yourself, and to name the cases where we would specify something else.
Two habits make this kind of comparison useful rather than decorative. First, compare over the life of the asset, not at the purchase order: a material that costs less on day one and needs a paint system renewed on a live plant is not the cheap option. Second, compare in the actual environment. Stainless steel is superb in one place and a liability in another, and the same is true of every material here, including ours.
One point of vocabulary before the tables. GRP (glass reinforced plastic) and FRP (fibre reinforced polymer) describe the same pultruded profiles we make; North American specifications often call them fiberglass structural shapes. The difference is naming habit, not material — it is set out in full on GRP vs FRP.
The table below is qualitative on purpose. Exact figures depend on the alloy, the coating system, the resin, the fibre content and above all the section, and a number pulled from a web page is not a number you can put in a tender.
| Criterion | BEST CHOICE GRP / FRP |
Painted steel | Galvanised steel | Stainless steel | Aluminium | Wood |
|---|---|---|---|---|---|---|
| Corrosion resistance | Does not rust and does not rot; the resistance sits in the material itself, not in a coating | Only as good as the paint film; every scratch, cut end and bolt hole becomes a rust site | Zinc protects sacrificially and is gradually consumed; cut ends and drilled holes lose the layer | Very good in most atmospheres, but the austenitic grades usually specified are vulnerable to pitting and crevice attack in chloride-rich water | Good in ordinary atmospheres thanks to its own oxide film; poor in strongly alkaline conditions | Does not rust, but absorbs water and is attacked by fungi and insects unless treated |
| Service life in an aggressive environment | Long, and independent of any coating being renewed | Short unless the coating cycle is maintained on schedule | Medium; ends when the zinc is spent, then the steel is exposed | Long where the chemistry suits the grade; can fail locally and quickly where it does not | Medium to long, depending on alloy and exposure | Short outdoors and in wet service, even when treated |
| Maintenance burden | Essentially inspection and cleaning; nothing to repaint or re-galvanise | High: surface preparation, repainting, access equipment, shutdowns | Low at first, then touch-up and eventual replacement | Low; mostly cleaning and watching for local attack | Low; occasional cleaning and checking of joints | High: treatment, sealing and replacement of failed members |
| Weight | Roughly a quarter the density of steel; usually carried and fixed by hand | Heaviest of the group | Heaviest of the group, plus the coating | Heaviest of the group | Roughly a third the density of steel | Light per unit volume, but the sections needed are bulky |
| Electrical conductivity | Non-conductive; an insulator by nature, so no earthing or bonding of the profile itself | Conductive; must be earthed and bonded | Conductive; must be earthed and bonded | Conductive; must be earthed and bonded | Highly conductive; must be earthed and bonded | Insulating when dry, far less so when wet |
| Thermal conductivity | Low; little heat is carried through the section and it is not cold to the hand | High | High | High, though lower than carbon steel | Conducts heat most readily of the metals here | Low |
| Total cost of ownership | Higher at purchase than coated steel, lower over the life once maintenance and downtime are counted | Lowest at purchase, highest to keep | Moderate at purchase, moderate to keep | High at purchase, low to keep where the grade suits | Moderate to high at purchase, low to keep | Low at purchase, high to keep outdoors |
| Handling and installation | Cut and drilled with ordinary site tools; bolted, so no welding and no hot work to join | Craned, welded, then made good and painted at every weld | Craned and bolted; welding destroys the coating locally | Craned and welded; welding needs qualified procedures | Light enough to handle, but welding is specialised | Easy to cut, hard to keep dimensionally stable |
| Fire behaviour | Combustible: an organic matrix that contributes fuel, though fire-retardant resin systems change how it behaves | Non-combustible, but loses strength rapidly as it heats and needs protection | Non-combustible, same loss of strength when hot | Non-combustible, best hot strength of the metals here | Non-combustible, but softens at comparatively low temperatures | Combustible and a genuine fuel load |
| Scrap value at end of life | Essentially none — this is a real disadvantage, not a detail | Real scrap value; the metal is recovered | Real scrap value; the metal is recovered | Real scrap value; the metal is recovered | Real scrap value; the metal is recovered | None; disposal or energy recovery |
↳ The column highlight is deliberately dropped on the last two rows. GRP does not win on fire behaviour and it does not win on scrap value, and a comparison table that pretends otherwise is worth nothing to an engineer.
Criteria only matter in a place. Below is how we would rank the six materials in the environments these profiles are most often specified for, with a one-line reason each. The last row is the exception that proves the page is honest.
| Environment | BEST CHOICE First choice |
Second choice | Why |
|---|---|---|---|
| Water and wastewater treatment | GRP / FRP | Stainless steel | Constant moisture, sulphides and washdown chemistry attack coatings faster than any maintenance budget renews them. |
| Coastal and marine structures | GRP / FRP | Stainless steel | Chloride is the whole problem, and a material with no metal to lose does not have to defend itself against it. |
| Power and energy | GRP / FRP | Galvanised steel | Non-conductive walkways, ladder guards and cable tray supports stay out of the earthing and step-potential problem entirely. |
| Chemical plant | GRP / FRP | Stainless steel | The resin is chosen for the specific chemistry, so the resistance is designed into the profile rather than applied to its surface. |
| Outdoor public realm | GRP / FRP | Aluminium | UV-stable and free of a repainting cycle over live pavement, and light enough to install without heavy plant or long closures. |
| Long-span structural frames, dry and indoors | Steel | GRP / FRP | Where deflection over a long span governs, steel’s much higher stiffness wins and no corrosion argument is available to offset it. |
Every material below gets the same treatment: what it genuinely does better than the others, and where it stops.
What it genuinely does better: it removes corrosion from the maintenance plan instead of managing it. The resistance is inherent to the glass and resin, so a cut end, a drilled hole or a scratch is not a defect waiting to spread — which is exactly the opposite of every coated metal on this page. Add roughly a quarter the density of steel, electrical insulation as a material property, and low thermal conductivity, and you get the combination nothing else here offers at once: a walkway that a small crew installs by hand, never needs earthing, and does not have to come out of service to be repainted.
Where it stops: modulus. The tensile strength along the length of a pultruded profile is high, but the stiffness is low to medium and strength across the section is lower than along it, so deflection usually governs the design rather than failure. It is also directional, which makes connection detail — edge distance, washer size, tightening torque — part of the design rather than an afterthought; see installation and fastening. And it has no scrap value.
What it genuinely does better: it is stiff, strong in every direction, universally understood, and cheaper per metre at the purchase order than anything else structural on this list. Every fabricator can work it, every code covers it, and every engineer can size it from memory. For long spans, heavy point loads and frames where deflection is the limit, nothing here competes.
Where it stops: the paint film is the whole corrosion strategy, and films get scratched, cut, drilled and weathered. In a wet or chemical environment the maintenance cycle — access, preparation, repainting, and the production stopped while it happens — is usually where the money actually goes. Painted steel is at its best dry, indoors and inspectable.
What it genuinely does better: it buys years of protection with one factory operation and no site work. The zinc layer protects sacrificially, so a small scratch does not immediately start rust the way damaged paint does. For outdoor structures in ordinary atmospheres — fencing, supports, secondary steelwork — galvanised steel (spelled galvanized in US specifications) is a well-judged compromise between cost and life.
Where it stops: zinc is consumed, and the clock cannot be reset without taking the member back to a bath. Everything cut or drilled on site loses its coating at exactly the point where water collects. In marine spray, in treatment plants and anywhere the pH strays from neutral, the layer goes far faster than the brochure implies, and what is underneath is plain steel.
What it genuinely does better: it is the only material here that combines full structural stiffness with real corrosion resistance and non-combustibility. Where high loads, high temperatures and a wet environment arrive together — process equipment, hygienic installations, hot chemical service — stainless does a job GRP cannot do at all. It also keeps a real scrap value at end of life, which matters on large tonnages.
Where it stops: cost, weight and chlorides. It is expensive to buy and it weighs the same as ordinary steel, so none of the handling and installation savings apply. More importantly, the resistance is conditional: the austenitic grades usually specified are vulnerable to pitting and crevice corrosion in chloride-rich water, which is precisely the environment coastal and treatment work provides. Choosing stainless without matching the grade to the chemistry is a gamble dressed as a safe choice.
What it genuinely does better: it gives metal stiffness at roughly a third the density of steel, with an oxide film that handles ordinary atmospheric exposure without any coating at all. It extrudes into complex sections cheaply, so aluminium (aluminum in US practice) is hard to beat for lightweight frames, enclosures, ladders and access equipment where handling matters and the environment is not chemically hostile.
Where it stops: chemistry and company. It suffers in strongly alkaline conditions, and it is the metal most likely to be sacrificed when paired with a dissimilar metal in a wet joint. It conducts heat and electricity readily, it softens at comparatively low temperatures in a fire, and its fatigue behaviour needs more care than steel’s. In a chemical plant it is usually the wrong answer.
What it genuinely does better: it is cheap, it is available everywhere, it is worked with tools every site already owns, and it needs no earthing and no specialist trade. For temporary works, low-consequence structures and anywhere appearance is doing most of the job, timber is entirely rational — and it is the only material here that is genuinely renewable.
Where it stops: water and time. It absorbs moisture, swells, splits, rots and hosts insects and fungi; treatment slows this down and does not stop it, and the treatment itself is a repeating cost with its own chemical questions. It is combustible, it is dimensionally unstable, and its strength varies from one piece to the next in a way no specification fully controls. In wet industrial service it is a maintenance commitment, not a material choice.
Stiffness is the honest limit. A pultruded profile is strong along its length, but its modulus of elasticity is much lower than steel’s, and deflection grows very fast as span grows. On a long unsupported span the section needed to satisfy a deflection limit in GRP becomes large enough that steel is simply the better engineering answer — and if the environment is dry and indoors, there is no corrosion argument left to offset it.
There is a middle path that gets used more often than either extreme: steel for the primary frame, GRP for everything the environment actually attacks — gratings, walkway decking, handrail, ladder guards, cable tray supports, kerbs and trim. That combination is what most of our industrial applications look like in practice.
Comparing purchase prices compares the smallest number in the calculation. Over the life of an installation the costs that decide the outcome are the recurring ones: surface preparation and repainting, the access equipment or scaffold needed to reach the member, the trained crew doing it, the inspection regime, and the production lost while the area is out of service. A handrail on a live aeration tank is not expensive because of the handrail.
Installation is the other place the arithmetic moves. A profile at roughly a quarter the density of steel is often carried and positioned without a crane, by a smaller crew, in fewer shifts, and it is bolted rather than welded — so there is no hot work permit, no welding procedure, no site galvanising and no touch-up. On refurbishment work there is a further effect that has nothing to do with price: replacing steel with composite reduces the load added to an existing structure, which occasionally makes a project feasible that otherwise was not.
The comparison NA-ME will not dress up: on purchase price alone, painted steel wins and timber wins. If an asset is temporary, dry, or scheduled for replacement anyway, that is the right answer and we will say so. Where GRP earns its place is where the environment is corrosive, access is expensive, or electrical safety is in play — and how long the material lasts once installed is set out on maintenance and service life.
Name the section and dimensions, the span and load case with the deflection limit you will accept, the service environment and chemistry, and any fire or electrical requirement. Then ask each supplier for the resin system, the surface veil and the test method behind every figure they quote. EN 13706 is the European standard covering pultruded structural profiles and its classification system is what a specification normally references; ASTM D638 and D790 are the tensile and flexural test methods you will see behind published property tables in North American documents. Asking which method produced a number is what makes two offers comparable — the background is on quality, standards and testing.
Yes, and this is one of the quiet advantages. GRP is not a metal, so it takes no part in galvanic corrosion — a composite member cannot sacrifice a metal fastener or be sacrificed by one, which is a recurring headache when aluminium and steel meet in a wet joint. The fastener still has to survive the environment on its own account, so stainless is the usual choice in wet or coastal service. What does need attention is bearing: the area around a bolt hole in a composite is sensitive to crushing, so edge distance, washer diameter and controlled tightening torque matter more than they would in steel.
With ordinary site tools. A diamond or carbide-tipped blade cuts it, standard drills make holes, and no welding, hot work or specialist trade is involved. Cutting and drilling produce glass dust, so eye protection, gloves, a dust mask and extraction or wetting are the sensible precautions, and every cut end or drilled hole should be sealed with resin, which closes the exposed fibre and protects the cut face. Full detail is on installation and fastening.
It expands and contracts, and the amount differs along the profile and across it because the material is directional — the fibres restrain movement along the length far more than across it. In practice this means slotted holes and expansion gaps are planned on long continuous runs, exactly as they would be for a metal system, but the movement is not identical to the metal member it may be replacing, so it should be calculated rather than assumed. Stiffness also falls as temperature rises, because that behaviour belongs to the resin; where the service temperature is high, resin choice comes first — see resin systems.
Colour is pigmented through the section rather than applied on top, so a scratch does not reveal a different colour underneath and there is no coating to flake. Outdoor exposure can produce some surface chalking and gradual colour change over the years, which is cosmetic rather than structural; a UV-stabilised surface veil is what limits it, and that is a specification decision made before production, not a repair afterwards. The profiles can be painted if a colour has to be matched exactly, but for most projects choosing the pigment and veil at the order stage is the better route — see surface veil, UV and fire.
Composite profiles are bulky and light, which makes freight distance expensive in volume terms rather than weight terms. From Ankara, delivery into the EU travels by road in three to seven days, against thirty to forty-five days by sea from the Far East, and under the EU–Turkiye Customs Union industrial goods enter without customs duty. The United Kingdom sits on the same road route, under its own trade arrangements. It also means small and mixed orders are practical, so a project can take three sections and a few lengths of grating in one consignment instead of ordering a container it does not need.
Tell us where the profile will live, what it must carry and over what span, and whether electrical insulation or a fire requirement is in play. We will come back with a section, a resin system and a surface — or, if the honest answer for your case is steel, we will tell you that instead. Dimensions are enough to start.
Send your dimensions, get a quote
Related reading: what a GRP profile is, the pultrusion process behind it, the structural shapes we hold as standard, and handrail and platform systems built from them.