I just bought some WS castings, (stone tunnel, retaining walls and culverts). I got a bottle of their latex rubber to make some copies. I know about painting on 3 or 4 layers and adding gauze for strength, what I don’t know is if I should use some kind of a release agent on the casting first so the mold comes off easy. Should I paint the casting first so the latex doesn’t soak in? (flat white spray paint?) Does anyone seal their castings first before painting and staining them or do you just let the color soak into the plaster?
I’ve made a few of these things, from “master” copies that were plastic, plaster and even modelling clay. I didn’t prepare the surfaces other than to make sure they are free of dust. You definitely don’t want to paint them, because that will smooth out the fine details of the master casting. The latex will release pretty easily.
Things I learned the hard way:
Make sure the latex forms a complete “bowl” that will hold your hydrocal liquid. I made castings of some sheets and neglected to do that, so now I need to make up a styrene “retaining wall” when I use these. Not a big deal, but it would have been easier if I had molded the latex up the sides as well as just on the flat face.
Remember that the mold will probably be filled upside-down to the way it is made. That is, you’ll put the master on the table and then paint the latex on top of it, but then you’ll invert the mold and pour the hydrocal in from what was originally the underside. So, it’s important that the top of the mold be flat when you’re forming it. The latex is thick and viscous, so it will not necessarily settle to a nice, flat surface when you paint it on. Be careful not to leave lumps or ridges, because that will lead to uneven castings.
Once I make my hydrocal castings, I usually spray paint them first with gray primer, the cheap stuff in a can from Lowe’s. That’s basically the rock color I want. Then I go over them with several applications of an India Ink in water wash. The black ink settles in the cracks and really highlights the details of the casting.
Thanks! I probably try the culverts first. They came 2 to a pack so I’ll have a back up set if something goes wrong.
because the mold is filled upside down ,you can cover the back of the mold with more plaster before you take it off the original. the mold will lift out so you can peel it off the original. Then before you pour a copy place the latex mold into the plaster backing so it will hold its proper shape without distortion.
loathar, the “releasing agent” you are referring to is called “pounce” or “a pounce”. I will own up to not having done any castings in quite awhile but it was recommended to me early on that talc or talcum powder was a very good pounce and I have used it with good effect.
Practically all of my casting has been done with epoxy but I can’t see that it should not work with hydrocal. I pounce the master before I do the RTV pour and then I pounce the mold before I pour the epoxy.
I just spray mine lightly with wet water. Also I prefer 7 to 8 layers of latex in quart jars from an art supply store. The extra thickness makes the molds last a lot longer. You can reinforce them with gauze or fiberglas sheetrock tape. You can also use cardboard to add rigidity to the shape.
I’ve cast plaster, water putty and envirotex in my homemade molds with no problems other than the envirotex casting wants a bit of release compuond in the mold or it sticks to the latex.
For your second question, I sometimes paint first (no need to seal) and sometimes spray with an india ink solution (no desire to seal). I prefer color to soak in a bit so that chips are less noticible. I can’t see any harm in sealing though. How about some cheap spray primer?
Karl
A few years back I did some rock molds using the liquid latex. After I made my molds, and before I used them I lightly sprayed them with silicone spray, that one can find at any automotive store. Works good, but you can use baby powder too! Usually when I make castings I mix the hydrocal with a little patching plaster(powder form) and if i need a real hard casting I add a tablespoon of water putty( also in powder form).