Plaster Track Casting Procedure
By Kim A. Cabrera
|Find a track to cast. This may sound easy, but good clear prints can be difficult to find. Look in soft mud near water sources, damp sand, and other such easy surfaces to find tracks in. Once you have found your track, you may want to remove any leaves or sticks that have fallen into it. Do this carefully and do not attempt to remove sticks or leaves that are compressed into the track. Removing these will damage the track. You can remove them from the plaster later.|
What you need to make plaster casts: Plaster of Paris (or dental stone), mixing container, water, paper clip, cardboard strip. If you are near a water source, you may not need to carry water with you. Also, you may not need the cardboard strip, although it is recommended to make a thick cast, especially when using plaster of Paris, which can break and needs the extra thickness to make a more sturdy cast. You can also add dry twigs, wire, or string to the plaster cast to reinforce it. If you use dental stone, you will not need to reinforce the cast as dental stone has a higher compressive strength than plaster of Paris. Less dental stone is needed to make a cast of the same size. Although dental stone seems more expensive, the fact that you use less per cast means it costs probably about the same as plaster.
|Use your cardboard strip to build a wall around the track. Hold it in place with the paper clip. Be careful not to damage the track when you place this around it. Gently press the strip into the surrounding soil so the plaster will not run out from under it when poured.|
|Now mix the plaster. You should use about two parts plaster to one part water. For example, two cups of plaster mixed with one cup water. The consistency should be like that of pancake batter, or thick motor oil. It is recommended that you add the plaster to the water and begin mixing immediately. Plaster begins to set as soon as it comes in contact with water, so work quickly. If you use pre-measured quantities, add the plaster to the water all at one time, and begin stirring immediately, this will give you the best results. Stir it for 3 to 5 minutes and get rid of all the lumps.|
|I always tap the mixing container on the ground to remove any bubbles that may have accumulated in the mixture. This will give you a higher quality cast. You will see the bubbles rise to the surface.|
|Carefully pour the plaster into your pre-prepared mold. Do not pour the plaster directly into the track as this can damage it. Pour the plaster onto the ground next to the track and allow it to run into the track. Start with the finer details, such as claw marks, first. An alternative method is to pour the plaster onto a spatula or spoon held low over the print and let it run off into the track. The utensil takes the force of the falling plaster, rather than the fragile track. Make sure you fill in all details of the track with plaster. Pour it relatively thick to make a good strong cast. This is the time to add and reinforcing materials such as string, wire, or twigs. Once you have finished pouring, let the track set for at least 1/2 hour. Some types of plaster may take longer to set.|
|As the plaster dries, it will go from a glossy wet appearance to a dull matte appearance. It will give off heat as the chemical reaction takes place. After about 1/2 hour, you can gently touch the surface of the cast to see if it is dry or still soft. Do not press too hard as you could crack the cast. If it is dry, you can try tapping it gently with your knuckles. If it is firm and has a ceramic ring to it, then it is safe to pick up the cast. Pick it up by reaching underneath it and lifting it. Do not lift by prying under it with a stick. This could crack it. Try to lift it from opposite edges. If it is cast in mud, the mud may hold it firmly You may need to carefully dig out some of the mud or soil from beneath the cast before lifting it.||
Your cast is finished.
|Allow it to dry for several days before cleaning it or painting it. Never wrap plaster casts in plastic bags as this prevents the moisture from escaping. When you clean a plaster cast, do not scrub too hard with a brush as this will erode away the plaster and take the details of the track with it. Plaster is soft and will eventually dissolve if left immersed in water. The best way to clean casts is holding them under running water and gently rubbing excess dirt away. Do not rub over the details of the track itself, but rather the areas around it. Scrubbing on the details of the track may sand them off. There will be some dirt or sand remaining on the cast. This is normal. If you use dental stone, you can scrub the cast and not lose detail as it is a much stronger material.|
Tip for making great casts.
|Plaster casting can be fun and easy. It is also inexpensive. Enjoy your time outdoors and learn all you can about tracks and tracking. You may not see the animals, but you will know they have been there when you find their tracks, which are their signatures on the landscape.|
Text and all drawings © Kim A. Cabrera 2001-2007.
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