I bought several plaster portals and stone walls from Woodland Scenics and intend to use them as masters for making latex rubber molds. Is there any special prep I must do to the plaster portals/walls before I apply the latex rubber?
It’s been a while since I made a mold, but I have several rocks awaiting a through cleaning, then I will make some molds. I would think as long as they are good and clean that you should have no problems. Don’t know if it will take a little paint off your pieces or not. I have a retaining wall I plan to duplicate also. One thing I will suggest is that after a couple of layers of latex, cover a layer, while still wet, with some fiberglass tape (wallboard tape), then give it another layer or two. It makes the mold much stronger and it will last a lot longer. Good luck,
I have used used dryer sheets. Due to the finer mesh they are a little more difficult to get soaked with the latex but seem to have resulted in comparable results. I have used my ‘dryer sheets supported molds’ many times without a problem.
This is a timely and interesting subject for me as I am contemplating trying to mold some interesting rocks my daughter collected for me. Can anyone please give me a brand name or two. Also is it available at Michaels? My two nearest hobby shops don’t carry anything like this. As always thanks.[:)]
Brent
The pieces I have now are brand new raw plaster. They have never been painted or stained. I didn’t know if the latex rubber would react with the plaster, i.e. soften it which would destroy much of the details.
Mark:
The raw plaster of the master will present a problem in that it will adhere strongly to the rubber in places with the result that you will risk either tearing the rubber or damaging the master when you try to remove the mold. I found that sealing the plaster master a couple of coats of Minwax Polyacrylic varnish gave a nice surface and the rubber molds separated nicely. I sprayed the finished mold with a little wet water (water plus a drop or 2 of liquid dish detergent) before adding the plaster and the finished castings separated nicely.
Joe
Brent,
The only brand I know of is Woodland Scenics “Latex Rubber” it’s number is C1204. Since I have no Michaels or the like around I am not sure what you should look for. Try asking for Latex Rubber. If that doesn’t work ask your LHS to add it to his next order. They are usually happy to do this, they can special order, but that usually costs more and for that you’d probably do better to place an order with a mailorder or online store.
Good luck,
#### Mold BuilderCastin’ Craft® Mold Builder is ideal for making molds to cast Clear Polyester Resin or epoxy, plaster, candle wax and even concrete! This liquid latex rubber product brushes-on almost anything,
I was just looking at the Micro Mark cataogue, which shows a number of different one and two part molding rubber compounds. The current catalogue pages 26 and 27 show a considerable number of items for making molds and castings, while on page 76 they list a Mold Maker Liquid Latex rubber, a single component item, 32 ounces for 22.85.
An article on molding parts I just scanned into a JPEG file show the author spraying the master with spray paint to seal the surface and make striping it from the mold easier.
It’s been a while since I read articles in MRR and RMC about making rock molds, but I seem to recal the rocks may have been sprayed with water or “Wet Water” (water with a couple drops of liquid soap added.
If you get the liquid rubber, just get a couple random rocks of little interest and expirement.
Latex? yeah~ The stuff has been around for quite some time. I have had decades of using it. Everything this thread has said is true.
Finding it in a fairly large quantity can be hard. I could not longer find it in a hardware store… or even a craft store. And if I found it, it was usually too small of a portion to do any real mold making. I found latex on ebay, and it was fairly cheap.
Latex has a few drawbacks. One… never leave the latex out in the sun. Two, it takes time to make a mold. Lots and lots of coats. If done correctly if it fairly flexable but if you add the cloth (and you should)… fiberglass cloth or the wall tape it makes the mold stiffer. The more difficult the mold… the harder it is to release after pouring. And if you have stiff latex molds… trying to pull the plaster out of the mold can cause some damage. But then again, I don’t use everday plaster, I use dental plaster. Its finer than most… and usually a whole lot stronger.
Now on the other hand. Silicone is the 21st century of choice. Latex is a bit of ‘old school’. Silicone is very expensive but tops the others in many ways.
One Silicone is extremely flexible. Two, is easy… just pour and let it dry… you’re good to go… the next day. Three. silicone can take very high temps for pouring… in case you choose to pour metal in the mold. With latex, plan on a week, especially if you don’t have the time… to apply one coat… after the next … and so on.
So, latex or silicone can be bought off ebay. AS far as learning how to make molds… its on the internet… its fairly easy… but time consuming. Try YOUTUBE also, I have found so much “How to do stuff” on youtube, I’m sure there is som
That’s a very clever suggestion-- thanks! I’m going to remember that one.
I wonder how well cheese-cloth would work? I’ve not tried it myself but the weave is looser than the dryer sheets and the fabric is easily available.
John
More good information. This is a very useful and informative thread-- thanks guys! I’m learning a lot just reading along.
John
A 50/50 mix of what?
EDIT: Nevermind, I re-read it and figured it out-- a 50/50 mix of the parts ‘A’ and ‘B’ resin & catalyst.
It would probably work ok. I can’t say that working with the dryer sheets was something that thrilled me but I had plenty and it was worth a try and I am content with the results (e.g. not had any problems) so I would use it again.
Give the cheese cloth a try and post your results. I, along with others I am sure, would like to know how it worked.
Randy
You can also try Handi-Wipes. Very strong with a loose weave that soaks into the latex. Makes the mold stronger and last for many castings.
It just goes to show that with a little creative thought not EVERYTHING needed has to be purchased specifically for a task…if you look around enough you can find free substitutes that can be re-purposed for our tasks.
I made up my own latex rubber molds of the WS portals with WS latex. I brushed the castings lightly to remove the dust, but otherwised I didn’t treat them at all. It took several coats of latex to create the mold. The hydrocal castings I made with the mold came out very well, with plenty of detail.
Remember to cover the sides with latex as well as the face. You will need some depth to your mold to hold the plaster, so the molds need side walls.
Why bother making molds looking like everyone else’s or possibly infringe on someone’s property rights? Fifty years ago I made a multitude of hand-sized rock molds from a stone retaining wall at my parents’ home. Wash the selected surface with water and paint brush. Apply two or three layers of liquid rubber (let it set between layers), and before the last of these coats set, apply some cotton gauze. Then apply a couple more layers of rubber. Once set, gently peel to remove. I still have these molds.
My molds are essentially flat. After pouring about a quarter-inch of plaster on the mold, the mold and plaster would be applied to the landform surface after the plaster had set just enough so it wouldn’t run off the mold. Remove the mold once the plaster has firmly set.
Mark
Something like this?
http://justtrains.railfan.net/Model_Layouts_CVRR_RockMolds_pg1.html
(note: the site itself is incomplete but the content of the page is ‘done’)
Do you know what kind of spray paint he used as a sealer???