I have just started using Woodland Scenics rock moulds, and am using plaster of paris. I am unsure of the correct mixing ratio for the plaster. The instructions on the box say to mix 1:1 with water, but when I do I end up with a white liquid about the consistency of milk. Of course , it pours into the moulds easily, but when setting forms a pool of water on the surface which has to be soaked up. On removing from the moulds, I have to be very careful not to break the casting, and thin casts just crumble in my fingers. Even completed casts remain very soft.
So, is there a generally accepted wisdom about what ratio to mix the plaster? What I am using seems very thin, espcially when compared to other scenery materials such as Sculptamold or WS Smooth-It. Are there any other caveats about using this material that would be helpful to know?
Thanks,
Paul.
Woodland Scenics recommends using its product, Light Hydrocal, in its rubber molds. It is a lot more reliable than generic Plaster of Paris.
Rich
Alton Junction
I believe you will have better luck using 2 parts of POP (plaster of Paris) to 1 part water.
Also make sure your POP is fresh , if it feels grainy in you hand is has gotten moisture in it. NOT GOOD
Thanks, I'll try a thicker consistency next time. My box of plaster still seems fresh enough, so no immediate concerns there.
I'll also give Lightweight Hydrocal a try when I next buy.
Good luck, Paul. Let us know how it all works out for you.
I'm also a hydrocal fan for plaster casting.
If you find you like rock face and stone wall castings, you might also look at Bragdon Enterprises. They use a two-part chemical resin that sets up very well but can actually be softened later with a hair dryer to allow the castings to be bent around curves later. The castings are thin and light, and can even be cut with scissors. The Bragdon rock molds are very finely detailed and the foam material brings out all the fine details well.
It takes an iron man to play with a toy iron horse.
I mix it about the consistancy of pancake batter, which works fine for me.
If you have ever been to the casting room at the hospital as I have on many occasions you will notice the Dr./Tech has a big apron and gloves to the elbow on and is often covered in plaster. Putting a cast on a broken leg or arm is a messy business and dipping the bandages in a vat of 1:1 mix ensures the material of the day is well impregnated with the PP. That being said I think the 1:1 mix suggestion is for dipping cloth in which I have done to make rolling hillsides. For use in moulds I think something a little thicker would be required and I am not sure how well it would hold together after coming out of the mould anyway. Hydrocal or some of the other suggestions would be a better choice I would think. Wait for Dr. Wayne to show up and see what he uses.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
BATMAN Wait for Dr. Wayne to show up and see what he uses.
Wait for Dr. Wayne to show up and see what he uses.
richhotrain BATMAN Wait for Dr. Wayne to show up and see what he uses. Yes, that will be the defining moment. Rich
Yes, that will be the defining moment.
And you can buy a 50lb bag of the stuff for pennies compared to what WS will charge you.
BATMAN richhotrain BATMAN Wait for Dr. Wayne to show up and see what he uses. Yes, that will be the defining moment. Rich And you can buy a 50lb bag of the stuff for pennies compared to what WS will charge you.
With all the reno's I have done over the years and not wanting anything to go to waste, I have put leftover tile thin-set and grout that was in the bucket on this portion of the layout. It is super hard and once painted and gets a little greenery sprinkled on it, I think it will look great.
The different colours are just because they are different products.
Whenever I was tiling or grouting I had the drop cloths down in the train room pryer to starting.
I'm sorry, but I've spent over an hour trying to compose a reply, but the Forum has been freezing every few minutes, and eventually simply deleted what I had managed to add, including photos.
Wayne
I tried a mix of pancake batter, and the results are much more successful. It's not self-levelling, but it sets well and comes out of the mould very well. I may experiment with maple syrup for my next effort.
Thanks, all.
Macman44The instructions on the box say to mix 1:1 with water, but when I do I end up with a white liquid about the consistency of milk.
Most instructions for mixing plaster are by weight, not volume. This easily causes confusion. If you use an inexpensive digital kitchen scale you can pretty easily get the weight the same.
By volume, you will use far less water than plaster powder.
I have never used the Woodland Scenics plaster, so I cannot say for certain what their instructions specify. All the commercial hydrocal and ultracal I have bought specified the mixing ratios by weight.
EDIT--
Just found the instructions on the Woodland Scenics website. They are now stating to use a 2.5:1 ratio by volume.
I guess they updated their instructions.
-Kevin
Living the dream.
Hi, I'm a bit late to the party.........
I've used plaster of paris since 1956 when I had a basement Lionel layout. I bought it for 5 cents a pound at the local hardware store. Moving up the the 1990s, I picked up several of the rubber rock molds and made literally a couple of hundred castings for my HO layout at that time. All I used was plaster of paris.
The trick was to make a mix thick enough so as to not run, but to make sure it was thin enough to fill the cracks, and to make sure there were no lumps. I never used a formula for the ratio, and the results were always good.
Some comments......
- too thin a mix will lead to cracks when it eventually hardens
- you will find the casting warming up as it cures. Be patient and pull after it starts to cool down.
- make sure that the casting is well secured to a flat base.
- any tinting or painting you do will end up darker than intended.
- plaster of paris works well for the molds, but doesn't do well for roads and the like. For that, I found Woodland Scenics "Smooth It" to work beautifully.
Hey, I'm not knocking other products, just saying plaster of paris is what I used for molds as it was what was available and I was experienced with.
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
SeeYou190I guess they updated their instructions.
Mike
When the Hydrocal instructions say that working time is 5 minutes, they are not kidding. In my experience working with Hydrocal, you need to precisely follow the instructions and work fast.
You don't need to measure with plasters. it is more of an eye thing. Hydracale is best for rock molds and other castings and plaster for general scenery work. With plaster you start with powder and add water to consisancy you want, forget about Hydracal, been awhile.
Water Level RouteNote the instructions say to add the plaster powder to premeasured water. Numerous other manufacturers, suppliers, etc, advise the same. For example, from DAP: Add DAP Plaster or Paris to clean water.
Yes.
I may have missed it in the earlier comments, but when using Woodland Scenics rock molds, I spray the mold with wet water before pouring the plaster in. This aids in removing the castings. I found another tip, especially when using large molds, is to let the plaster set up until it cracks when you flex the mold. Spray the area where you'll be adding the casting with wet water, then press the mold into place. Sometimes, I have to use push pins to hold the mold in place. Give the plaster a good hour or so to set up. Starting from the edges of the mold, gently peel the mold off. When you have all your castings in place, blend the castings together with more plaster.
Marlon
See pictures of the Clinton-Golden Valley RR
Looks like that's where I initially went wrong. The plaster of paris I am using isn't Woodland Scenics and it simply states to mix in a 1:1 ratio, without specifying by volume or by weight, especially since that is easier to do rather than weighing (who has access to small scales to weigh stuff, anyway?). I would think that most people reading that would expect it to mean 1:1 by volume. Shows how one needs to read and interpret instructions carefully, but I think manufacturers should be more explicit (as WS now seem to be).
At least I am now forewarned.
The Woodland Scenics product is simply indutrial Hydrocal manufactured by US Gypsum that they repackage into consumer-friendly sizes.
I am sure they just copied-and-pasted the instructions from the industrial product originally. In the industrial world weight is used because it is more accurate and easy to control. In the consumer world, it is confusing.
My experience is with hydrocal, but people use all sorts of plasters. The pancake batter is what you want. I add the water to the plaster and add less water than I think is neccesary and mix. Then I add more water to get the right consistency. I measure the plaster. I don't think I ever measured the water. I certainly never weighed anything.
Henry
COB Potomac & Northern
Shenandoah Valley
This is a great combination. I've used it also and try to bend the plastic mold a bit to help it not get stuck and unable to come out of the mold.
The OP has his answer.
Copy-and-paste answering is in full effect.
The merry-go-round is beginning.
I have always found it best when experiencing difficulties with something and not following manufacturer instructions, it's best to go back to square one and follow the directions. Curiously, that sometimes solves the issue.
What gets added to what may not make a difference in many cases. However, there are some where it makes a big difference, such as acid dilution. Always add acid to water, not the other way around. Logically shouldn't make a difference. Reality shows otherwise.
SeeYou190 The OP has his answer. Copy-and-paste answering is in full effect. The merry-go-round is beginning. -Kevin
Water Level Route I will cease and desist in respect of that as well. Thanks for pointing that out.
Our "smarter than everyone never wrong argues about everything" guy showed up in here, and the level of conversation took an immediate plunge.
Steve had to lock another thread yesterday after it was "Spiked" by this guy.
I am so tired of this merry-go-around in what should be the premier Model Railroading discussion forums on the internet.
Funny, many times the instructions are just wrong. With plasters the instructions they give are for (hopefully) never fail jobs of a larger nature, we can be much more percise to get what we need as it is ussually small batch. In other words a little more or a little less may be what works. This is because in small batches and the way we work, it may take a bit more time or less time to do a pour. This was learned by me when working in the 1-1 world.