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How to Make a 2-Piece Core Mold: Concrete Urn Example
Simplifying An Advanced Mold Making Application

This gallery outlines the steps for creating a two-piece cored mold using Reoflex® 40 urethane rubber from Smooth-On.
 Our model is a detailed  urn made of concrete.

1 - Our model is a detailed urn made of concrete.
 Urn is measured for dimensions.

2 - Urn is measured for dimensions.
 Acrylic coated boards are cut to size.

3 - Acrylic coated boards are cut to size.
 Mold box walls will follow the contour of the model.

4 - Mold box walls will follow the contour of the model.
 Construct mold box and secure with drywall screws.

5 - Construct mold box and secure with drywall screws.
 Two handles are attached to mold box to make handling easier.

6 - Two handles are attached to mold box to make handling easier.
 Use a black marker to mark inside edge of mold box to define clay bed perimeter.

7 - Use a black marker to mark inside edge of mold box to define clay bed perimeter.
 Remove mold box to expose perimeter line.

8 - Remove mold box to expose perimeter line.
 Form a 3/4'' (2 cm) thick clay bed inside marked area.

9 - Form a 3/4'' (2 cm) thick clay bed inside marked area.
 Place mold box over clay bed.

10 - Place mold box over clay bed.
 Fill any voids with additional clay.

11 - Fill any voids with additional clay.
 Use a rolling pin to smooth out clay bed.

12 - Use a rolling pin to smooth out clay bed.
 Smooth beveled edge around perimeter.

13 - Smooth beveled edge around perimeter.
 Drill vent hole: Allows air to escape during mold making process.

14 - Drill vent hole: Allows air to escape during mold making process.
 Make a clay gasket around perimeter.

15 - Make a clay gasket around perimeter.
 Center urn on clay bed.

16 - Center urn on clay bed.
 Firmly push urn into clay bed.

17 - Firmly push urn into clay bed.
 Registration key is cut into clay bed with large paper clip.

18 - Registration key is cut into clay bed with large paper clip.
 Overhead view showing registration key in clay bed.

19 - Overhead view showing registration key in clay bed.
 Apply Superseal® sealing agent to urn surface.

20 - Apply Superseal® sealing agent to urn surface.
 Apply Universal® Mold Release to mold box and urn.

21 - Apply Universal® Mold Release to mold box and urn.
 Place mold box over urn.

22 - Place mold box over urn.
 Seal seams with hot melt glue.

23 - Seal seams with hot melt glue.
 Dispense ReoFlex® 40 mold rubber 1A to 1 B by volume.

24 - Dispense ReoFlex® 40 mold rubber 1A to 1 B by volume.
 Mix thoroughly for three minutes, scraping bottom and sides of container.

25 - Mix thoroughly for three minutes, scraping bottom and sides of container.
 Pour rubber into cavity and let mold rubber cure for 16 hours at room temperature (72F / 23C).

26 - Pour rubber into cavity and let mold rubber cure for 16 hours at room temperature (72F / 23C).
 DO NOT COVER BOTTOM OF ORIGINAL MODEL. Exposed area will represent pour spout.

27 - DO NOT COVER BOTTOM OF ORIGINAL MODEL. Exposed area will represent pour spout.
 Next day, flip over mold box.

28 - Next day, flip over mold box.
 Slowly remove baseboard.

29 - Slowly remove baseboard.
 Remove rubber flashing.

30 - Remove rubber flashing.
 Carve notch into rubber with a knife for registration.

31 - Carve notch into rubber with a knife for registration.
 Inside the mold box is marked to identify registration point.

32 - Inside the mold box is marked to identify registration point.
 Apply Superseal® sealing agent to the inside of the urn.

33 - Apply Superseal® sealing agent to the inside of the urn.
 Apply Universal® Mold Release to mold box and urn.

34 - Apply Universal® Mold Release to mold box and urn.
 Clean modeling clay off baseboard. Once cleaned this will be used for the core section base.

35 - Clean modeling clay off baseboard. Once cleaned this will be used for the core section base.
 MAKING THE CORE SECTION. Place a plastic container on the center of baseboard and mark outline.

36 - MAKING THE CORE SECTION. Place a plastic container on the center of baseboard and mark outline.
 Drill four 1'' (2.5 cm)  holes. This is where the mold rubber will be poured to make the second half.

37 - Drill four 1'' (2.5 cm) holes. This is where the mold rubber will be poured to make the second half.
 1/4'' (6mm) vent holes will be drilled in highlighted areas.

38 - 1/4'' (6mm) vent holes will be drilled in highlighted areas.
 Vent holes will minimize air bubbles in cured rubber.

39 - Vent holes will minimize air bubbles in cured rubber.
 Hot melt glue is used to adhere plastic container to center of board.

40 - Hot melt glue is used to adhere plastic container to center of board.
 Hold in place for ten seconds.

41 - Hold in place for ten seconds.
 Place core section into mold caviity. Alignment point is marked on the outside of base and mold box.

42 - Place core section into mold caviity. Alignment point is marked on the outside of base and mold box.
 Adhere core section with drywall screws.

43 - Adhere core section with drywall screws.
 Use modeling clay to seal seams.

44 - Use modeling clay to seal seams.
 Dispense ReoFlex® 40 mold rubber 1A to 1 B by volume.

45 - Dispense ReoFlex® 40 mold rubber 1A to 1 B by volume.
 Mix thoroughly for three minutes, scraping bottom and sides of container.

46 - Mix thoroughly for three minutes, scraping bottom and sides of container.
 Pour rubber into cavity.

47 - Pour rubber into cavity.
 Let mold rubber cure for 16 hours at room temperature (72F / 23C).

48 - Let mold rubber cure for 16 hours at room temperature (72F / 23C).
 Remove drywall screws and slowly lift-up core section.

49 - Remove drywall screws and slowly lift-up core section.
 Remove mold box.

50 - Remove mold box.
 A sharp knife is used to extract the original model.

51 - A sharp knife is used to extract the original model.
 Mold reflects perfect detail captured from the original model.

52 - Mold reflects perfect detail captured from the original model.
 Apply Ease Release 2831 to all rubber surfaces.

53 - Apply Ease Release 2831 to all rubber surfaces.
 Use alignment point to help assemble mold for casting.

54 - Use alignment point to help assemble mold for casting.
 Reproduction will be made with duoMatrix® NEO (Polymer Modifed Gypsum).  Mix ratio 2 Parts A to 1 Part B by volume.

55 - Reproduction will be made with duoMatrix® NEO (Polymer Modifed Gypsum). Mix ratio 2 Parts A to 1 Part B by volume.
 One part play sand will be added for addional texture.

56 - One part play sand will be added for addional texture.
 Mix all components  thoroughly for three minutes, scraping bottom and sides of container.

57 - Mix all components thoroughly for three minutes, scraping bottom and sides of container.
 Add So-Strong® Brown  pigment to mix for color.

58 - Add So-Strong® Brown pigment to mix for color.
 Pour Matrix NEO slowly into cavity.

59 - Pour Matrix NEO slowly into cavity.
 After Matrix® NEO cures for 90 minutes remove mold box.

60 - After Matrix® NEO cures for 90 minutes remove mold box.
 Demold casting from the rubber mold.

61 - Demold casting from the rubber mold.
 Perfectly detailed reproduction of the original model.

62 - Perfectly detailed reproduction of the original model.
 Add color to the casting with brown wood stain.

63 - Add color to the casting with brown wood stain.
 Wipe-off any extra stain with soft towel.

64 - Wipe-off any extra stain with soft towel.
 Rubber mold is ready for production casting.

65 - Rubber mold is ready for production casting.
 Different finishes can be achieved by varying  color, tints and stain.

66 - Different finishes can be achieved by varying color, tints and stain.


Simplifying An Advanced Mold Making Application; Making Your Own 2-Piece Core Mold Of A Concrete Urn

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