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Circuit Owner
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5,890 Posts
Discussion Starter · #1 ·
Well I followed the instructions - shake the hardener/catalyst bottle well before use, add 10 parts to 100 parts of silicone by weight (used very accurate scales with a zeroing facility) stirred gently to avoid air bubbles then more vigorously.

Wondered why the mix wasn't salmon pink like in the instructions.

Anyway - carried on mixing, poured into second container and mixed again.

Then poured carefully into moulds ensuring air bubbles kept to a minimum.

Still wondered why no salmon pink.

Watched for a few minutes quietly satisfied that the few air bubbles had worked their way out and the mould looked nicely settled.

As I put the bottles away BLOW ME DOWN there is a layer of solid pink deposited at the bottom of my hardener/catalyst or whatever the damned stuff is called.

Now wondering whether the silicone will EVER set.

Bummer.

Reckon the stuff needed a scrape and stir not a blinking shake. OK it's 4 months old - maybe I should have used it before now.

I'm now hoping the solid layer of residue is simply a dye to make it easier to tell if the mixture is well enough mixed. I'm sure it was mixed well but had no dye indicator.

Does anybody know what the likely outcome is going to be?

And if it's disaster - any idea how I can clean up my plasticard chassis master and my scalextric superslix so I can try again???

That will teach me won't it
 

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Joel LeNoir
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952 Posts
good to see others having problems too. I went through $ 100 worth of the stuff before I resolved all the problems I was having. I don't think it will set up. One good thing about when you do get bad moulds and you will. You can cut them up and use some of it in the inside moulds.

Don't Give up it does get better. And the satisfaction of saying..... Ya I made that, makes all the pain go away.
 

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Premium Member
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5,717 Posts
The harder should be mixed at the ratio stated, however I've just been recommended to reduce the ratio to give me longer working time as for some reason t wa setting too fast.

Great idea to use te old moulds.
 

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Circuit Owner
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5,890 Posts
Discussion Starter · #4 ·
I will certainly use the old silicone to fill out voids trick as well - once I get my first successes!

Wraith - I did use the ratio prescribed (100:10) but as the dye and whatever it was bonded with was left in the bottom of the bottle as a solid lump I used more of whatever chemical remained liquid - probably accelerating the setting.

What I am worried about is whether the solid residue was chemically important to the hardener or whether it was simply a dye as a visual aid to mixing and could be omitted without problems.

Anyway -I will leave the silicone on the moulds for a couple of days and then open them up and see what happens (over a suitable drip tray!!!)

Not giving up yet!!!
 

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Mike Newns
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629 Posts
If your going to work with silicone it is worth investing in a can of "Orange Solvent" which is quite expensive but you'll find a little goes a long way. It's useful for cleaning mixing pots etc. but indespensible when a mix goes wrong and you need to clean the master.

Mike
 

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851 Posts
The thing about things like this is, until you know how it's supposed to go, you don't know how it's supposed to go. I don't know what silicone system you're using but there may be a chance, albeit a small one, that it was mainly pigment that settled out, the pigment added to aid in even mixing and identification of the molding material.

If it starts to gel at all, it might be worthwhile giving it some extra time to see if will cure. If it stays liquid, chalk it up to experience, and get ready for a clean-up.

I have a vague memory of "Orange Solvent" from my special effects days... I don't think it was citrus based, but I may be thinking of something else. Mike, where do you get such stuff these days?
 

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Senior Slot Car Mechanic
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2,230 Posts
I was told by the guy that taught me about resin/silicone molding that, the color was indeed just pigment, and, does not affect the curing process.

I guess we'll see if he was right.
 

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Circuit Owner
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5,890 Posts
Thanks for all your responses - much appreciated.

QUOTE (bwaminispeed @ 30 Oct 2011, 14:37) <{POST_SNAPBACK}>I was told by the guy that taught me about resin/silicone molding that, the color was indeed just pigment, and, does not affect the curing process.

I guess we'll see if he was right.

He was right!

I went out this morning to take a look and the surface of the silicone was set - looking like a lucky escape then.

I couldn't resist finding out. Having prodded the moulds and noted that the silicone was very springy (less rebound = more risk of centre being uncured or so I have read) I decided to pop one out.

Here's what I found...





So it would appear that the solid residue in my hardener was indeed a simple pigment to aid mixing.

I think I have had a lucky escape.

The silicone feels OK, it's holding its shape well so the next step is to cast my resin and urethane.

I know I have to leave the moulds to evaporate something or other for about a week before I cast resin (I have read it helps the moulds last longer). I know that I could cast plaster straight away but does anybody know if I can cast urethane straight away or should I wait for a week for that too?

Oh and if anybody asks - the tyres are Scalextric superslix for my minis, 260z's and Mk1 escorts. I have also done 2 other moulds for large superslix (Porsche 935's) and modern Scalextric F430's (I have a few of these and the Porsche 997 which uses the same as the F430 fronts and Scalextric don't do spares for these).

The chassis is destined for the basis of transit conversions and will double up as the base for my hot rod/rat rod project when I get around to making and casting the body panels.
 

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Joel LeNoir
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952 Posts
Good news indeed. Glad to see all is coming out so good for you. This is the 1st I have read about letting your molds breath. makes since. Will have to give it a try. Have a 1/43 70-73 trans-am that is almost ready for the molding process.

Keep us in the casting loop.
 

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Registered
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1,149 Posts
Glad to hear it cured.

In my experience, I only let my molds cure about 24 hours and then I cast. The key is using a resin mold release agent. I can routinely get 50-90+ pulls out of my molds if I take care of them. The other key is to not pour a bunch of them in a row. The mold never gets to cool down and reusing it so quickly does shorten it's life.
 

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Interested to watch this one as I have just done my first silicone and resin moulding / casting. See here, http://www.slotforum.com/forums/index.php?...58091&st=60
Just about to do some other bits and it's always good to know about pit falls to look out for.
Thanks SF guys for being so helpful to us beginners.
 

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Senior Slot Car Mechanic
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2,230 Posts
You can also cook the molds, takes about an hour or so, quicker than waiting a week.

Most silicone companies have this info on their sites (temp and time etc), and, recommend you do this.
 

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WRP World Champ 2015/2016
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4,279 Posts
Well done Mr Modifier! no shoes ruined and garage floor remains untarnished.

Very very interesting thread, and as usual, a great amount of support and help from posters.
 
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