Making a 2-Part Block Mold of an Architectural Bracket
After Hurricane Katrina hit New Orleans, city native Chep Morrison used Mold Max® XLS II LOW SHRINKAGE silicone rubber to replicate an ornate bracket for an architectural restoration project near the Garden District.
After the unique, two-part block-mold was made using a custom-shaped mold box, the ornate brackets were cast in a two-step process that involved coating the surface of the mold first using duoMatrix® NEO Polymer Modified Gypsum. This was done to create a hollow piece and reduce the overall weight of the casting.
Once the duoMatrix® NEO was applied and allowed to cure, the second step involved backfilling the hollow castings to add dimensional strength and stability to the bracket structure. Foam-iT!® 10 SLOW is a 10 lb. / cubic foot expanding urethane foam that was used to backfill the hollow castings. Foam-iT!® 10 SLOW expands approximately 6 times it's original volume and cures to a rigid finish. After measuring and mixing the foam, it began to expand and fill in all the nooks of the interior aspect of the hollow casting and was allowed to cure at room temperature (73°F / 23°C).
By using Mold Max® XLS II, Mr. Morrison could create many exact replicas of the original bracket, not only for this project but for future projects as well. In using duoMatrix® NEO and Foam-iT! 10 SLOW, the brackets display remarkable dimensional strength and stability, while maintaining an overall lightweight finish. Maintaining a lightweight finish enabled Mr. Morrison to easily install the ornate brackets, helping to reduce labor costs.
1 - Example of this the type of bracket after being installed.
2 - The painted wooden bracket (model) is placed on a flat level surface.
3 - Dimensions are approximately 72'' x 30'' x 4'' (182cm x 76cm x 10cm).
4 - To make the 2-part mold, the model will be divided into two halves horizontally and a parting line will then be constructed.
5 - Craft paper is placed under the model and will be used to create a template for the parting line.
6 - The pattern is transferred onto the craft paper (template) with a pencil.
7 - Scissors are used to cut out the template.
8 - Cut out pattern.
9 - The pattern is then transferred onto a piece of wood with a pencil.
10 - A jigsaw is used to cut the wood.
11 - Pattern cut out. This will be used to establish the parting line.
12 - The wood parting line is elevated and secured in the correct position.
13 - Non-sulfur based clay is used to fill any voids between the parting line and the model.
14 - Clay is smoothed out.
15 - The original template is used to create a new template for the mold box side walls.
16 - The line is offset 2'' (5 cm) to provide enough space around the model to allow for suitable rubber mold wall thickness.
17 - Scissors are used to cut out the template.
18 - The pattern is transferred onto a piece of wood with a marker.
19 - A jigsaw is used to cut the wood.
20 - Additional wood is cut to build mold box side wall.
21 - Mold box side walls are placed onto the wood parting line and secured.
22 - The space between mold box side walls and model allows for suitable mold wall thickness.
23 - A mold box lid is constructed to contain the silicone rubber.
24 - The lid is reinforced with wood to provide additional support.
25 - Channels are routered into the mold box lid to function as a registration key for the rubber mold.
26 - Vent holes are drilled to allow air to escape as the mold box is filled.
27 - Additional wood is cut and attached to complete the mold box.
28 - Mold Max® XLS II silicone rubber - very low long-term shrinkage.
29 - Mix Ratio: 100A:10B by weight.
30 - Mold Max® XLS II Part B being measured.
31 - Mix Mold Max® XLS II for at least 3 minutes.
32 - Mold Max® XLS II pot life is 40 minutes.
33 - After mixing, the rubber is vacuum degassed.
34 - Mold Max® XLS II is poured over the model.
35 - Mold Max® XLS II being poured.
36 - Mold Max® XLS II poured.
37 - Mold box lid is placed over the silicone.
38 - Mold box lid is secured with screws.
39 - Additional silicone is poured in the top of the mold box to fill the open void.
40 - Non-sulfur oil based clay is used to plug pre-drilled vent holes.
41 - All vent holes are plugged with clay.
42 - Additional wood is used to cap the mold box.
43 - Mold box cap is secured with screws. Let Mold Max® XLS II cure for 24 hours at room temperature (73°F / 23°C).
44 - Mold box is turned over...
45 - ... the parting line wood is removed.
46 - Wood removed.
47 - Clay is removed from the model.
48 - Model in cured silicone rubber; thoroughly cleaned.
49 - Wood is cut to form mold box side walls.
50 - Wood is secured with screws.
51 - Additional wood is cut and attached on the sides to complete the mold box.
52 - Mold box assembled.
53 - Ease Release® 200 is applied to the cured silicone surface to prevent adhesion between pours of rubber.
54 - The silicone spray is brushed into the surface detail.
55 - Mold Max® XLS II is dispensed, mixed and vacuumed.
56 - Mix Ratio: 100A : 10B by weight.
57 - Mold Max® XLS II Part B being measured.
58 - Mix Mold Max® XLS II for at least 3 minutes.
59 - Mold Max® XLS II pot life is 40 minutes.
60 - After mixing, the rubber is vacuum degassed.
61 - Mold Max® XLS II is poured over the model.
62 - Mold Max® XLS II being poured.
63 - Second-half mold box lid is placed over silicone and secured with screws.
64 - Additional silicone rubber is poured in the top of the mold box to fill the open void.
65 - Non-sulfur oil based clay is used to plug pre-drilled vent holes.
66 - Additional wood is used to cap mold box. Let Mold Max® XLS II cure for 24 hours at room temperature (73°F / 23°C).
67 - Mold box is disassembled.
68 - Mold box disassembly.
69 - Mold box disassembly.
70 - Demold.
71 - Demold.
72 - Mold box is turned over and the second half is removed.
73 - Demold.
74 - Demold.
75 - Mold Max® XLS II captures excellent detail and is ready for casting.
76 - Wood legs are attached to the plywood lid.
77 - Legs will keep mold assembly orientated vertically during casting.
78 - duoMatrix® NEO Mix Ratio: 2 Parts A: 1Part B by volume.
79 - duoMatrix® NEO Part A dispensed.
80 - duoMatrix® NEO Part B dispensed.
81 - Ure-Fil® 9 is added to thicken the mix to allow for a brush-on application.
82 - duoMatrix® NEO with Ure-Fil® 9 measured out.
83 - duoMatrix® NEO with Ure-Fil® 9 is mixed thoroughly with a drill mixer.
84 - duoMatrix® NEO is poured into the mold.
85 - Material is then spread onto the mold surface using a clean, disposable paint brush.
86 - duoMatrix® NEO is applied to a thickness of 3/16'' (4.7 mm).
87 - duoMatrix® NEO is applied to the second half of the mold.
88 - duoMatrix® NEO is allowed to cure for 90 minutes at room temperature (73°F / 23°C).
89 - Mold halves are joined together.
90 - Mold box halves are secured.
91 - The mold assembled.
92 - Additional duoMatrix® NEO is measured, mixed and poured along the seam to help join the two halves of the casting.
93 - Foam-iT!® 10 SLOW Rigid Polyurethane Foam.
94 - Foam-iT!® 10 SLOW Part A is dispensed.
95 - Foam-iT! 10 SLOW Part B is dispensed.
96 - Foam-iT!® 10 SLOW Parts A & B are mixed thoroughly with a drill and Turbine Mixer attachment.
97 - Foam-iT!® 10 SLOW is poured into the cavity and allowed to expand.
98 - Multiple small batches of foam are added to fill the cavity as needed.
99 - A board pre-drilled with vent holes is placed over the mold box opening and secured to create back pressure.
100 - The material in the assembly is allowed to cure for 2 hours at room temperature (73°F / 23°C).
101 - Mold box is disassembled.
102 - (Mold box disassembly).
103 - (Mold box disassembly).
104 - (Mold box disassembly).
105 - Rubber is slowly pulled away from the casting.
106 - (Rubber demold Side A)
107 - (Rubber demold Side B)
108 - (Rubber demold Side B)
109 - Rubber demolded.
110 - Casting is an exact lightweight reproduction of the original bracket.
111 - Mold Max® XLS II mold is ready to be cast again and again.
112 - At the Job Site: the Mold Max® XLS II mold has been cast is ready for demolding.
113 - The mold box is disassembled...
114 - The Mold Max® XLS II silicone rubber mold pulls away from the casting effortlessly.
115 - The Mold Max® XLS II silicone rubber mold pulls away from the casting effortlessly.
116 - The casting reflects all of the surface dtail of the silicone mold perfectly.
117 - The 2nd Half of the silicone mold being Demolded.
118 - The Newly made bracket casting fresh from the mold.
119 - The casting comprised of duoMatrix® NEO and Foam-iT!® 10 SLOW is structurally lightweight but ultra strong and dimensionally stable.
120 - The casting reflects all of the surface detail of the silicone mold perfectly.
121 - The house where the newly cast brackets will be installed.
122 - The first bracket has already been installed in place.
123 - Before the brackets may be installed, excess Foam-iT!® 10 Slow is trimmed off with a grinder to level the surface that will press against the porch ceiling.
124 - Trimming the excess expanded foam will help prevent causing any gaps in between the bracket and the ceiling.
125 - Excess foam is trimmed along the entire length of the bracket.
126 - The bracket is ready for installation.
127 - The bracket is held in place using a brace.
128 - The bracket is attached to the ceiling using anchoring screws.
129 - Multiple brackets are all cast from the single mold.
130 - Installing the cast brackets only takes a few minutes.
131 - The house now displays an architectural charm that is unique to New Orleans.