Scenery
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Buildings
Constructing a Mine and Ore Processing Plant Out of Concrete
Apr 30, 2008
By Ray Turner |
Author
Bio
Ever since I built my Mystic Mountain Railroad there has been this bare hillside with a siding next to it that I thought would be perfect for a mine and ore processing structure. This winter I finally got around to constructing Mystic Mountain Mining and Manufacturing – 4M (“One better than 3M”).
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 Mystic Mountain Mining and Manufacturing (One better than 3M) Ever since I built my Mystic Mountain Railroad there has been this bare hillside with a siding next to it that I thought would be perfect for a mine and ore processing structure. This winter I finally got around to constructing Mystic Mountain Mining and Manufacturing – 4M (“One better than 3M”). I could have used acrylic as I did for my roundhouse, but I wanted to try casting concrete. I first saw this technique at a National Garden Railroad Convention several years ago and used it for a tunnel portal which came out looking very nice. Casting concrete allowed me to create walls of random shape with simulated wood siding. I could have cast windows and doors into the walls as well, but I decided for the simpler approach of gluing them on afterwards. My objective was not to model a specific prototype or even model a “correct” plant. I wanted to create an interesting-looking building to fill a space and to provide an industry for my railroad. I had been running an ore train for years. Now, finally, it would have a place to take on its cargo.  Site for mine building Create templates for the walls
Since ore processing plants (aka “stamp mills”) were usually located on hills to take advantage of gravity, the first step is to make some cardboard templates of your hillside for the side walls. To make the structure look less boxy, I put a break in the roofline. In my case the front and back walls were rectangular, so I just took measurements and didn’t need templates. Your terrain may be different.  Templates for side walls to fit land contour
Create forms for the walls
The forms for the walls are made using 3/4” or 1” thick extruded foam for the base and sides. This foam is usually pink or blue and can be found at larger construction supply stores (e.g. Home Depot, Lowes) Using the largest cardboard template made above, cut a piece of foam at least 6” larger on all sides. Place one of the templates with the outside of the wall face down on the foam sheet and trace the outline with a marking pen. Now we’ll cover this area with the “casting masters” - plastic sheets with the texture you want on the walls. I used a clapboard surface which is horizontal planking where the top of each plank is covered by the bottom of the plank above it so that water will run off the wall and not get inside. This is important because it means there is a top and bottom to the sheets. Make sure to position these sheets horizontally – perpendicular to the front and back sides and not aligned with the roof or earth sides. Also, the top and bottom are reversed because the sheets are used upside down – the sheets are a negative of the wall we’re going to cast. At the risk of redundancy, identify the top and bottom of the casting master and place the top upside-down to the top of the form. Using straight pins with large plastic tips anchor the sheets to the foam base. Use these pins sparingly and try to put them outside the wall area as much as possible. You’ll need to use pliers to force them through the casting masters. Make sure they stick up above the foam base by about 1”.  Simulated Clapboard casting masters Place the cardboard template over these casting master sheets (cut/punch holes for the pins, as needed). Start with the longest, straight sides and cut foam pieces about 2-3” wide to make the sides of the form. Use 1 5/8” self-drilling screws to anchor the sides to the base. For smaller pieces you can use pins to hold them to the base. The bottom of the wall is probably free-form to match the earth on site.
Pull the cardboard template out and draw this edge on a piece of foam and use either a hot wire cutter or a box cutter to cut a foam side piece and screw it into place. I wanted an opening in one wall for the trestle for ore cars dumping non-bearing rock. Holes in the walls are created by cutting a foam block to size and anchoring it to the base. (Pins are probably best here for small openings.) Look over the inside of the form for gaps between side pieces and each other or the base. Fill these with Vaseline. Perfection isn’t critical; a grinder with a diamond blade will be used to fix any imperfections later.  Form with wire mesh There’s a refinement you can do to the corners of the walls, if you choose, to improve appearance. When you butt a side wall to the front and rear wall, there will be the 1/2” exposed end of one of these showing. You can reduce this to 1/4” (which will be covered later). To do this use a 1/4” square piece of {plastic, wood, foam core board, . . . }and secure it with pins 1/4” above the casting masters on the side walls of the form (not the top and bottom). Alternately, you can skip this step and, using a diamond cutting wheel in your Dremel, grind a clapboard pattern into the wall ends. Or you can skip this altogether, if the building doesn’t need to stand close scrutiny.
Cast the walls
The casting needs to be done on a flat but flimsy table, not a solid workbench or on the ground. This is because we have to vibrate the table to drive out the air bubbles from the concrete. You can make one from a 1” sheet of plywood with 2x4 legs loosely attached. Note that the table must be flat or the walls will bow out in the middle. Because of their size and weight, these walls need steel reinforcing. Use 1/2” hardware cloth cut to fit inside the form. Cut these 1/2” – 1” short on the top and bottom of the wall and 1” long on the sides of the walls. Flatten this mesh as best you can except for bending the wall sides up 1” inside the form. These will stick up out of the walls and be used to tie the side walls to the front and back walls. For large walls I also cut 1/8” thick by 1/2” wide steel strips to place every 8-12” in the form. Remove the steel reinforcing and mesh and spray the inside of the form with Silicone spray (mold release).  Form with steel bars added for strength I used Quickcrete Vinyl Concrete Patcher. Compared with other concrete products, it gives smoother surfaces, is stronger and is easier to pour. Mix enough vinyl concrete to cover the bottom 1/8” of the form; mix this very soupy. Use an old paintbrush to work this mix into the bottom to cover it completely and get any bubbles out. Mix a similar amount thicker -- to the consistency of pancake batter and spread it evenly into the mold. Use a jigsaw (without blade), or some other vibrating tool, against the table for 2-3 minutes to get any air bubbles out of the mix – you will see small bubbles rise out of the concrete. Place the wire mesh into the mold and any steel strips. Mix twice as much concrete as before to the consistency of pancake batter, pour it into the mold, and spread it evenly. Make sure the mesh is still located correctly. The walls will be about 1/2” thick. Vibrate again for 2-3 minutes. Carefully pull out any pins that are inside the wall.  Concrete poured into form
Cure time depends on temperature; about 24 hours in the hot summer months and 2-3 days in the cold winter months. Scratch the back of the wall with a screwdriver or putty knife. You should be able to scratch it, but not deeply. This is called the “green” stage – strong enough to handle (carefully) but soft enough to carve and clean up. Remove the sides of the form. Run a wide blade “putty knife” around the edges between the concrete and casting master sheets. Use the putty knife in the middle of the long side to slowly lift the wall free of the form. If it shows any signs of crumbling or cracking, stop and wait another day. Turn the wall over and let it rest on the wire mesh sticking out the back. There should be only a few small bubbles in the finished surface, if you vibrated it well enough. Use carving tools and a diamond bit in a Dremel to clean up the surface imperfections if you wish. Let the wall cure for a few more days to gain strength. Meanwhile, clean off the casting masters and prepare a form for casting the next wall.  Removing wall from form Paint walls and add windows and doors, lights
I painted the walls with two coats of dark red house paint (not too thick, you don’t want to obscure the surface detail). Then I glued on windows and doors. In doing this I assumed certain (multiple) levels of flooring in the building. I put a row of small windows on the roof break wall, which would be high above the floor at that point. I drilled holes in the walls and added Christmas tree lights to light the exterior of the building. I use strings of five 2.5V lights in series run off 12 VAC. For added interest I wanted to make it look like the plant was built on a stone foundation at the front. I used cut stone blocks from Stoneworks. I could have cast these into the walls but it was easier to glue them on afterwards. Four stones high (about 1”) gave a good appearance.  Side walls painted and decorated
Assemble walls on site
For my structure the walls used about 70 lbs. of concrete dry – probably over 100 lbs. when cast. So assembly in place was mandatory. First each side wall was “fine tuned” to the ground with a diamond blade in a 4” grinder. Then the side walls were propped in place with blocks and rebar and made vertical and the back and front walls put in place and wired to the side walls. Concrete was poured in a column in the corners of the walls to create a very strong joint. After that, forget about moving this building. (You could skip this step sacrificing rigidity in favor of future mobility.) The small front wall at the roof break is glued into place with construction adhesive. Finishing nails through drilled holes provide additional strength to the joints. After the concrete cures, caulk the joint seams. Glue 1/4” angle styrene on the building corners and touch up the paint, as needed.  Mine building assembled on site
Build roof
I made my roof out of 3/16” acrylic because, 1) it’s light (concrete would be very heavy), 2) you can see through it (you’ll see why later), and 3) I had some on hand. Measure the roof sections to the outside of the walls. Don’t be surprised if the structure isn’t perfectly rectangular. Add 3/8” on all sides for roof overhang and cut the roof pieces. Place each roof piece where it goes and, using a marker pen, draw the outline of the inside of the walls; they won’t necessarily be of uniform thickness. On the bottom side, glue double-think (3/8”) scraps of acrylic here and there along the lines delineating the inside of the walls. These scraps will position the roof correctly on the walls and keep it from sliding off. Since I had extra scraps of acrylic, I added stiffeners as well. I doubt the roof would develop any sag anyway, since the deformation temperature of acrylic is about 200 degrees F. After test fitting and adjusting the roof, I glued simulated steel (Aluminum) panels to cover the roof and painted them to appear rusty. I glued some scrap steel on the bottom of the largest and highest roof panel to keep the wind from catching it and blowing it off.  Front roof section  Rear roof section
Build extension
I put a building extension over the track for loading ore into railroad cars, and just to make the structure less boxy and more interesting, and I put this at an angle to the main building for added interest. To keep the weight down I used acrylic scraps to build this. Because of the angle, the left side is longer than the right side. I decided to use a gabled roof – again just to make it more interesting. Here I made a mistake. I should have made the side walls taller than the main building so that the gabled roof would be above the main roof, avoiding the “collision” of the two roof lines. Oh well, next time. I cut up some of the casting master panels I used in casting the concrete main walls and glued them on the acrylic side walls. I also glued on angle styrene to finish the corners. As before, I glued simulated steel (Aluminum) panels to cover the roof and painted them to appear rusty. I painted the side walls with the same dark red house paint. Then I added windows, doors and lights. The extension was temporarily supported on blocks and anchored to the front wall of the main building with small angle brackets. The other end of the extension is supported on posts and a footer on top of a small block wall. I used the same stone blocks as for the simulated foundation on the lower walls.  Extension painted and ready for door and windows Ore dump trestle
To add more interest I decided there would be a trestle with hand-push ore cars to dump the non-bearing rock from mining operations. On30 seemed perfect for this. I got a couple of Bachmann On30 V-dump cars and a 3’ piece of HO track (HO track is On30 gauge). I built the trestle with .188 square styrene for the posts and 1/4” thick styrene under the track. I covered the ties with styrene and carved something resembling planking into the top. I sprayed the whole thing with dark brown paint for protection. Then I hit it with a little earth color and boxcar red color lightly here and there and finished up with dry brushing some gray and bronze yellow acrylics on it, especially on top. I distressed the ore cars and painted them rusty and weathered them a bit. I glued them onto the trestle along with someone pushing each one. The trestle is anchored by tying it to a brass rod in the ground to keep it from blowing over in the wind. (We’re having 40-50 MPH gusts outside as I write this.)  Trestle for dumping non-bearing ore  On30 ore dump car on trestle
Add details
I added a coupe of stone stairways to the doors on the lower level. These also serve as places to put a person, and people always make a scene look complete. I added an exterior walkway from a door on the side wall to the opening for the ore dump track - just to add more interest – and another opportunity to add a person. I also added a door on the front of the extension with a landing and stairway down to the yard below – more interest, two more people. It must be lunch time ‘cause there’s a few people sitting on the wall chatting. I don’t know what they’re building, but those four guys are working up a sweat at something. I added two smokestacks - one on top of the roof and one on the side of the building, using left-overs from Pola kits.  Details added: support posts, stone wall, stairway, yard workers  People make the difference  Yard gang building something
Weathering
Put a little of the dry concrete in a can. Dip an old paintbrush into the concrete and dry brush it onto the building surface, working it into the surface. Brush more or less on to get the effect of weathered paint you desire. The moisture in the air will cure this into the paint over a few days. I decided to weather the main building but not the extension simulating new construction added on to old. The ore my plant is processing is a yellow-tan color. I mixed gold fines with stucco mix and spread a thin layer all around the dump trestle. I got some small tan-colored rock chunks and spread them around under the trestle and used a diluted mix of Titebond II glue to keep them from disappearing.  Completed 4M ore processing plant Other ideas
You could add a water tank on the roof or a flume to bring the water needed into the plant. You could add a mine hoist from the upper level. Or a mine portal on the hillside with On30 tracks bringing ore into the plant. If you have a lot of space, you could run a G scale mine train back and forth from mine to plant, although using a smaller scale makes the building look bigger. Outside the plant there’s the opportunity for mine tailings piled up, dumped into a valley below, or carried away by a flume. Materials
Quickcrete Vinyl Concrete Patcher: OSH, hardware store. Casting masters, stone blocks: Stoneworks (http://www.rrstoneworks.com/) Extruded foam sheets (3/4” – 1” thick): Home Depot, Lowes Silicone spray, acrylic caulk, construction adhesive: auto store or hardware store Steel hardware cloth, steel strips: hardware store, metal supply warehouse 1 5/8” self-drilling screws, long pins Stairs: Boxcar Bruce’s E-Bay shop People: On E-Bay from Hong Kong, less than $1/ea even with shipping, closer to 1:29 than 1:24 scale. I add a drop of paint for eyes, eyebrows. Tools
Wide blade putty knife, tin snips, box cutter, pliers, screwdriver 4” grinder with diamond blade Power saw (preferably table) Optional: Dremel with diamond cutting disk Ray Turner, Mystic Mountain Railroad (http://www.mysticmountainarts.com/MMRR)
| Construction Technique |
| Very interesting construction technique and especially interesting industry. |
| Rick Henderson - 04/30/2008 - 04:26 |
| Stamp Mill |
| Ray, You written a very clear, concise how-two article. Your result with this construction technique is first rate. Thank you for sharing with clear text and great pictures. |
| Jon D. Miller - 04/30/2008 - 07:15 |
| Techniques |
| Ray, This was a most enlightening construction. I'm about to start a Griss mill and can't decide on what material to use. This will help. Great article. |
| Gary Condry - 05/01/2008 - 14:10 |
| Concrete structures |
| Ray, Well done mate. I found your article on making the processing plant well written and easy to follow. Even with the name differences between what you have used in America and what we have in Australia, I found enough information from your write up and pictures to be able to source similar products here. Keep up the great work. |
| Dave Clarke - 05/03/2008 - 21:31 |
| Concrete Stamp Mill |
| Ray-- I really enjoyed your article. Would you mind telling us what you used for the doors and windows? Did you use commercial products or did you make them yourself? Thanks> |
| Steven Kamm - 05/07/2008 - 09:32 |
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