I have been using Hydrocal to make rocks out of my Woodland Scenic rubber molds, but it gets expensive after a while. I know a lot of people have used plaster of Paris to make the rocks, but I don’t know what plaster to water ratio to use. Those using plaster, could you please tell me the ratio you are using. Are you happy with the results?
Woodman:
I use 2 parts plaster of paris to 1 part water. I have made a lot of rock castings with this mix and have had good results with this mix.
Joe
Woodman,
I used some plaster of paris in a rock mold as a test to see how it performed compared to white art plaster ( a higher grade of hydrocal type plaster). I wasn’t pleased with the results. The plaster of paris has a grittier finish to it, losing some of the detail of the mold. It also has a darker color than the plaster I use, so I figured it could affect the final outcome of the colors of washes I planned on using on my rockwork.
Don Z.
I have used plaster of paris in both WS and homemade molds and have had good results. I sprayed the molds with wet water before pouring in the plaster. It takes washes well. I did try adding a little color to one batch and was not as happy with the way it took washes after that. I have a box of hydorcal, but haven’t used any as yet. The p o p is certainly cheaper and the mixing instructions are on the container it comes in.
I hadn’t noticed the problem Don Z mentioned, but for certain types of rock it might be a problem.
Good luck,
Richard
I have used over 400 pounds of Hyrdocal B-11, selected because of the longer set-up time allowing corrections, and hardness, on my home layout and the Glendale Model Railroad Club over a period of 25 years. I find Plaster of Paris too soft, and subject to scratches and breakage. Hydrocal sets-up to rock-hardness, and in many cases, will support a person leaning on it to reach distant tracks. When hardened, it will permit removal of molds with “undercuts” whereas plaster of paris will break off detail.
I tried use of colors mixed in the Hydrocal, and found that enough color to make any appreciable difference weakened the mixture after set-up, and any lesser amount resulted in pastel, not colored, rocks. It was a waste of time and money. Use acrylic washes to color castings, repeating until satisfied.
I use a 2 to 1 ratio in my plaster of paris mixture. I cut my teeth using p.o.p. so I am comfortable with this for scenery and rock molds. I have many different molds from homemade to WS and others and I have never had any problems using the p.o.p.
Ray
Sounds to me like you are buying the WS pre-packaged Hydrocal. Try buying it in 50 lb bags from a building supply house…Not usually at a Home Depot, look for the store specializing in lath and plaster supplies (there is usually one in most towns) Much cheaper in bulk.
I agree with A. Wallace on the superiority of hydrocal if you are looking for strength and clean castings…
Guy
Has anyone tried using drywall ‘mud’ in place of Hydrocal or plaster of paris? I was wondering about this idea after helping my son-in-law hang sheetrock and mudding the seams.
Ray
Most drywall muds are designed to shrink up more than platers or hydrocal type products. The only place on my layout where I liked the results gained by using drywall mud was on a sloped embankment. When the drywall mud shrank back on itself , I gained some erosion channels and short narrow ravines randomly along the embankment. Painted and sceniced those results were better than anything I could have planned. Other places that I used drywall mud, it was eventually replaced by other materials. Your results and mileage may be different, of course.
I’m in agreement with Walace also. For casting of any molds Hydrocal can’t be beat. For my club we could never afford using those WS packages. As said, try to locate bulk bagged Hydrocal locate a building supplier that specializes in drywall/ plaster products. Our supplier has the plaster in 99# bags. These outlets will also have the “veneering” plasters like Unical. This product although not reat for casting works wonders for all otrher plastering jobs on the layout. This is the plaster that is used for skim coating blue board. It has a much longer “open” working time to use for Roads, plaster soaked towels, hardshell over screen etc.
What I like to do w/ that huge bag of Hydrcal is to rebag in smaller more managable amounts. I will fill coffee cans and place in quart size plastic bags. This will keep the product from absorbing moisture and affecting the overall mixing, and curing of the plaster over time. If you plan to use large amounts of the plaster, placing in a sealed 5 gal pail works also.
This supplier may also carry masonry supplies. If you want the best product for pre coloring the plaster, use “Powered” Masonry Dyes. The Sacrete liquid, and paint just doesn’t work that well. It usually will only lightly tint. Excessive amounts can affect the overall drying and curing of the product. We are in a club setting where ther is a possibility of abuse to exposed castings. A real pain to touch up those “bright” white chips.
We had the “pleasuer” of having Jeff Adam of Motrac Models as a club member. He specializes in some fantastic castings. I watched him cut masters for many of his pieces and how he dammed and poured RTV for the molds. I don’t really recommend trying to cut a master for your own use but Making molds of existing origionals is easily done w/ the RTV. M
Many of the castings on our layout are his. I believe these are offered commercialy now. Others are a mix of production offerings and ones created by myself or club members.
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