Mold Making: Poured Blanket Mold vs. Poured Block Mold

In this article, we will demonstrate two different mold making methods using the same plastic lion head model [pictured below] and the same silicone mold rubber. The methods are the poured blanket mold technique and the poured block mold technique.

 

Plastic Model for Mold Making


 
Based on the size and shape of this particular model, either mold making method could be used with success. The following information is designed to give you a better idea of the advantages and disadvantages of each technique as you decide which method to use for your mold making project. Below, we note the basic comparisons of each technique and then detail each method with pictures and instruction.
 

 

Basic Comparisons:

  • The poured block mold is considered the simplest type of mold, while poured blanket molds can take some time to master.

 

Mold Complexity-01

 

  • Poured blanket molds generally require less mold rubber than poured block molds.
    • In this specific tutorial, 4.3 lb of silicone mold rubber is needed for the poured blanket mold and 12.5 lb of silicone mold rubber is needed for the poured block mold (i.e., less money is spent on mold rubber). NOTE: Keep in mind that poured blanket molds do require construction of a mold shell (next bullet point), which requires more materials.
  • Poured blanket molds require construction of a “mold shell” or “mother mold”, while poured block molds require a containment area often referred to as a “mold box”. The following materials are often used to make mold boxes: melamine-laminated particle board, plywood, PVC pipe, plastic pails, metal flashing and many other options. The construction of mold shells take practice, while the construction of a box can be rather simple.
  • Removing castings from poured blanket molds can sometimes be easier because these molds are generally more thin and flexible compared to block molds. This depends heavily on the shape of the model, however.

 

Demonstration of Each Method:

The first step in both methods is to construct a containment area around the model. For the poured blanket mold method, a mold shell is constructed from liquid plastic. For the poured block mold method, a mold box is constructed from melamine-laminated particle board.

 

Rubber Blanket Molds vs Rubber Block Molds-01


 
Both methods are detailed below:
 

 

Poured Blanket Mold: Construction of Mold Shell

First, secure the model to the baseboard. We insert a wood screw through the bottom of the baseboard and into the plastic model. Another option is to adhere the model to the baseboard with epoxy. The baseboard in this tutorial is a piece of melamine-laminated particle board.
 

SecureModeltoBaseboard_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Place plastic wrap over the model.

 

 

CoverModelwithPlastic_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

CoverModelwithPlasticWrap_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Form a uniform layer of clay over the model and plastic wrap. Make sure to use a sulfur-free, oil-based clay (we use plasticine clay) as sulfur can inhibit the cure of silicone mold rubbers.

The layer of clay should be approximately 1/2″ thick and should fill in any undercuts on the model. The clay represents the space that the mold rubber will later fill, so uniform thickness is important (i.e., you do not want thin spots or holes in your finished mold).

 

Clay over MOdel

Poured Blanket Mold: Construction of Mold Shell

 

 

Create a clay flange that extends ~1 to 1.5 inches beyond the model. Smooth out the clay as best as possible.

 

 

CoverModelwithClay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Build-up an area that will serve as the pour hole, which is where mold rubber will later be poured.

 

 

Build-UpPouredHole_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

SmoothOutPourHole_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Again, smooth out the clay as best as possible.

 

 

UniformLayerofClay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Spray Pol-Ease® 2300 Release Agent onto the clay and surrounding baseboard. This will help remove the plastic mold shell from the clay and particle board later in the process.

 

 

Pol-Ease 2300 Release Agent_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Apply Release Agent to Clay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Select a mold shell plastic such as Poly 1512X Liquid Plastic. This polyurethane plastic has a working time of 5 minutes and a demold time of ~30 minutes.

 

 

Mold Shell Plastic_BlanketMold

Poured Blanket Mold: Construction of Mold Shell

 

 

Poly 1512X has a 1A:1B mix ratio and can be measured by volume or weight.

Measure Part A:

 

 

Measure Mold Shell Plastic_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Measure Part B:

 

 

Measure Poly 1512X Mold Shell Plastic_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Plastic Measured by Volume_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Thoroughly mix together Part A & Part B and then add PolyFiber II thickener to bring the mixture to a brushable consistency.

 

 

PolyFiberII Thickener_BlanketMold

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Mix Mold Shell Plastic with Thickener_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Add PolyFiber II thickener until a thick, non-sag consistency is reached.

 

 

PlasticBrushableConsistency_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Apply the thickened Poly 1512X to the layer of clay, leaving an opening at the top of the pour hole. Note: get the Poly 1512X plastic out of the mixing pail as quickly as possible; it will cure faster in larger masses (i.e., sitting in the pail).

 

 

Apply Mold Shell Plastic to Clay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Spread the plastic evenly over the plasticine clay using disposable dry brushes or other tools like stainless steel spatulas.

 

 

Apply Plastic with Brush_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Mold Shell Creation_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Distribute Mold Shell Plastic Evenly_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Create a plastic flange that extends 1-2 inches beyond the clay on the baseboard.
 

 

Mold Shell_Poly1512X_BlanketMold

Poured Blanket Mold: Construction of Mold Shell

 

 

Before the plastic completely sets, add legs that will hold and level the mold and mold shell for casting later.

 

 

LevelWoodenLegs_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

AddWoodenLegs_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

When the Poly 1512X plastic has set (after ~30 minutes – this time will vary depending on temperature and humidity), create a reference point with a permanent marker indicating the location of the mold shell in relation to the baseboard for proper re-positioning later in the process.

 

 

Mark Location of Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Drill holes evenly throughout the plastic flange – the mold shell will later be re-positioned and screwed into place in these locations.

 

 

Secure Mold Shell to Baseboard_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Loosen the edges of the mold shell and carefully remove it from the baseboard. CAUTION: Edges of the plastic mold shell can be very sharp.

 

 

PryMoldShell

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Remove Mold Shell from Model_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Remove the plastic wrap and clay from the mold shell.

 

 

Clean Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Clean Interior of Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

If necessary, trim the top of the pour hole.

 

 

Clean Pour Hole_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

 

 

Finished Plastic Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Apply a release agent, like Petroleum Jelly, to the interior of the mold shell.

 

 

Apply Petroleum Jelly to Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Apply release agent to the model and surrounding baseboard before placing the mold shell back over the model. We have selected a silicone rubber as the mold material, so Pol-Ease® 2500 Release Agent is used.

 

 

Pol-Ease 2500 Release Agent_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Spray the release agent onto the model and then brush it out with a dry brush to encourage even and thorough coverage.

 

 

Brush Release Agent onto Plastic Model

Poured Blanket Mold: Construction of Mold Shell

 

 

Re-position the mold shell in its original position over the model. Align the marker and holes.

 

 

Reposition Mold Shell over Model_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Secure the mold shell to the baseboard with screws.

 

 

SecuretoBaseboard_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Seal around the screws and the edges of the mold shell with plasticine clay to help prevent rubber from leaking out.

 

 

SealEdgesofMoldShell-01

Poured Blanket Mold: Construction of Mold Shell

 

 

Construction of the mold shell is now complete.
 

Poured Block Mold: Construction of Mold Box

Start by securing the plastic model to the baseboard.

 

 

Bottomboard

Poured Block Mold: Construction of Mold Box

 

 

Seal the edges of the model with oil-based, sulfur-free clay (e.g., plasticine clay). Hot glue and caulk also work.

 

 

Caulk Edges with Clay_Block

Poured Block Mold: Construction of Mold Box

 

 

 

 

Smooth Edges_Block

Poured Block Mold: Construction of Mold Box

 

 

Smooth out and flatten the clay as best as possible.

 

 

Prevent Model from Floating_Block

Poured Block Mold: Construction of Mold Box

 

 

Apply Pol-Ease® 2500 Release Agent to the model and surrounding baseboard and then brush out with a dry brush. This step can be completed after the mold box is constructed; however, it is a bit easier to accomplish prior to construction.

 

 

Apply 2500 Release Agent_Block

Poured Block Mold: Construction of Mold Box

 

 

 

 

Spray 2500 Release Agent_Block

Poured Block Mold: Construction of Mold Box

 

 

 

 

Brush Out Release Agent_Block

Poured Block Mold: Construction of Mold Box

 

 

Construct walls around the model. We recommend leaving at least 1/2-inch of space between the model and mold box walls (sometimes more space is required, depending on the size/shape of the model and the casting material that will later be used).

We are using melamine-laminated particle board for the mold box. These adjustable mold boxes are available for purchase on www.polytek.com.

 

 

Construct Mold Box_Block

Poured Block Mold: Construction of Mold Box

 

 

 

 

Particle Board Mold Box_Block

Poured Block Mold: Construction of Mold Box

 

 

Secure mold box walls together. We use C-Clamps.

 

 

Secure with C-Clamps_Block

Poured Block Mold: Construction of Mold Box

 

 

Secure the mold box walls to the bottom board with screws; this will help to prevent rubber from seeping between them and lifting the walls.

 

 

Secure Baseboard to Walls_Block

Poured Block Mold: Construction of Mold Box

 

 

Seal the interior edges and corners of the mold box with clay (or hot glue or caulk) to help prevent leaking.

 

 

Seal Interior Edges_Block

Poured Block Mold: Construction of Mold Box

 

 

 

 

Smooth Clay in Mold Box_Block

Poured Block Mold: Construction of Mold Box

 

 

Here are the finished containment areas pictured side-by-side.

 

 

Finished Containment Areas_Blanket Mold_Block Mold

Mold Shell  /  Mold Box

 

 

Poured Blanket Mold: Pouring the Mold Rubber & Demolding

For both molds, we use PlatSil® 73-20 Silicone Rubber. It is a soft, platinum-cured silicone rubber with a 5-minute working time and a 1-hour demold time.

 

PlatSil 73-20 has a 1A:1B mix ratio. Carefully weigh out Part A & Part B and then combine and thoroughly mix. Scrape the sides and bottom of the mixing container several times.

 

 

Two-Part Platinum Silicone Mold Rubber

Poured Blanket Mold: Pouring the Mold Rubber

 

 

 

 

Mix Silicone Rubber

Poured Blanket Mold: Pouring the Mold Rubber

 

 

 

 

Poly Paddle Mixing Tool

Poured Blanket Mold: Pouring the Mold Rubber

 

 

4.3 lb of PlatSil 73-20 rubber is necessary to complete this mold (compared to 12.5 lb of rubber needed to complete the poured block mold).

Carefully pour the mixed rubber into the pour hole until it reaches the top.

 

 

Fill Mold Shell with Silicone Rubber_Blanket

Poured Blanket Mold: Pouring the Mold Rubber

 

 

 

 

Fill to Top of Mold Shell_Blanket

Poured Blanket Mold: Pouring the Mold Rubber

 

 

Allow the rubber to cure for about an hour at room temperature and then carefully remove the mold shell.

 

 

Remove Plastic Mold Shell from Mold._BlanketJPG

Poured Blanket Mold: Demold

 

 

 

 

Silicone Poured Blanket Mold_Blanket

Poured Blanket Mold: Demold

 

 

Loosen the edges of the silicone mold and then remove it from the model.

 

 

Peel Mold from Model_Blanket

Poured Blanket Mold: Demold

 

 

 

 

Loosen Edge of Mold_Blanket

Poured Blanket Mold: Demold

 

 

 

 

Finished Poured Blanket Mold_Blanket

Poured Blanket Mold: Demold

 

 

When ready for casting, place the mold back into the mold shell and align properly.

 

 

Place Silicone Mold in Mold Shell_Blanket

Poured Blanket Mold: Finished

 

 

 

 

Place Mold in Shell

Poured Blanket Mold: Finished

 

 

 

 

Poured Blanket Mold_Polytek_Blanket

Poured Blanket Mold: Finished

 

 

Poured Block Mold: Pouring the Mold Rubber & Demolding

Mixing procedure for the mold rubber is the same for both options.

12.5 lb of PlatSil 73-20 rubber is necessary to complete this mold (compared to 4.3 lb of rubber needed to complete the poured block mold).

Pour the mold rubber into one corner of the mold box and let it rise. Pour rubber into rubber and avoid pouring directly on the model.

 

 

Fill Mold Box with Rubber_Block

Poured Block Mold: Pouring the Mold Rubber

 

 

Fill the mold box to at least 0.5″ above the model.

 

 

Fill to Top of Mold Box_Block

Poured Block Mold: Pouring the Mold Rubber

 

 

Spraying release agent across the surface of the rubber immediately after pouring can help to release air bubbles.

 

 

73-20 block mold

Poured Block Mold: Pouring the Mold Rubber

 

 

Allow the rubber to cure for approximately 1 hour and then demold. Remove the screws that secure the baseboard to the mold box walls.

 

 

Remove Screws from Mold Box_Block

Poured Block Mold: Demold

 

 

Remove the C-clamps and mold box walls.

 

 

Remove C-Clamps_Blanket

Poured Block Mold: Demold

 

 

 

 

Remove Mold Box Walls_Block

Poured Block Mold: Demold

 

 

Loosen the edges of the mold and then remove it from the model. A prying tool may be helpful.

 

 

Remove Block Mold from Model_Block

Poured Block Mold: Demold

 

 

 

 

Lift Mold from Model_Block

Poured Block Mold: Demold

 

 

The mold is now ready for casting.
 

Resin Casting with EasyFlo 60

We prepare enough EasyFlo 60 Liquid Plastic to pour into both molds. EasyFlo 60 is a two-part, low-viscosity polyurethane plastic in the EasyFlo Series. This fast-setting plastic has a 2 to 2.5-minute working time and a 15 to 30-minute demold time.

Measure EasyFlo 60 by volume (1A:1B) or by weight (100A:90B) and mix thoroughly.

 

 

Fast-Setting Casting Resin_EasyFlo60

EasyFlo 60 Liquid Plastic

 

 

 

 

Measure Out EasyFlo Liquid Plastic

EasyFlo 60 Liquid Plastic

 

 

Carefully pour the mixed resin into the molds.

 

 

Poured Resin into Mold Cavity_BlanketMold

Poured Blanket Mold: Resin Casting

 

 

 

 

Pour EasyFlo Resin into Silicone Block Mold

Poured Block Mold: Resin Casting

 

 

Allow 15 to 30 minutes before demolding. This resin is a translucent yellow/amber color in liquid form, but cures to an opaque white color.

 

Allow EasyFlo to Cure

Demold the poured blanket mold by first removing the plastic mold shell.

 

 

 

Demold Poured Blanket Mold

Poured Blanket Mold: Demold

 

 

Peel back the blanket mold to remove the casting.

 

 

Peel Back Silicone Mold from Model_Blanket

Poured Blanket Mold: Demold

 

 

 

 

Demolding Plastic Model_BlanketMold

Poured Blanket Mold: Demold

 

 

 

 

Finished Casting_Blanket Mold

Poured Blanket Mold: Demold

 

 

To demold the poured block mold, loosen the edges and pull out the casting. This demold requires a bit more effort as the model has some undercuts and the mold rubber is thicker and less flexible compared to the blanket mold.

 

 

Demold Block Mold

Poured Block Mold: Demold

 

 

 

 

Remove Model from Mold_Block

Poured Block Mold: Demold

 

 

 

 

Demold Plastic Lion Head_Block

Poured Block Mold: Demold

 

 

We put some finishing touches on the plastic castings with black and green wax.

 

Apply Wax to EasyFlo Casting

 

 

 

EasyFlo 60 Plastic Head with Wax

 

 

 

Black and Green Wax Applied to Plastic Model

 

 

 

 

Poured Block Mold vs Poured Blanket Mold

left: casting from the poured block mold | right: casting from the poured blanket mold


 

 

Video Tutorial

This is one of the projects that we worked on with BITY Mold Supply (a distributor of Polytek products) when he paid us a visit back in December. Here is this video tutorial of the project:

 

 

 

 

Do you need assistance in selecting an appropriate mold making method and material for your next project? Ask our technical support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.