Hi guys,

Apologies in advance for the somewhat misleading and bizarre thread title. ........  but it's not too far off the result I actually got  
The intention of this thread is to find out what  went wrong, or if I did something wrong.  Also,  it's to find out if the same thing has happened to anybody else.

First of all to put you in the picture ....................  I'm working on two ( OffSide & NearSide ) headlight covers silicone moulds for some custom headlights I'm making.  My plan was to cast 'Vac-Cast Epoxy Resin' into the silicone moulds to make two headlight covers ,  that I'll be vacuum forming on my vacuum forming machine.  Tooling plugs basically.  I've had great success in the past with EC CS25 Silicone rubber in the past,  but this time things went drastically wrong.

I first placed an order for 2 x 5Kg silicone + the Catalyst at the beginning of last month.  Then realised that I would need in the region of 5100 grams to fill  each of the moulds!  So 10 days later I placed an order for another 10Kg of silicone.  I've got the full EC degassing system so I had to split the pour into 2 parts.

The method I use has always worked for me in the past - fill the mould cavity with dry rice to get the volume,  pour dry rice into evenly into x2 10L buckets ( 10L buckets fit perfectly into my degassing chamber ),  make a mark on the bucket to the level of the rice ( equal levels = same volume of silicone needed ).  Weigh the 10L bucket, minus weight of bucket ( 250g ) gave me 3414grams.  Then it's just a case of working out the ratio of catalyst.  5% as it's 100:5 which gives me 172 grams of catalyst.  Where did I go wrong?  Did I do it wrong somehow,  as the result I got was an utter disaster ....................  moulds are damaged as are my original plugs  

The very first thing I wasn't happy about! ................  Usually CS25 is white,  at least it's always been in the past when I've used it (  but now I realise it's final finish is based on the colour of the catalyst ),  as I keep all my moulds and store them for future jobs if needed,  these last ones look like crap!  The one of the left ( top ) was the first one I did ( white ).  The next one discoloured and grey in parts was the second one I did ......................  and no,  it's not an indication of a pour mixed silicone/catalyst    >>



De-moulding is usually very easy from the mould setup boxes,  as it was this time also,  as I always use Melamine wood boxes >>



However .......................  de-moulding my plug from the silicone rubber was an absolute mare!  The sides of my plug came away easy enough so I could slip my fingers into the gap,  but then I struggled for about an hour to release the plug from the silicone mould!  In places,  you can see that the silicone has adhered itself to the Pattern-Coat Primer finish on my original plugs,  tearing it away leaving Pattern-Coat Primer glued to the silicone surface!   I used EC 'EaseRelase' release agent ( even used the special application cloths ) to apply the releae agent.  As I was getting nowhere releasing my plug from my mould, I had to resort to spraying water into the silicone mould >>



The image above and this one is Pattern-Coat Primer that's stuck to the silicone!  I had to pick it out using a pair of tweesers!   You can also see the result of the other silicone pour ( grey patch ),  it's now obvious to me that no two orders will despatch the exact same product.  The silicone may be white ...............  but the catalyst will vary in colour,  making your mould look totally different.  And garbage in my mind  >>



And here's my original plug ...............  including some stuck-on silicone where it's been torn while trying to de-mould it!  Not a happy chappy I'll tell you.    The finish on my plug was like a gloss highly polished finish, now it looks as though the silicone has reacted somehow with the pattern-Coat Primer,  and it  even feels sticky!!!   What on earth has gone wrong?  >>



Silicone moulds 'cleaned-up' as best I could after chipping away at the Pattern-Coat Primer.  Obviously,  this has damaged the moulds so I can't cast Vac-Cast Epoxy Resin into them >>



The whole process ( a very expensive one ),  was an utter disaster.  So what's next? is this still recoverable? >>



And one more thing ..................  As I had a little silicone left over in my bucket,  as a test I poured the reminder of that silicone in a Teflon coated baking tray ( a brand new one )  and that too stuck like glue!  That's quite worrying!  >>




So what's going on? any one got any ideas?  where did I go wrong?  did I get my ratios wrong? or is there an issue with this particular product?  Has any one encountered problems like this in the past when using CS25?

What baffles me is,  Teflon is non-stick ( well known ) ...............  silicone sticks to virtually nothing,  yet I managed to turn into an adhesive!  This has left me straching my head,  any help or suggestions greatly received.

I'm now in two minds as to continue using CS25 silicone rubber for mould making, as the results seem to be very hit and miss!   



TURK

Hi Turk,

It is a bit bizarre what is going on.  The easiest thing to explain is the colour difference.  The manufacturer uses a pigment in the catalyst. The pigment can settle  so if not heavily shaken between uses, you can get different amounts of pigment and hence the different shades and  colour as youve seen.

In terms of the sticking to polyester,  it might well be that the polyester  is too fresh.  Sometimes  relatively fresh polyesters can be quite active  as a surface so it may be possible for the silicone to get somekind of a grip into porosity or some kind of grip or  material draw in as styrene outgases.   Certainly never seen anything quite as  bad as that. 

It is the fact it demoulded fine from the melamine but not from the  polyester that raises some suspicions that it is a material interaction between the two. 

Can you email me (technical@easycomposites.co.uk) the batch numbers etc and we will look into the batch and see if we can find anything like it or replicate it.  At present we've no known issues with the CS25.






Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Many thanks Warren for your quick response,  always very helpful,  and a pleasure talking with you   
The silicone did release from the Melamine,  even though it was quite difficult,  but at least it didn't tear!  You have to kind of 'pry it off' if you know what I mean.

Now I understand why the catalyst is so different from one bottle to another!  they put pigment in it!  Would it be OK to mix two different bottles of catalyst together so you get a uniform colour?

My bucks ( positive moulds ) are always made in the same way .............  built-up with Pattern-Coat Primer,  sanded to a very smooth finish, then polished  ( buffed-up to a high gloss ) and then prior to usage a few coats of release agent.  I've obviously had a major reaction somehow,  just don't know what!  My exercise ( test ) with the Teflon baking tray,  really makes you think though doesn't it.  What on earth is that about!?  That should never of stuck.  As far as the Pattern-Coat Primer,  I bought that stock about 6 months ago.

I'll email you the batch numbers tomorrow,  should you get any other queries concerning issues with this product.

Thanks all.



TURK

If you are mixing the silicone all in one go then no reason why you cant mix the catalysts into one to get an even colour throughout the pour.

I have had a quick look at the batch numbers and there is no reported issues I can see so a bit more digging needed on my end to  see if anything else is going on.

The pattern coat primer is a bit old  but as long as that has fully cured, I would not expect an issue.

I am wondering if it is more to do with the silicone perhaps not being fully cured - eg if there was too much pigment in one bottle and not enough catalyst and it was enough to throw the cure out of sync so you were demoulding something that wasnt't quite cured.  I shall have a deeper look at the batches to see if you had a batch from the end of the bottle or the start for example.

There may a combination of factors at play.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I have had a similar issue in the past.
In my case I believe it was my Frekote release agent.

Frekote is a silicone based release system.

Like you said silicone typically sticks to nothing else, but silicone sticks to silicone really well!

I changed my release agent to a wax and then the same silicone released ok.

Frekote isnt silicone based John, it's a blend of naphtha, alkanes and other hydrocarbons suspended in a blend of solvents - same as most other chemical release agents.

Although Hanaldo is right about Frekote and many other chemical release agents, it is interesting that it bonded with a release agent  but was fine without in Fasta's case. 

Might be something worth looking into. 

Turk, when you made the previous set of moulds a while back by the same method, was that using a release agent  too?


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I have used both condensation cure and platinum cure silicones over Frekote prepared surfaces without any issue, so I'd be confident that it isnt the release agent that caused a problem unless there was something strange like the release agent hadn't dried before the silicone was poured - highly unlikely. So it feels more coincidental than directly related.

My gut feeling is that this is undercured silicone as Warren suggested. This is the only time I've ever had silicone 'bond' to a surface that wasnt either porous, glass, or silicone.