Resin Question

[junkroom]

I'm new to the forum, so if I put this thread in the wrong spot, feel free to move it. Thanks...

I'd like to make a handful of hard plastic prop grenades for a photo shoot.
I've used ezflo resin before with good results on other things, mostly very small items,
but that stuff is relatively expensive for this purpose. (These props may never be used again)

So, another idea I had was using fiberglass resin, which I can get in larger quantity at any hardware store.
I'm not sure what the actual resin is (polyester etc?)
But I wonder if I could use just the liquid resin, (plus hardener)
without using any fiberglass mat or cloth.
If this works, I'm sure there will be several projects in the future
where I could use this more budget friendly option over more expensive plastics.

Any thoughts or suggestions from the pros?
Thanks a bunch for your consideration.

 

[logan74k]

Casting things will never be uber cheap - polyester resin (the stinky stuff commonly used with fiberglass) gets extremely hot in thick sections, like, it can combust at thicknesses greater than half inch (I'm guessing here, I've seen a 1/4" leftover in a cup smoking) It would also, I imagine, be very brittle without the reinforcing mat.

Ways to cast using less material are to rotocast urethane plastic and/or fill it with cheaper filler material. I would recommend the cheapest urethane plastic you can find at Smooth-on, and try hand rolling your molds to get hollow parts.

I'm sure others will pop in with more options/ideas.

 

[Zlurpo]

I've used a few different types of resin for similar things. A couple options: Smooth on and several other retailers will have resins that will work. SpecialtyResin.com and TheEngineerGuy.com are a couple of sites I would trust. Or as a cheaper alternative you can try using "rondo" (a made up term for Resin/Bondo mix). Buy a can of Bondo (or other brand auto-body filler), and add some fiberglass resin. About 5 parts bondo to 1 part resin, but really it's just... enough to make it kinda runny. Pour off maybe a quarter cup of that, and add a marble-size blob of bondo hardener and 5-10 drops of resin catalyst (MEKP). That is, for the record, way more of both catalysts than you need, but it will make it cure faster. Mix the 4 ingredients well, pour into the mold, and keep turning it over and around and coating everything until it kicks. Repeat if you need it thicker than one layer (you will).

One of the nice things about rondo is that it sands very well and takes paint really well. Beware of air bubbles in your casting though, they're easy to get with rondo.

 

[Blaxmyth]

Yep, what Zlurpo said.

Half bondo, half polyester resin - the same catalyst works for both, but more is better with rondo - it cures quicker. Keep the mould rotating while it sets. Maybe stir in some sand as a filler - it's rough, but it'd be OK for a one-off prop. A thick coat of paint and some judicious weathering will mask any flaws.

 

[Darksyde13]

Casting things will never be uber cheap - polyester resin (the stinky stuff commonly used with fiberglass) gets extremely hot in thick sections, like, it can combust at thicknesses greater than half inch (I'm guessing here, I've seen a 1/4" leftover in a cup smoking) It would also, I imagine, be very brittle without the reinforcing mat.

Ways to cast using less material are to rotocast urethane plastic and/or fill it with cheaper filler material. I would recommend the cheapest urethane plastic you can find at Smooth-on, and try hand rolling your molds to get hollow parts.

I'm sure others will pop in with more options/ideas.

WIth polyester resin that usually means you used too much catalyst. I've cast several items that were 3inches tall and 6 inches square on the bottom with no over heating issues. Just remember the large it is the less catalyst you need. And as mentioned it is smelly stuff so work oustide if posible.

 

[minifig]

Also...the more filler you add the less the exotherm. Polyester resins can be used for casting, it just seems a bit...'1970's'...

 

[IKB1806]

As the other guys said you can use polyester resin for casting, it's all I've ever used, (40 years). You can mix it with an inert filler like talc, uses less resin and cut's down on the heat. too much catalyst will always cause hot mixes, potentially dangerous obviously. What sort of mould are you using?

 

[cavx]

If you want to make cheap, hard "plastic" like objects, then you should just go with the cheap embedding and casting resins. These are polyester resins and smell quite bad until they fully cure. They are exothermic and can produce enough heat to start a fire, so measure and mix your catalyst properly.

You can use pretty much anything to make a mold. I simply used the foil wrapper of the M&M. This is one of the first things I ever cast from back in 2005 and was done without a vacuum chamber. Note it almost bubble free which was a result of very careful mixing and pouring.

This part is about 3/4" thick. It is hard plastic and has remained quite clear. It has a slight yellowish tint to it now, but not bad for about 10 years old. You can add tints to this type of resin to change or add colours.

I'll be using more of of this stuff soon to make a mold for my BTTF 2 jacket sleeves as the silicone I want to use on the jacket re-acted to the rubber I wanted to make the master part from. This stuff does't seem to care what it is poured into or comes in contact with. It just sets and after it has cured, is hard. Probably not a good idea to drop it on concrete though, as it is also brittle and will shatter if the parts are thin.