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Using different silicone rubber during mould building.

http://www.talkcomposites.com/Topic30968.aspx

By t140v - 11/8/2018 10:42:23 AM

Morning all,
I am currently constructing a 3 part "bucket" mould to cast reproduction headlamp shells, the outside is completed having used a platinum cure rubber coated with a fibreglass support shell and is in 2 parts to enable easy pattern extraction.
I am now coating the inside of the mould with a platinum cure silicone to build up the thickness ready for the glass fibre support.
If i use all my platinum cure rubber can I use CS25 to build up the inside rubber thickness or is it not compatible with overlaying it on top of the platinum cure type material.

Regards Stuart
By t140v - 11/9/2018 11:08:01 PM

 
Hanaldo - 11/9/2018 3:46:53 AM
Yeh it's not a good idea. Most silicones will suffer inhibition when cured in contact with another type of silicone (ie. addition poured over condensation, and vise versa), so chances are it won't actually cure. 

Then even on the off chance you dont experience inhibition, the different shrink rate between the two materials will mean they wont bond to each other and your mould will fall apart after a little while.

Thanks for the advice, had done a bit more research and came to a similar conclusion so ordered some more platinum silicone, mold is in final stages  an a pity to ruin it for the sake of £30.00

Regards Stuart