Rubber not curing HELP ! PLEASE !!

tk1608

tk1608

Sr Member
Hi Guys, I seem to have messed up a mould, the rubber doesn't seem to be setting.
I've done a few before and not had this problem. A recent one seemed to set a bit too quick, while I was pouring it in fact...it was ok... but I decided to add a bit less catalist in this one.
It's been three days and it's just as liquid as when it was poured.
Can this be saved ?...I'm really worried that I'll never clean off the un-cured rubber to be able to start again..

Any help would be great..pleeeaaassse !

Cheers

Phil
 
tk1608 said:
Hi Guys, I seem to have messed up a mould, the rubber doesn't seem to be setting.
I've done a few before and not had this problem. A recent one seemed to set a bit too quick, while I was pouring it in fact...it was ok... but I decided to add a bit less catalist in this one.
It's been three days and it's just as liquid as when it was poured.
Can this be saved ?...I'm really worried that I'll never clean off the un-cured rubber to be able to start again..

Any help would be great..pleeeaaassse !

Cheers

Phil
Click to expand...

Lets me guess- yellow catalyst from CFS?
If its a solid product you are molding- ie wood, resin etc, then drain off the silicone into a beaker etc and you can remove the remaining silicone left on your model with lighter fluid ( turps maybe?)

You can probably reuse the silicone if you fancy it;-)

Not sure what to recommend doing if its a soft product inside the silicone, like soft clay etc- but prob do all of above, but just v-e-r-y c-a-r-e-f-u-l-l-y ;-)
 
tk1608 said:
Hi Guys, I seem to have messed up a mould, the rubber doesn't seem to be setting.
I've done a few before and not had this problem. A recent one seemed to set a bit too quick, while I was pouring it in fact...it was ok... but I decided to add a bit less catalist in this one.
It's been three days and it's just as liquid as when it was poured.
Can this be saved ?...I'm really worried that I'll never clean off the un-cured rubber to be able to start again..

Any help would be great..pleeeaaassse !

Cheers

Phil
Click to expand...

if you added anything less than the 10% most rubber reqiuires it will cure eventually but it will take a long while
 
Ok that's making me feel a bit better..I'll leave it a week before I do anything else and see if it starts to set.

Failing that I'll try the cleanup route.


Thanks a lot guys

Phil
 
You can also try and heat the mold up to accelerate curing. Not too hot but around 90-100 deg. will help. Don't heat the mold directly,
put it in a hot room or build a little warming box. If you have to redo it alcohol will help get the silicone off the original if it's a rigid part. Good luck.
 
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I wish you luck with this. I had this happen to me when molding up a saber years ago. I didn't cure in the proper amount of time so I left it for a week. I even put it outside in the L.A. summer sun (because I was living there at the time) during the day, and it still didn't cure.

If this ever happens to me again, I'm just going to demold it, clean the part up, and remold it. I'm over waiting and hoping for silicone to cure.

I hope you have better luck than I have had with this!
 
Sounds like it didn't cure because your mixing ratio was off.Was this a silicon or urethane RTV rubber?Sorry,I didn't read every post.RTV rubbers are very sensitive to their part A&B/mixing ratios.Allot are done by volume,some by weight.Other times if you don't mix the ratios thoroughly, even if the rations are correct it will cure funny.
 
It say's it's RTV....This doesn't sound too good does it?

I'll leave it the warm water tank room for another week and see what happens,...from what you've all said though, I'm not too hopeful.

Some parts I was trying to cast are resin, which I'll try to clean up as advised earlier with alcohol, but others are plastic kit parts. Will the alcohol clean those too ?..I'm worried it could melt them.

Thanks again guys

Phil
 
Are you sure you don't have anysulphur based clay in there? That will definately inhibit the cure (I wasted about a gallon of RTV learning this!)
 
If its still a liquid would it hurt if he added more catalist ? he would be able to mix it in the mold maybe?

tk1608 said:
Some parts I was trying to cast are resin.
Click to expand...

Is there not a liquid that you can mix into resin that messes up Silicon molds if anyone tries to recast the parts? I seem to remember a thread about it some years ago.....hmm maybe the resin parts is like that.
 
Last edited:
If it's an RTV rubber and you got your ratios too far out of the tolerable allowances, regardless of too much or too little, it's not going to cure. I found this out the first time I tried it years and years ago. Clean off your masters and start over. :(

Oh, and RTV just stands for 'room temperature vulcanizing', nothing bad.
 
If you decide to warm it up, do so in a humid environment. If you make a "hot box" with a cardboard box and a hair dryer, put in a coffee cup full of water so that the atmosphere in the box gets humid. That will help to accelerate the cure.

-Gordon
 
I'll need lots of alcohol, if I have to clean all this off,...for medicinal purposes only you understand..:lol

The clay question, I have chavant clay in there, (the stuff that stays soft) but it's worked ok before. Could that be the problem ?

Right so, project for tomorrow, 'cos it's 11pm here now.., humid hot box..
Do I leave the hair dyer running for a while, or just enough to warm it up, and then seal it up ?

I'll let you know what happens.

Phil
 
If some of your parts are made of resin,I'd use a stronger solvent to removed the uncured RTV from it,like Naptha solvent.It's nasty/toxic stuuff,so be careful.The styrene parts will only get "so clean" with alcohol..maybe it will work well?Unfortunately short of getting new stryene parts(whether they are moldel parts or scratch built parts) you may have to get new ones as the uncured RTV may not come off 100%.I don't know if your RTV is silicone or urethane.If using a RTV urethane you have to use some really strong mold release.Urethane sticks to everything with the exception of a few materials.Now,as for the clay/sculpted part....you have to "seal" sculpts...especially it is is a sulpher based clay(which it is).I didn't think of this at the time,but if you didn't seal the sculpted clay part the sulpher will wreck havock on the RTV silicone.It will never cure no matter what you do.Seal your clay sculpts with some clear coat(gloss),be it lacquer,enamel or acrylic.Give it a good couple of light coats(each progressing to a slightly heavier one).2-3 should do the tick,be sure to let them dry between sparying.No effot you make now will make your RTV cure I'm afraid to say,you need to start over again my friend,hopefully this wiull be a lesson you will never forget to alieviate future headaches.Good luck:).
 
Sadly, it still ain't setting, so I've begun the cleanup. :cry.

I had an idea so, I brushed over some catalist to set the rubber that was left in the nooks and crannys. This seems to work ok, and I can peel off what's left. This is only on the resin bits though. I'm worried that if I brush catalist onto the styrene, it might ruin those parts, so I'll go with the alcohol, when I get chance to go buy some.

When I started to clean this up I noticed the rubber had set a little bit near the parts themselves, but not further to the edges of the mould. It's just weird that it had partially cured. I gave it a really good stir too.

I didn't realise what a pain in the ar** it would be if the rubber didn't set. It's kinda putting me off trying it again..Grrrrrrrrrrrrr.:angry

Thanks again for all your advise guys, I really appreciate it.


Phil
 
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if the pure catalyst might damage the styrene, make a small batch with more catalyst in it and then brush it into the uncured silicone and mix it up :confused

.
 
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