I am sure this has been asked many times before, but need your help. I am inserting hydrocal formed rocks, (I know many modelers on this forum use natural rocks from the mountains), but since this is my first layout, I am not at the level of modeleing than many on this forum are.
So here is my question. I am cutting into varous parts of my mountains (plaster) and inserting these hydrocal rocks. When in bunches, or agadenct to each other, such as a ridge, it becomes rather loose up there. The double layer plaster cloth gives in when you’ve got a horizontal ridge of rocks running side by side. Smothering the back of these rocks with hydrocal (which does consists of a mild glue, according to WS), insn’t good enough for a permanaent hold. I really want to avoid laying strips of plaster cloth around the these rocks, but thought that perhaps paintable silicone caulking would work the best? Again, I want to put a strong bond or adheseive. Is there a particluar recommendation on caulking? Does it matter:? Is silicone good? Clear? Thanks.
There are several videos that might help in the user videos section here. See blue area below posts.
First of all plaster cloth is not that strong on its own. if you plan to encumber you hillsides and cliffs with castings, you should make a solid backing. a 1/4" piece of plywood would be nice while many used the thick pink insulation underlayment foam materials.
I particularly like the one video that shows casting those molds as hollow, less massive castings. This involved paint brushing in the thick hydrocal and making sure that the mold’s detailed areas are all filled and not filling the mold, otherwise. From here they are broken up and added into holes and voids as needed filled with joint compound or hydrocal. painting and coloring comes last, of course.
That’s true. The plaster shell can be strengthened with additional coats of plaster brushed on and/or applied with your hands. It takes surprisingly little extra plaster to reinforce the basic shell. Once you’ve done that, many adhesives can be used for dry rock castings. Adhesive caulks work well. The exact type probably isn’t critical, as none of the adhesive should be visible when you’re done.
Any gaps around the castings can be blended with more plaster, which can also be chipped and carved away to blend the rocks into their surroundings. Additional plaster cloth doesn’t work especially well for that kind of thing.
I use Sheetrock brand patching plaster. I buy it in 18 lb bags and mix it myself. I use the 90 minute version so I have lots of time before it sets up. I use an old ‘cheap’ paint brush and ‘paint’ the soupy stuff over the plaster cloth hills. I also use it to fill in between the hills and rock castings. Once everything is dry, it is quite strong.
I use light weight Hydro cal for everything. I make the castings out of it , then spread some on the back and glue the casting to the wall. After that has set I take some on my finger to smear around the edges to blend the rocks to said wall, and to other castings. If you use the light weight Hydra-cal for casting the rocks they are not as heavy and it works quite nicely for gluing them to the wall.
I also like to use the method descibed by Lee, you can also place a partially hardened/ wet mold directly on the surface and press to conform to any irregular shape. By buttering up the backside w/ a fresh batch will help and any plaster tha oozes out can be smeared or wiped off w/ a finger.
Thin pours in a mold work well too, I have done this and buttered the backside of a hardened casting and pressed w/ enough force too crack the casting, just hold in place for a few minutes, wait about 1/2 hour then peal off the rubber mold. Any chunks that may break off and stay in the mold can be popped out and later glued on.
Instead of trying to “caulk” around molds, you can also glue on broken bit/ pieces of other castings, I will make a few castings just to have on hand to break up and even shape w/ diagonal cutters/ tile nippers to fit in the missing spots of the rock outcroppings…
I noticed you said you were cutting into your mountain (plaster shell) before putting the castings in place. You are weakening your shell when you do. I just put a gob of latex caulk on the back of the castings and settle them into place, Fill around them with like material, as suggested above. If you choose to use plaster (hydorcal) to attach your castings, be sure to wet your plaster cloth with a spray of water before applying the adhesive mix.
As an additional thought, you don’t have to use Hydra-cal brand. There are other brands that do the same thing. I believe the Light weight Hydra-cal is just plaster of Paris with ground up paper or something similar in it. I get my off brand stuff at Hobby Lobby, cheaper than the branded product.
I use a skim-coat of Gypsolite over most of my “natural” scenery. Gypsolite is a gritty plaster. I mix it thin, almost a slurry, and coat all the plaster cloth. I find it’s easy to work it between rock castings so it looks like the rocks are poking up through the “earth” rather than sitting on top of it. The Gypsolite gives me a rough surface that looks much more natural (to me, anyway) than plaster cloth or pink foam alone. I add a bit of brown craft paint so the Gypsolite, which is naturally a pale gray, comes out tan.
In that picture, I’ve already painted on a “camouflage” pattern using a thinned wash of green acrylic craft paint. After that, I apply talus, turf, ground foam, trees, tall grass and, if you look closely, a hillbilly out hunting.
Over the years, I’ve accumulated several different cannisters each of turf and ground foam, and different colors of field grass. I apply all of these by hand, using small pinches of each to create a non-uniform scene.
Richard has the right answer, I think. I would not cut into my mountains, if I were you. If you intend to attach rock faces to them, build them as smooth as you can and “glue” the rock faces in place with Hydrocal, Sculptamold, caulk, or some other thick substance. Any gaps around the castings can be filled with Hydrocal or Sculptamold.
An alternative that I have found very satisfactory is simply to cover my future rock faces with about a 1/2" layer of Sulptamold. When it has set up for a few minutes, I simply carve the rock detail into it with artists clay sculpting tools (available at art and craft stores like Michaels).
