Making the Fibre Glass Outer Part of the Mould

Hi guys! Here is the next step of making our silicone inner and fiberglass moulds..

So, once we had prepared the silicone inner for the mould we were then ready to start the process of creating the fibre glass outer section of the mould.

The reason we are applying a fiberglass section is to support the silicone as it would not hold its shape throughout the casting process as it is a flexible material. Therefore the fibreglass acts as a lightweigh support for the the silicone. It would be possible to use plaster and plaster bandages however fibre glass I more durable and a lot lighter.

So lets begin,

DSCF0173 So to begin with we removed the mod-roc and clay wall from around the edge of the cast. Then we used paper towel to remove any moisture that may be resting on the top of the silicone – If the silicone is damp or wet, the fibreglass would not cure. We also trimmed away any excess silicone around the edges leaving a clean edge.

Depending on the surface you apply fibreglass on top of a releasing agent may be needed as fibreglass adheres to pretty much anything however silicone is felxible and can easily peel away.

Once preped, we were then able to move onto mixing the first gel coat of the fibreglass. To do this we began by measureing out half a cup of the gel coat.

 2To ensure we didn’t dip the gel coat over the floor we placed down some plastic sheets to make it easier to clean if we did spill. We also used a wooden flat stick to help scrape the excess off the side of the cup before bringing it over to the table.

It is always to keep in mind cross contamination as you do not want to ruin the full tub of gel coat so we made sure that the cup and stick we used were clean.

 DSCF0179We then added a catalyst which would allow the gel coat to vulcanise. We used the measurer on the bottle to measure up to the ‘2’ mark. Any more that that would result in the gel coat curing quicker than we need which may cause a problem!

 DSCF0180We then thoroughly mixed it together and applied a thick coating over the top of the silicone with a cheap brush.

Health and safety: Never place the cups and brushes directly into the bin after use – Fiber glass heats up when it cures, meaning it is a fire hazard. It is best to let it cure in sight completely.


Usually you would add a layer of fibre glass strands to the gel coat (however we forgot to do this part!)

Once the gel coat was applied we then left it to cure for around an hour. This would allow the gel coat to cure but not become completely dry – leaving the surface slightly tacky ready for the next step.

 DSCF0191We then cut 3inch square pieces of fibreglass matting in preparation as our hands were about to get sticky! We cut around 13-15 pieces just to make sure we had enough. We then laid out another piece of plastic sheeting onto the table to protect the surface. we then laid out 4 pieces of the matting onto the plastic to preparation for the next step.

 DSCF0184Next we measured out half a cup of laminating fibreglass resin (using a new cup – to prevent cross contamination) we also added the catalyst to the resin using the same measurement as before (up to the measurement of ’2’ on the neck of the bottle). We then mixed it thoroughly.


We then used a brush to paste a layer over the tacky surface of the gel coat this will help the next layer adhere. We then used a brush to saturated the 4 piece of matting we had laid out with the resin. Once all four have been coated the first square we painted would have had time to absorb the resin making it softer – allowing it to mould to the shape of the silicone inner.


We then applied each square onto the surface of the painted on layer of the resin. We then used a paper mache method by pasting another coat over the top of the matting to make sure it was flat without any air bubbles. We made sure each square overlapped slightly to make sure there was not gaps.


We then left it to dry for around 20 minutes until it goes a green colour. To prevent using power tools we cut the edges of the fibre glass at this time as the fibre glass is solid but still flexible. We then repeated the process – adding a second layer. Then we left it to dry completely over night.

That is all for now! I shall be posting the next stages after next weeks lesson!

Thanks for visiting my blog!

Katy xx


One thought on “Making the Fibre Glass Outer Part of the Mould

  1. Pingback: Making the Fiberglass Positive | Kathren Elizabeth

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s