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How to apply gelcoats

Applying Crystic gelcoats for optimum performance

Follow our guide below to achieve your desired finish when applying Scott Bader’s Crystic brush or spray gelcoats.

Mould prep

  1. Start by cleaning the mould thoroughly and ensure that it is free of dust, debris and contaminants.

  2. Next apply an appropriate release, again as per the manufacturers recommendations.

  3. If the mould is new, a sealing system may also be required prior to the release agent.

Gelcoat prep

  1. First check that the containers are damage free before opening them.

  2. Next, mix the gelcoat using a low shear mixer and allow the gelcoat to stand for at least 10 minutes to regain thixotropy.

  3. Your gelcoat and workshop temperature conditions should be between 18oC and 25oC before use.




High quality medium reactivity MEKP such as Butanox M50 (or equivalent) is recommended



Catalyst level should be kept between 1-3% and should remain constant for an entire moulding


Nozzle / spray tip selection

Spray tip advice is dependant on the type of part you are spraying and also the access achievable to the mould such as; platforms, scaffolding, length of hose from spray gun etc.

Always use minimum pressure required to achieve a uniform ‘finger-free’ spray pattern.

Spray application

Spraying should be carried out in a properly ventilated spray booth, in a separate part of the workshop. The mould to be sprayed should be positioned in the most practical position ergonomically, to allow for an even coverage and to reduce fatigue of the operator. Keeping the wrist flexible, start by spraying away from the mould and bring the gun towards it maintaining an even left to right spraying pattern at a consistent distance of approximately 50 – 80cm. The gun should always be perpendicular to the mould.

An arched spraying motion as per the illustration below will result in an uneven coverage, as will tilting the gun vertically.

Note: Test the Gelcoat when coat is still wet. The wet film thickness target should be 500 – 600.


Spray with continuous parallel strokes, left to right then up and down to lay a mist coat that covers the mould. A mist coat is best practice to avoid colour faults (grey arrows first pass, green arrows second pass.



Brush application

Just like spraying, brushing on your gelcoat demands equal care and attention for optimum results:

  • Always use the best quality lacquer brushes with long and soft hair
  • Stir gelcoat in its original packaging before use
  • Decant the required amount of gelcoat into a clean pail
  • Add 2% medium reactivity MEKP catalyst to the gelcoat and mix thoroughly to ensure even distribution of catalyst through the liquid
  • Apply immediately using consistent continuous strokes to achieve an even wet film thickness
  • Use a thickness gauge measuring tool to check the wet film thickness during application – your target should be 500 – 600 μ

Important: Always wear protective clothing, gloves and goggles.

Discover how to handle your gelcoats here.