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Clinic - Making Structures In Hydrocal

Hydrocal is a product of U.S. Gypsum and can be purchased in some Hobby Shops, Cement and Ceramic Supply Stores. It has  great strength, much more than plaster and reproduces detail to a very fine degree. Another advantage of this product is the relatively low cost. A 100 pound bag is less than twenty dollars and can be used to build scenery as well as creating structures and assorted detail parts.

To begin the process, draw the building sides (to scale) on a piece of paper then tape the paper to a sheet of glass with the drawing against the glass. Turn the glass over so you are looking through the glass at your drawing. Using rubber cement, glue strips of 1/8 inch strip wood over the outside lines of the drawing and glue blocks of 1/8 inch thick wood where the doors and windows will be. It is important to make sure the openings you are creating are the right size for the door and window castings you plan to use.

Allow 10 to 15 minutes for the rubber cement to dry, then using a cheap disposable brush, “paint” the glass and strip wood with a liberal coat of petroleum jelly. The jelly will make it easier to remove the Hydrocal from your mold.

Using a paint stirring stick, mix the Hydrocal with water in an old butter tub. Hint: hot water seems to cause the Hydrocal to harden faster while cold water slows the setting time.

Mix  the Hydrocal and water until you have the consistency of ketchup. Pour the mixture into the mold and use the stirring stick to scrape along the strip wood to level the mixture with the top of the mold. Allow the Hydrocal to dry for about 30 minutes and remove the strip wood and the structure side from the glass. Turn the structure side over and use a metal ruler and the back edge of a hobby knife or a dental pick to “carve” brick or rock detail into the face of the wall. To make the assembly easier, bevel the corner edges to 45 degrees and glue the walls together. If your joints have a small gap, just mix a little more Hydrocal and fill the joints, then add the carved detail once the joints have dried. As the Hydrocal dries, it gets harder and is more difficult to carve. If you find yourself in this situation, spray some water on the wall and the surface will soften making it easier to carve. After the walls have been assembled, color the structure with acrylic paints to the desired color, then apply a greatly thinned coat of acrylic gray or white to simulate mortar. Apply this as a “wash” and immediately wipe the excess “wash” off the surface with a damp paper towel, leaving the mortar color in the joints between the stones or bricks.

Paint the doors and windows to the desired color and install. Build the roof using card stock, styrene or the material of your choice and apply shingles or "rolled roofing” made from masking tape glued to the roof and painted with weathered black. Add details to the outside of the building and surrounding area. 

See the figure below for a diagram showing one side of a sample structure drawing. Note the gray areas where the doors and window will be.  Click on the image to see a full size version of the drawing.

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