Still a new guy. I would like to do some scratchbuilding and use plaster to make castings for a road bridge, and some walls for buildings. I am a woodcarver (other hobby) and can pretty much carve anything from wood but that is extremely time consuming when I could carve one part and make copies in plaster. I understand that there are several products out there from which you can make the molds for the plaster castings. I would like to see some opinions, guidance, tips, warnings, etc on the various products and how to use them. If it wasn't for all the help I get from this forum I would probably still be looking at an empty basement floor instead of an HO layout. Thanks
wdcrvr
One way to work faster in a case like this is to make a mold that uses a master that was made with textured brick, stone, etc sheets. You need not carve everythjing, just enough to blend things together. Not as easy as it sound, but with those skills it would help you get good looking results faster.
Remember that in many cases you need only one side of a culvert, etc because you either can't see the other side or it simply wasn't modeled. That area under the tracks you can't see? Might as well be a cardboard tube -- and it often is
Mike Lehman
Urbana, IL
A few things to keep in mind
-molds need to have a draft. Using silicone rubber to form a mold from a master can help. Any seams must be darn near water tight, or the plaster will simply leak out.
Use a plastic container a little bigger than the part to make the mold. To small and the walls will be to thin and prone for tearing or distortion. The container is reused to hold the empty mold.
Use a wisk to mix the plaster, and do it somewhere (the whole operation for that matter) where you don't care if it gets all over, including clothes.
Gently tapping on the mold can help removeair bubbles. I don't recommend the "bombs away" method someone tried on another site I frequent.
Let it set up before de-molding it. It will be brittle
Oh, an most importantly,
DON'T POUR ANY EXTRA DOWN THE DRAIN!!!
Let it set up in the container and simply squeeze and break it out of the container.
wdcrvrI understand that there are several products out there from which you can make the molds for the plaster castings.
You can use a 2-part rubber like Oomoo to make the mold.
http://www.dickblick.com/products/smooth-on-oomoo-30-silicone/
They've got videos on how to use it...
http://www.smooth-on.com/Silicone-Rubber-an/c2_1113_1136/index.html
Steve S
Have thought about making a cement bridge like so many that are around the state, mostly put in in the late 20's after the flood of '27 and are now being replaced as they are very narrow.
I was thinking of using styrene sheet for the general height and length. Then adding thin strips on the inside where the bridge had indentations. Since the top of the sides is slightly rounded, I thought I would have to sand that to shape. For the floor of the bridge a simple rectangle to glue the sides to should work.
The mold would have to be made in two sections due to the varring thickness of the sides. I would probably make a wooden holder to place the form in while pouring and letting it set.
Haven't tried it yet, but hope to someday.
Good luck,
Richard
"I would like to see some opinions, guidance, tips, warnings, etc on the various products and how to use them."
Hmmm.. large subject. I'll give you the Reader's Digest version.
Use a smooth slick bowl and a very plain spoon. Clean up is much easier. If you just wipe down the bowl with left over paper towel, well what is left and dried comes out with cold water, providing you have a slick bowel. Wet and push away from the bowl.
I am quite familar with Latex and silicone. But on a side note, I have made an extra side of a building just using Modelers Clay. I was kit bashing and needed an extra wall. LOL.. why not. Here's what I have found, lets see if I can find the finished product. (just wanted to share)
It was a fun test, I did use some extra strong plaster so that the windows would not break.
For thin, relatively flat plaster castings, two pours and an intermediate layer of stiff screen material will reduce the probability of cracks from handling. (Scale rebar, anyone?) Since I have a lot of masonry (tunnel portals, fill facing...) in my future I expect to use this trick.
Chuck (Modeling Central Japan in September, 1964)