FAQ

1. What can replace conventional welded steel mesh?

The correct answer is: not always and not with the same logic as for steel. The publicly documented scope of ETA 25/0367 clearly refers to fiber grids for reinforcing cement, anhydrite and resin screeds, particularly to limit shrinkage cracks - including use in aggressive or corrosive environments. That is exactly the segment where the question "what to replace welded steel mesh with" makes the most sense: screeds, residential and lighter industrial floors, slabs on a base, repairs and precast elements.

The first practical rule: for area reinforcement you do not compare the wire diameter, but the function of the reinforcement - the tensile capacity across the area and the weight.

The comparison applies to anti-shrinkage and distribution use, not to replacing the main load-bearing reinforcement. The values come from the KOREFIB catalog.

In anti-shrinkage and distribution use, the certified KOREFIB variants therefore offer a very favorable capacity-to-weight ratio - and on site this means less carrying, more compact transport and unrolling from a roll instead of handling heavy sheets.

The installation is just as important as the material. The ETA explicitly notes that the aggregate grain size must be assessed in relation to the mesh opening, so that the grid is not damaged and the mesh does not act as a separation layer. A mesh lying loosely on the base does not work as it should - a level base, the correct position, laps and spacers are needed. Laps and placement details follow the manufacturer’s instructions or the specific layer design.

2. What are the main advantages of composite reinforcement over steel?

The strongest advantage of GFRP is not an "exotic material", but a specific combination of three properties.

3. What is the service life of composite reinforcement in concrete?

There is no honest one-sentence answer of "lasts forever" to this question. Technically, it is necessary to distinguish the product from the regulatory framework. European assessment of FRP has long moved away from the idea of a short-term "auxiliary" material: the EAD for FRP bars as reinforcement of structural elements assumes a working life of 100 years.

For FiberMesh, specific laboratory data on property retention after chemical conditioning is publicly available:

These numbers show two things at once: GFRP does not corrode like steel, but its long-term performance is determined by measurable composite ageing processes. Academic literature confirms this logic. A 2024 study on GFRP with E-CR glass showed a strength retention of 92-96% by diameter after 180 days in an alkaline solution at 20 °C; only under aggressively accelerated conditions of 60 °C did retention drop to roughly 80-87%. An Arrhenius extrapolation for 50 years at 10 °C came out at around 89-90% retention.

4. How to choose the right composite mesh?

The most common mistake when choosing a composite mesh is to look only at "2 mm, 3 mm, 4 mm". The practical function of the mesh in a floor or screed is much better described by the tensile capacity per m² and the weight. The numbers below already show that "a larger diameter = a better mesh" does not hold - the mesh spacing and the resulting area capacity also play a role.

These are not structural calculations, but rational application filters based on public KOREFIB parameters. The final choice depends on the layer build-up and the loading.

And the placement is equally important: a level, clean base, the correct position, spacers and inspection during concreting - a poorly placed mesh does not turn material performance into structural performance. When cutting and handling, we recommend eye protection and gloves.

5. How much G40 macro fiber to use in concrete?

The biggest misconception about macro fibers is the idea of a single universal "correct dosage". It always depends on what the fiber is meant to do: limit early shrinkage cracks, increase toughness, carry tension after a crack forms, or even perform part of the design function instead of conventional area reinforcement.

More important than kilograms per cubic meter are the residual strengths the product actually achieves in testing. The KOREFIB G40 technical data sheet reports, at a dosage of 7 kg/m³, values per EN 14651+A1: fL 2.6 MPa, fR1 2.6 MPa at CMOD 0.5 mm, fR2 2.0 MPa at 1.5 mm, fR3 1.8 MPa at 2.5 mm and fR4 1.6 MPa at 3.5 mm, together with a fresh concrete consistency of C2 per EN 14845-1. The fibers are therefore not "just against cracking" - they have a measurable benefit after a crack forms too.

The Technical Building Certificate (STO) additionally defines the monitored levels: a minimum of 700 MPa for the tensile strength of the macro fibers, a modulus of elasticity of at least 24 GPa, alkaline resistance Ret ≥ 80% and Em ≥ 80%, and residual strengths of at least 1.5 MPa at CMOD 0.5 mm and 1.0 MPa at 3.5 mm. The G40 data sheet actually exceeds these levels.

6. What certifications do KOREFIB products meet?

Certification is the area where a technically strong product is most quickly separated from unsupported marketing - which is why we name it precisely, not with a generic "we have certificates". KOREFIB has two different documentation regimes:

Complete documents to download can be found on the product pages FiberMesh 2×50×50, FiberMesh 3×100×100, FiberMesh 4×100×100 and MacroFibers G40.

7. When to choose GFRP and when steel?

Materials should not be chosen by impression, but by what they are meant to do in the structure. In Czech construction practice, the answer most often splits between two worlds:

In Europe, FRP bars are understood as a material for load-bearing elements too, but with a separate design approach - not as "steel without corrosion", but as a different structural material. Mixed scenarios are also interesting: the question is often not "either/or", but which part of the system can be composite and where traditional reinforcement is needed. For G40 macro fibers too, they do not automatically replace every steel reinforcement, and for structurally significant structures the use must be verified by design.

8. Is composite reinforcement more environmentally friendly than steel?

The question is legitimate, but technically it must be posed more precisely: in what functional unit, with what production route and for what structural function. First, honestly: a product EPD/LCA directly for FiberMesh or G40 is not yet publicly available, so we do not publish any "official KOREFIB CO₂ figure". We work with independent peer-reviewed studies and reference EPDs for steel.

Even more important than "per kilogram" figures is the real application: for a comparable function, significantly less mass of GFRP than steel is often needed. In a specific case study, total emissions came out 77.89 to 85.26% lower for the GFRP variants depending on the reinforcement spacing. For reinforcement, the mass needed to ensure the function is therefore often decisive. The spread of steel values is not an error, but a consequence of a different production route and geographic mix - a single "steel CO₂ value" simply does not exist.

9. What happens to composite reinforcement at the end of the structure’s life?

Honestly, two things must be said at once. First: at the end of the structure’s life this is not "unmanageable waste". Second: the current end of life of GFRP is not as simple as for steel.

For thermoset systems - which include epoxy and vinyl ester matrices - a cross-linked structure forms after curing that cannot simply be re-melted like thermoplastics. Other strategies are therefore used: mechanical recycling, thermal methods and chemical recycling, with mechanical recycling being the most common for GFRP and having been deployed at industrial scale too. The material is crushed or milled and reused as a filler or component in another composite or cementitious material. Recycled GFRP already has documented uses: for example, a study on cement mortars showed that replacing sand with GFRP waste at around 3% did not lead to a significant drop in mechanical strength.

The practical difference from steel is in separation: when processing demolished concrete, steel is typically removed by an electromagnetic separator during secondary crushing. Composite reinforcement is not magnetic, so ordinary magnetic separation does not capture it - the resulting solution depends on the specific recycling line, the required fraction purity and the target use of the recyclate. After crushing it is commonly left in the fraction; the crushed composite improves the mechanical properties of the subsequent use. Case studies are underway in which crushed GFRP waste is added to concrete mixes for better mechanical properties.

10. Is composite reinforcement worth it economically?

The economic question is often wrongly framed for GFRP: a "per kilo" or "per piece" comparison is distorted, because with composite reinforcement other cost items are decisive - the mass needed for a given function, transport, storage, manual handling, placement speed, the risk of corrosion and future repairs. This is clear from public data: FiberMesh 3×100×100 has 101 kN/m at 283 g/m², while steel KA16 has only 63 kN/m at 1,973 g/m². The first saving therefore arises already on site: lighter transport, less demanding carrying, faster placement.

The second effect comes in the life cycle. Life-cycle cost studies for infrastructure (GFRP bridge decks) report that despite higher initial costs, using GFRP can reduce life-cycle costs by more than 20%, and by up to 37% when accounting for the longer service life. For floors and screeds in ordinary construction these figures cannot be copied mechanically, but the principle holds: a higher entry price does not mean worse economics over time.

A recommendation for every customer: do not compare only the catalog price, but do a simple TCO:

1. The material price for the required function, not per kilogram - compare the tensile capacity per 1 m².
2. Transport and storage - composite in a roll versus heavy steel meshes.
3. Placement and handling - time, physical effort and the risk of damage on site.
4. The risk of corrosion and future repairs in the specific environment.
5. The expected maintenance and service life of the whole build-up.