Mold Release

Model Railroader Layouts and layout building
1

Starting to pour some rock molds. I have heard the following for mold release:

  1. Pam cooking spray

  2. Silicone Spray

  3. Wet Water on the mold

Which is the better of these methods. I have every mold the woodland scene makes so figure LOTS of pours.

2

I can not speak for the first two, but I used the wet water on my WS molds when I used them. It worked just fine.

3

I don’t know if i would want to use Pam or silicone spray on my plaster molds…but I definately recommend water with a little dish soap in it…that is what I use in all my Woodland Scenics molds and I have no problems with the rocks coming out of the molds…Tim

4

I used wet water for all of mine. A good tip someone gave me was to mix the plaster into the water. Not the other way around. REALLY cut down on air bubbles.

5

Thank you all, Wet Water it will be.

I heard that about the plaster into the water. I will use that method also.

6

I too use only the wet water. I find that the Hydrocal pours and fills the mold much better when thinned to almost a cream like consistency. You find that some proping of the edges of the mold will be nec. I just use bunched paper towels for this. You can change the shape of the casting somewhat by this forced proping to misshapen the rubber. Light flicking or tapping the mold brings any air bubbles up the the surface.

I like to color my plaster with powdered masonry dyes. Add the color to the dry plaster, then add the plaster to the water. You will need to experiment on how much water for the size batches that you need. I always have extra molds or some places to use any excess plaster from the mix instead of tossing it out.

You can also place a partially hardened mold directly on the layout. I will butter the back w/ a fresh patch oif plaster and place as desired. This allows you to push and shape a casting to fit a contoured surface. You need to hold the mold for a few minutes. You can feel the heat as it begins to set. Too many times, one is tempted to pull the mold off after a few minuted thinking it is dry. leave it for a good 20-30 min. Use care when peeling. If any parts break away these can be glue on if needed.

I have also waited to a casting is starting to really firm up and then purposely flex it to gain fracturing and then place it. Can get nice effects this way.

These were done this way

This still needs more work w/ trees and weeds

7

Bog, so you pre-color your plaster? I like the colors you used; what did you do to get the rust colored staining in the 2nd picture? Dave from Sierra Scale Models recommended blending some of the weathering powder with denatured alcohol, and then letting it drip down a surface. Similar method?

8

Greg-The Woodland Scenic Earth tone stains work very well for coloring rocks. They go a long way too. You can add whatever craft paint you want into your plaster when pouring your molds. I found it better not to seal the plaster before you stain and color it. This way the stain can be absorbed by the dry plaster and give it a very natural, uneven color.

9

Yeah, tahts what I figured would be best. I was hoping to win a sick auction on ebay for the paints, but i didn’t. lol. Anyway, are you saying though that you should spray rock molds with a scenic cement? I mean, i understand this if you have ground foam on it or something. Do some people actually then paint the molds after spraying with adhesive?

Also, I’m reading that you can kind of press the molds into place after they’ve begun to set. I remember making molds as a kid, but could never get them to look right on the mountains we’d built. Instead of covering your hardshell base with plaster, do you think it would be a good idea to place molds in place on the cardboard web, and then layer the plaster cloth so that you can kind of blend the mold into the base first? This way you wouldn’t have to use any sculptamold or spackling (would spackling work?) i would think. I understand you’d still have to paint it, but if you’re going to paint the mountains with some earth tones anyway, do you think that would be advantageous at all?

but anyway, how long after you have poured the mold should you put it onto your scenery base? will it be kind of squishy? i mean, not really squishy, but maybe the consistency of play-doh, where its got some stiffness but can still be molded.

10

The castings can be placed in various ways. Contoured scenery areas where you need the rock to conform to the convex and concave shapes, I find it better to apply when wet and shape. To judge when ready the Hydrocal surface starts to loose that real wet look, check by lifting a corner/ edge. If it can be lifted and the plaster is firm enough that it won’t move the casting can be placed. If pressing you realize it is still somewhat wet, let sit or hold for a few minutes then continue to press and shape. For sporatic outcroppings or even a full rock cut, the already dried castings can be g

11

I used WD-40. I wiped out the mold after spraying it so that only a very thin film was left. Worked fine.