DIY - Rock Molds?

[tetters]

Hello again.

I would like to make some rock molds to make some rock out crops and formations for my scenery. I read one suggestion that says to use heavy duty tin foil folded over and over again to simulate the tin layers of strata seen in Igneous Rock formations. I also remember seeing a tutorial a couple years ago from a modeler who used ceiling tiles basically broken and layered to give that look of a jagged rock edge.

Any other ideas or suggestions?

Thanks,

Shane.

[MasonJar]

The "layers" are most often seen in sedimentary rocks, and the ceiling tiles are a good representation of this formation. I have not heard of the foil method. I have also simply "scarred" partly dry spackling compound with an old xacto blade to form sedimentary rocks.

Igneous rocks (like granite) are more uniform and have no discernible layers. You can simulate those by carving, or by using crumpled foil as a mould. Sometimes outcroppings will be smooth where worn by glaciers (if you're in such an area) or jagged if broken (e.g. by blasting a cut for the right-of-way). Most commercial rock moulds are of this type.

Hope that helps.

Andrew

[tetters]

Hi Andrew. Thanks for correcting me. I would like to simulate both... depending on the locale. However for the shoreline, I think I'd go for the igneous rock worn down by glacier.

I sometimes let my impatience get the better of me and gave it a try last night. I folded some foil dozens of times in very narrow strips, playing with the angles, carefully unfolded it to get the rock layers, and then crumpled it to break up the lines and make it look more natural. I then shaped the foil into a bowl like form. I mixed up a batch of Hydrocal and poured it into the mold. Couple things I learned.

1) Hydrocal sets up really fast! I almost waited a minute too long, and barely got my rock in place on the scenery before it started to harden. It did crack some, however I was able to salvage my efforts by using a wet paint brush and small trowel to smooth out the cracks and fill them in. I was able to shape it and carve off some excess areas...

2) I'm not sure if I like the result. The result is kind of subtle...which might be to my advantage, however I guess I was hoping for a little more relief from the foil. So tonight, I'll give it a good hard look and decide whether or not to keep it, I'm sure I can knock it off with a hammer and chisel as I didn't prep the surface too well, just in case. Perhaps I'll try a different mold.

Maybe take some pictures first. Not too bad for a first attempt I think.

[nachoman]

Harold (hminky) had a good tutorial using ceiling tiles on his website, and that is probably the one you are thinking of. Unfortunately it seems to be offline (!).

All rock types can show layering. I've seen granite weather into a layered appearance because of a paralell fracture pattern and successive lava flows or volcanic ash deposits that make a distinct layered pattern. And I have seen sedimentary rocks that make relatively massive homogeneous cliffs, especially limestone and sandstone. The layers come about when the sedimentary beds have a variation in texture from coarse to fine or a variation in composition. Often sandstone has coarse and fine layers, or has mudstone intermixed, and as the different layers weather differently, they produce the layered appearance. Geologists recognize rock units as ledge formers or slope formers, with weak layers tending to form slopes and durable layers forming cliffs. Metamorphic rocks can also show a strong layered appearance, but in those cases the rocks are almost always folded or tilted.

The height of your individual "layers" really depends on the rock units you are modeling. In the Grand Canyon for instance, many of the rock units are hundreds of feet thick, and are relatively homogeneous from a distance. That means your scale "layer" needs to be hundreds of feet thick. Other rocks may show distinctive layers on a scale of only a few feet. That ceiling tile method looks good for rocks that have narrow layers, but I would try hand carving foam for rocks that have thicker layers.

For non-layered rocks, plaster castings in rubber molds is perhaps the best compromise for speed and cost. The drawbacks are that they are often too jagged and generic looking. That's what I used on one half of my layout. While they look adequate, they also look rather generic. I just didn't want to spend the time carving a more accurate representation out of foam blocks. The rock molds (and crumpled aluminum foil) often look best in places where the hillside has been blasted away for a road or railroad cut. Of course, how you arrange and paint your rock castings can also go a long way into improving their appearance.

[nachoman]

Glaciers are very effective eroding agents, and are pretty non discriminatory at rounding over any rock type. The action of a glacier is likely to obliterate many textures inheirent to certain rock types, as the glacial features dominate the overall landscape appearance rather than the rock features.

You may want to try rubbing a wire brish along your plaster rocks to give that rounded texture. Run the brish in one direction only, paralell to the path of the glacier. This would not only round over the jagged rocks, but also produce stiations indicative of glacial erosion.

[ocalicreek]

Harold (hminky) had a good tutorial using ceiling tiles on his website, and that is probably the one you are thinking of. Unfortunately it seems to be offline (!).

Harold is probably changing scales again (or creating yet another new scale designation) and rebuilding the entire site to reflect the changes.

As for rocks, I have used home-made rubber molds and still have a few of the 'masters' that I collected to make them in case I wanted to make more. Been carting those rocks across the country for years now.

The issue I have found with using these molds is two fold - one, you end up with a wall of hand-sized lumps that need to be blended together somehow, or two, you get a hand-sized outcropping here or there with greenery in between. The real problem comes from the size of the mold and a lack of knowledge about scenery in the area a person is trying to model.

One of the better solutions I have seen is the variety of mold sizes and shapes made by Bragdon Industries. Their molds are designed for use with expanding foam resin, but I think you could use plaster as well. It is still up to the modeler to place the rock castings on the layout and integrate them together in such a way that resembles reality and not the 'clone' function on a graphics program.

Another idea besides what has been mentioned so far is using lightweight spackle. I have not tried it in a mold yet - my fear is that it would stick to the mold and not release without destroying the detail of the mold itself, and applying a mold release agent wouldn't work since you have to spread the spackle in the mold with a knife. However, techniques like the foil technique or simply turning a good rubber mold inside out and using it to press the texture into the setting spackle may have more promise. The latter is what I intend to try on my layout when I reach the scenery stage...hopefully later this year.

Galen

[ocalicreek]

Tetters - here is a link to the Bragdon site:

<!-- w --><a class="postlink" href="http://www.bragdonent.com">www.bragdonent.com</a><!-- w -->

Apparantly the molds can be used with either the expanding foam resin or plaster.

Galen

[P5se Camelback]

... As for rocks, I have used home-made rubber molds and still have a few of the 'masters' that I collected to make them in case I wanted to make more. Been carting those rocks across the country for years now. ... Galen

Galen ... I have been doing the same thing! One of the boxes labeled "LSW" (and a number) is also labeled "Strata." If my now-former wife had know that it was a box of rocks, she never would have permitted them to be put onto that first moving vanback in the mid-eighties! (They had been collected in the seventies and already had thousands of miles under their tiny little belts!) She always complained that the reason it cost so much for us to move each time was the weight of the incredible number of hard bound books that I have been carting around with me, back and forth, from coast to coast since the mid-seventies. If she had known part of the weight was a box of rocks, there would have been a rather nasty "discussion," I'm sure!

The "Strata" is question are all rocks which display 1:1 reality in miniature, both igneous as well as sedimentary, all gathered in several of the counties in Northeastern Pennsylvania, the geographic home of the Lehigh Susquehanna & Western.

Over the years, I have pulled numerous molds from those rocks -– using a build-up of several coats of latex + a layer of latex-impregnated gauze (for strength) + several more coats of latex and the molds work beautifully. Each mold also has a plaster "backing" that it can sit in while the plaster is poured into the mold and begins to set up. They actually look a lot like the ones pictured on the Bragdon Enterprises web site.

[I still have that box labeled “Strata” and all of its contents … it is one heavy box!]

[Sumpter250]

The rock in this picture, is "hand carved":
   
I start with an "oatmeal consistency" of Hydro-cal, and as it begins to harden, work in the rough form of the rock strata. Then, as the hardening continues I use finer, and finer yet, "tools", to work in the strata, cracks, broken pieces. When the Hydro-cal is fully set, I use some old dental tools, to work in the finest seams, cracks, strata lines.
Very thin washes of browns, tans, black are then used to color the rock ( I'm looking for gray-dark gray colors ).
I work in sections that are about 7" (avg) wide, it's fairly easy to lay the next section up, and blend it into the previous one.
It actually goes almost as quickly as setting up molds, mixing and pouring plaster,waiting for the molded plaster to cure, and applying the cast rock to the scene. Even here, some carving might be necessary to blend the cast rock into the scene, or blend separate castings together.
I also did this at the club layout, and was about to vacuum up the debris, when one of the members suggested leaving it in place, coloring it, and securing it with a water/white/glue/detergent mix. The debris made an excellent talus pile, and looked very natural. since then I've left the pile where ever I've carved the rock.

[ocalicreek]

Wha...huh...OH, you want us to look at the rocks in the picture! That purty little mallet is just too nice a distraction.

The same goes for working with the lightweight spackle. I think it's a little trickier to carve than plaster, since it's a little 'stickier'. But dipping your carving tools in water regularly as you work alleviates this problem tendancy.

Also a really nice thing about the spackle is that it stays the same color when it dries. I tint it with black acrylic for a nice gray color, but any earth tone would work. After carving some rocks once, I spread the remainder of the spackle on a plate and let it dry, then broke it into boulders and talus.

Galen