Instructions for processing GRP


Fiberglass (GRP) is used both as a mold for a workpiece to be created from a different material and for the creation of a workpiece itself. The processing is fundamentally the same, but differs in the location and positioning of the smooth outer or utility surfaces.

Positive and negative forms

When processing GRP, the functional direction or task of the workpiece must first be taken into account. In so-called positive forms, the target use is on the later inside of the created form. Typical examples are containers of all kinds and the structure of the GFK for pools.

On the outside, the user surface is reversed in negative forms. The workpieces later form buildings, parts or bodies. The processing with negative forms can be found above all in the miniature model of architecture to the flight model. Many bonnets of both machines and vehicles are made of FRP.

Separating layer between mold and component

If the inner side is used for the later workpiece or component, the casting mold must act as a positive mold; for the position on the later outer side, the casting mold is always a negative mold.

To produce a component or workpiece, both a negative and a positive form is required in many cases. If both forms are made of the material GRP, a separating layer of liquid wax and a paint layer is required. Put simply, it avoids the connection between mold and workpiece or component.

Consider weight and density

Lamination of the GRP is the transitional step in the actual creation of the final workpiece or component. At this time, all other materials needed should be ready.

Anyone who wants to make GRP himself should think in preparation of the possible necessity or unimportance of the weight of the workpiece. While the density of the GRP plays a subordinate role in a pool shell, it is crucial in model making.

How to process fiberglass (GRP)

  • gelcoat
  • epoxy resin
  • Fiberglass chips and glass cloth
  • Release wax and release varnish
  • roving
  • Electronic balance
  • Brush and / or roller
  • mixed containers
  • gloves
  • Respiratory and eye protection
  • parting board

1. Remove the original form

The original model is the base of the outline and the shape of the workpiece, the shape of which is taken from an existing model.

2. Define dividing plane

To mount on the divider board, you must define the parting planes.

3. Apply a release layer

Coat or spray release wax onto the surface and apply PVA release paint.

4. Laminate

Spread or evenly coat the gelcoat.

5. Distribute and aspirate glass fibers

Sprinkle glass fibers evenly over the still damp gelcoat. Vacuum loose fibers after drying.

6. Apply coupling layer

Stir after epoxy resin and hardener according to manufacturer's instructions for coupling compound and distribute them.

7. Fiberglass fabric mats

Put on a first fabric mat and coat with GFK-compound. Lay alternately glass fiber fabric and roving fabric and build up your workpiece layer by layer.

Tips & Tricks

Lay the fiberglass and roving fabric across the previous mat and use a roller to brush out any air bubbles.


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