Casting Material Choice Help

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sculptedson

New Member
Hi all, first post here and I am probably in completely the wrong forum but this seemed like an appropriate place to post. I'm looking to create some tiki torch holders that are a mold of my arm and fist - basically a "lifecast" of my arm/fist with a space in the fist to hold a tiki torch if that makes sense. I attached a super crude drawing of what I'm talking about. I plan to mount the whole works to a wall. Making an alginate mold of my arm seems like the right first step and I was thinking I would hold a hollow piece of PVC to keep a free space for where the torch would go while the alginate sets up.

My question is if anyone has any tips/pointers on the right material to use for casting this? It needs to be rigid and strong enough, as lightweight as possible, not brittle, and paintable. I would probably reinforce it with some kind of re-bar or a piece of wood (kind of like a bone where my radius/ulna would be) to strengthen it too.

Thanks in advance =)

torch.holder.jpg
 

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udog

Active Member
Alginate would be the first molding step. But it would only stand one casting in good conditions (don´t know ho many you want). The ideal thing would be to cast in stone plaster (UC30 or similar) from the alginate mold and then mold that in silicone so you have a durable mold. You can also pour molten clay in the alginate in order to correct possible defects and then mold in silicone.
Another option is to mold in a silicone like Body Double (instead of alginate), that would result in a durable mold too.
As for the casting there are some things to take in account.
Alginate will contain moist/water. So initially it´s no good for casting PU resin (a casting option for what you want). But it can be done. A fast setting PU resin is the best for this (less time to absorb moist) and swirling acetone in the mold will help to draw out moisture. Also sealing the alginate mold surface with a fast setting paint spray would help. There is always a chance you get some foaming in the PU resin anyway.
In any case I prefer getting a silicone mold at the end of the process.
For the casting you will be looking for a resin initially. It will also depend on how durable yo expect the casting to be. Will it be indoors or outdoors?.
Your options would be:
PU resin (not sure how loong that will stand out doors) would be a first option.
Polyester or epoxy (with a filler) would probably stand better outdoors. Not good with alginate, better a silicone mold.
Acrylic resin.
Stone plaster.
These last two will be less durable outdoors in first instance.
 

clonesix

Sr Member
RPF PREMIUM MEMBER
Yeah, I will agree with udog on that.

First Question: How many do you intend to make?
2nd Question: What material do you want the finished product to be?


If you want more than one casting, it is best to go with Smooth-On body Double, skin-safe silicone. Do you know how to do life casting? You may need helpers. A silicone mold will allow you to make multiple copies of the piece.

Material? Lots of choices depending on what you want out of the finished piece.

1. Plaster (ultracal) inexpensive and paintable.
2. Polyurethane resin. more costly, but longer lasting casts. can be tinted or painted.
3. 4 lb polyurethane foam. Light weight, and paintable. May have porous surface due to foam.

I don't know how heavy the tiki torch is, but it would be unlikely that you would need to reinforce.
 

sculptedson

New Member
Thanks so much for the pointers, this helps me a great deal already. This would be my first molding/casting ever so I may try to find some folks locally (I'm in Sacramento, CA if anyone is reading this local!) who could assist.

I want to make two torch holders, but I want a left and a right arm, so it would be OK if the molds were one time use only. I guess a more durable mold would be better given its my first time and I'll probably screw something up.

These will be outdoors and exposed to rain so something that can hold up to the elements is critical. A good coat of outdoor paint that I can reapply every few years I think will help with the longevity of them too. But since they will be exposed to wet conditions I'm thinking the plaster and foam options may be out, I'm interested in opinions on that. If those can take paint well, I may be able to preserve them through wet seasons that way. The torches are probably less than a pound even when filled with citronella fluid so if the casting material has lateral strength I agree probably wouldn't need reinforcing, unless my kid decides to hang on it someday =D

My experience with epoxy has been with construction type and that seems very solid/durable if the casting epoxy available is the same kind of material, and would probably last a very long time even outdoors. I'm not sure how well that would take paint, but maybe it wouldn't even need any? Will have to experiment with a small object before doing the full cast.
 

udog

Active Member
If it´s for outdoors I would choose a resin for sure. Pu resin is not thought for outdoors (at least the ones I know), but with paint you will protect them.
Epoxy or polyester (with a filler added, better) will stand better outdoors. Epoxy can be painted with no problem as long as you use a correct primer first (this applies to any resin). You can also play with fillers (metal, stone powder) and try to achieve different looks if you want to avoid painting.
In any case, for a resin as said above, the best thing ist to have silicone mold in this case.
If it´s going to be attached o a wall you might want to include some metal part inside or something to rig it to the wall.
 

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