In the August issue of MR, Step By Step feature, Pelle describes casting tunnel portals common in the Tehachapi Mountains area. I'd like to try this as I'm modeling the same area on my layout and will need to create 8 portals.
He describes using alabaster (dental) plaster for these castings. Unfortunately there was no reference as to where we might find this plaster other than Pelle says he found it in a "craft store." So far, I have not found an Internet source, at least in the US. So....does anyone have a source they might share? Hobby Lobby seems to have only plaster of Paris.
In the photos of the finished casting going along with the article, a prominent feature of the finished portal is an approximately 1/4" lip across the top edge of the portal. How this is achieved is not explained in the article. I'm thinking this might have been just a strip if the same styrene used for the mold, glued across the top edge of the casting?
john
I was disappointed that the cover showed a picture of a cut stone portal but the instructions were for a flat concrete portal. Could I use stone textured styrene to make the mold for a more elaborate copy and has anyone done this with success?
The type of plaster isn't that critical. Use whatever's available. Something like a concrete tunnel portal doesn't require rendition of fine detail, so a product like alabaster or dental stone isn't really required. I've used plain old casting plaster for such things and it works fine.
As for the lip across the top of the portal, build up the bottom of the mold with a piece of styrene that's as thick as the lip you wish to represent, then build the edges around it, leaving a space between the top of this extra piece and the top of the portal. This arrangement is shown in the article photo for Step 1, but isn't explained (see the 1/4" measurement shown at the top left of the photo).
Rob Spangler
I needed a few tunnel portals. I bought one from Woodland Scenics, and then I used liquid latex rubber (also available from WS) to make a mold from that portal. Then I cast them with Hydrocal. They come out very well.
It takes an iron man to play with a toy iron horse.
The capping stones are not nec to add to the mold itself. The mold can be made easier and those caps can be installed using styrene or stips of Hydrocal (cast a panel and rip to width required- bandsaw is excellent for this) I perfer working w/ Hydrocal for castings, just like the properties of the material. As for cut stone over flat concrete, I was quite lucky to have a real expert, Jeff Adam of Motrak models in the club during all this casting work. he would carve a master to fab a mold in RTV. I ended up w/ dozens of castings of cut stone to match the WS portrals/ retaining walls. I believe Jeff (Motrak) offers these cut stone, rubble and block cast panels. Other simpler castings I will fabricate by building the appropriate mold. Various textured sheet material can be laid in the bottom to simulate differing textures to the finish of the casting. One in particular that works well is that sheet "crinkled" foam packaging.
This arched bridge was done w/ the cut stone panels glued to 1/4" ply substrate. The arc was cut into the ply and the panels cut larger allowing for the arch/ keystones space to be glued. the capping stones are ripps of hydrocal placed to match the WS portals and retaining walls.
The long retaining wall is modified production molds. Height, panel width and caps altered on a master and new mold of RTV.
This abutment done by club member fabricating stepped mold by stacking acrylic sheets within the mold.
I would like to note: A good portion of the castings shown are basically the dried/ cured color of the "dyed" Hydrocal. I find it much easier to add powdered masonry dyes to the dry hydrocal and adjust that dried color before mixing. If you add dyes to wet plaster they are far too dark to guess the dries/ cured result. (think of tile grout- how it returns to it's origional color once dried)
Once castings of structure or rock is placed final coloring, staining and weathering can be done.
You can see some of the scoring, cobbling, chipping. I find that hydrocal works best for doing this. Carving is done mostly w/ #11 blade and chisel. To aid in heavy carving simply wet the casting and it will carve quite easily. Cobbling, chipping is better done totally dry.
Modeling B&O- Chessie Bob K. www.ssmrc.org
eaglescout I was disappointed that the cover showed a picture of a cut stone portal but the instructions were for a flat concrete portal.
I was disappointed that the cover showed a picture of a cut stone portal but the instructions were for a flat concrete portal.
You do know that the portal on the cover was on someone else's railroad?
Maxman,
No I didn't. I guess just like a good deceptive political advertisement it led the reader to believe that the instructions would be for the portal shown in the cover photo. Another poster explained he used a commercial portal to make his own mold so, I guess that is what I will try. I wonder if that is legal. Like making a copy of a CD or DVD can be illegal in certain circumstances.
eaglescout Maxman, No I didn't. I guess just like a good deceptive political advertisement it led the reader to believe that the instructions would be for the portal shown in the cover photo. Another poster explained he used a commercial portal to make his own mold so, I guess that is what I will try. I wonder if that is legal. Like making a copy of a CD or DVD can be illegal in certain circumstances.
If it's for your own use it should be fine. If you were to use the mold to make more copies for sale, that would be illegal.
Its hardly deceptive. Its pretty straightforward actually.
Its not illegal. Its pretty much the literal definition of fair use.
eaglescoutI guess just like a good deceptive political advertisement it led the reader to believe that the instructions would be for the portal shown in the cover photo.
I figured the cover image was for a layout story, and the article blurb didn't say anything about that portal specifically. It surprised me a bit to see on this thread that some readers expected the two to be linked.
Another poster explained he used a commercial portal to make his own mold so, I guess that is what I will try. I wonder if that is legal.
The laws on this point are fairly clear. It's normally permissible to make a copy for your own private use, but you may not distribute any such copies to others, even free of charge.
I was also under the impression that the portal building story was to be fabrication of the cut stone portal. I was actually hoping that someone had come up w/ some ingenious method to cast them and not to have to go though the time consuming route I had to.