So, this a pitiful translation of my own tutorial about making pre-vulcanized lated mold.
I used this method in order to create simple damaged scenery things and create a mold in order to do them fast and spread them to my gamers friends.
Its only one method, but it simple and cheap (and cheap is good in our miniatures' world).
It's for simpe molds, "Boat molds", you can't mold a miniature with this but crashed vehicules (like in this session) can be molded.
We need pre-vulcanized latex and normal plaster.
Think about great quantities of plaster 'cause i make also a shell of plaster in order to maintain the mold in place when i'm gonna pour plaster in it.
1 : What i (you - we) need.
In the following picture, there is the pre vulcanized latex, plaster, casting plaster (resin plaster for the model is good too), the model to copy, modelling clay (the cheaper the better), old big brushes (cheaper better etc.), a cheap wooden plank covered with duct tape and some plastic nice shapped cup (used to to some "i've made too much plaster and i can use it to do some funny stuff and not waste it". You'll also need a hair dryer to fasten the drying of the latex.
2 : Preparing the model
You have to make small balls of modelling clay, put them under the master,
and tack the master on too the wooden plank.
Push as hard as i'm dumb (maybe less, don't break the plank) and it's tacked.
3 : Put on the latex.
Right before latexing the master, be sure the hair dryer is ready to be used.
Pre-vulcanized latex dries faster when it's hot hair dried, it can dries naturally but you may have a week befor you to be sure all the latex layer dried well. Be carefull, the latex can ruined clothes. So wear an apron and it's also better when you'll pour the plaster or the resin plaster(not like in the pictures where i do not wear any apron).
So, you have to "paint" a layer of latex onto the master and dry it with the hair dryer.
Then use the hair dryer.
The first layer is really important : you may fill all the holes to avoid a really bad replica.
Add many layer in order to obtain something like that.
Dried latex took this color (in the following picture)
When you've got about 2-3 mm of dried latex, the mold is done, you can 'try to) use it that way but i improve the method with the plaster shell.
4 : Create the "plaster shell" (in french it's "le porte-moule" and it's a funny pun but in english it lost all the fun, sorry).
So, before pouring plaster all around the master covered with latex, i pre-detach the border of the latex mold, but i do not release the master of the mold.(but you can listen to the master of puppets when you do that, it's refreshing), and then i cut the to wide edge 'cause it will be easier for the following steps(it's just an advice but if you don't you'll risk to tear appart the mold and raging tears can be released from your eyes).
X-acto and else can be used (be carfeful, it cut well like adamantium on steel, so think about it on your fingers).
Then, you pout modelling clay all around the edges to avoid plaster under the master (but if your using an Igor he can be under the master, it's his kind of work).
Then i make a formwork with big construction bricks (yards sales rules).
And i put modelling clay around the inside edges of the formwork to minimize the plaster loss.
Then i pout the wooden plank on bits of foam sheet, i'll used them to be "string" when i'll tap the plank to get rid off the major air bubble inside the plaster.
After that, i make plaster and pour it into the formwork.
Every time you'll pour plaster, tap the board to make the air bubbles burst on the surface (and it's funny to do, recall of old olympics NES Games).
It'll train you to know how to tap when you'll use the mold to make copies.
When it's covered, let dries about 20-30 minutes and unforwork it.
Here you can see the plaster shell, the latex mold and the master.
Get the master out.
5 : Making copies
Make plaster, pour it and tap.
(see above, i'm tapping good)
I pour the "too much plaster" in the funny shapped cups to have nice weird plaster blocks.
Une fois que le plātre est dur.
It's dry, you can unmold.
On the right it's the master, on the left the copy.
That's all folks
(for the translation errors, do not hesitate to ask me for corrections)