Casting With Expanding Foam?

[SotF]

I keep considering making some molds of terrain pieces I've made. The big thing is that I'm not entirely sure if I want to cast them in resin, both because they're ones that would take a lot of work due to the shape of them or just that filling them with resin would be comparatively expensive next to just making more of them.

Then I noticed the expanding foam at the hardware store and started wondering, would it work to capt the molds and either just use the expanding foam or apply a layer of acryllic into the mold and then fill it?

[beefcake]

Casting plaster is cheap. I can get it for less than $20NZD delivered and that is about 20kg of the stuff. You'd get more use of the plaster and it would take detail much better. Bloody heavy compared to expanding foam though. As you said you could do a mix of a few different mediums. First a shell of resin or plaster then expanding foam to bulk things out and provide interior support.

[Elk101]

I tried it once attempting to make cavern sections and it went horribly wrong. The foam is hard to control and doesn't look great once cut.

[Juxt]

I used to cast things with expanding foam all the time for prop work- but not the foam in a can type product, it was a two component chemical that you mixed in equal parts and poured as a liquid into the mould. It then expanded to fill the mould cavity- I'm sure a casting supply company like Smooth-On would sell an equivalent.  Quite often I would apply a skin of poly-resin to the inside of a mould to capture the detail and then back-fill with the rigid expanding foam.  Rigid, light weight casts, full detail captured and strong enough to withstand rough usage.

[Elk101]

It was the spray can stuff I tried, hence the disaster!

[Vagabond]

This is an intriguing idea, I'm curious as to what you would want to repeat cast as a finished terrain piece. Unless it is for resale in which case Juxts idea sounds feasible and a good one.

In the distant past I've done small wall sections and bridges cast in normal plaster of Paris cast into the Bellona vac formed range, they have lasted for years but I've always been careful with them. The bridges are heavy, they don't move about much on the table.

[SotF]

This is an intriguing idea, I'm curious as to what you would want to repeat cast as a finished terrain piece. Unless it is for resale in which case Juxts idea sounds feasible and a good one.

In the distant past I've done small wall sections and bridges cast in normal plaster of Paris cast into the Bellona vac formed range, they have lasted for years but I've always been careful with them. The bridges are heavy, they don't move about much on the table.

It's mainly more of my cut off tree trunks that I want to make more of...some to sell or hand off isn't out of the question, but I want to be able to make a bunch more because it takes a while to finish each of the trees due to repeated drying time that can take a few days at a time.

Hunks of plaster are just a bit to heavy for what I want to do with it...

[beefcake]

I'd go for plaster on those.

[FifteensAway]

Hmm, plaster would be heavy but I'm wondering - and I haven't tried this - that maybe the premixed light-weight spackling compounds might work for your tree trunks?  They wouldn't by themselves be real durable but perhaps with the right coating the material might work out.  And certainly lighter than plaster.  Not sure about getting the stuff out of a mold, though.

Separate thought, but maybe using acrylic caulk, like the DAP brand, might also be worth a try - and you can get it in a few different colors as a head start.  Again, haven't tried it - except for making roads, which works great.  Ditto here about the mold issue.

[SotF]

Hmm, plaster would be heavy but I'm wondering - and I haven't tried this - that maybe the premixed light-weight spackling compounds might work for your tree trunks?  They wouldn't by themselves be real durable but perhaps with the right coating the material might work out.  And certainly lighter than plaster.  Not sure about getting the stuff out of a mold, though.

Separate thought, but maybe using acrylic caulk, like the DAP brand, might also be worth a try - and you can get it in a few different colors as a head start.  Again, haven't tried it - except for making roads, which works great.  Ditto here about the mold issue.

Unfortunately, the trees I'm making are a bit to large to dry correctly with the spackling compounds...the tops of the trunks are still in the 3 inch range with the bases around 5.

[beefcake]

My reason for saying plaster is that it is going to take a lot to fill it. Plaster is cheap and the weight could help with stopping them toppling if given a slight bump (or perhaps destroying whatever minis are beneath it).

[FifteensAway]

SotF, maybe try using a 'hollow' dowel inserted into the trunk so that you have a thinner layer of sparkling that might dry better???  Again, not sure it will work.  Going to have to do some experimenting of my own.

[winder]

I have a mate who has done this, he "shells" the piece with resin first (a thin layer all around the mould to preserve details and give a hard exterior) then fills it in with expanding foam...seem to come out pretty durable and maintain good detail but i am not super knowledgeable about it.

[gpruitt]

When I was doing model railroad scenery I found a product (in the US) called Lightweight Hydrocal from Woodland Scenics.  It works just like plaster but, as you would guess by the name, it is fairly lightweight.  I have a collection of hydrocal rock castings that I have used for wargaming for many years now.  They paint up pretty nicely, but have been a bit chipped due to rough handling over the years. 

[Vagabond]

It sort of sounds as if Juxts mail is going to answer your needs, I guess depending on cost of the material you could use a core of wood or dowel to avoid using too much of the foam.

Would be interested to see what you are trying to replicate, I'm not sure when you say cut off trees if this is the base of a bigger tree i.e. you add branches and foilage, or the sort of of dead tree with just a bole and a few low branches.

Sounds interesting either way