In-Situ Ice Palace Construction
The St. Paul Winter Carnival Ice Palace has been open for a little over a week now, and they're doing a land-office business. For those not familiar with this odd tradition up here in the Frozen North, every decade or so on average since the late 1800's, the city of St. Paul has built a huge palace from blocks of ice cut from a nearby frozen lake. Lit with colored spotlights from the inside, the result is truly spectacular.
My reaction on seeing the Ice Palace was probably the same as most guys of my age and personality type: "Cool! I want one for my backyard!"
Unfortunately, this presents a number of significant logistical problems:
I do not have a lake from which I can cut blocks of ice. True, there is a pond behind our house, but it would probably not produce enough ice to build anything larger than an Ice Doghouse.
Even if I had a sufficient source of ice, the blocks they use in the St. Paul Ice Palace are very heavy: hundreds of pounds each. Enough to require big equipment to move and lift them into place.
Even given enough ice and the right equipment, I don't have the time to cut and place hundreds of blocks of ice, and I'm unlikely to get much volunteer help. Hiring people for the project would almost certainly turn She Who Puts Up With Me into She Who Used To Put Up With Me.
I need another way. And there is one: in-situ casting of the Ice Palace. Just as more buildings are made from cast concrete (either on site or prefab) than by laying individual bricks, casting the Ice Palace as a preformed block of ice on-site is likely to be faster, cheaper, and simpler than the traditional method. It also offers the opportunity to build a wider variety of structural forms, and have a stronger building.
Constructing an Ice Palace this way involves four steps: Building the Form, Filling the Form, Removing the Form, and Finish/Detail Work.
Building the Form
The form is essentially a big water tank in the approximate shape of the finished Ice Palace. Once built, the form will be filled with water, and then removed after the water freezes. There are actually two forms required, one for the exterior, and one for the interior. The interior form keeps the inside of the Ice Palace from filling with water and becoming an Ice Block instead of an Ice Palace.
Both forms have some specific engineering requirements. They must be capable of withstanding the water pressure when the forms are filled (approx. 1/3 atmosphere per ten feet of water depth). They must be sufficiently watertight to hold the water for a day or two as it freezes. They must allow the water to expand as it freezes. The exterior form should be a reasonable heat conductor, which implies that it should be made of metal. The interior form can be an insulator (relatively little cooling will happen through the inside anyway), but it should be disposable, since it will be destroyed when we remove the form. There is no need to include negative spaces (i.e. doors, windows, etc.) in the forms, since they can be carved later; this keeps the forms relatively simple and easy to build.
Begin with the interior form. I propose using 2" rigid foam insulation, which comes in 4x8 sheets and is easy to work with and cut to size. The form should be sized to allow for a reasonable wall thickness (several inches), and be tapered towards the top. The taper (a) keeps the form from floating (water pressure will hold it down, as long as water doesn't leak under the form), and (b) may help relieve the pressure of freezing, since (we hope) it will freeze solid from the bottom up and allow water to escape out the top. Inserting horizontal "floors" inside the form will provide strength against the water pressure.
The interior form should be covered with plastic sheeting as tightly as possible to keep it watertight, and set in place. Anchoring the bottom of the form to the ground with slush (which is allowed to refreeze) will help seal it and prevent water from leaking underneath, which would cause the form to float up when filled.
Next, the exterior form is constructed around the interior form. I'm not sure what the best material is for this, but some sort of metal sheet, possibly with 2x4's strapped around the exterior to provide rigidity. Small-mesh hardware cloth (metal mesh) anchored to a wood frame might also work, or even metal door screen, or plexiglas sheets, also anchored to a wood frame. The inside of the exterior form should also be lined with plastic sheeting to make it waterproof.
Construct the exterior frame to allow ice walls 3-6" thick, and thicker near the top (since the interior form is tapered). For structures more than one story high, even thicker walls may be needed. I'm not an expert on the structural properties of ice, so you're on your own. The exterior form should be at least several inches taller than the interior form, to allow the roof to be cast at the same time as the walls.
Filling the Form
Once the forms are built, it needs to be filled with water and allowed to freeze. The temperature should be well below freezing, and ideally below zero, to keep the freezing time as short as possible, and the forms should be filled around sunset to allow a full night of freezing without any solar heating.
I propose filling the form in a two-stage process. First, fill the form to a depth of about six inches above the ground, and let it freeze solid. That will provide a solid seal around the base of the form, where the water is most likely to leak out under pressure, and also firmly anchor everything in place for the second stage.
Then, once the bottom has frozen solid (probably overnight), fill the rest of the form as high as needed: probably 3-6" above the top of the interior form (at least) to allow for a thick roof.
If a transparent material was used for the exterior form, it will be easy to see when the Ice Palace has completely frozen. It might take a few days.
The Ice Palace can also be frozen in several stages. The advantage is that it won't provide as much stress on the forms (less water pressure). The disadvantage is that every stage will likely leave a horizontal fracture in the ice, which would both be visible, and weaken the Ice Palace.
Removing the Form
Once the ice has frozen, remove the exterior forms. Then, rough-cut the door using a saw (hand saw is better than electric, since the saw may get wet), and break up the interior form to remove it.
This is also a good opportunity to rough-cut any other openings, such as windows, since that would facilitate removing the interior form.
Some of the plastic sheeting will almost certainly stick to the ice and be difficult to remove. A hairdryer or hot air gun will probably work to melt just enough surface ice to get the sheeting off. This will probably give the ice a nice "polish" as well.
Finish/Detail Work
At this point, if all went well, there should be an Ice Palace which looks like it was carved from a single block of ice. Pretty cool. Now is the time to smooth any imperfections in the ice, carve any decorations, and so forth. I'm not a sculptor, so I'll probably just smooth out everything and maybe do some crenelations in the roof.
This is also the time to add dramatic colored lights, or maybe a banner flapping in the breeze. Remember that lights generate heat, so keep them away from the ice.
What Next
Will I ever actually do this crazy project? Who knows. If I do, I'll document it here.
One other thing is worth noting: in St. Paul, they demolish the Ice Palace after the Winter Carnival is over. This is to prevent it from collapsing on someone come spring. This sounds like a really good idea to me, since it will crash down at some point, and you don't want to be underneath when it does. At the very least, when the weather starts getting warm, put a fence around it.