Making the Fiberglass Positive

Hi everyone! Thanks for visiting!

During this post I will be explaining the next steps towards finishing my fiberglass mould. If you have missed the previous posts and are interested in have a look. Just click the following links:

Ok so here we go!

1 (3)


Once the negative was finished we could then move onto making the positive in which we are going to be sculpting onto. To do this we first had to free the fibreglass and silicone inner from the plaster live cast.

1 (2)

Using a wooden sculpting tool I gently prized them apart being very careful not to cause any damage to either part. This was quite difficult as it was suctioned together however once air had got in between the silicone and plaster it come away quite easily.

1 (4)

We then placed the plaster live casts to one side to create more space for the next step.  As precaution we covered the tables with plastic to make any spillages easier to clean up and to prevent any damage to the surfaces.

1 (10)

Next we then placed sausage shaped of clay onto the front of the negative to ensure it did not roll around the table or get damaged when it was placed face down.

Combo gel coat


We then mixed up a half cup of gel coat to begin the fibreglass process. Same as before we used the same ratio of catalyst and applied I layer all over the silicone inner. This would pick up the detail of the silicone giving us a perfect surface to sculpt on top of. We then added a generous layer of fiberglass fibres of the top of the gel coat to pick up further detail.


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

1 (14)

Although the ratio of the fibre glass was the same we decided to experiment and add another element to the mixture. We wanted to change the colour of this part of the mould so we added a metal powder colourant. We mixed a significant amount of the powder into the gel before applying the first coat. This would give us a metallic brass colour which we could polish up later. I also sprinkled a small amount of bronze onto the gel coat to see how it would turn out. This is a useful method to experiment with as I may want to make something directly out of fibreglass in the future instead of only using it as a mould making material.

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.


We 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.

combo 2


Next 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 placed four pieces of the matting onto the plastic sheeting and saturated them 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.

1 (25)


Once dry we were able to use a variety of tools to separate the silicone from the fiberglass positive.



Once the two parts were separated we were left with the fiberglass positive! I was shocked to see how much detail the gel coat had picked up.


Although I was happy with the positive I noticed that it was a little sticky to the touch as the fiberglass had not cured completely so I decided to try and get rid of this texture with wire wool. This would also polish up the colours in the fiberglass revealing a metallic shine.


Thank you for readying! Hope you found this helpful. Stay tuned for the next steps!

Katy x

Evaluation / Reflection:
During the making of the fibreglass positive it became clear to me why we created the silicone inner and other fibre glass section. The silicone was used to pick up the detail from the plaster face cast. The silicone was then supported by fibreglass (to keep its shape) which then allowed us to remove the plaster life cast.  I was really pleased with how the positive turned out as the first gel coat had picked up even the finest detail (some details that I wasn’t aware of) I have yet to try and sculpt on this type of positive however I like how lightweight and strong it is. It also has a smooth texture which will help me blend out the plasterline.


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