Everything you ever wanted to know about GRP


What is a Composite?

Composites are combinations of materials. They are often referred to as fibre-reinforced plastic or glass-fibre-reinforced plastic – GRP for short. The name itself suggests that the material is made of various components, such as resin and reinforcement materials like glass fibre. The combination of the individual components together offers better properties than they would have provided separately. Composite plastics are cost-effective, very resilient in terms of mechanics and offer excellent corrosion behaviour.


What is a Fibre-reinforced Composite?

Fibre composite materials, or simply composites, are materials that usually consist of two or more components – glass, carbon or natural fibres, for example, and resins. Through the interaction between the components, this composite material delivers higher quality properties than each of the two components separately.

Why choose a Composite instead of Metal?

Composite components are light in weight, a lighter alternative to metal. The term “composite” is therefore frequently equated with “lightweight”. Composites are, in particular, the material of choice wherever weight savings are required or advantageous. With reinforcement made e.g. from glass fibre, such components have mechanical properties that can only be achieved otherwise with metallic materials, but they are significantly lighter.

What is the difference between thermoplastics, thermosetting plastics and elastomers?

Thermosetting plastics, thermoplastics and elastomers are three different types of plastic.

Thermosetting plastics are made of closely linked macromolecules and are not ductile and cannot be melted.

Thermoplastics consist of linear or branched macromolecules. On heating, they become ductile and at high temperature they also melt.

Elastomers are often referred to as rubber. They consist of macromolecules interlinked in a wide mesh, which allows deformation when a load is applied, but they spring back as soon as the load is removed. The interlinking makes it impossible to melt elastomers.

Can GRP Components be repaired?

Pores, scratches and fibres protruding from GRP components can be repaired with resin and thus “re-resinated”. Fine grooves, damaged edges, roughened surface areas and exposed fibres can be sealed again and protection against environmental factors is restored.

You will find an article about repairing GRP moulds in the “Expertise” section.

Processing information for repairing a GRP mould

What does Lightweight Engineering mean?

Fibre-reinforced plastics (GRPs) are a byword for lightweight design. GRP is often used with the aim of reducing the weight as far as possible to save costs, energy or raw materials. Increasing payloads is also an argument in favour of lightweight engineering. Composite materials with low density and high mechanical properties are used in particular because of their light weight.

What is a Gelcoat?

A gelcoat is applied to the mould surface as a first layer, and this subsequently forms the visible side of the component. A gelcoat is therefore the outer protective layer of a GRP component. Choosing the right gelcoat is crucial for the quality of the component. The quality of the gelcoat determines the durability, weatherproofing, light fastness (UV radiation), degree of gloss, chemical resistance and finally the mechanical properties of the surface. Gelcoats can be dyed a wide range of colours. Gelcoats are applied either manually (with a brush and roller) or by a (mechanical) spraying process. 


Where does BÜFA Composites produce its special Products?

The headquarters of BÜFA Composites is in Rastede in Germany. We also have a plant in the UK and several distribution sites, which make tinting products on site.

What is the minimum amount in Kilos – of a Gelcoat or Topcoat, for example – that Business Customers can order from BÜFA Composites?

We deliver orders from 25 kg of gelcoat or topcoat in one RAL colour and sell only B2B, in other words exclusively to business customers.


Does BÜFA Composites also supply small Quantities of Resins or Gelcoats?

We deliver to business customers from an order volume of 25 kilos. For smaller quantities, we are happy to refer you to the firm Selvida in Germany. Selvida supplies small quantities of resins and glass fibre mats.

If you are abroad, you are welcome to contact one of our distribution outlets, where you will be given further assistance.

Resins     Gelcoats     Distribution outlets

Can BÜFA Composites make Gelcoats or Topcoats in my Choice of Colour?

Yes, in most cases we can adjust the gelcoat to the customer’s colour of choice.

Pigment pastes

To which Countries does BÜFA Composites Deliver?

BÜFA Composites ships throughout Europe. However, the goods can also be collected by a shipping company directly from the factory. 

With Europe-wide distribution sites, BÜFA guarantees an internationally reliable service network.


Does BÜFA Composite Systems have Processing Machines for Resins?

Yes, BÜFA’s own machine technology arm, BÜFA Tec, makes a range of machines for mechanical processing of resin (vinyl ester and polyester resins). Depending on the production method, fibre spraying systems, gelcoat spraying and metering systems, bonding paste and RTM systems and lamination roller machines are available.


Do you also have Metering Equipment in your Product Range?

Yes, BÜFA Tec has a wide range of metering pumps for various additives, with a focus on the polyester industry. But other chemicals can also be dispensed with this technology. 

In addition, BÜFA Tec offers a wide selection of durable and efficient processing machines. 



The Cobalt REACH consortium has decided to tighten the classification of cobalt bis- (2-ethylhexanoate) with effect from 01/11/2018.

This raw material is widely used in the composites industry for the production of pre-accelerated UP resin systems. BÜFA Composite Systems has taken on this task, examined it in the interests of our customers and developed appropriate solutions.The good news for you as BÜFA customer: All resin specialties from the BÜFA complete range are still available for you in the usual quality and all BÜFA products containing cobalt are below the specified limit values or have been provided with substitute products. This means that these BÜFA products do not required additional labelling and nothing changes for you in terms of handling and use – the BÜFA products can be handled and processed as usual!

If you use other UP resin systems in your company, we recommend that you clarify the current status of future classifications via the product safety data sheets. If you continue to use products according to the stricter classifications, extensive measures are necessary at your plant.

If you have any questions about the topics listed above and in particular about cobalt accelerators, please do not hesitate to contact us.

Cobalt accelerators are a special case, as they may contain the cobalt bis-(2- ethylhexanoate) concerned in a concentration >= 0.3%. From this concentration onwards, labelling as toxic for reproduction category 1B (Repr. Tox. 1B) is expected to be mandatory from 01/11/2018. This reclassification means that you need to check whether you are allowed to use products with this labelling in your plant. In this case, please contact the authority responsible for you.

BÜFA Composite Systems can continue to offer an accelerator portfolio with various options. The alternative products listed in the following table contain a 1:1 replacement that corresponds to the current classification. This means that nothing changes for you in terms of handling and use – BÜFA products can be handled and processed as usual! We are happy to support you with sample quantities for your internal qualification if required.

In addition, we can offer the following polymer cobalt variants that already exist in the present portfolio:


The industry association AVK ( has sent out a newsletter to its members on the categorisation of cobalt. The following excerpts are from the ‘AVK News’ of 21 September 2018:

Cobalt octoate classification

Contrary to previous assumptions, the reclassification of cobalt bis 2-ethylhexanoate will not take place on 1 January 2019, but already on 1 November 2018. There are currently no new safety data sheets available so it is recommended to contact the relevant supplier to obtain up-to-date information.
Classification from 0.3% concentration is considered toxic for reproduction. H360 F may impair fertility and H360 D may cause harm to the unborn child.
This entails a number of organisational measures for processing companies:
It must be checked whether this substance was already included in an authorisation in accordance with the Federal Immission Control Act (BImschG). If not, authorisation must be requested for use beyond 01/11/2018. If so, the authorising authority should be informed of the reclassification, at the latest after the updated safety data sheet is available.
In the case of a corresponding classification below 1B, the corresponding substance must be replaced in accordance with the Hazardous Substances Ordinance (in compliance with specific requirements). In any case, a corresponding substitution test must be carried out and this must be comprehensively documented. If it is not possible to replace the substance in question, appropriate technical, organisational or personal protective measures must be taken (in this order of priority).
This also includes a comprehensive risk assessment. The relevant employees must be instructed in handling (specialised knowledge).
The recirculation of extracted air into the room in which this substance is handled is not permitted. In addition, the relevant principles of the Chemicals Prohibition Ordinance, the Youth Protection Act, the Maternity Protection Act and the Technical Instructions on Air Quality Control (TA-Luft) must of course be observed. According to TA-Luft – draft 2016, this substance would be considered a class 1 substance, with a quantity threshold of 1 mg/m³ in fumes. In addition, it must be expected that this substance will be added to the SVHC candidate list in the future.

Source: AVK-TV GmbH | Am Hauptbahnhof 10 | 60329 Frankfurt am Main | Germany | Phone: +49
(0) 69 / 27 10 77 - 0 | E-mail: | Web:

Our partner for organic peroxides, United Initiators, focuses exclusively on the development and production of peroxides. The head office and production for the European market are located in Germany. United Initiators was the first manufacturer of 100% phthalate-free peroxides in Europe and thus also fulfils its claim to sustainability. They products are characterised by a high quality standard and product safety. The range is perfectly matched to your applications.

Important information
Curing agents, accelerators and, if applicable, inhibitors must be exactly matched with one another to achieve the desired effect. The choice of the optimum cold curing system depends on the processing conditions on the one hand and on the requirements to be placed on the finished part on the other.

It is extremely important that peroxides and accelerators are never mixed with the resin at the same time, but one after the other, in order to avoid fires or deflagrations.

Addition 03/2024
2-Ethylhexanoic acid salts are now generally classified as toxic to reproduction. These mainly include cobalt bis-(2-ethylhexanoate), potassium bis-(2-ethylhexanoate) and calcium bis-(2-ethylhexanoate). BÜFA Composites has already replaced these metal salts in its current product range with less harmful accelerators.