I’m having trouble consistently getting my hydrocal rock castings to release from the Woodland Scenics rubber mold in one piece once they are cured. The instructions say to spray a wet water coating first before pouring the hydrocal, but I found, even with distilled water (not hard tap water) and dish soap, that I had trouble with breakage. I’m not overfilling the molds and I am waiting until it is cured before gently removing.
Is there another technique or wetting/release agent I can use? I don’t want to lose the details of the molds.
(This post came to mind after reading forum responses regarding track ballasting and wet water vs. alcohol)
I think that you’re not supposed to keep the part in the mould until completely cured – just mostly cured (I believe “no more cool/damp feel” is about right).
Yes what I’ve been doing is removing the castings after about 20 minutes from pouring. That hydrocal sets up very quickly. Almost too fast for my taste.
Tap water and dish soap works fine for me. I rinse the mold thoroughly with water before I start. But, I do let it set up hard, certainly more than 20 minutes.
I peel back the edges of the entire mold first, and then go slowly from one end to the other.
How old is your Hydrocal? I was at the bottom of a big jar, so it was probably several years old, as I had finished the castings for Phase 1 a few years back, and was just starting Phase 2 of my layout. My first castings were terrible - soft and prone to breakage. I tossed those, and opened a new jar, and got very good results. I’m guessing that the old Hydrocal absorbed a lot of moisture over the years, even in a screw-top container.
Just removed several plaster of paris rocks from a WS mold. Poured them last night. Used wet water, soaked them heavily, poured the excess out, didn’t seem to loose any detail. The excess that I poured onto a piece of crumpled tin foil was to be ground to make talas. Some of it came out so nicely it may remain in tact and become small rock faces here and there. Wet water on that also.
I’ve found that with Hydrocal, so much depends on temperature and humidity when casting. Out here in a dry climate, on my garage layout, I’ve found that using Hydrocal castings results in a too-fast drying time in the mold, no matter how much I try to ‘time’ it. I’ve used both the WS and Bragdon molds, and both seem to be problematic with Hydrocal, even using the ‘wet-water’ releasing agent.
What I eventually did was experiment with Sculptamold, mixed 50-50 with water and letting the soupy mixture set for about 20 minutes into the mold before applying it to the scenery. It turned out much better for me, the Sculptamold remains much more flexable and the mold peels off very evenly. The resulting casting because of the Sculptamold mixture has a slightly ‘grittier’ face to it, that takes stains very well. Total ‘curing’ time is several hours, which allows you to make any contouring around the edges very easy with a putty knife or X-acto blade.
I’m working on a rather large rock-face on my layout, and the Sculptamold–though it takes a little more time–is turning out to work extremely well.
I spray the inside of the rock molds with plain tap-water in a sprtizer to which I add about 3-5 drops of liquid detergent.
The wet water helps cut the surface tension and allows the casting medium to get in all the nooks and crannies, it is NOT a mold release. Skip the wet water and try Pam, it will do both.
I have used Hydrocal B-11, (apparently no longer available) and Latex molds since 1974, and have never used a “release agent”. I wait until the mold feels quite warm, and then starts to cool before removing it, and have had good luck in keeping fine details. For those who use “release agents” such as “Pam”, have you noticed any effect on color absorbsion or color change from the “release agent” on the face of the casting?
I’ve used a generic version of Pam for quite a few rock and structure castings and haven’t noticed any appreciable effect of the oil on color absorption or color change. The important thing to remember is to use a light spray rather than a heavy coating.
There is an article in the December Railroad Model Craftsman by Paul Scoles that states that the wet water is to allow the paster to fill the mold completely, as mentioned in an earlier post, and not as a releasing agent.
Since I am using the castings themselves to determine their placement, I want to make the castings and let them cure/dry completely before I arrange them on the layout for permanent palcement. If I need to contour a casting to fit a curve in the landscape then I will re-cast the mold and place it “wet” in the appropriate spot.
Thanks for all the responses. I will try PAM, and Sculptamold and do some more experiments.