Am i doing something wrong

[pod1138]

hello all
i'm trying my hand at resin casting and my moulds i'm making are coming out really well very clean, no bubbles i am very happy with, But heres my problem, i'm using a Polylite Water Clear Casting Resin (its not ideal for what i need & i will be asking for a replacement in another post) i'm finding i get vaining over some of the flat surfaces which i can live with (it looks cool) & random shrinkage between 1-6 mm
any advice

pod

[Fleafa]

How thick are your casts? Excessive thickness can cause a lot of heat during curing which can lead to more shrinkage.
Do you have any pictures?

[pod1138]

ok i'll give it in mms & ins
the original
10" x 2 1/4" x 1 1/8" (256mm x 61mm x 26mm)
and the casting comes out at
9 11/16" x 2 1/8" x 1" (250mm x 54mm x 25mm)

i will post some pics once i'm finished, knowing my luck its something dumb like using the wrong resin

[Fleafa]

That shrinkage (between 2% and 8%) is more than I would expect.
You could try adding less catalyst. How much are you adding currently?
You could also try pre-warming the mould.
Have you read the ?

[pod1138]

this is what is on the tin

clear (unpigmented) blue/green liquid casting resin
activate with MEKP catalyst 1% min(10cc per Kg) 2% max (20cc per Kg)

each tin is 500g, i've mixed 2 lots with 10cc (as per the max)

i'm working from a side room at home i guess you should think laundry room,

[Fleafa]

You should try less catalyst.

Also, please tell me you have good ventilation and are using a mask. Polyester resin fumes are BAD when inhaled.

[mangozac]

[pod1138]

[Fleafa]

Let us know how you get on.
Good to hear you're not killing yourself! Make sure you have vapour filters as well as particulate filters

[pod1138]

ok just an update
And its going ok i've been casting for 6 weeks i'm trying other resins & silicones. i still get the vaining on some on the castings i do have some problems with bubbles i think its something like 1 good cast in 3

[johncast]

Hi Pod

Patterns on the casting and sounds as if you are using Polyester resin. Not good

I'd be trying a new resin, polyester resin are not compatable with many rubbers and you get TRYPING affect on the casting and in cases stays sticky. Try a urethane resin.

The other advantage is the mixing where there are problems . Urethane resins need in most cases a 50% 50% mix or somewhere in that order. With other resin a 1% cat into a mix is hard to get right in small volumes if you don't have a accurate scale such as a jewellers balance to weight it absolutely spot on.

Johncast

[pod1138]

ok john i've just looked for urethane resin & i may have some problems buying it but i will keep looking but what i will do in put up a lynk to show what i am buying & where from & see if any more ideas come to mind
http://www.ebay.co.uk/itm/Polycraft-GP- ... 35c352e6e7

http://www.ebay.co.uk/itm/Polycraft-Pol ... 35dffc6823

[Fleafa]

Are you UK based?

[pod1138]

yes

[Fleafa]

So you've found the distributor I am currently using! My bread & butter are:


So I use the same silicone you found.

The resin you found is polyester resin, as previously discussed. They can be tricky. They don't like to cure fully in contact with air, for example, so you can end up with a sticky surface. A wax additive can be used to minimise that problem, but there are others. My biggest issue with the PE resins is cure time and the foul vapors.

So, you could try a "water clear" polyurethane resin. Expect to pay considerably more:


You may even want something like this:

Without knowing your project, it is difficult to make a good recommendation.

Your next consideration is that water clear resins are intolerant of condensation-cure (tin-based) silicones. This may be the problem you are having. You need to use addition-cure (platinum-based) silicones. Again, expect to pay more:

These silicones are longer-lasting but sensitive to cure-inhibiting substances - avoid any moisture. Most manufacturers steer you away from wooden spatulas for mixing as they may contain moisture!