Given the many technical talents of the folk on this forum, I was wondering if they could answer a question that came up with a Terram "builder" magus. How feasible is it to make a building entirely out of stone? More precisely, a building that simultaneously is slender (a tower, rather than a ziggurat) and has large chambers (at least 20 feet by 20 feet). The typical example would be a Conjured Mystic Tower with 5 foot thick walls.
The reason I'm asking is the following. It's pretty hard to span large spaces with just stone, because stone resists well to compression (pushing), but not to traction (pulling) or shear (cutting). Wood (or, in modern day, steel) is much better, and is typically used for beams supporting floors. Sure, you can span very wide chambers with arches (a brilliant engineering invention), but the arc pushes outwards, so you need a squat building: Gothic cathedrals look tall, but in fact have a tall central section, that pushes on two smaller side sections, that often push in turn on two even smaller sections or on butresses.
2c: I'd allow the magic to construct floors of that size from stone and not worry too much about the particulars of physics; unless the magus wished to do something huge or heavy in the rooms (construct a stone gollem).
I noticed too that the flying castle example in one of the recent books used a very large stone disk as the basis, and "real world" physics would make that utterly impossible without a lot of re-enforcement by steel or some-such. So if its good for that crafted item, then fine for a conjured tower.
My problem is specifically when magic does not come into play. If magic comes into the equation, I can accept everything is possible. But if you build with mundane materials -- including using Creo Rituals of Momentary Duration -- then I start to wonder, particularly because the unsuitability of stone for long beams was well-known throughout antiquity and the middle ages. It's not "modern physics" here: any architect in the middle ages knows that to span long distances you either need wooden beams, or stone arches with some side support.
Get yourself a master mason with inventive genius. There, you just invented gothic style and arches in your covenant The guys in Chartres will be eager to copy you, so you have a nice story hook of people appearing at your doorstep to see what you have done.
I always envisioned this kind of thing to be done with reduced stones. You build your construction on a small scale. The thing is that you cast a MuTe spell of maintaining the demanding spell in a LARGE circle. Then you keep casting "reduce this 2 paces by 2 paces stone to a fist sized thing" spell. You place the construction materials inside your mega-circle. And you basically build a model Once ready, you break the circle. BAM! Insta-large building MIcro and macro managing things to make them easier to practice should be a common feature in covenants. After all, having your grogs trained to fight giants and griffons is a good idea, but it is easier to reduce their size and have them fight a normal soldider or a chicken than go out and capture a giant or griffon for their practice! Same with working those intrincate details of artistry in the sword's hilt: if the hilt is the size of a tree it is easier to carve intrincately. Muto can be real fun
Repeat above answer. Even natural stone could handle what you ask, but created with magic means you can make the stone perfectly or abnormally uniform and/or dense. Just a perfectly uniform natural stone of one of the stronger sorts could handle far beyond what you require.
If you want to justify it, add a Muto requisite to the creation and say that the stone is unnaturally strong. Or pretty much anything. If you want to stretch it really far, just add magnitudes as far as you think is proper.
But as i said above, even just making the stone perfectly even in creation, its the uneven parts that is the big reason for stone to be truly poor for supporting structure.
Unless you demand perfectly straight angles(ie allow enough arching), you could pretty much probably manage to get a tower with 20*20feet rooms from hacking out a regular stone hill.
One knowledgeable enough would also know how much stronger some kinds of stone is, obsidian(IIRC and not messing up which is which) being one such.
As I understand, much of the problem with stone as a building material is that it is a nature material - meaning that it is in-homogeneous and liable to have small cracks and fault lines.
Magically created stone could (would) be free of these by design.
That said, you'd probably want a bit of arches in your design to optimise the strengths of stone and minimize shear.
Very thick walls (good for a keep) are used. And the highest level doesn't have a stone ceiling, you need the weight of its wall to redirect the lateral forces from the stone vaulted ceilings below to the ground (within the walls). The same principle as the flying buttress. High-tech architecture of its time.
It can be certainly done with Rego craft magic and enough finesse.
With thick outer walls and substantial foundations you can build a big slender tower and keep everything in compression. Walled gardens and a first floor main door with stairs give opportunities for discreet buttressing. Steel ties and floor joists are also Terram if you can put up with the anachronism. If you cast a moon duration rock to water spell and soak wooden beams and planks you should end up with wood that is harder, stiffer, heavier and very resistant to fire and rot.
One of the reasons why masonry lacks tensile strength is because it's made from blocks/bricks/stones dry fit or held together with some type of mortar. When it comes to tensile forces verses compressive the actual stone has more strength and flexibility then the fittings. You can see this in carved statues. Solid stone carved into shapes that could never be constructed out of masonry.
In theory monolithic stone walls can be thinner then masonry walls and still support the same size arch. Thiner walls means a lighter structure in general which means you can build that much taller.
Of course the actual difference probably needs a Civil Engineer to figure out. Still I would imagine Magi could construct something taller and more impressive then the Leaning tower of Piza.