I looked a bit more into admixtures.  I see what they're for now.  They should work marvelously with any gypsum based product.  Though with the break strength of excaliber on it's own, I can see why you might not bother.  Does the piece with the admixture have to cure overnight in the mold, or do you demold it first?

Canadian here.  We had an election a short while ago.  No real changes resultant.  Just like the US (zing!!). 

Exactly.

I just want to say that I wasn't being in any way accurate with that foot cube comment.  For all I remember, it could have been 9 or 10 inches (though I think it was bigger).  That makes quite a big difference once you're working out volume.  I'd ask for the dimensions/volume and mix ratios from any seller.  Find out exactly how much you're getting in true casting volume.

One of the problems with filling a slush/roto-cast resin piece with plaster is that plaster expands.  While not lots, you could get a crack in the resin shell from the pressure.  I know time is of the essence for many hobby pursuits, but I'd probably pour the inside of the resin shell in two stages, letting the plaster cure at least part way between the two.  My current thinking is to simply fill them with an expanding polyurethane foam or a plaster/die stone with lots of filler to keep the weight down.

And yes, you can slush/roto-cast with die stone and plasters.  It just takes a bit of patience.  Die stone that sets rapidly is obviously better than plasters that usually take longer.  I don't think it would work very well by hand.  You'd probably need to build some crazy roto-casting contraption.  Or be willing to sit there watching TV rotating a small mould by hand for half an hour.  If you get a die stone that is made for quick setting, you could probably get that down to 10 minutes.

Yeah, I did some hirst arts blocks.  Took an awful lot of work/time unless you had multiple moulds or made moulds of blocks you wanted in higher quantities.  I always thought the Linka approach was better, where you cast wall pieces rather than individual blocks.  But that's the wrong scale for me, so I'll have to make my own wall moulds for 10mm/N-Scale buildings.

It's a totally different material to resin.  I'd recommend gettting a smaller amount if you're not familiar with it or know that you want to cast something definitely with plaster/die stone.

I'm heading the opposite direction.  I've worked with die stones and dental plasters and am just getting started with resins (started with cheap polyester resin from an autobody supply shop).

The last 50 pound box of die stone I bought was like a foot wide cube.  The die stone was bagged inside of that and filled the box up about 90% of the way.

Die stone feeds and feeds into water.  You'll be surprised at how much a given volume of water will absorb.

My general thinking is that plaster/die stone is better for some terrain and resin for miniatures.  Whether or not I'd go with resin or die stone would be a decision made on a case by case  basis depending on the shape of the piece and the nature of the mould.

Also, never dispose of plaster/water solutions down the drain.  Always let the plaster set completely and throw it out.  Sounds like a no brainer, but it's easy enough to forget and it only takes one time to block a pipe.  And even a really thin plaster/water solution will cause a build up over time.

My thinking is that for a meteor, the rotating with polyester resin to make a mostly hollow cast might be the way to go.  Like the guy did with the rock casting on the taxidermy site.

Die stone is about strength rather than volume, so it takes a surprisingly high weight of dry powder to make a given volume of plaster.  So as far as cost effectiveness goes, if you can mix up polyester resin in small quantities and get good results with it, that'll probably be cheaper than die stone.  Die stone has the advantage of being all water based with no nasty fumes though.  And it's more sandable/workable than polyester resin.  Also, less heat is produced, so you can get a longer mould life.

I've done a bit of casting (hirst arts moulds) with dental stone and it's quite strong.  I had this crazy micro resin bubble reinforced stuff with like a 20,000 psi break strength.  Bought it at a local dental supply place.  Check your phone book and give them a call.  Tell them you want to get some high psi (10,000+) dental stone.  Expect to pay about a dollar per pound.

I could spike the 20,000 psi stuff I had on concrete and I'd only get corners chipping off the blocks on a single throw.  Took a couple throws to make it shatter.  Thin pieces though, broke far more easily, that was an inch x half inch x half inch block.

It's not light though.

Clint Sales sells Merlin's Magic for hobby use.

http://www.clintsales.com/dental.htm

A tutorial sort of thing:

http://www.hirstarts.com/casting/dental.html

Got things a bit more specific.  Japan vs USA

The USMC (United Stars Mechanized Corps) will be generalists, with every mech having a variety of weapon systems to accomplish lots of differing roles.

The Dai-Nippon Teikoku Kaigun will be specialists, with mechs built for specific roles equipped for just that one task.

As well, they'll both have infantry, tanks and VTOLs.  Once again, the initial military doctrine will be one of generalists vs specialists here as well, with the DNTK having fighters and troop transports while the USMC has troop carrying VTOLs that are capable of fighting.

This combat doctrine split is just for starters.  I'm sure me and my buddies will want to switch things up and have the sides modify their doctrines as they learn more from the actions of the spreading war.  I'm sure it won't be too long before the Britannian Empire and the Neo-Sovs get involved as well.  The Stellaren Königreich has also been militarizing recently as well.

Here's some shots of Spaceman Spiff's painted ones:
http://www.classicbattletech.com/forums/index.php/topic,38137.0.html
http://www.classicbattletech.com/forums/index.php/topic,35521.0.html
http://www.classicbattletech.com/forums/index.php/topic,35485.0.html
http://www.classicbattletech.com/forums/index.php/topic,36034.0.html
http://www.classicbattletech.com/forums/index.php/topic,36031.0.html
http://www.classicbattletech.com/forums/index.php/topic,32987.0.html

If you search/look through the general miniatures section of the CBT forums, you'll find spaceman spiff likes to photograph his miniatures in his city made up mostly of N scale buildings.  Pretty inspirational stuff.

Mine just arrived.  I ordered from EM4 rather than Red Shirt Games because I didn't need 30 of them and shipping from the UK was both cheaper and faster.  They arrived in 5 days from when I ordered them. From the UK to the west coast of Canada.  I have no idea why I can have things sent to me from overseas (got some stuff from Japan today as well) that's faster and costs less than stuff from inside Canada.

The actual detail on the pieces is deeper and crisper than I thought it was going to be.  As for using them in N Scale, they'll work, but they'll definitely be lighter mechs/power suits at about 5-6 metres tall.  The deep recesses will work well for my painting style as well, as I generally go with a base coat, dark wash, base coat again and then a highlight.

I haven't seen any of Iron Wind Metals recent releases for Classic Battletech, but these plastics strike me as being nicer and more detailed than the odd looking boxy stuff that was produced for Battletech under FASA.

3 parts silicone, 1 part naphtha based thinner.  It was enough to make it paintable with easy but no more.  One guy quoted on that myheap site says you could go 50/50 and it should still work.  My thinking is to not thin it any more than necessary though.

Did you also add a catalyst?  I also just painted the mixture onto some glass to see how thin I could get it and the 3:1 silicone/naphtha with paint as a catalyst didn't deform, even at the edges where it was thin enough to be translucent.  I forgot about the mould release though and couldn't get it all off the glass (which is made from sand/silica, so silicone sticks to it).  I'm going to get some cheap corrugated plastic "for sale" signs at the dollar store for future mould box use.

We ended up postponing the trial mould making after it came to light that some of his pieces will require a two part mould.  So we're going to need some non-sulfur clay for that process.  It's going to be a challenge, combining brush on mould making with the techniques for making a pourable mould.  I think we'll give the PVA a go.  Vegetable oil spray seems to be working fine as a mould release agent off of the glass and sprue I've tested the silicone on so far.

Thanks for the link.  What an odd process.  You'd figure right by the rating, they'd have a button that's like "rate this game" or something.

I was also thinking their 15mm power armour might work well also (for, well, power armour).  They have a variety throughout their 15mm Stargrunt range.