expanding foam?

[BlindSquirrel]

I need to fill a styrene kit with expanding foam. Can someone recommend a brand to buy? I am concerned about heat and weird chemical reaction destroying my kit.

 

[Harry Harris]

I can't recommend a brand as I'm in the UK but I would advise on you buying the 2-part liquid version and not the aerosol foam.

The liquid foams up really quickly (solid in about 30 minutes or less) and is very consistent in terms of density. On the other hand the areosol takes quite a while to go off and has a tendency to contain some large air bubbles sometimes.

You shouldn't have a problem with heat, the reaction is only 'fairly warm' I would say and it won't damage the plastic but don't get any foam on the outside of the kit, it can stick really well.

Most fibreglass suppliers will stock it; if not try looking for boatbuilding suppliers too, they usually carry foam too as it's used for filling boat sections to aid boyancy.

Harry.

 

[Forsaken]

I have had very good results with Wasco's http://www.taxidermy.com/ WASCO X.R. Urethane Foam
it comes in a two part mix I use it to fill 1/6 scale vinyl figure models. If you use it be careful though it really expands allot. I think it is a great product. Hope this helps.

 

[Harry Harris]

Good point Forsaken about the rate of expansion, it can be quite a surprise in terms of how much the stuff 'grows' and how quickly it does it.

I'd do some tests first in a plastic beaker and mix abut a half inch of each part. Remember to do this in a well ventilated area and wear a respirator if you can.

Also cover your work surface with something to protect it in case you spill any foam or it overflows.

Harry.

 

[BlindSquirrel]

Thanks for the info guys. The Wasco foam looks good and is reasonably priced. I'll be ordering soon.

Do you happen to know what kind of paint it can take? Is this kind of foam vulnerable to enamels and the like? Will it need to be sealed before I paint?

 

[Harry Harris]

It should take most kinds of paint but I'd use a primer first anyway just to be sure.

I'm confused as to why you're concerned about painting the foam though as this should be inside the model you're planning to fill, right?

Harry.

 

[Chris Martin]

Urethane casting resin is the non expanding version of expanding foam. They add an agent to stop it foaming, however this can evaporate out or degrade with contact to moisture and that's why old casting resin starts to generate small bubbles when you mix it. Any paint or adhesive you use for cast resin models is fine for the expanding version. One word of caution if filling vacform models with it: Although it expands, it also shrinks slightly again as it sets and cools. This can distort the model if it's "flimsy". Injected kits should be OK.

 

[BlindSquirrel]

Originally posted by Harry Harris@Aug 14 2005, 03:59 AM
It should take most kinds of paint but I'd use a primer first anyway just to be sure.

I'm confused as to why you're concerned about painting the foam though as this should be inside the model you're planning to fill, right?

Harry.

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I guess my concern was in those areas that foam may be exposed....I'll be doing a few tests before I hit the kit, I can paint those to make sure. Thanks for the advice.

 

[Chris Martin]

It's all the same material even if you break the foam open.

 

[Harry Harris]

Like I said earlier it pays to test this stuff before you use it, I got ALL this foam from just three 1½" round x ½" high measures of each mixture part.

(My 2AA cell maglite is for scale).

Harry.

 

[BlindSquirrel]

Great Scott.. :eek
That's amazing.. I will indeed test BEFORE it goes in the model. Thanks for the demo.

 

[badger]

I have a royal guard helmet that is torn up the back in a major, non fix-able way.

I'd like to fill it with foam, cut it down the sides, and use it to make a new vac mold out of.

Is that something that can be done? Is it even possible? If I pour the foam in, will it change the shape of the helmet? Or wil it push out the top, and not deform the helmet?

Obviously I'll have to stop up the visor hole, and duct tape the torn area together, but I'm wondering how much the helmet will deform if I do this.

and do I only have on chance at it? or is there a way to fill it, and pull the foam "plug" out if it isn't the way I want it to be?

badger

 

[Chris Martin]

I wouldn't risk it. I think there's a 5% chance of it working and a 95% chance of it screwing up what you've already got. The density of the foam you mix yourself is not really hard enough to vac form with without it crushing slightly. Even those odds might be over optimistic.