Can you spread plaster directly on the foam or is the cardboard grid/newspaper/masking tape layer essential? Will it stick? Will it be more likely to crack?
I’m carving the mountains into near finished shapes, so I don’t have contour steps that need filled, just the final frosting layer to harden the terrain, provide a glue surface for vegetation, allow for color and to create terrain detail like gullies and rock outcrops. How thick can the plaster layer be before you run into problems? How thin before that causes problems? How far a distance are you comfortable spanning with plaster only, like a 1/8" crack between foam sections or a three inch header for a tunnel entrance?
I’ve got three sections of ridgeline that will end up just sitting in place, removable to allow access to the tunnel and staging system underneath. These run a foot to a foot and a half wide at the base, a foot to to two and a half tall feet at the ridgeline, and from two to four feet long. The planned approach is to glue the two inch foam layers together for these monoliths, but not to glue the whole section down. What’s the ideal plaster thickness, to balance between durability and weight? Since the sections join at ridge intersections occur, the plan is to camoflage the joints with evergreens, since the trees grow hiogher near water. What about above treeline? Most of the track is accessible from around the edges, which are largely open behind removable fascia board, but early operations with the mountains blocked out indicate that occasional access will require removing the mountains from time to time. I’ve read a lot about modern terrain building, but haven’t really seen this subject covered in depth. Any tricks here from the school of hard knocks?
Any downside to including pigment in the plaster mix? I’d like to match finished colors as nearly as possible, gray for rock, yellow green for lichen above treeline, reddish brown for bare dirt, and a deep green for eventual pine forests. That would allow
I use pre-mixed drywall mud over foam for most of my scenery. This however needs fairly close tolerances between the foam sheets to work, as it tends to shrink and crack when applied in thick layers (over an 1/8").
Regular plaster can be mixed to any consistancy you like, although mixing at other then the recommended 2:1 ratio can effect the final strength and hardness. A stiffer mix will slump less.
Adding pigments to plaster can effect it’s setting time as well as it strength and hardness. This depends on the pigment used. But in any case you do want to use some type of water based coloring.
Plaster will not support inself without some sort of substrate. Be it foam, cardboard, newsprint, or paper towels. It can be applies right over the foam. Using a slightly stiffer mix will help it stick better. So will rubbing it in with your fingers, which is what I do with drywall mud.
Plaster soaked paper towels or the plaster inpregnated cloth can span open areas over 4 inches, provided they have some support until the plaster sets. A single layer is self supporting after the plaster has set, but two layers is better.
I also use the light weight dry wall mud. I fill big cracks with it. Sometime the shrinkage takes a light second coat, but many times the cracks look good as part of the rock strata. The one danger with the premix is that the first coat of paint, regardless of type, needs to be put on with little brushing because the premix will disolve if scrubed. Many coats of wash work and there is less disolving with each coat. I am slowly learning to get good results with it, though I am also learning to get good results carving directly in the foam with no plaster, only many washes of acrylic paints.
Here is a real nice How To on scenery using lightweight spackling compound on top of foam. Since the spackling compound never completely dries, it’s almost impossible to crack, and can be reshaped later on if you want to change something around.
I’ve been using a skim-coat of Gypsolite directly on foam with good success. It is a rough, gritty surface that looks very natural, and takes paint, ground foam and flocking well. Drywall compound is OK, too, but I don’t like the surface texture as much. I mix cheap dark brown acrylic paint into the Gypsolite to give me an earth-tone base.
There is no need to apply thick plaster. Build up and carve your base to the contour you want and cover with plaster-soaked toweling or the plaster gauze you saw in the hobby shop.
I use plain white paper towels or those brown C-fold towels you see in men’s rooms. Mix the plaster to a thick soup consistancy, dip pieces of towels into the mix and apply to your base structure. Support with crumpled newspaper if spanning more than about 1". Remove the newspaper after the plaster dries.
You can pre-color the plaster with powdered pigment paints from an art supply store, but the pigments can affect the drying time. They might also make the plaster more brittle. Food coloring works, but is difficult to control the color tint. Acrylic-based paints will work, but some colors won’t mix evenly and the plaster won’t set properly.
The plaster towel method allows you to have a final layer of very thin plaster that is amazingly strong after it has cured. It allows you to add plaster castings to those vertical surfaces using plaster, acrylic silicone caulk, white or yellow glue and even hot melt glue.
When you coat the removable sections of your mountains, use plastic wrap, like Saran Wrap, to cover the bottom unmovable sections, put the mountain top in place, and apply the plaster towels to the mountain tops, allowing a slight overlap (less than 1/2 inch) onto the plastic wrap. Leave it in place until it dries. When fully dried, you will have a very thin lip on the mountain top that will help disguise the joint.
Keep any plaster applications and castings thin. Thick plaster may crack after it cures and adds wieght to the layout.
Thanks for the info, guys. I still have few days carving yet to go, more if I turn out terrain I don’t like and have to do it over, and I’m going to let it sit for bit to make sure it’s the way it should be before casting it in stone.
A handy carving aid I discovered (but you all probably already know all about) is wooden shish kabob skewers. They hold the layers tight together for blending them smooth, one to the next, but can be removed for disassembly, unlike glue.
It seems like paper towels would just fall apart with thick soup consistency liquid dripping from them, but if you guys say it works, that’s good enough for me.
I’ll put some pics up when Photobucket lets me out of the penalty box.
Why in the world would you want to cover perfectly good foam with plaster? After you’ re done carving, sanding and shaping the foam, you’ve already GIT a perfectly fine base layer for paint, ground foam, trees and the rest of your scenery. Why go through all the extra time, effort and expense to slap down some plaster or gauze sheet?
“There’s cracks in my foam joints”. So add some latex caulk to fill them.
“The final contours aren’t right”. So keep sanding/carving.
“I need rock outcroppings”. So either wood glue on some molded plaster rocks, or learn to carve the foam to look like rocks.
“I need final landscape effects like gulleys”. You realize that they’re easier to do with foam than with plaster, right?
One added benefit of foam over plaster as a top coat for a layout’s scenery base: foam is stronger. Whack a plaster base with a hammer and you’ll end up with a crumbling hole that will take several hours to fix. Beat the snot out of a foam base, and you’ll end up with a few more dimples which will add to the randomness of the terrain.
Trust me; there’s absolutely ZERO reason to cover foam with plaster.
How about transitions from foam to other things such as plywood?
I can buy spackling compound way cheaper than foam. If you use less foam, there’s less cost involved. That stuff ain’t cheap, you know?
I use it all because in nature, no two hilsides look alike. For large areas, straight foam sure is easy. To fill little areas between grades (I have cookie cutter sub bed) newspaper and gauze is fastest, but putting in the rock casts is harder. For large rock cliffs carving in the foam is becoming my favorite. My floor to ceiling model of Yellowstone Canyon will be pure foam.
I agree with Ray that you don’t really need anything over foam. A hot knife, a surform blade, a light saw, a carpet cutter, a craft knife, and sanding block all do a good job of cutting and shaping foam, and you can make almost any non-dense material look like rocks with the right materials and technique. By the way, my favourite foam shaping tol is one of those wooden-handled wire brushes. Remove the scraper if it comes with one attached on the nose-end, and then use the longest strokes you can to shape contours, road bed, streams banks, beach fronts, etc.
If a gap appears between layers of foam, and you don’t want to go to the trouble of dealing with it as in the previous paragraph, use a single layer of plaster cloth cut in tthin strips, or use the mud-like product that will not make it look like you patched with a sandy or gitty material. Once you paint it all and pour ground foam, there will be no hint of the gaps.
Before it’s all said and done, I’ll probably use all the techniques discussed in this thread, and maybe some others too. The area being modelled is complex terrain, a very old magma dome base, heavily weathered from around 30,000 feet tall originally down to nearly flat, then built up by a long series of volcanic explosions, leaving very light and crumbly rock exposed to the elements for around 26 million years, where some sections eroded very quickly and others much more slowly.
I don’t have any decent pictures of the exact area this layout represents, but these were all taken within ten miles of that drainage and show how the terrain varies widely:
There are areas where I’ll probably be able to paint directly on the foam, and other areas where a medium that goes on plastic and then dries to a hard surface will be necessary.
The cost of foam hasn’t been a problem, from building this house I have green and blue foam in two inch sheets, from my mom’s craft stuff which dad was going to toss out after she died, I have two inch white foam sheets, and from my old marine construction days, I have the big logs of foam used to float piers and docks, 12" by 24" by 96 ". Sheetrock mud is easy to come by, and I have a big box of plaster of paris from my old layout circa 1970 that’s still in good shape. In a pinch, I’ll just ooze a dab of Crest toothpaste on there and work it till I like it, that stuff dries harder than rock, at least it does when the kids slop it on the sink, anyway.
It’s great having a place like this where people can discuss different techniques, because I will probably need all of them.
Actually, I don’t know. Foam’s cheaper than plywood, so I use as little ply as possible on my layouts. And foam’s even cheaper once you also factor in the traditional cardboard/staples/screen wire/newspaper/plaster terrain building technique.
But, if you ARE transitioning between plywood and foam, then joint compound would be a good choice. Just not over the entire layout surface.
I know sheetrock mud sticks to wood well, too well in fact. I’ve spent a lot of time cleaning up after messy drywallers trying to get clearance to set doors and put in the trim carpentry.
It takes a chisel to get it off, and even then I’m usually cutting the mud, not separating it from the wood, leaving a thin layer still visible on the framing.
