Casting urethane rubber in a one piece mold? Possibly foam backed?

Hello everyone,

I would like to cast a urethane master to make a plaster mold from for latex mask making (fullhead) without the master shrinking. The mold is showing some signs of wear and I'd like to prolong the life of the original sculpture with making this "master".

My mold is one piece though and I've never worked with urethane rubber specifically (just used the foam to fill latex props). I was wondering what precautions I would have to take to use the hydrocal mold for urethane? Is there a specific shore to look for?

I imagine some release would be necessary, if anyone knows a specific one to look for that would be very helpful. Should the mold be sealed first? Would filling it with a soft foam make it harder to get it out of the mold? I have flex foam 5 on hand.

Sorry for all the questions, I'm very new to urethane and worried about ruining my mold.

HI
If you seal the mold, much better (or a must). You can use shellac for example.
For urethanes I use wax as a release. Release the dang out of it, urethanes are glue and Hydrocal is porous.
As for filling it with flex foam 5 I´d say it should be ok. But it will depend on the shapes you have there.
Anyway, if you can, make some release tests,.

A workaround could be making a tin silicone foam filled casting,and then mold that in resin so you can make "master castigs" any time you need to remold in plaster for latex. Something like a "master mold".
This wouldn´tt be so risky for your mold. Not sure what is the lowest contraction rate you can find in tin silicone on the other hand.

udog said:

HI
If you seal the mold, much better (or a must). You can use shellac for example.
For urethanes I use wax as a release. Release the dang out of it, urethanes are glue and Hydrocal is porous.
As for filling it with flex foam 5 I´d say it should be ok. But it will depend on the shapes you have there.
Anyway, if you can, make some release tests,.

A workaround could be making a tin silicone foam filled casting,and then mold that in resin so you can make "master castigs" any time you need to remold in plaster for latex. Something like a "master mold".
This wouldn´tt be so risky for your mold. Not sure what is the lowest contraction rate you can find in tin silicone on the other hand.

Click to expand...

Thank you very much! That is very helpful.