1. 1.Using a pair of scissors cut some ‘tissue fibre-glass matting’ and some ‘course chop-

    strand fibre-glass matting’ into pieces around the size of banknotes.

  1. 2.Gel-coat is applied directly onto your master’s surface, which has already been primed 

   with a suitable release agent (PVA blue is a popular release agent for fibre-glass). We 

   leave the gel-coat to cure for around 35 - 45 minutes. When our surface is firm but

   tacky, we are ready to mix a cup full of GP resin.

  1. 3.Apply a liberal coating of GP resin onto the gel-coat surface. Lay a piece of tissue fibre-glass matting over the wet resin surface and using the brush in a stippling action, press the matting into the resin until saturated. Working from the centre out, ensure all the air bubbles are removed from under the matting (Air bubbles are clearly visible through the wetted matting). The next piece goes on overlapping the first, wetted down with more resin on the brush, and matting.

When you are doing this, try to make sure you keep your gloves from touching the resin, as you can end up in a real mess, very quickly.

You do NOT need to wait for each layer to set before starting the next.

  1. 4.The next step in to de-laminate the course chop strand matting we cut earlier.

   Although it can be used as it is, peeling the two layers of fibre-glass apart is helpful   

   because it makes it easier to apply to a complex form, like a human face. Using the

   same technique of stippling, wet the matting down, again ensure all air bubbles are

   evacuated from beneath the surface. Usually two layer of this matting is enough for a

   mould the size of a face. Larger moulds will need more layers to add strength.

  1. 5.This same process is repeated two to three times with a thin tissue-like fibre-glass

   matting and another two or three times with a much coarser matting. This laminating

   layers of glass fibre matting and polyester resin is what gives the finished product its


  1. 6.In order to avoid glass splinters from the finished piece it is recommended that a layer of

    gel-coat is applied to the outside of the fibre-glass mould.

   Smother the exterior completely with catalysed gel-coat, ensure all the splintery textured 

   glass fibre is covered.

  1. 7.Once all is fully cured the mould can be removed from the master. This shouldn’t take 

    longer than an hour.

    If it is a multi part mould, it can be cracked apart along the shut lines using wedges and 

    small pry bars. This can be tricky sometimes, so ask a technician to help you.

Tip: At any stage though out the whole procedure, pigments may be added. Adding pigment when fibre-glassing is helpful to check you are getting an even coverage.

To cast a fibre-glass object the same method must be used, in the same order on the inside of a suitable mould.

Innovative use of Gel-Coat

Over recent years I have seen gel-coat used in some unique ways. Through knowledge of the materials property’s, students have begun to use gel-coat as a means to draw in three-dimensional space. This process begins with inflatable objects, the most common being a balloon. The balloons can be used separately or stuck together with double-sided tape, a design can then be drawn onto the surface using marker pen. Once you are ready to begin, mix up a batch of gel-coat (with your chosen colour already mixed in), transfer this to an icing piper or a large syringe (without the needle). Squeeze out the gel-coat following your design pattern. Leave it to set for a day or two and deflate the balloons (do not pop them). You should be left with a basket type design in resin.

A similar technique was used when decorating pottery by one student. Gel-coat was mixed and a colour added, this was added to a syringe then piped onto the pottery, once set this produced a striking contrast between the rough texture of the pottery and the slick candy-like finish of the gel-coat.

Gel-coat has also been used recently as a brushed on coating for an MDF structure. The gel-coat was saturated with aluminium powder prior to application which, when sanded and polished gave the appearance of tarnished, beaten steel. Very effective!

Using your knowledge of how a material will perform, will allow you to bend rules that govern material properties. This will open doors to innovative practices.

Price is around £6.00 per kilo


How do I use Gel-coat when Fibre-Glassing?

Prior to fibre-glassing, gel-coat is used to capture detail and protect the surface of the mould from the texture of the glass fibres.                                                                                                                                                                                                                                                                                                                                                       

As with most mould making, the most important thing to remember is you must plan ahead, make sure that once cured and solid you can get the object you are moulding out again, this is particularly important if you are making a rigid mould without a skin.

Creating shut lines or flanges involves making clay, wood and hot glue or pin and tape flange walls. Flange walls are short walls that lay at a right angle to the masters surface. These serve to separate each part of your mould and make it possible to bolt the mould together again once the master has been removed. Often, locating keys (dome shaped indentations) need to be added to the flange in order to lock the mould in the correct position once the original is removed.

Care should also be taken when choosing the appropriate route of shut lines and release agents. Always consult a technician before you begin.


Gel - Coat

What is Gel-Coat?

Gel-coat is a very thick gel-like polyester resin, it is traditionally used as a pasted or sprayed coating prior to fibre-glassing a mould with GP resin.

Gel-coat has quite limited applications in terms of mould making and casting. It was designed for use as a surface coating, such as on the inside of a mould to capture surface texture and form. However, we can also use it as a safety measure; It can act as a protective barrier between the user and the sharp fibre-glass splinters on the outside of a fresh fibre-glass mould or jacket.

Carbon fibre, Kevlar and fibre-glass matting may all be used with gel-coat and the general application technique is the same as when using fibreglass.

‘Fibre-glass’ is a term often used out of context; it is in fact the resin we use with the fibered glass matting that gives it strength, hence its correct name; ‘Glass reinforced plastic’.

Health and Safety

When working with these resin’s we must always wear protective gloves and goggles, long  but not baggy, sleeves are advisable especially if you have sensitive skin.

The use of an adequately ventilated working area (like our workshop) is essential. If you are using any polyester for a prolonged period or using a particularly large amount, then the additional protection of a respirator, to protect yourself from the fumes is advised. The fumes can make you feel light headed and a little nauseous if you are over exposed to them.

Fibre-glass tissue

Chopped strand fibre-glass




Fibre-glass mould making with gel-coat


Gel-coat surface of a fibre-glass mould


Gel-coat/metal powder casting taken from a multi-part fibre-glass mould


Gel-coat casting’s taken from an inflatable core


Gel-coat casting’s taken from inflatable core’s


Gel-coat piping on a ceramic bowl’s


Gel-coat piping on a ceramic bowl’s