BREAKTHROUGH Issue 89 Page 67

MOLDING & CASTING

The rock I chose was 25 high, 18 wide, and 16deep. The rock you choose should have multi anglesand levels. Molds are not cheap to make so the morevariations you can get from one rock mold the better.(These rocks are harder to find than you think.)

1. Full Rock Table Mount2. Half Rock Table Mount3. Half Rock Landscape4. Half Rock Wall Mount

AS TAXIDERMISTS, WE ARE ALL STRIV-ing to make our work stand out in front ofour competitors work with accurate anato-my, finishing, and composition. Our work

needs to have realistic groundwork to elevate the stan-dard of our mounts.

This article is to show you a few techniques I usewhen molding and casting large impressive rocks.These are the rocks we all see with large cracks, shapededges, and uneven voids.

MOLDING & CASTING

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Page 68 BREAKTHROUGH Issue 89

MOLDING & CASTINGThe rock was placed at a good working height

with ample working room around the rock. All theloose soil and moss were cleaned off with a soft brush.Using a toothbrush, I worked around the rock clean-ing out all the small cracks and fine details.

5. Silicone rubber was brushed over the rock,working it into the cracks and crevices. Once it fullycovered the rock, I used a hair dryer set on a cool-fastblow setting and moved slowly over the rock. Thisremoved any air bubbles trapped in the cracks anddetails of the rock.

6. Once the first coat was fully cured, thixtropicadditive was added to the second coat, which thick-ened the silicone so it became spreadable. A goodcoat was worked over the rock, mixed in smallamounts to give me more working time.

To extend the life of the mold, I built an air valveinto the silicone mold, which was used to blow airinto the mold to help release the casts without puttingtoo much stress onto the silicone mold.

7ab. I use the valve from an old inner tube tomake a mold valve. First, remove the valve from the

tube. (The rest of the inner tube can be cut into stripsfor reinforcing strips.Cutting across the tubemakes large and verystrong rubber bandswhich come in handyfor strapping togethersmall molds.)

8. Wash the valveand cut around the edges so it will follow the shape ofthe rock.

9. Cut a small X through the silicone mold downto the rock beneath. This was done at the top of therock, but can also be done on an edge of the mold.

10. Glue the valve to the rock using silicone.Make sure the valve is over the X.

11. Apply silicone over the valve to secure it tothe mold. A final coat of thick silicone was workedover the rock. On a rock this size I want a good (5mm) layer of silicone over it at this stage.

The next problem was that the rock had severalvoids which needed to be filled to create a smootherrounded shape and to make a more simple backingjacket.

12. Using a wire brush, I scraped apart a piece ofpolystyrene packaging to use as a filler. This was per-fect as it was bulky and flexible.

13. I added the polystyrene to a small amount ofsilicone, mixed it in wellto produce a putty-likefiller.

14. This photoshows the large voidsfilled in with the filler.Once fully cured, a finalcoat of silicone wasworked over the rock,bringing the final thick-ness of the silicone to (8mm).

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BREAKTHROUGH Issue 89 Page 69

15. Once the rock was covered in the final coatof silicone, I generously coated it with talcum powderand smoothed it by hand.

16. When the silicone was fully cured, all thetalcum powder was removed and any unwanted sili-cone was trimmed from the edges of the mold. NowI drew a line over the mold to use as a guide to followwhen making a backing jacket.

17. For making a backing jacket, I tried out aplastic paste, a new material to me. There are many onthe market, and the one I used is a Smooth-On prod-uct called Plasti-Paste. Its a two-part product that isclean, very easy to use, and has a fast setting time ofaround 8 minutes.

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Page 70 BREAKTHROUGH Issue 89

MOLDING & CASTING

18. As I worked the plastic paste over the rock,I used playing cards as separators between the twohalves of the jacket.

19. The area around the valve can be very looseas the strength of the valve will support the mold.

20. I used 5killograms of Plas-ti-Paste on thisbacking jacket, butran out when I gotto the flanges, sothese were built upwith a little Bondo

just for extra strength. The flanges were drilled to takesmall bolts before releasing from the mold. Then theplaying cards were removed.

21. I now connected a foot air pump to thevalve, and pumped just a small amount of air intothe mold to help release the silicone.

22-23. The rock was removed and the siliconemold placed into the backing jacket and bolted to-gether. I drilled screws around the opening into thejacket to be used as anchors. Thin wires were pushedinto the silicone mold around the edge, then bentover and wrapped around the screws in the jacket.

The resin mix I used was the same one I used inmy previous article in BREAKTHROUGH (see Issue #84,page 77, Competition Base Work with a Differ-ence). The mixture was worked into the mold, push-ing the resin into the details, but not trapping any airin the mold. Once fully cured, a second coat of thesame resin mixture was worked over the first, pro-ducing a thickness of about (5mm). Then I lay-ered the casting with 2 ounces of fiberglass matting.The casting now should have a thickness of around (8mm) of resin.

Once fully cured, the casting was removed fromthe mold using the same techniques as removing itfrom the original rock. This was finished the sameway as the gargoyle was in my article in Issue 84.

24. Here is a closeup of the cast rock details.

25. This photo shows the artificial rock, straightfrom the mold with no finishing work done, next tothe real rock.

26-27. The cast rock was given a base colour. Idid this with thinnedwood stain, givingone complete coat,working the stain intothe cracks and detailsof the casting. Thisdried quickly. I thengently rubbed overthe casting with steelwool just to highlightareas which stoodproud. I used severalcoats of an oil-paintwash to get the cor-rect finish. n

CARL CHURCH is a bird specialist taxidermistbased in North Yorkshire, England. You may contacthim through www.birdtaxidermy.co.uk.

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