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Crystic GT-900 Clear Isophthalic...

Crystic GT-900 Clear Isophthalic Polyester Gelcoat - SPRAY

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Crystic® Gelcoat GT-900 is a high performance isophthalic gelcoat. It is filled, pre-accelerated and formulated for spray application.
Crystic® Gelcoat GT-900 has been developed to have excellent intrinsic water and weather resistance.


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Product Description and Approvals

Crystic® Gelcoat GT-900 is a high performance isophthalic gelcoat. It is filled, pre-accelerated and formulated for spray application.
Crystic® Gelcoat GT-900 has been developed to have excellent intrinsic water and weather resistance. The viscosity profile ensures even coverage with minimal drainage and low film porosity. Crystic® Gelcoat GT-900 has been approved by Lloyd’s Register of Shipping.

Crystic® Gelcoat GT-900 is recommended for use in the marine, building and transport industries. It is also suitable for general moulding requirements.

GelTint offers the latest in pigment and gelcoat technology producing a high quality product for ease of use, finish and longevity. There is a vast range of colours available. Custom colour matching is also available if required once you contact a Castro Composites representative.

The biggest benefit of GelTint is the speed

Features and Benefits


Isophthalic base resin

High elongation

Easy to apply

Low styrene emission


Excellent water / blistering resistance

Good impact resistance

Excellent surface finish

Less exposure to the environment and operators

Spray set up

Application temperature: 15 - 25°C
Catalyst: 2% MEKP 50% or equivalent catalyst.
Nozzle airless gun: 423 - 535
Pressure: 3 to 4.5 bars
Distance to mould: 50 cm minimum
Wet film thickness: 600 - 800 microns

Spray Application


- Ensure the gelcoat has attained workshop temperature of 15°C - 25°C before use.
- Add 2% MEKP at 50% or equivalent catalyst.
- Gently stir the gelcoat by hand or low shear stirrer.
- Spray at the minimum practical pressure whilst maintaining an acceptable spray pattern and full fan width.
- Apply a mist coat and then build up thickness in long, even passes of 100 - 150 microns until the recommended wet film thickness of 600 – 800 microns is reached.
- Apply the first layer of laminate within 24 hours of the gelcoat.


- Stir the gelcoat with high shear mixers as this will temporarily break down the thixotropy leading to drainage.
- Exceed a wet film thickness of 800 microns as thick films encourage air retention.
- Apply excessive thickness in corner areas as this can cause pre-release.
- Apply backing laminate before the gelcoat has reached an appropriate degree of cure.
- Catalyse more gelcoat than can be applied before it starts to gel as this will lead to wastage and possible exothermic reaction.
- Allow vapour to be retained in deep mould sections as this can cause slow curing.

Additives and Variants

Crystic® Gelcoat GT-900 should only be used with specified GelTint pigments. The information contained in this technical data sheet applies to all pigmented versions.

A topcoat version of this material is available called GT-900 PAX.

Incorporation of additional material may affect the working, weathering or cured properties of the gelcoat. Please check with Castro Composites’s Technical Service department before using the gelcoat outside of specified parameters.


Satisfactory laminates for many applications can be made with Crystic® Gelcoat GT-900 by curing at workshop temperature (15°C - 25°C). However, for optimum properties, laminates must be post-cured before being put into service. The moulding should be allowed to cure for 24 hours at workshop temperature and then oven-cured for 16 hours at 40°C.

Recommended Testing

It is recommended that customers test all pigmented gelcoats before use under their own conditions of application to ensure the required surface finish is achieved. We recommend that Customers new to GelTint or customers using new GelTint colours test the product before use in full scale production. Due to the nature and fast service of the GelTint process, retain samples of the final product are not taken.

Packaging and Storage

Crystic® Gelcoat GT-900 should be stored in its original container, under cover, and out of direct sunlight. These must be kept closed and airtight. It is recommended that the storage temperature should be less than 25oC and the product should not be frozen. Storing the product outside of these conditions may affect the properties of the product and reduce its shelf life. Ideally, containers should be opened only immediately prior to use. Material should be used within 5 months of production.

Health and Safety

Read and understand separate Material Safety Data Sheet before using this product. Unsaturated polyester products release heat when they cure in bulk.

Type of supply

Crystic GT-900 x 1 kg container supplied with 20 g of catalyst

Crystic GT-900 x 5 kg container supplied with 100 g of catalyst

Crystic GT-900 x 18 container supplied with 0.5 kg of catalyst

20 Items

Typical Properties – Uncured

PropertyTypical Value
Viscosity, 25°C 0.6s-1

325 poise

Viscosity, 25°C 4500s-1

2.3 poise

Specific Gravity at 25°C


Styrene Content


Typical Properties – Cured


Test MethodTypical Value
Barcol Hardness (Model GYZJ 934-1)*EN59


Water Absorption 24 hrs at 23°C*BS EN ISO 62 part 6.2

18 mg

Heat Deflection Temperature† (1.8MPa)BS EN ISO 75-2 (1996)


Elongation at Break*BS EN ISO 527-2


Tensile Strength*BS EN ISO 527-2

75 MPa

Tensile Modulus*BS EN ISO 527-2

3600 MPa

Flexural Strength*BS EN ISO 178

110 MPa

Flexural Modulus*BS EN ISO 1782800 MPa

* Curing Schedule - 24hrs at 20°C, 3hrs at 80°C.

† Curing Schedule - 24hrs at 20°C, 5hrs at 80°C, 3hrs at 120°C.

Gel time & Backup time

Catalyst level and temperature will influence the gel time. The product only requires the addition of catalyst to start curing. We recommend the use of a 50% MEKP which should be added at 2% in the gelcoat.


Gel time (2% 50% MEKP)**Backup time (2% 50% MEKP)**
15ºC17 minutes

55 minutes

20ºC15 minutes

45 minutes

25ºC7 minutes

40 minutes

30ºC5 minutes

25 minutes

**Measured under laboratory conditions. Information should be used as a guide only.


Some products will be considered dangerous goods (ADR) when their container exceed certain amounts. ADR products must be transported by special transport agencies, such as DACHSER or TXT.

* The following products will be considered ADR (Dangerous Goods) when their container EXCEED the values shown in the table below. Products of equal or smaller size than those shown will not be considered ADR, so they may be transported also by SEUR/DPD and GLS.



Polyvinyl and Isopropyl alcohol ................................................  1 L

Ethylmethylketone / Methyl ethyl ketone ................................... 1 L

Acetone ....................................................................................   1 L

Methyl ethyl ketone Peroxide (X-8 MEKP Catalyst) ...................125 ml

Liquid Amine or Liquid Polyamide (Epoxy Resin Hardener) ....... 5 L

Resins, Top Coats and Gel Coats ................................................ 5 L

Paints ......................................................................................... 5 L

Styrene and MW Paraffin Solution .............................................. 5 L


If you have selected a product whose container size is considered ADR and you choose SEUR or Correos EXPRESS as carrier, those ADR products will be transferred into smaller containers to not breach the European Agreement concerning the International Carriage of Dangerous Goods by Road. That is, if you order a 25 kg resin drum and you select SEUR or Correos Express as carrier because you need the products sooner, the resin will be supplied in 5 containers of 5 kg each and its catalyst will be supplied in 5 containers of 100 g.

In any case, drums bigger than 25 kg must be shipped by TXT or Dachser.

* Shippings to Portugal will be always carried by Torrestir

Download Technical Data Sheet            


Crystic GT-900                           


Download Safety Data Sheet              


Crystic GT-900 

Lloyd ´s Register

Lloyd´s Register Certificate 

Handling Guide

Gelcoat Handling Guide 

    Asked by: Rene Trowe
    Date: 2020-10-26 19:09:38
    I would like to paint my boat with a new gelcoat. He still has his old gelcoat completely. I want to repaint it.

    A gelcoat should not be applied over an old gelcoat as it will peel off over time. Even if you sand the old gelcoat. To apply a gelcoat/topcota, you would need to remove the old gelcoat and then apply a new resin and fiber laminate. Another option  would be to sand the old gelcoat, then apply an epoxy primer and finally 2-3 coats of 100 g/m2 each of a high-resistance polyurethane paint.

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