Mold Making Question. asking for a friend (no, seriously!)

[clonesix]

Hi Folks, I got a DM from a new user who asked me the following question:


I have a question about mold making so here is my situation, if you have time to answer it
i will really appreciate it!

I just made a plasticine model about 55 inches heitgh, its a male torso with no arms (Barroque style)
I`ve made models and molds in order to cast be on resin (hard resin) before but he biggest that i`ve ever
got before it was 27inches the biggest.

Im at the "making" the mold part, by this moment i already applied the a thin layer of rubber on my model,
i know it as the "flow coat" wich is enough for the rubber to get the information from the model but not as thick
as the "later" coats.

Now i want to add the shim with basketball collectable cards (plastic ones).

How do think will be the best option to add the shim?

Should i mark where my divisions are going to be, and then make a thin cut on top of the rubber and place
the shim throught the rubber against the plasticine and then continue brushing the rubber to cover the shim?
My concern with this option is what if when i make the thin cuts on the silicon air gets filtered and affecting my mold?

or

Should i make a small stripe of rubber, attach it to the mold and then put the shim on top of that stripe and then continue brushing the rubber to cover the shim?
my concern about this option is mainly the materials, not spend that much of it if there is another way to do it
with less material.

The purpose of the piece its just an experiment, im planning to make a show and this is my first approach to it!

thank you so much for your time!

 

[clonesix]

I will address this here rather than in PM, so that others can chime in and possibly answer future questions for those who use the "SEARCH" feature.


The question that you seem to be asking is 'How do I divide my mold into two halves?'

The issue of adding cardstock shims to divide the halves has come up. There are 2 ways to do this, 1) Divide the model with cardstock FIRST, and then brush RTV onto the model, and 2) Do NOT add cardstock, but brush RTV over the entire model until there is a minimum of 1/4" RTV covering the entire model. Then a shell must be added to support the RTV. The shell can be plaster bandage, plaster etc, but it also must have a parting surface for the two halves of the plaster to separate, and thus requiring cardstock or other method.

If these are your choices, I would go with #1, and apply your cardstock paring line first and then brush RTV onto half the model, then add mold release, and apply RTV to opposite side. Don't forget to add location devices to locate the RTV back into the plaster shell.

Then when it comes time to add the plaster shell, there is already a parting line in place.

I personally do not use cardstock, but clay to create my parting lines. So best of luck.

 

[Elpa]

Thank you so much Clonesix!!!!

If i already add the RTV on my model and im willing to go for option number 2 then (i already brush the RTV on the model) does the cardstock divison
should penetrate all the way into the clay? or should i just place the cards gently on my channel?

 

[clonesix]

You Tube has videos on this. Here is a mold similar to yours.