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Thread: Terraforming with spray foam

  1. #1
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    Default Terraforming with spray foam

    I've used Great Stuff canned foam on my layout to build terrain, then covered it with Sculptamold and Durabond plaster.

    Advantages of spray foam over foam sheets are
    1) The stuff is Gorilla Glue with bubbles. It strengthens your benchwork as it binds to it.
    2) You don't need a flat surface to put it on. I cut up cardboard, staple it under the wood roadbed and on top of any plywood bench top at any angle I want, and apply the foam so it glues the cardboard to the wood. The result is surprisingly stiff, like foam core products.
    3) You can add more any time you want and carve away after it cures.
    4) It's not pink.

    Disadvantages:
    1) The stuff is Gorilla Glue with bubbles. Don't get it on your hands or any valuable part of the layout, like track work. Don't let it drip on anything.
    2) You can't create a flat surface with it, though you can carve a flat surface into it.
    3) You don't have much control over the expansion.
    4) It looks like snot.

    This is one of the last "protomolecule" areas of the layout. Over the years I've done sections, and when there is leftover foam in the can I add it to the next sections. 20 year old foam is dark orange on the surface (UV exposure I think). The first layer was added to cardboard stapled under the benchwork. I always add in layers. Add too big a blob and huge hollows form on the blob's interior.
    [IMG][/IMG]

    I use a serrated steak knife to carve the foam. 1st carving step is make sure there will be enough clearance next to the tracks to add Sculptamold or Durabond rockwork.
    [IMG][/IMG]

    One way to make a layout look realistic is to have consistent slope angles on all the man-made fills. I use a drafting angle and point the knife parallel to it when starting the cuts.
    [IMG][/IMG]

    Sculptamold and plaster won't stick to the slick cured surface of the foam. Cutting into it exposes the underlying open cells. Then when I start applying Sculptamold or Durabond I smear it into the foam and hear bubbles pop. That creates a good mechanical bond using the open cells as keyways.
    [IMG][/IMG]

    One advantage of using Great Stuff is you can always add to your terrain later. There are two issues here. One is there is no reason for that curve to be where it is on that mid-level track. I need a rock outcropping to justify it. The other is the changing slope between mid and lower level tracks on the left. There needs to be a retaining wall or a cut into solid rock.
    [IMG][/IMG]

    After marking the areas that need building up, I added about half a can of foam. This will expand over the next hour or so. Great Stuff's nozzle-end valve helps, but once its used the shelf life of the rest of the foam in the can is limited.
    [IMG][/IMG]

    In an hour the foam has expanded some. I misted it with water to speed curing. That also limits the expansion somewhat. Wet foam sticks to everything but once it skins over it won't stick to what it touches up to as it expands.
    [IMG][/IMG]

    It'll take a day or so to cure, at which point I can carve some more.


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    Great information, @NtheBasement!

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    I've used this once or twice, with mixed results (mostly due to my skill, not inherent to the technique itself). Nice to see a good thorough how-to on it!
    Never mistake a guy who talks a lot for a guy who has something to say...

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    Day 2. I carved the new foam, which makes a static charged mess. Now the curve in the track gets around a rock outcrop. I still have half a can of foam but no place to put it. The new foam is much more flexible than the old stuff, and so whitey bright!


    Durabond time.
    I don't use untinted plaster or Sculptamold because its white, which means any little nick in the rock shows up like a beacon. I've used Tempera, inks, and dyes to tint it but concrete tint is by far the cheapest option. There are not a lot of color choices but they are all sort of a rock color. One bottle colors a whole bag of cement so a little goes a long way.


    I added a dab of Buff cement color and two dabs of Charcoal to a Durabond mix of about a cup of water and cup and a half of Durabond. Then I added some yellow food color.


    Whoa, not the color I was looking for. It looks green! I know it will lighten up when it dries but this was not what I had in mind. I'm thinking this will be a layer of shale. Regarding the mix consistency, you want "whipped cream tips" to hold up. A vertical slope should slump a little but not a lot. And let the mix slake for a few minutes before applying to avoid lumps.


    I use a putty knife to apply the plaster to the foam. My layers run at a slant, and I try to do a whole layer in one batch so that the color and texture will match. I smear some plaster on, then smoosh it into the foam with my finger to get adherence. Then I add a thick layer, maybe a quarter to half and inch, depending on how deep I want to carve, with the putty knife held vertically. I leave some big divots that will will be carved out as joint lines later, trying to line them up across layers. Joint lines are weak fracture planes in the rock. For sedimentary though the layers are the key.


    Durabond 45 is supposed to give you 45 minutes of working time but in my cool basement it takes twice that long to start to set. Next time I'm getting Durabond 20. Once it sets up enough to not stick to a tool I start working it. My favorite tool is a screwdriver but for shale I'm mostly going with the putty knife. You can see on the left how it looks working when the mix is still a bit mushy. As it hardens you can get sharper and sharper detail, but it starts to crumble if you abuse it. An eroded face would not have the sharp features that a dynamited cut would have. I try to get continuous layers into it with the knife and add vertical joints by pushing in with the blade. I cut the tops flat to mimic the tops of layers.


    I don't worry about the bottoms of vertical faces or the more horizontal slopes as they will be covered with debris, soil and vegetation. Speaking of debris, save the carved up scraps. And rather than washing out your mixing bowl before the stuff sets up, let it harden and then break it up to create more talus and debris.


    Also you can see the thin stuff is drying to a color that comes closer to the foam's snot yellow. I'll add more layers with Durabond over the next few days and then get into limestone layers with Sculptamold.

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    Those rock carvings are looking great! I've just recently started using Durabond mixed with perlite as a top coat for ground work. I wasn't too careful with it as I figured it would be like hydrocal and I would just take an exacto knife to it after it hardened and change any shapes after the fact. Well, I found out this stuff is more like concrete than plaster and a knife won't even touch it when cured. I'll have to give your method of letting it set up for a bit and then doing a bit of carving and shaping while it's still soft. It seems like a better method than a hammer and screw driver.

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    Took a couple of days to get back to this. Saturday was actually nice, which around here means the sun is out (a rarity in SE Michigan in the winter) and it got up into the mid 30s, so I put 20 miles on the kayak. And yesterday, well, Bell's Hopslam arrived and my COVID beer drinking buddy (my daughter) helped me taste this year's batch. Tonight I've got an NMRA meeting which, ironically, got rescheduled to Monday nights from Saturday afternoons because so many of the members watch college football. It starts an hour before the championship game...

    The previous layer dried to a light yellow, a problem easily addressed with ink washes. I couldn't find Durabond and bought an 18 lb sack of Proform Quickset Lite 20. It seems very similar to the Durabond. I used a dab each of terra cotta, brown, and black concrete color and it somehow ended up pinkish. Stay tuned for the dry color, I'm guessing a very light pink.


    The Quickset 20 took maybe 45 minutes to start setting. I got a bit nervous about the "20" because it was setting up so fast when I started carving but it turned out just fine. I used mostly the putty knife, cutting along the bedding plane and adding vertical joints that crossed the beds.


    As the plaster hardens it gets more crumbly and you can get finer details. I usually save the man-made cuts for this stage. Lots of small light raps with the putty knife, across but mostly along the bedding plane. When things are dry I'll brush off the crumbs. Brushing now would make the rock look more water-worn.


    I'll probably add another layer today before the game. Er, meeting.

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    Great, now I'm getting ads for a spray foam contractor on a canoeing forum. Looks like Google's surveillance bots are watching us here. Lets see what I happens if I mention Ohio State Buckeyes.

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    Very nice looking rock work!

    You mentioned earlier about the foam carving creating a static-induced mess. We had a presenter at a NMRA meeting a while back who was talking about using styrofoam (which is really static-y) for landscapes, and her trick for handling this was to wet (or, I suppose more accurately, dampen) the foam down before carving. It worked like a charm in her demonstration. I wonder if a bit of dampening would also work with the Great Stuff foam...
    Never mistake a guy who talks a lot for a guy who has something to say...

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    It helps. I've misted after carving and before cleanup and vacuuming. I've even had to spray my shirt, the wall... Not sure what the isocyanate curing reaction is but it definitely sucks moisture from the air. Similarly if you look at the instructions for cyanate glues they specify dampening the surfaces to be glued.

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    For variety the next stratum is Sculptamold. Although initial application is similar to plaster, its has very different characteristics. It sets like plaster but also contains fiber and a glue, probably PVA powder. When it starts to set it has the consistency of clay but you can't carve it because the fibers tear out and you get fur instead of rocks. When the glue finally dries it is very hard and strong, not brittle like plaster, due to the fiber reinforcement. Another huge difference (and detriment) is you can't really apply washes because they don't soak in. I think the PVA migrates to the surface during drying and creates a skin that makes washes bead up. So I color it with a lot more color than the plaster. I'm hoping this black will dry to a medium gray.
    Also I like it lumpy so I don't let it slake before applying.


    I apply same as plaster, smearing some into the foam and then applying a quarter inch or so layer. This mix is actually too wet - it took a couple of hours to set.

    Sculptamold isn't as cheap as plaster. I bought a 50 lb box, probably enough for my whole layout, from a Dick Blick store an hour away for well under $2/pound. This is way less than the little craft store bags.

    Instead of carving Sculptamold, after it sets you shape it by pushing it in and around. In this case I mostly use the end of the putty knife to make the layers. Like plaster, as it continues to set you get sharper and sharper edges. But they are never as sharp as carved plaster.


    With Sculptamold the fineness of the detail is liimited only by your patience. If you keep going with plaster as it sets up harder, you start to crumble it. Sculptamold always has that weathered look to it due to the rounded edges.


    This mountain is also Sculptamold over foam. As it set up I emphasized the dents and wrinkles by pushing them in with a screwdriver blade to get the glaciated granite effect. Dramatic glancing light angles are a plus for any rock work.

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    In the last photo I see that @NtheBasement has succumbed to the temptation of photographing real rocks and claiming he made them with Sculptamold.

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    Snowing out so I got 3 layers done.

    Start of a Sculptamold strata. This brown color is Charcoal and Buff.


    The two layers of Sculptamold are supposed to model dolomite. At the top is a layer of Quickset. A lot of it will be obscured by vegetation.
    Once a layer is completely dry I can clean off the "crumbs" with a wire brush. Brushing hard along the grain also add grooves that mimic shale.


    The track now looks like it has a reason to be routed around that bend.

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