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