I've seen several people ask about how to cast plaster / resin wall. First, I will assume you have a piece already to make the master from... the "investment original"... if not, you need to carve one (I suggest using Balsa Foam... it is GREAT and EASY to work with - and yes, I sell the stuff!).

Once you have your original, you next need to make a container for the mold itself. Some folks like Aluminum Foil, but I find it "quirky"... it tears and wrinkles, and will often stick to RTV (room temperature vulcanizing rubber). I prefer to go to the hardware store, and buy a 4ft x 8ft sheet of rigid pink insulation sheeting, about one inch thick. It has a film on one side that is waterproof, and acts like a Teflon barrier when in contact with RTV...

Now cut a section of Foam with your box cutter knife or hobby knife. Place the original in the middle of this piece, and then draw off the SM ALLEST RECTANGULAR area needed serve as the base... RTV is VERY expensive, you don't want to waste too much! I like to leave a 1/2 in perimeter around the original to add side strength to the finished mold.

Now cut "walls" that will fit your exact minimum rectangle, and TAPE then around the edges with old fashioned shipping tape (or even scotch tape if that is all you have). Next, drive pins through the corners to help reinforce the shape of the walls.

You now have a waterproof "dam" to contain your RTV.

Use white glue to paste the back of the original to the bottom of the rectangle. Allow it to dry...you will be able to pull it up later, but you don't want the original to "float up" once you start pouring your RTV.

I first use a paintbrush to dab the entire surface of the original to insure that there are no air bubbles in the final mold. Make extra sure you cover the entire piece with a thin film of liquid RTV... once this is done, you can pour in the rest of the RTV to fill the mold completely. Let this cure (about 2-3 hours), and then pull the walls away from the cured mold. Pry the rubber away for the original, and you have a duplicate mold, ready to accept either plaster or resin castings!

Would this make a good article for DIGITAL DIAMONDS?

Keith,

this would make a perfect article for the DD series for sure !!! Please add this article to the wonderful series of Digital Diamonds.

Keith,
Jus a tip: for your walls, why don't you use LEGO blocks? These are easily adjustable, reusable and waterproof.
Just my 2 €cents!

I have used legos before (and still do for a small piece), but for something really large (remember - I do a TON of different products), the Legos format is too limiting. The largest bottom sheet I've found for Lego is about 6 x 10... some of my pieces need to be 12 x 16! (yeah - i do some huge stuff!). Likewise a sheet of the pink foam insulation (4' x 8') only runs around $$5 us... far less than a box of legos with everything i would need (around $30). And finally, one sheet of the pink foam will last months! That is 32 square feet of totally flexible, and waterproof stuff.

And finally, guess it all comes down to preference... I like the extra control that cutting my own shape allows me. I can have "long and skinny", small and tall, or even round if the situation fits.

I guess I'm lucky then that I am in the possesion of a base plate of approx 50x 50 cm's. Good old childhood! I agree about the round thing though!

I picked up some stuff which you melt down then pour it like normal but the good thing about this is that if your finished with the mould you can melt it back down and reuse it sinks though if you leave it to burn

Good morning everyone!!
I tried some casting for the first time about a month ago. It was for some sections of cobblestone road. Not knowing the "proper" way to do this, and knowing that RTV is crazy expensive, this is what I did: I took my master, then rolled out some playdoh with a rolling pin. Then I pressed the master on top of that to make the impression. And since I could never get the playdoh completely flat, the impression was uinque, as it would be slightly raised in some areas, lower in others to give that uneven road look. Anyways, after my imprint, I took a knife and trimmed the edges square, and then made a form around the mould out of the big lego blocks. I mixed up some plaster ultra thin, and poured it in. Came back later, removed the blocks, peeled off the playdoh, and I had a road section. Some playdoh remained on the new piece, but with some soap and water, and a toothbrush, it came off. New road section!! Now, the other day, I was in our hobby shop stocking up, when I saw some new items from Tamiya. They have some herringbone road section and a stone section. They are roughly 8x11, and it's almost like the material is paper, with the brick work slightly raised, and it seems to be made out of some sort of felt or rubber. All you need to do is cut, glue, and paint. I wanna cast this stuff, would the RTV work on this would you think? Then I can go and pour some plaster and have lots kicking around for future projects.

Kelly - while the RTV would certainly pick up the pattern, the problem may be in getting a thickness when you re-cast. You will need to somehow build up the sides so that you get enough thickness when you re-pour. Again... RTV is SO expensive, and the Tamiya sheets are so cheap, you might be better off just buying more sheets!