Difference between Poured Block and Blanket Molds

The uses of silicone rubber across mold making and casting are too many to list. It can be used to make both block and blanket molds. Find out how to make these poured molds using silicone rubber.

Silicone rubber is an inherently versatile material which lends itself well to various applications in both mold making and casting. When it comes to mold making, both the poured block and poured blanket molds can be made using silicone rubber. Let us take a look at both these techniques:

Poured block mold – This is considered the simplest method for making a mold. All it requires is making a containment area or a mold box. For this, the model is first secured to a flat base and the edges are sealed with clay or glue. The walls of the box can be made using particle board, plywood, PVC pipes, etc. These walls will have to be secured together as well as to the bottom of the box before sealing the interior edges and corners to prevent leakage of any kind. Alternatively, the walls can be fashioned with clay itself.

Once the mold box is ready, making the mold is as easy as simply pouring the mixed silicone rubber into the box till it completely covers the model and then some more. This should be done from a corner while avoiding pouring directly over the model. Let it cure proper before demolding by dismantling the mold box and prying the mold loose. The mold will be ready for casting.

This technique does require a lot of rubber but is preferred for its simplicity.


Poured blanket molds This is a more complicated process as it requires constructing a mold shell over the model which will take some practice. Here also the model is first secured to a base. Then it is covered with plastic wrap before applying clay to about half inch thickness. This should be uniform and fill all undercuts in the model. The clay is extended to form a flange and a pour hole is also needed.

A thickened mixture of polyurethane resin is applied over the clay and legs are added that will serve to hold and level the mold later on. Holes are drilled evenly throughout the plastic flange that will help in repositioning and screwing later.

Once cured, the mold shell is demolded and the clay is removed from inside. The model is again glued to the board and the plastic shell is repositioned over it by aligning the holes before securing it to the base with screws. Sealing the edges with clay will prevent leakage.

Mixed silicone rubber is poured inside through the hole at the top. This will cure to form a mold in place of the clay. The mold shell is removed and he edges of the silicone mold are loosened for demolding it from the model. When casting, the mold has to be placed in the shell mold again.

It is clear that this process may be complicated, but will require much less mold making material. The final casting will be easier to demold too as the poured blanket molds are thin and flexible.

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