Smooth-On Rebound 25 Substitue ??? [CALLING EUROPEAN RPFers]

Ciwi said:

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Side question: Would one of the small kits smooth-on sell (I believe it's about a pint) be enough for say a helmet?

Hi, definitely not, you're mold won't be thick enough and you will have distortion even with a mother mold...

The problem is that in Europe, Smooth-On products aren't cheaper but you can find an alternative for molding in RTV Silicone, it's cheaper but it's not as easy to use as Rebound 25

There's several type of RTV and some of them don't need a vaccum chamber.
I use it for small sculpt molding and for fishing lures and it's perfect and easier to find than Smooth-On products... And i'm sure that it will work perfect for an helmet mold. The major fault is that it need to "dry" for 12 to 24 hours.

Hope it helps.

Hi there guys,

Perhaps you could ask someone in the good ol' U.S. of A. to assist you in getting your hands on the products you need ... mind you eventhough the goods maybe cheaper the costs for shipping heavy packages and even sometimes custom charges for purchases over $50 (including shipping?) nowadays, is not!!!

-Chaim

wrcromu said:

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Hi, definitely not, you're mold won't be thick enough and you will have distortion even with a mother mold...

The problem is that in Europe, Smooth-On products aren't cheaper but you can find an alternative for molding in RTV Silicone, it's cheaper but it's not as easy to use as Rebound 25

There's several type of RTV and some of them don't need a vaccum chamber.
I use it for small sculpt molding and for fishing lures and it's perfect and easier to find than Smooth-On products... And i'm sure that it will work perfect for an helmet mold. The major fault is that it need to "dry" for 12 to 24 hours.

Hope it helps.

That helps a lot! I found another Irish supplier with reasonably priced silicone and was going to ask about it here, but you cleared that up, it's RTV-3322
Silicone Rubber (Brush On)
I'll have to contact them and ask does it need to be vacuumed, but thanks a million for the suggestion.

Sym-Cha said:

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Hi there guys,

Perhaps you could ask someone in the good ol' U.S. of A. to assist you in getting your hands on the products you need ... mind you eventhough the goods maybe cheaper the costs for shipping heavy packages and even sometimes custom charges for purchases over $50 (including shipping?) nowadays, is not!!!

-Chaim

I was thinking that, I have a few relatives in America, but you're right. the shipping costs more than the product itself and the import tax would be huge

Ok, so just having the letters RTV helped my search immensely, made it much easier to find info and suppliers. This place offers a good price and very reasonable shipping
Polycraft GP-3481-F General Purpose RTV Silicone Mould Making Rubber - mbfg.co.uk

So does anyone have any experiences with Polycraft products because these guys have everything I need and reasonable prices and if it was a trusted name I'd go for it. Also is the silicone I linked suitable for brush on molding?

I'm going to put the answers I found to my own questions here should anyone in the future search and stumble across this, also gives people a chance to correct me if I'm wrong

After looking at a lot of datasheets for various silicones, I've found that most of the general purpose silicones that dont need to be vacuumed have a hardness around ShoreA 25 (rebound 25 ) and that seems to be linked to the enlongations at break values. that being the main discernable thing about rebound 25 I figure silicones with a similar value will do the job. (the silicone I posted is ShoreA 27)

Of that Silicone I posted they had a conversion of 200ml of silicone = 250g. By that I figured out that roughly 4.7 Kg is a US gallon.
Now that I know that it led me to another important question...
How much silicone does it take to make a decent (3/8") cast of a helmet ?
(Obviousy different helmets vary in size, but a rough estimate of a human head sized item is all I'm looking for )

Again thanks for the help, not having a whole lot of money I like to analyse everything and know as much as possible before buying big vats of expensive silicone

I've used the polycraft stuff, it's pretty good. You will need a scale to mix it, as it's a 10:1 by weight mix ratio, unlike rebounds 1:1 by volume. It's too thin to be a brushable rubber like rebound, however most places will sell a liquid often called a thixotrope that you mix in with the silicone, and like the name suggests, it will thicken it. That said, even rebound 25 will need to be thickened, unless you want to put a dozen coats of silicone on there.

1 gallon of rebound (it's actually 2 gallons, as you get 1 gallon of each part) weighs about 8kg I think, and you will use about half of that making a decent helmet mould, depending on the size of the helmet obviously.

The only other downside to the polycraft silicone is that is stinks. Hold your nose...

Ok, that's handy to know I need a scale, thanks. Yeah, I've been watching a bunch of tutorials, seeing the different things people did and I figured I needed some thickener.

So taking that into consideration, I should likely be able to get a decent helmet mould from the 5.5Kg container (also handy to know they mean a gallon of both parts, thanks )

Haha, I'll keep that in mind again, all the info is very much appreciated!

No worries. With the polycraft, you will get 5kg of the silicone, and 500g of the catalyst, but yeah, you should easily get a good mould from that much.

Ok cool, great know
Thanks

Ok, one last question. Are other smooth-on products suitable for brush on molds? I found a local guy that has Oomoo 25/30, Mold Max 10/15T/20/27T/30/40/60 and Dragon Skin cheaper than the Polycraft. He said with some thickener Mold max would work but it may need vacuuming. What are your guys' experiences with these and would any work?