I have tried several different methods on making molds using latex rubber from Woodland Scenics. One method was building a frame of wood keeping 2.5" wider around the piece your going to mold. It work well, But, I found it takes longer to dry this way. I also tried taking the piece hot glueing it to a piece of 1/8 thick board and laying thin layers of rubber down. Stilll takes to long. Is there a faster method that you Gentlemen know of. Also,when I remove the rubber It comes out distorted and hard to stretch out to lay out. What in the world am I doing wrong. I have to make several retaining walls for an area on my layout. Saving money.
NickyB
nickyb I have tried several different methods on making molds using latex rubber from Woodland Scenics. One method was building a frame of wood keeping 2.5" wider around the piece your going to mold. It work well, But, I found it takes longer to dry this way. I also tried taking the piece hot glueing it to a piece of 1/8 thick board and laying thin layers of rubber down. Stilll takes to long. Is there a faster method that you Gentlemen know of. Also,when I remove the rubber It comes out distorted and hard to stretch out to lay out. What in the world am I doing wrong. I have to make several retaining walls for an area on my layout. Saving money.
nickyb,
Years ago made several silicon rubber mold castings by alternating layers of cotton gauze and liquid silicon by WL Scenics. This worked, but took a long time because you have to let each layer dry completely before going to the next layer.
And it takes many layers before the mold is stiff enough to be usable (so we're talking 3-4 days to make a mold this way). Did this to cast plaster bases for a bunch of water columns and footings for a water tower.
Today, I use a much better way that involves building a retaining wall around the object you want to reproduce and pouring in a tough silicon rubber product.
I use stuff made by Alumilite. The link to their molding rubber is http://www.alumilite.com/store/p/756-Amazing-Mold-Rubber-3-4-lb.aspx
They also have tutorial videos on their website to answer all your questions. You can use plaster or their casting resin material to make your copies.
Joel
Modeling the C&O New River Subdivision circa 1949 for the fun of it!
I've made a few latex molds, too. It's not a fast process, although there is very little labor involved, mostly waiting.
Make sure you add latex not only to the top surface but also to the sides. Remember that you want a shallow bowl, not a flat sheet, so that the sides will hold the Hydrocal in while it sets.
I have some of that black plastic garden screen that's used as a weed block. After 2 or 3 layers of latex, I add a layer of screen and then more latex. This significantly stiffens the mold, and keeps it flat while I'm making castings.
It takes an iron man to play with a toy iron horse.
You can make curved castings with Hydrocal, too.
This particular mold is from Sterling Models. They call it "Weathered Rock Wall."
To make it, I cut a template from pink foam with the curvature I wanted. I poured the Hydrocal into the mold and let it set for about 10-12 minutes, until the Hydrocal was starting to set. It was firm and would no longer flow, but it wasn't hard yet. At that point, I put a piece of plastic wrap over the back and set the mold down on to the foam template, allowing it to bend to the curvature. You could do the same thing to get a convex curve by putting the template on top of the plastic-wrap-covered mold back and flipping the whole thing over.
nickyb Stilll takes to long.
How long is too long? Oomoo brand has two types of rubber; one that takes six hours to cure and one that takes 75 minutes.
http://www.smooth-on.com/Silicone-Rubber-an/c2_1113_1136/index.html
Steve S
RTV rubber molds would be more of what you may be looking for. It usually is a 1:1 mix and sets rather quickly. http://www.aeromarineproducts.com/125-qt-lp.html?gclid=Cj0KEQiA6dGmBRC_3Mi-x_XywKsBEiQA1lcFP7N_wph4ESc-1WgwGY2rcc7ZM01bEVWKHq71-OO1oZwaAgHd8P8HAQ
You place the "master" on a non pourous flat surface , set barrier dams (hot glued) and pour the mix so that the RTV covers the master. This produces quite a rugged mold that is extremely flexible and can be used hundreds of times. The other advatage of the RTV pour like this, is once inverted you need not support the pour or have any unwanted flex or distortion. This is ideal for numerous castings where consistancy and flatness of the casting is nec. retaining walls, concrete abutments, stone wall panels etc.
A previous club member Motrak Models, showed examples of his methods. He does quite an excellent job of not only carving his masters but building the RTV molds for maximum continuous commercial use. http://www.ebay.com/sch/i.html?_nkw=motrak-models&clk_rvr_id=776234926365&adpos=1t1&MT_ID=71&crlp=19951368060_2416792&device=c&geo_id=10232&keyword=motrak-models&crdt=0
My trouble w/ forming latex molds, is even w/ many coats and reinforced w/ cheesecloth, they are rather flimsey, will need to be propped/ supported or create some sort of frame to hold as you pour. On intricate pieces, or craggy rocks etc, the mold doesn't stand up to too much use/ abuse from removing from the casting. The RTV is rather pricy, but is rather quick and the mold will last.
Modeling B&O- Chessie Bob K. www.ssmrc.org
Just tried to do what your doing. Experimenting using a series of Woodland Scenics double track tunnel portal to make arch bridge. Came across a product call 'Composi-mold'(www.composimold.com). Worked great especially since I never did anything like this before. First casting came out perfect and didn't lose any detail (used WS super strength plaster). What's great about it is that it's eco friendly and you can remelt the mould and re-use it up to 35x (per manufacturer). Only issue is after 24 hrs when I removed cast, part was still soft due to thickness of cast so be careful.
There are two common types of rubber molds used in model railroading. There is the latex molds, commonly used in scenery, and there is the RTV molds commonly used in casting resin and other types of parts. The latex rubber is brushed on in layers, while the RTV is poured over a master in a mold frame. The latex rubbler will make a very thin, flexible mold. The RTV mold can be more of a semi-rigid mold that produces flatter castings.
I use latex for rock molds and RTV for casting railcars.
If you want flatter castings you could try RTV from Micro Mark, Smooth On, Alumilite, Hobby Silicones.
Dave H. Painted side goes up. My website : wnbranch.com
As stated, latex molds don't take much time to make, but take awhile to dry. Instead of the screening like Mr B used, I just used cheeze cloth to strengthen the mold after two or three coats, then added at least two more. I have done a number of different rock molds and they have all held up well over time. One rock can yield several different molds by coating different areas of it. Sometimes I can to two at the same time, if the original is big enough. I haven't tried to make any other type of mold, but have had the idea and plan to do a few.
Good luck,
Richard