OK all you model building wizards out there, this weekend I plan to build a 1:50 scale model of a 100 foot high concrete wall about 20 inches thick (model size 2ft high, 2ft long, and about a half an inch thick). I hope to cast the model in a material that will resemble concrete at scale. Does anyone have suggestions for a material to use? Will regular concrete work using a very fine aggregate? Or should I look for something else?
Thanks
Concrete should work fine. Use fine aggregate and put a thin wire mesh through it to act as rebar. I've used chicken wire or something similar. Add thicker wire at the higher stress areas.
Use Foamcore for your formwork. Secure it tightly with Duct Tape, and spray the inside with Wd-40 for a release. You can get a grainy texture by throwing in some salt down on the foamcore, for a board texture put in thin strips of duct tape so that lines are cast into the face, for a glassy finish lay down some plexi in the formcore. I suggest using Rockite, normal concrete gets too crumbly. I also agree with Andrew in using the rebar.
you can use Quickrete from Home Depot and if you can find polystyrene (styrofoam) pellets they will substitute well as an aggregate...they look like little rocks as long as the paste doesnt spall off and reveal their white color. dont use to much aggregate though or your 'crete wont stick together.
as for reinforcement, chicken wire will work but for something only 1/2 an inch thick you run the risk of exposed reinforcement since chicken wire usually doesnt lie completely flat. i would suggest a plastic mesh like some sort of low grade geotextile from the Depot Home and Garden department or the stuff used to hold stucco on walls...if forget what it's called---basically a plastic grid. makes sure there is a high void ratio in whatever you use so the reinforcement doesnt delaminate.
i'd love to see a picture of your form as well. if you make it out of wood, be sure to grease the sides with a lubricant so it wont stick.
Here's an image of a detail model I did out of plaster representing concrete. I realize it doesn't show off the texture very well, but it might give you a basic idea.
after pouring into the forms, you might need to do something to get the excess air out. moving a power sander across the form work usually does a good job of vibrating out any bubbles.
I used to take board, spray it grey (or use a grey paper board, forgot the name of it.) then scrape a mixture of gesso and pencil lead over it. let it dry then cut it up and use to build. it looks pretty good.
Rockite is the way to go. If you cannot find it you can sift concrete to eliminate all but the finest aggregate and then add plaster to the mix. This is basically what rockite is. This way the concrete will cure fast and will have the color/texture that you want.
Before you cast it though, think of how you are going to attach it so that you can cast something into the base if you need.
Consider this another vote for rockite (i.e. expansion cement) very smooth and gives you a scaled concrete look. Double thick chipboard works well too though maybe not for the scale your using.
Thanks for the help everyone. I think I found what I needed. At least for a first attempt. I bought a sheet of 1/2 inch Durorock cement board. One side is ugly with the Durorock logo etc.. but the other side has a quite beautiful light mottle grey concrete finish, pretty close to what I wanted. The main disadvantage is it won't have the form work lines but its for an interior model that will only be shown in my presentation in photographs and it's meant to be a little dark inside so I think it should work alright. If it doesn't look right, I'll start over and probably try the rockite. The ductape to simulate the formwork sounds like a great suggestion. I'll let y'all know how things work out.
Concrete Model
OK all you model building wizards out there, this weekend I plan to build a 1:50 scale model of a 100 foot high concrete wall about 20 inches thick (model size 2ft high, 2ft long, and about a half an inch thick). I hope to cast the model in a material that will resemble concrete at scale. Does anyone have suggestions for a material to use? Will regular concrete work using a very fine aggregate? Or should I look for something else?
Thanks
just use plaster and dye, add some sand for a bit more texture
pourstone
i think it will be almost cooler to see the form you construct for this model, design that thing like no ones business...
rockite
Concrete should work fine. Use fine aggregate and put a thin wire mesh through it to act as rebar. I've used chicken wire or something similar. Add thicker wire at the higher stress areas.
Floor Leveler. You can buy it at home depot and it dries a dark grey color that is very nice.
Use Foamcore for your formwork. Secure it tightly with Duct Tape, and spray the inside with Wd-40 for a release. You can get a grainy texture by throwing in some salt down on the foamcore, for a board texture put in thin strips of duct tape so that lines are cast into the face, for a glassy finish lay down some plexi in the formcore. I suggest using Rockite, normal concrete gets too crumbly. I also agree with Andrew in using the rebar.
I've had good success using window screen as reinforcement for plaster.
BTW, does it need to be good on both faces?
you can use Quickrete from Home Depot and if you can find polystyrene (styrofoam) pellets they will substitute well as an aggregate...they look like little rocks as long as the paste doesnt spall off and reveal their white color. dont use to much aggregate though or your 'crete wont stick together.
as for reinforcement, chicken wire will work but for something only 1/2 an inch thick you run the risk of exposed reinforcement since chicken wire usually doesnt lie completely flat. i would suggest a plastic mesh like some sort of low grade geotextile from the Depot Home and Garden department or the stuff used to hold stucco on walls...if forget what it's called---basically a plastic grid. makes sure there is a high void ratio in whatever you use so the reinforcement doesnt delaminate.
i'd love to see a picture of your form as well. if you make it out of wood, be sure to grease the sides with a lubricant so it wont stick.
Here's an image of a detail model I did out of plaster representing concrete. I realize it doesn't show off the texture very well, but it might give you a basic idea.
after pouring into the forms, you might need to do something to get the excess air out. moving a power sander across the form work usually does a good job of vibrating out any bubbles.
I used to take board, spray it grey (or use a grey paper board, forgot the name of it.) then scrape a mixture of gesso and pencil lead over it. let it dry then cut it up and use to build. it looks pretty good.
come on! real concrete is so cool!
Rockite is the way to go. If you cannot find it you can sift concrete to eliminate all but the finest aggregate and then add plaster to the mix. This is basically what rockite is. This way the concrete will cure fast and will have the color/texture that you want.
Before you cast it though, think of how you are going to attach it so that you can cast something into the base if you need.
Good luck.
Consider this another vote for rockite (i.e. expansion cement) very smooth and gives you a scaled concrete look. Double thick chipboard works well too though maybe not for the scale your using.
Thanks for the help everyone. I think I found what I needed. At least for a first attempt. I bought a sheet of 1/2 inch Durorock cement board. One side is ugly with the Durorock logo etc.. but the other side has a quite beautiful light mottle grey concrete finish, pretty close to what I wanted. The main disadvantage is it won't have the form work lines but its for an interior model that will only be shown in my presentation in photographs and it's meant to be a little dark inside so I think it should work alright. If it doesn't look right, I'll start over and probably try the rockite. The ductape to simulate the formwork sounds like a great suggestion. I'll let y'all know how things work out.
Just use motar mix because it is a form of concrete so noe dye needed and maybe just maybe you can have concrete look like Alvar Aalto makes it look.
I ended up using the Durorock cement board. Here's an interior shot (the whole point really).
Thanks for all your help. Made some notes for the future.
i was waiting for someone to suggest durorock, its what a contractor would use when he needs the "concrete look" as well. ha too funny
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