Preparing an ear cast for silicone and fibreglass moulds

Hi everyone, so this blog post is all about preparing for fibreglass and silicone moulds . On this post i will specifically taking you through the process of bedding in an ear cast into water based clay . The reason we bed in an ear is to eliminate any undercuts where the future fiberglass mould could lock .

Products and tools needed :

  • Water based clay
  • Clay tools
  • Wooden board
  • Mod rock
  • Part A of silicone
  • Part B Silicone
  • Accelerator
  • Thixo

Method :

  • To eliminate any undercuts  you need to build up a  bed of clay around the ear cast. placing the ear cast onto a wooden board  and start building clay up around  each side of the cast.If you are un-sure about what an under cut is  take a look at the cast from a bird’s eye view – anything that you can’t see from this angle  needed to be filled in with clay.
  • When happy with the ear you have bedded in you need to next build up a clay wall . For extra strength wrap two layers of mod rock around the outside of the wall for strength                                                                                                                                                       5
  • Next  applied a light layer of Vaseline to the ear cast as silicone can adhere to plaster and the Vaseline acts as a relive agent .
  • You now need to mix up the first layer of silicone .You need to make  sure you  have  all the necessary materials and tools to do this.  You need to start by  zeroing the scales whilst the plastic bowl  is on  top to make sure you  get an accurate reading .The equation for silicone is:

–              Part A of silicone:100%

–              Part B Silicone:10%

–              Accelerator: 1%

For the size of the positive ear cast you will be covering you will need  to mix up 70 grams of part -A 7 grams part -B and 0.7 grams of accelerator to speed up the vulcanisation process.

  • Before mixing  make  sure that the tubs of silicone are  very close to the scales as it can drip really easily which can be difficult to clean up when not mixed as it stays in its liquid form. To avoid any drips whilst measuring out the silicone use a lolly pop stick  to scrape the excess silicone from the sides of the cups.
  • Start by measuring out parts A and B and then added the accelerator and mixed them together really well to ensure all the silicone will cure.
  • To avoid air bubbles during pouring  the silicone into the ear cast   it is always best to pour the silicone from a height as this eliminates some of  the air bubbles as it pours.                                                                                                                                                                   DSCF0113
  • Set the positive aside on a flat surface to allow the silicone to level out and cure this will take about 2hr as you have added an accelerator  to the silicone .
  • The next later of silicone is a  different consistency to the first as you need to  use  a different product – Thixo Additive. You need to  carried out the same process as the first layer however we mixed the Thixo at the very end. There was no precise measurement for this ingredient  the consistency needs to look and feel like  a  thick paste which I would be able to apply generously over the first layer of silicone. If the first layer is still a little tacky that doesn’t matter as it will help the next layer adhere better.  Once the past is  mixed you then need to use a new lolly pop stick to spread the mixture around                                 kldjakd (11)
  • then  leave it to cure for a further 2-3 hours.
  • Once the second later had cured, then added another liquid layer over the top same as the first layer this creates a smoother layer  over the second layer                                                                                                                                                                                                        The next step is creating a fiberglass cover for this silicone , I will be blogging about this next week so stay tune .

Thank for reading

bex 🙂


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