Preparing and making an silicone inner for fibreglass moulds.


So this semester i am concentrating on making fiberglass moulds and the process of doing this . So let’s get started . First you need a life cast i used my class mated face cast from last semester. If you want to create a face cast you can look to my previous blog posts hear is a link :


Products and materials needed :

  • Clay
  • Mod-Roc
  • Vaseline
  • x2 cardboard cups
  • Silicone part A and B
  •  Accelerator Suitable for silicone
  • Measuring scales
  • Wooden lolly pop stick
  • Gloves
  • Plastic bowl


Method :

  •  To ensures the silicone will  not spill out over the work surface you need to build a clay wall around the face cast .To make neat clay walls wall , used a clay block to flatten out the clay so you  are able to cut the clay evenly  to fit around the face cast . For extra precautions blend the clay onto the wooden board under the cast. Also ass two layers of mod rock for extra support .
  • apply a light layer of  Vaseline to the cast for an extra realise agent . This is to make sure the silicone you are going to pour onto the cast will not  adhere to the surface of the plaster.                                                                                                                                             work experinace photos 227
  • Once the cast is prepared  , you need to start mixing up the silicone . Always makeup sure you are fully equipped before you start with all the products and persona protective equipment .



  • Make sure the scales are at  zero before measuring any products . The products and equation  needed for silicone is :

–          Part A of silicone:100%

–          Part B Silicone:10%

–          Accelerator:1%


For the cast I am filling I need :100 grams of part -A 10grams part -B and 1gram of accelerator to speed up the vulcanisation process.

  • Start by measuring out parts A and B and then added the accelerant and mixed them together really well to ensure all the silicone will cure. When doing this step Its important  to remember when mixing up a batch of silicone, avoid cross contamination of each part as this could ruin the full tub of silicone. To avoid this make sure to use different cups and wooden sticks when measuring out each product .                                                                                                                                                                               work experinace photos 228
  • Then once mixed pour the silicone into the centre of the positive to allow it to drip over the entire surface. This is only the first layer so it doesn’t need  to cover everything in a thick layer.                                                                                                                             work experinace photos 229

GOOD TO KNOW: To avoid air bubbles during this process it is always best to pour the silicone from a height as this eliminates the hair bubbles as it pours.

  • Set the cast aside on a flat surface to allow the silicone to level out and cure. By adding the accelerator you can come back and add the next layer in around 2hr .
  • The next later of silicone is a different consistency to the first as you need to used a different  product – Thixo Additive. Do the same process as the first layer however this time mix the Thixo at the very end. There is no precise measurement for this ingredient as its simply to thicken the silicone up to a  consistency that looks like a  thick paste which will be able to apply generously over the first layer of silicone. If the first layer is still a little tacky that does not matter as it will help the next layer adhere better.
  • Once the past is  mixed you then need to use  another lolly  pop stick  to spread the mixture around the cast .
  • You then need to let it cure for a further 2-3 hours.
  • Once the second later has cured, you  then need to  added another liquid layer over the top (same process as the first layer) this will  smooth’s over any uneven surface  from the second coat.

This is the first process for making a fibre glass mould watch out for the next blog post for the next step .

Thank you for reading



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