Polyurethane molding question

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tubachris85x

Master Member
RPF PREMIUM MEMBER
Need to know if you can make a two part mold with polyurethane rubber? In other words, will one half be destroyed by me applying rubber over it in the same manner as doing a two part silicone mold?

I searched on google without success, just need to be sure I won't ruin the existing mold..thanks

-TC
 

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Finhead

Sr Member
It'll work just fine if you use a release agent on it between the two halves. Vaseline or a silicone spray will work fine.
 

Jaruemalak

Well-Known Member
Paste wax is used on fiberglass or other polyester resin molds - basically hard shell molds, but you shouldn't need anything like that on a polyurethane rubber mold. Silicone release agent should be fine.
 

tubachris85x

Master Member
RPF PREMIUM MEMBER
Paste wax is used on fiberglass or other polyester resin molds - basically hard shell molds, but you shouldn't need anything like that on a polyurethane rubber mold. Silicone release agent should be fine.
Well the reason for the paste wax was to use as a sealer for porous material, as I had to do that with my plasticina clay model I molded before.
 

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Finhead

Sr Member
Are you asking if you have to seal your model or piece before pouring the Urethane for molding? If that is the question then yes you have to seal off any porous surface to use molding rubber regardless the material used.

Well the reason for the paste wax was to use as a sealer for porous material, as I had to do that with my plasticina clay model I molded before.
 

Jaruemalak

Well-Known Member
I assumed you meant use paste wax as a barrier between the layers of urethane, so it wouldn't stick to itself. If you mean use it on the object you are molding... maybe. Depends on what it is. If you are molding something porous, then as Finhead said, it does need to be sealed. Urethane tends to stick to something porous a LOT better than standard silicone molding material.
 

tubachris85x

Master Member
RPF PREMIUM MEMBER
Are you asking if you have to seal your model or piece before pouring the Urethane for molding? If that is the question then yes you have to seal off any porous surface to use molding rubber regardless the material used.
Sorta, I was asking if I had to seal the polyurethane of the cured half before applying fresh rubber on top of it for the 2nd half so it would not adhere to itself and ruin the whole thing.

I assumed you meant use paste wax as a barrier between the layers of urethane, so it wouldn't stick to itself. If you mean use it on the object you are molding... maybe. Depends on what it is. If you are molding something porous, then as Finhead said, it does need to be sealed. Urethane tends to stick to something porous a LOT better than standard silicone molding material.
Very true!

As an update, I did apply the paste wax over the cured half and the model just to be safe, and it all turned out very well! Thanks guys!
 

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