Demoulding the legs

The top two parts of the leg mould slowly eased away from each other and popped off fairly easily. Unfortunately and strangely - the bottom part of the mould has bonded to the silicone just like the arms....!

After noticing how difficult it was getting the arms out - I decided to be as gentle but firm as possible and if that didn't work I would literally cut the mould part into loads of pieces so they were easier to pull off without damaging the surface of the silicone.

I was driven to the latter plan. I ended up dividing the mould into 15 different parts. Each part was a struggle to peel off - the third pic below shows how it felt like I was fighting against a strong glue!! If I could pinpoint the cause of the chemical bond then I could have learned something from this and if it was a mistake I had made then at least I could blame myself but no!

After removing all parts of the mould, I also realised I'd positioned the right arm slightly too close to the body which meant there was a large gap at the shoulder because the right knee was stopping it from going all the way into the hollow box section I'd glassed into the torso core. I'll now have to dremel all that out and reposition it again with bridger etc. Not ideal.

Foaming the arms and legs

So Easter holidays are over and I have access to the workshop again. I used Mould Foam 8 (R8) polyurethane expanding foam to fill the arm and leg moulds. The arms are actually surprisingly thin and only took about 400g each (with lots of excess). First pic shows how I will suspend the solid box section I milled down to fit inside some hollow box section (set aside for later), in the moulds so they'll be securely imbedded onto the arms after demoulding. Second pic shows part A ready to be poured into a bowl of part B - mixed quickly with a big disposable brush. Third pic shows the other arm mould after the foam has finished expanding and has totally cured.

The legs are a little bit more complex so I'll let the photos make sense of it - I temporarily taped the metal plate (that I made to sit embedded in the Kijimuna's bottom) onto the solid box section protruding from the inside of the torso's core (I put the torso back into it's mould for this whole process)). I then sealed the torso core from the leg/bottom cavity with several layers of polythene sheet - this is to stop the foam from expanding into the torso core (I want these parts to remain separate so they can be detachable for transportation purposes). I poured one leg at a time until there was only the bottom section not filed with foam. I then bolted the sealed off torso mould onto the legs and poured the rest of the foam through a hole at the bottom of the leg mould (I obviously cut away the flap of silicone that originally covered the fiberglass section I cut out).

You can see that the metal plate is now hiding inside the bottom and the torso will now locate perfectly onto the legs every time (hopefully!)

Casting Issues / Repairing the arms

So after a successful demould of the head and torso - I have come across a BIG problem when attempting to demould the arms. Most (if not all) silicones are known for not sticking to anything but themselves... and (unless casting silicone into silicone) release agents are not essential at all.

I covered my moulds in a light dusting of Macwax - a very common spray release agent that works well with Platgel pieces and many other materials. Despite this, I realised I was having problems getting the parts of the arm moulds off the cast because the Platgel had CHEMICALLY BONDED to the fiberglass. There is normally resistance when demoulding because of the suction created by the silicone - once the air creeps it's way back between the mould and cast, the mould parts eventually come away fairly easily. My arm moulds have no undercuts or heavy texture so there is no chance of this simply being a mechanical bond. The moulds were clean, dry (before the macwax was sprayed) and loosely covered with clingfilm to prevent dust n bits falling in - because of this I am confident that the gelcoat was normal and prepared properly for casting.

I realized the Platgel had bonded when I had been slowly knocking wedges all the way round the flanges, instead of new parts of the Platgel's surface becoming visible as the gap got bigger - it was the same area of silicone stretched between the two flanges. I attempted to pull the silicone away from the inside of the mould and was successful but it was incredibly stuck on there! Suction does not do this, it wouldn't do this even if I hadn't waxed the moulds.

I submitted my problem to a large community of industry professionals and hobbyists on Neill Gorton's Make-Up Effects 911 facebook group. This is exactly the kind of thing that they encourage people to post - so everyone can benefit from other people's experiences...

I had '0' explanations to my casting issues - go figure!


After eventually getting the first arm demoulded - I decided to slice the skin of the other arm as close to the existing seam line as possible in order to get the mould open enough to be able to grab the silicone and pull it away from the mould with force. I would then have to glue the silicone back onto the expanding foam core.


Here are a few hideous pictures of the damage caused:
I didn't take that many cos it is, quite frankly, embarrassing....

The damage on the first arm from the silicone being peeled off the mould looks like someone's dragged a disposable shaver over the surface (first pic). I will have to cover this in the seaming process as well...

Here are some snaps of me attempting to repair the right arm (the worst one). I used clear RTV bathroom sealant to glue the majority of the silicone back into the foam. I then used a fast setting silicone adhesive called ELASTOSIL A07, to glue the meeting edges together as neatly as possible. I will potentially have two seam lines to cover after I've finished...