Spray up is good for low to medium volume production. It can be used on smaller parts but very well suited to larger parts such as swimming pools or boat hulls. Spray-up is a faster process than hand lay-up. Although the process can be robotised, it generally requires skilled operators to obtain consistent high quality parts. The same low cost open moulds that are used in hand lay-up are used in spray-up application. Spray-up is primarily for polyester and vinyl ester resins and glass fibre.

Many types of spraying systems are available. The three main pump systems are:

  • airless atomisation
  • air assisted airless
  • high volume low pressure systems

Other types of spray equipment are gravity fed, siphon and pressure pot systems.

allnex products commonly used:

  • Mould preparations
  • Gelcoat, flowcoat (optional)
  • Unsaturated polyester resin or vinyl ester resin
  • Catalyst
  • Reinforcements: multi-end (gun) roving
  • Accessories (Rollers)
  • Chemicals  (Acetone)
  • Complimentary (fabric reinforcement and cores)


  1. The mould surface must be well prepared with a release agent.
  2. Gelcoat is first applied to the mould either with a brush or with a spray gun and allowed to cure.
  3. A hand held gun is then used to spray catalysed resin and reinforcing fibres onto the mould at the same time. The fibres are fed into the gun as continuous multi-end roving and chopped to lengths of 20 to 75 mm by the chopper unit attached to the spray gun. The resin can be catalysed before it passes through the spray gun (internal mix), or alternatively catalyst can be sprayed at the same time as resin from the gun tip (external mix). The catalysed resin wets out the chopped fibre as it is sprayed onto the mould.
  4. A hand held roller is then used to consolidate the laminate and remove entrapped air. 
  5. Additional layers of chop laminate are added to obtain the required thickness.
  6. Roll stock reinforcements such as fabrics as well as core materials can be used in conjunction with the chopped laminate.
  7. The curing reaction occurs at room temperature.  At ambient temperature, initial cure occurs within first 24 hours at ambient temperature, and full laminate cure may take up to 28 days.
  8. Finished part to be removed from the mould after initial cure is complete.1
  9. A Flowcoat may be applied to the cured laminate as a cosmetic enhancement. 2


1Early removal from the mould often results in damage to the laminate and loss of surface finish integrity of the part.
2The laminate surface must be abraded/sanded before flowcoat application to assist bonding.