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Advanced Mold Making Technique: Brush-On Mold of a 3D Hollow Model

The Challenge: Filling the void on this hollow puma head so an efficient brush-on mold can be made.

Making a mold of a hollow model presents a challenge to the mold maker. The void must be filled as the primary step of making the mold. A "mouth core" will be used to fill the mouth void and a "mold plug" will be employed to duplicate the hollow space which runs through the original model.

This challenging mold of a puma head will be made using Smooth-On's Rebound® 25 brush-on silicone rubber. There has never been an easier to use brush-on silicone rubber than Rebound 25. Mixed 1A:1B by volume (no scale necessary), Rebound 25 self-thickens and will hold a vertical or inverted surface, and will cure to a soft, flexible rubber (Shore 25A) that is incredibly strong. Three to four layers is all that is necessary to make a strong, durable production mold for casting wax, gypsum, concrete or resins (urethane, polyester, etc.) and because Rebound 25 is a platinum silicone, it will last for many years in your mold library.
 Puma head cast out of concrete.

1 - Puma head cast out of concrete.
 Begin by cutting several
slices of water clay to use
as filler.

2 - Begin by cutting several slices of water clay to use as filler.
 Use a piece of melamine board for a base.  Center head on board and fill the  cavity with clay to eliminate the void at the back of the head.

3 - Use a piece of melamine board for a base. Center head on board and fill the cavity with clay to eliminate the void at the back of the head.
 Two cut off bolts are enbedded in the clay to serve as place holders for later use.

4 - Two cut off bolts are enbedded in the clay to serve as place holders for later use.
 SuperSeal® is applied to the model and the clay to seal the porousity.

5 - SuperSeal® is applied to the model and the clay to seal the porousity.
 Rebound® 25 silicone rubber is mixed 1A:1B and the first coat is applied to the model.

6 - Rebound® 25 silicone rubber is mixed 1A:1B and the first coat is applied to the model.
 This “detail coat” should be thin so that any bubbles that form will pop and not be trapped against the model.

7 - This “detail coat” should be thin so that any bubbles that form will pop and not be trapped against the model.
 The second coat is pigmented with Silc Pig® so its easier to see areas that are missed.

8 - The second coat is pigmented with Silc Pig® so its easier to see areas that are missed.
 Next a batch of Rebound® 25 is thickened with Thi-Vex® II.

9 - Next a batch of Rebound® 25 is thickened with Thi-Vex® II.
 Potential problem areas are filled in to allow for easier application and removal of the support shell.

10 - Potential problem areas are filled in to allow for easier application and removal of the support shell.
 A third, unpigmented coat of Rebound® 25 is applied to the model.

11 - A third, unpigmented coat of Rebound® 25 is applied to the model.
 The fourth and final coat of Rebound® is pigmented and applied to the model.

12 - The fourth and final coat of Rebound® is pigmented and applied to the model.
 The “placeholder” bolts are located and the mold rubber cut away to expose them.

13 - The “placeholder” bolts are located and the mold rubber cut away to expose them.
 Needle nose pliers are used to remove the spacers from the clay and rubber mold.

14 - Needle nose pliers are used to remove the spacers from the clay and rubber mold.
 Ease Release® 200 is appliedto a pair of 5 inch long machine bolts.

15 - Ease Release® 200 is appliedto a pair of 5 inch long machine bolts.
 The bolts are reinserted into the clay ports that were created
by the placeholders.

16 - The bolts are reinserted into the clay ports that were created by the placeholders.
 Parts A & B of Plasti-Paste® are mixed 1A:3B by volume and the Plasti-Paste is spread into the mold cavity and around the bolts to form the mouth core.

17 - Parts A & B of Plasti-Paste® are mixed 1A:3B by volume and the Plasti-Paste is spread into the mold cavity and around the bolts to form the mouth core.
 Cavity is filled with
Plasti-Paste®.

18 - Cavity is filled with Plasti-Paste®.
 Next, more clay is rolled out.

19 - Next, more clay is rolled out.
 Clay is cut into strips to make the shims that will divide the mold in half when applying the support shell.

20 - Clay is cut into strips to make the shims that will divide the mold in half when applying the support shell.
 Draw the parting line for the support shell.  Be careful to watch for mechanical locking.

21 - Draw the parting line for the support shell. Be careful to watch for mechanical locking.
 Apply the shim along the parting line  across the model and down the board.

22 - Apply the shim along the parting line across the model and down the board.
 Use additional clay on the reverse side of the shim to reinforce it so it doesn’t move when Plasti-Paste® is applied.

23 - Use additional clay on the reverse side of the shim to reinforce it so it doesn’t move when Plasti-Paste® is applied.
 A clay extension is applied to the extended bolt to act as a spacer against the Plasti-Paste®.

24 - A clay extension is applied to the extended bolt to act as a spacer against the Plasti-Paste®.
 The bolt extension and clay shim are sealed with spray shellac.

25 - The bolt extension and clay shim are sealed with spray shellac.
 Sonite® II wax is applied to the clayed areas.

26 - Sonite® II wax is applied to the clayed areas.
 Universal® Mold Release is applied to the clayed areas.

27 - Universal® Mold Release is applied to the clayed areas.
 Plasti-Paste® is mixed together with a 1A:2B by volume mix ratio.

28 - Plasti-Paste® is mixed together with a 1A:2B by volume mix ratio.
 The Plasti-Paste® is spread over the entire first half of the model, including the shim.

29 - The Plasti-Paste® is spread over the entire first half of the model, including the shim.
 The clay is removed from the first half of the  Plasti-Paste® shell after it has cured.

30 - The clay is removed from the first half of the Plasti-Paste® shell after it has cured.
 Sonite® II Wax is applied to the Plasti-Paste® shim and mouth plug.

31 - Sonite® II Wax is applied to the Plasti-Paste® shim and mouth plug.
 Universal® Mold Release is applied over the Sonite® II wax to assure good release.

32 - Universal® Mold Release is applied over the Sonite® II wax to assure good release.
 The second half of the Plasti-Paste® shell is applied and left to cure.

33 - The second half of the Plasti-Paste® shell is applied and left to cure.
 Three drywall screws are drilled through the shell edges and will be used to reassemble the shell.

34 - Three drywall screws are drilled through the shell edges and will be used to reassemble the shell.
 The mold and Plasti-Paste ® shell are pried away from the board.

35 - The mold and Plasti-Paste ® shell are pried away from the board.
 The rest of the clay is cleaned from the cavity and Sonite® II Wax applied to make a plug.

36 - The rest of the clay is cleaned from the cavity and Sonite® II Wax applied to make a plug.
 Sonite® II wax is applied to the bolts and nuts are threaded halfway onto the anchor bolts.

37 - Sonite® II wax is applied to the bolts and nuts are threaded halfway onto the anchor bolts.
 Drywall screws are used to secure a board across the mold and will help pull the plug out.

38 - Drywall screws are used to secure a board across the mold and will help pull the plug out.
 Smooth-Cast® 45D semi-rigid liquid plastic is mixed 1A:1B by volume and poured in the cavity.

39 - Smooth-Cast® 45D semi-rigid liquid plastic is mixed 1A:1B by volume and poured in the cavity.
 The anchor bolts are removed from the shell so the mold plug can be removed.

40 - The anchor bolts are removed from the shell so the mold plug can be removed.
 The plug is removed from the underside of the mold.

41 - The plug is removed from the underside of the mold.
 Remove the drywall screws that were previously installed.
Screwdrivers and a hammer are used to separate the two mold 
halves from each other.

42 - Remove the drywall screws that were previously installed. Screwdrivers and a hammer are used to separate the two mold halves from each other.
 Plasti’Paste® shell is removed.

43 - Plasti’Paste® shell is removed.
 The mouth core is then 
removed from the mouth 
cavity.

44 - The mouth core is then removed from the mouth cavity.
 The shape of the model and the configuration of the Rebound 25 mold allowed for the making of a “glove mold” that can be peeled off without making any cut marks that would leave a seam line that might be visible.

45 - The shape of the model and the configuration of the Rebound 25 mold allowed for the making of a “glove mold” that can be peeled off without making any cut marks that would leave a seam line that might be visible.
 Care is taken not to rip the mold or damage the teeth.

46 - Care is taken not to rip the mold or damage the teeth.
 The mouth core is placed back inside the mouth cavity and the mold seated in the shell half.

47 - The mouth core is placed back inside the mouth cavity and the mold seated in the shell half.
 Place the first of the two core holder bolts through the shell and the mouth core holes.

48 - Place the first of the two core holder bolts through the shell and the mouth core holes.
 Place the second half of the shell in place, being careful to align it properly.

49 - Place the second half of the shell in place, being careful to align it properly.
 Place the second of the core holder bolts through the shell and the mouth core holes.

50 - Place the second of the core holder bolts through the shell and the mouth core holes.
 Replace the drywall screws used to hold the shell firmly together.

51 - Replace the drywall screws used to hold the shell firmly together.
 Brush the plug with Sonite® II Wax to keep material from bonding to it.

52 - Brush the plug with Sonite® II Wax to keep material from bonding to it.
 Put the mold plug back into the mold, taking care to align the bolts and nut holes.

53 - Put the mold plug back into the mold, taking care to align the bolts and nut holes.
 Tighten the bolts to hold the mold plug firmly into place in the center of the mold.

54 - Tighten the bolts to hold the mold plug firmly into place in the center of the mold.
 The mold is then placed into a box full of packing peanuts and leveled out.

55 - The mold is then placed into a box full of packing peanuts and leveled out.
 The casting will be made with Matrix® NEO® which has a 2A:1B mix ratio by volume.

56 - The casting will be made with Matrix® NEO® which has a 2A:1B mix ratio by volume.
 In this case, four cups of Part A and two cups of Part B will be used.

57 - In this case, four cups of Part A and two cups of Part B will be used.
 An iron oxide powder is added to the mix to provide color to the finished casting.

58 - An iron oxide powder is added to the mix to provide color to the finished casting.
 The Matrix® NEO®  Parts A

59 - The Matrix® NEO® Parts A
 The blended mix is poured into the mold around the mold plug.

60 - The blended mix is poured into the mold around the mold plug.
 Fill the mold and reaffirm that the mold structure is level.

61 - Fill the mold and reaffirm that the mold structure is level.
 When the Matrix® NEO®  mix has cured begin the demold process.

62 - When the Matrix® NEO® mix has cured begin the demold process.
 Slowly remove the plug and the support shell.

63 - Slowly remove the plug and the support shell.
 Gently peel back the rubber mold from the Matrix® NEO® casting.

64 - Gently peel back the rubber mold from the Matrix® NEO® casting.
 The mold and Matrix® NEO® have combined to produce a perfectly detailed reproduction.

65 - The mold and Matrix® NEO® have combined to produce a perfectly detailed reproduction.

                   
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