Which grade of rubber

[EV2UK]

Hi guys.

I picked up a casting kit from Sylmasta at Telford and now new to buy some more RTV rubber.

I've looked at there website and they do 3 x different grades 370 - 380 & 390

What's the difference and do the different grades have advantages or disadvantages over each-other.?

I've never tried casting till recently and I'm struggling with air bubbles in the RTV mould.

I've tried to make copies of a few 1/48 wheels and would like to have a go at copying some 1/48 fuel drop tanks.

Any advice on the rubber grades or advice in general would be much appreciated

Is the Sylmasta rubber any good or would you guys recommend another brand.?

Many Thanks

Tony

[John Laidlaw]

It looks like the kit comes with 380 grade, so I'd recommend getting it again, assuming you had success using it before?

It looks like the resulting mould gets stiffer going from 370 to 390, which means it gets stronger for multiple uses, but less flexible, making it tougher to get the cast out of the mould.

Can't speak to whether Sylmasta is good or not, but they appear to have been around for a while, and I've never heard anyone complain about it .

[Dave1973]

The grades are their sheer strength and softness, the softer the easier to remove parts, but the less stability.

The stiffer, the harder to remove parts, but is a longer lasting mould.

I used to use standard RTV moulding rubber for my moulds, but it gets expensive, especially making moulds of parts all the time.

I now use Thorassic RTV which is essentially the same, but much stiffer consistency, the softness sheer strength is the same as soft.

However, you mix it, and apply it as a thick coat over the part, then once set, use fibreglass resin and chopped matt to make a casing.

Works out much cheaper, and is way easier to make complex parts and difficult mouldings

As for airbubbles, first thing is your mixing technique. Slow down, and mix thoroughly, slowly folding the mix rather than whisking it. This prevents air being integrated in the mix.

I know its a pain but ALWAYS go slow, and let the mix sit for a few minutes. Pot life should be a good twenty minutes so no fear.

Then the next problem is pour technique.

Dont jist pour it in, choose the lowest point, and slowly pour in that area, allowing the silicone to build slowly. This helps,prevent air ingress.

If you still have problems, and cant get rid of the bubbles, you can buy a fixer which will help release them. But in my experience, proper technique will eradicate that

Edited December 18, 2015 by Dave1973