Making rock molds

X

XavierJ123

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Dec 17, 2004
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Lexington, Kentucky
Santa left me a 32 oz can of liquid latex rubber mold builder under the tree. I haven't made molds of real rock for 25 years and that was in the summer when it was nice and hot. You could paint the liquid latex rubber on some nice rock and it would try quickly for the second coat, etc. :cool:
This is winter and a whole new ball game here in Kentucky. I braved the cold a couple of weeks ago and dragged home some nice smaller rock to mold. I had to leave the big ones behind for spring. Why is it that the nicest structure is on a big rock that is too big to move. Murphy's law I guess!:mad:
The directions on this can of mold builder says to paint on thin layers, letting each layer dry before adding a second layer. So I am going to paint one thin layer every night for a week. I am doing this on my workbench in the basement since it is freezing outside. :mad:
I want to use the rock molds and try to make some John Allen Mountains on a layout in the basement. I am really into mountains, gorges and tressles. The idea of a floor to ceiling mountain really appeals to me. Wish me luck!:thumb:
 
What I do when I am making molds is to add tissue paper or gauze into my mold after the second coat. This gives the mold more body and makes a better mold. It also uses less mold rubber to get a nice thick mold. This is a good idea for bigger molds as well. It makes the mold stronger and last much longer too.

Paint the mold with a coat and then lay the pieces of gauze or tissue on the wet rubber and paint more rubber onto it. Just like fiber glassing, press the tissue down with the brush and spread out the rubber to form a even coat. Over-lap the edges of the tissue. Try this. It works.

TrainClown ;)
 
I'm in total agreement with Train Clown on that. I use gauze, like the 4 by 4 bandaide kind. They do all TC says plus are cheaper than latex. A small fan on them will speed drying time of the latex a bunch too. Fred
 
You can also place the project in the oven on low heat to speed the process.
 
Thanks for all the input. It has been a long time since I made any rock molds but it sure is fun. I will try the gauze tonight. The molds do produce some great looking rock mountains. I purchased an old used model railroading book and in it was a full page photo of John Allen's landscape in his Gorre and Daphetid layout. That's my inspiration.
 
Well, I am one for reading the instructions and the instructions didn't mention anything about preparing the rock or putting any kind of release agent. It been a long, long time since I made any rock molds but I have never done anything other than paint the latex rubber on in layers. I do however, often wonder, if different molding compounds require didn't methods of application. When you research the latex rubber products on line you will learn there are a lot to choose from depending on what you are going to use it for. I picked one that seemed apropos for what I needed. So far so good, I painted the second coat on this evening and I would imagine when the rubber mold is thick enough, it will peel right off. I used some of my old molds before Christmas and made a mountain with tunnel for my wife's Christmas village. She ran an HO train thru it this year. It's a plaster-of-paris mountian made with rock molds and the molds peeled right off without any kind of special preparation. I just put the plaster of paris in the mold and slapped it on a skeleton of screen and wood. It turned out real nice.
 
release

X,

John Allen's landscape in his Gorre and Daphetid layout. That's my inspiration.
I have the same issue! Amazing retrospect issue.

Your question concerning a release material. If your rocks have deep undercuts I would use some. My list of cheap mold release is WD-40, Pam cooking spray, or liquid canola oil. Thin coatings, don't flood. Test a small piece first if you decide to use a mold release with the latex.
 
Professor X,

I made some killer molds back in the mid-1980's using the WS latex. I lugged home good rocks... but scrubbed them clean with a really stiff brush and soapy water, getting all the cooties and critter droppings off them. The key is leaving soapy water on the rock, and before it dries, do a first layer of slightly diluted WS latex. I can't remember what I diluted it with. I believe it was distilled H20. Not tap water.

This ultra thin coat seeps into those neat nooks and cracks better than a full-strength layer. After that's dry - then do a full-strength layer. THEN lay on some drug store gauze material while it's wet. When that's dry, do about 3 more successive layers of latex.

I recently got them out of storage to let a local club use a few. They still looked awesome. Always wash them out with soapy water when done. The club guys thought I was obsessive compulsive! Then when you store them, shake some talcum powder in them and rub it around.
 
After painting the rocks laying on old newspaper with eight thin layers of liquid latex, two of which were reinforced with gauze, and letting them dry 24 hours between coats, I peeled them off with no problem. It was easy to find an edge of the latex mold and peel it off. Sort of like peeling an orange. To answer yellowlynn's question, I didn't use any release agent and it doesn't appear any is needed on rock.
Currently, I have four coats of liquid latex on a Woodland Scenics plaster-of-paris tunnel portal. I laid the tunnel portal flat on a piece of wax paper and painted it everywhere with liquid latex, especially around the edges so that I leave about inch lap. I reinforced this one with gauze and after four more coats will peel it off. Then I can pour plaster-of-paris in the mold and make as many duplicate tunnel portals that my heart desires. Since the mold is flexible it is best to support the sides of the mold in sand before pouring it with plaster-of-paris. Works great.
P.S. My four year old grandson wanted me to duplicate his hand print in soft plaster-of-paris. (you know like you do in concrete) Well, I did this for him is a tin lid without a release agent and you guessed it; the plaster-of-paris hardened and it will not come out. My wife said, "I told you so!" but I wanted to experiment. Anybody know how to get it out. LOL
 
Click here: Environmental Technology Inc. Here's a link to the source of the mold builder that I am using. It doesn't require a release agent and the clean-up is water. I apply it with a paint brush about 2 inches wide which is stored between applications in a 3 pound plastic Country Crock margerine container filled with water. When it's time for the next application, I dump the white diluted liquid down the drain and proceed to apply another coat of liquid latex. What fun!
 
Kim Paynter said:
Hey that sounds like a great Idea for the tunnel portal, hope Woodland scenics dosent surf here or you might find a lawyer knocking at your door.

Kim
Click to expand...

Actually, I think you're ok as long as the castings are for your personal use. There was an article in MRR a year or two ago describing molds and castings that stated this.

Val
 
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