Pam cooking spray works.
One thing to remember about this stuff is that it does freeze and that apparently will destroy some of its properties. If it’s shipped in the winter you can’t guarantee it isn’t stuck in a trailer or something in sub freezing weather. My LHS won’t order it in the winter for this reason.
Anyone else have experience with this?
A number of years ago I made some silicone rubber rock molds off large lumps of coal. The surface of the coal lumps looked like miniature rock faces. I don’t know where you could find large coal lumps now since most coal now comes as small lump stoker coal. In any case, when I made the molds I painted 2-3 layers of the mold material on the surface of the coal lumps. I think I may have sprayed the surface of the coal lumps with wet water before I started to apply the mold material. While the mold material was still wet, I embedded pieces of cheese cloth into the mold material and then added several more layers of the mold material to completely encase the cheese cloth. When the mold material was completely set, I peeled off the molds. I dip the molds in wet water before adding the plaster. I made plaster casts from each of the molds. I numbered each of the castings and the mold from which they were made so I can better visualize what each mold will produce. The cheese cloth can be found in the dairy section of your supermarket. Actually it’s usually found in the paint section of the big box stores.
I’ve read about people maintaining the shape of their rock molds during the casting process by supporting them in a bed of packing peanuts. Think I’ve seen this in some of the MR How-To videos.
Bob
Hi from AUS, I used cheese cloth when making a mould recently of a tunnel portal. It worked extremely well and the finished mould seems to be extremely strong yet pliable for easy removal from the cast. Regards Johnca51
Yes! I did the same as you have done. I bought all of the rock molds that that WS sold and made some 80 or more molds. If you don’t put 4 or 5 coats of acrylic on the masters (I used acrylic because it is clean and dries fast). Bob Whitten
You said “if you don’t put on 4 or 5 coats of acrylic on the masters”. Do you mean you put 4 or 5 coats on the master?
Hello Kieth,
Thanks for the info,I purchased some 2 part mix from Aero Marine on your advise and i’m dying to try it out.
While its being shipped…Is there any other items such as mold release that i should have on hand before I try the process. Do you use styrene as a base to glue your part on?
Thank you in advance,
Hogwire
The Woodland Scenics portals are about an inch thick. They’re also wider and taller than I wanted. So, by making a mold and then casting a copy, I was able to make a thinner, narrower version that fit perfectly.
I also created molds for casting the walls and platforms of my subway stations. The originals were styrene sheets with square patterns on them. For the platforms, I just think that a Hydrocal casting takes paint better and looks more realistic than trying to paint and weather plastic to look like concrete. For the tile walls, I can curve and shape the castings by bending the mold around a form after the Hydrocal sets up, but before it hardens completely.
Hogwire, ah no. There is no prep for the silicone. Well I’ve never used it. I was looking for some old portal I bought to show you … it came broken… glued it… and siliconed it. As of now, I can’t seem to find it. If I remember correctly the master had a very light blue tint left over on it. Not enough to clean… and the remnant of the silicone was nil. Enough to paint it… without any concern. Although I did not paint the master. Its around here … somewhere. But since you asked the question… and directed it towards me personally… well I shall give you one demonstration.
This is important.
You have to mix the stuff up really good before pouring. If you don’t, you might end up with a blemish. SO~ … turn each jub upside down… and then back again. This stuff is so thick… you have to do it… for about 2 hours. Well if you don’t, you run the risk of a blemish… as last shown in previous pics. Although, I’ve tried to figure out why I did end up with a blemish… IMPORTANT> If you mix the silicone in a cup… paper styrofoam cup… … heck pour the mix into one other cup… I don’t know… but I would have guessed… when I had scraped off the all the remaining silicone… from the side of the cup, well the stuff sticking to the side of the cup… WAS NOT properly mixed… even though all the other stuff was mixed. So, don’t scrap off the remnants of silicone sticking to the side of the cup. That is why I say mix in a second cup… then scrape off the remnants… of the first cup, and then mix that stuff up with the second cup. If you think thats a bit much… well… the stuff is expensive… so you do want to use evey last drop of the stuff.
Ok… since that probably doesn’t make sense… here’s what I am going to do.&nb
Well guys I am finding this thread really interesting, as I have all that is needed to make a silicone mould, but have yet to make the first mould, so all this advice is being read and will be used very soon.
Thanks Keith for the reply,
2 Hours seems like alot of time to mix,Why not pour 2 parts in mixing bowl and use a drill & small paint paddle to stir together well ???
You have to pardon me but what is milk glue?
I’ll look for your post,I’ll probably contact manufacture for his directions on this.
Thanks again
Hogwire
Hog, hey … lol… I can only find one jug. So, good thing I’ve already shown a pic … a couple reply’s above.
But in answer to your question. Yes… its seems you are a painter… and know what to do. But when I got my jugs… you could see a bit of ‘displacement’. Its kind of ‘oily’ and needs to be mixed up real well. I chose to watch a movie and just kep turning up side down… and back again. I knew of no other way~
I think the ‘small note’ on not scraping the cups… was / is a problem… of not mixing correctly. Like I said… sounds like you’ve got it all under control.
But hey… when you get it… report back and take a few pics. I’d like to see if its mixed pretty well. If you have any questions … go ahead and ask.
Milk glue… I"m sorry… Elmers… white glue… lol. All and all … its pretty simple and fast. Just take a bead around the edge of the master so no silicone will leak underneath. Master is face up. I make my own frame… as shown in the above pic. That allows me to just glue the bottom with paper… and its easy to peal off. I also add wood to the master to make it a bit thicker to handle. Using white glue… is good enough… soak it… and it comes off again.
Ok, but you asked how to make a latex mold. I replied… just go to youtube. First hit…
http://www.youtube.com/watch?v=h5ozmmKQeIo
This latex mold took an awful lot of coats. 20 coats plus a ‘boot’ in which he calls a mother mold.
I ask, how much will all this cost… plus applying 20 coats of time… spread out no more than 24 hrs of ‘in between’ coats. I went to the train show and lo
I was thinking of using large Lego bricks for the walling of the master ?
What do you feel about this ?
Interestingly, I just yesterday I scanned an article from an old MR into a computer file about using Lego blocks to form molds. The pictures showed a building front laid out with blocks, and other blocks taking the spots of windows and doors. The person writing the article mad a plaster casting using the mold. Definitely sounds doable and practical. In the next day or two, I’ll be scanning another article on making latex molds.
Somewhere in the unscanned mess, I believe I also have some copied articles about using Lego blocks as jigs for holding things together while gluing,
5500 pages scanned, only about 30000 more to go.
Since this original question has been giving silicon rubber its attention, I thought I should point out some other advantages of the material. I worked in a professional model shop in New York for 16 years and we had a casting department that used silicone molds exclusively. I designed molds for the models that we were going to cast, ususally 10 to 50 pcs, and mostly in epoxy. The biggest advantage of silicone vs latex is that the silicone mold can be 1 or 2 inches thick in one pour. Because you can pour that thick you can make 2 or more piece molds allowing you to cast solid parts with detail on all sides, not just the front and side as with latex. We made molds of bottles for Avon decanters with incredible detail reproduction. As a prank one of the casting guys molded his thumb and the casting had fine hairs on it! This is a more complex but really easy process once you see how the molds are made.
One other point: I made a few masters from modeling clay on a sheet of acrylic and made the mold over it and then cast it in epoxy, a real nice effect.
I realize this could get rather complicated and too long for this forum, but if anyone is interested in more detail I would be glad to discuss it further.
Bob
When I was in art school, in a class called “Plaster Workshop,” where we learned about making patterns and molds, we used to give a bare plaster pattern a liberal coating of “tincture of green soap” as a release agent. As I recall (it WAS a few years back) we never had any problems removing the pattern from the mold.
There is one very large caveat, however! Beware undercuts!!! Better to make a multi-piece mold than have just one undercut. An undercut will give you fits getting the original out and you’ll probably damage the mold in the process!
I’ve been building another subway station, and in the process I decided to upgrade the homemade latex molds I use for the wall and platform castings. The originals, my first molds, had no side walls so I had to use a styrene frame to keep the plaster in while it set up. This seemed silly, so this time around I made one last casting with the styrene frame, and then added side walls with latex. This was quite easy, and done in a few days with only 3 quick applications of latex. For those making your first molds, remember side walls.
I also added a mesh backing to one of my molds. It really does help keep the mold flat, particularly for the large flat tile molds I use for the subways. I went out to the garage and found some of the mesh that goes down on flower beds to control weeds. It works great.
i know this is an old post but i just found this web site. anyway, i used some air drying modeling clay and rolled out a piece that was 6"X4"X1/4 thick. i let it start to dry, then took an exacto knife and started carving out small areas that became my stone wall. when it looked good i waited for it to dry then bushed somekind of sealer my wife had for her crafts. then i just used house hold latex silicone and spread it on with a putty knife. i made sure not to make it too thick, 1/8" at most. then when it dried, i could just peal it up. i painted it and it looks great. i would just cut out the shapes i needed. i could reuse the mold over again without any trouble.
hope this helps