How to build a simple foundry (forge) and mold metal objects
In a survival situation, tools and weapons made from stone, bone, or wood will suffice but those same tools and weapons constructed from metal may prove overwhelmingly useful. However, metal construction requires use of a forge or foundry, a special furnace used to generate extreme heat – enough to melt (a foundry) or soften (a forge) metal. Here’s how to easily construct a foundry in a survival situation.
What is a foundry?
A basic foundry is simply an insulated container filled with fuel and built with the means to inject air in order to increase the temperature of the burning fuel. It requires a “refractory” or insulating layer that holds the heat without cracking.
The refractory can be made from cement, sand, fireclay mixture, or a mixture of plaster of paris. If plaster of paris is used, it can be mixed with perlite and sodium silicate (available in hardware and garden stores) to provide an extremely heat resistant refractory.
Injecting air into the refractory
The refractory requires a hole that allows air to be blown into the refractory. This makes the fire consume more fuel and generate much higher heat. Air can be blown into the hole using bellows but a blow dryer or shop vac work much better. A leaf blower can be used for large refractories.
Fuel for your foundry
As for fuel, most foundries use gas to fuel the fire but charcoal can also be used. Charcoal can be created in the wild by covering smoldering wood with earth and letting it sit for a few days.
Metals for your foundry
With a foundry, any metal can be melted but aluminum is the easiest to melt. Aluminum can be obtained from cans, foil, or car parts such as automobile pistons. If the rods are still attached to the pistons, the piston can still be melted and the rod fished out of the foundry before it begins to soften. Brass is also a popular material to melt.
Bits of metal work best. These bits are called ingots. Larger pieces of metal can be cut into ingots for best results.
How to create a small foundry
Given that a foundry is little more than a container for a fire with a means to blow air underneath the fire, building a foundry is a fairly simple endeavor. In an emergency scenario, you could even build a rudimentary foundry by digging a hole in the sand and shoving an air pipe at an angle through the sand until it emerges underneath the fuel. For a more permanent foundry, follow these directions.
- Large metal bucket
- 4-inch plastic pipe
- Refractory material (e.g. mixture of sodium silicate, Perlite, and plaster of paris)
- Drill and hole bit
- 1” steel pipe
- Blower mechanism (e.g. hair blow dryer)
- Stand a 4-inch plastic pipe centered in a large metal bucket or stainless steel stock pot
- Mix sodium silicate (also known as waterglass or liquid glass, available in industrial supply stores and larger hardware stores), Perlite (available in garden stores), and a small amount of plaster of paris. When dried, this will form a high-temperature insulating material which holds in heat.
- Pour the Perlite mixture into the bucket and around the plastic pipe.
- Once the mixture hardens, remove the plastic pipe leaving a “hole” or cavity in the middle of the plaster. This will be the area where fuel is placed.
- Next, create an air port. Using a 1 2/8” hole bit, drill a hole through the bucket and hardened plaster. Make the hole long enough that it penetrates through the plaster to the hollow cavity. Drill at about a 30 degree angle (downward) starting at a height that ensures the point where the hole enters the cavity is a few inches from the bottom of the bucket. The hole should be slightly larger than 1” in diameter in order to ensure the 1” steel pipe fits into the hole. Note that the only reason for the angle on the port is to keep material from pouring out if the foundry accidentally tips over. A straight hole can be used too along with pipe elbows, etc. to shape the blow pipe angle/position.
- Fit the 1” steel pipe (our blower tube) through the hole, stopping before the end of the pipe reaches the refractory cavity.
- Next, create a vented lid for the foundry. Fill a similar-sized bucket with about 5-10” of Perlite mixture. Push the ends of two U-bolts into the plaster to form handles for easy removal of the lid.
- Drill a small hole, about 1” in diameter, through the middle of the lid. This will act as the vent hole to relieve pressure.
- Fill the foundry with charcoal and light.
- Place the lid on top of the foundry and allow it to “cure” for about 12 hours.
Operating the foundry to mold molten metals
Firing the foundry
The foundry is operated by firing it with charcoal or hardwood and blowing air through the blower tube to increase the heat. Note that the blower tube can get hot so manual blowing by mouth is ill-advised. A blow dryer or any other high-velocity fan works well. If a hair blow dryer is used, a bicycle tube can be stretched across the mouth of the blow dryer and connected to the blow pipe.
Using a crucible to hold molten metal
Metal objects can be placed in a high-temperature steel container for melting. Depressurize an old fire extinguisher and cut off the bottom to make an excellent crucible for holding molten metal. In a survival situation, a crucible can also be molded from clay.
Tongs are typically used to place the crucible in the bottom of the refractory and to remove it. Note: use thick protective gloves, apron, and pant and shoe guards to protect yourself from the splashing, bubbling molten metal.
As an alternative to a crucible for holding the molten material, metal ingots can be dumped directly into the refractory if you build the foundry with a second, smaller metal pipe, located at the bottom of the foundry and angled downward, that acts as a “drain” for the molten metal to pour from.
Molding metal objects
Once metal is melted, the molten material can be poured into molds. Molds can be made from sand or whittled wood. If sand is used, it is typically contained in a thick, sealed wooden box.
To mold a replica of an existing object, create a solid wooden box with two equal halves. Pour your perlite mixture into each half of the box. Place the object to be “copied” into the mixture. Before the other half of the mixture hardens, work it onto the object so the two halves of the box can be joined back together, enveloping the object. Once the Perlite mixture dries, remove the wooden box halves to reveal the new mold.
How to build an even larger foundry
Note that a larger foundry, suitable for melting large pieces of metal, can be made using a large steel drum and a 5-gallon paint bucket. The construction process is the same as the method used to build the small foundry. Place the 5-gallon paint bucket into the center of the drum and fill around it with Perlite plaster. Once dry, remove the bucket. Drill a hole through the drum and hardened Perlite and run the steel pipe through the hole into the foundry’s center cavity to form the blow pipe.
How to build a medium-sized foundry
An old propane tank makes an excellent container for a medium-sized foundry. The top of the tank can be cut off and filled with refractory material to form the lid.
Examples of homemade foundries
The gallery below features homemade foundries and some very interesting potential enhancements.
About refractory material and example recipes
Below are a few proven recipes for refractory mix. Note that in most recipes, add as little water as possible. You want a mixture about the consistency of cookie dough.
For optimal results, the refractory should be cured before use. To cure the refractory, let the mixture dry for several days (longer for larger refractories) and then fire up the furnace using low heat. For the first burn, burn for 15 minutes and let it cool completely. Then burn for 30 minutes and let it cool. Then 45 minutes. Finally, burn it at a high temperature until there is no smoke or steam being produced.
With all recipes, make sure pure Perlite is used, not Vermiculite or a blend intended for plant use.
Portland cement refractory
1.5 parts Portland cement + 2 parts Perlite + 2 parts silica sand + 2 parts fire clay (or well driller mud)
Make sure the Portland cement is pure – no rocks or sand.
Furnace cement refractory
1 part Furnace cement + 4 parts Perlite
If too much Perlite is used the refractory will be brittle and weak. If not enough Perlite is used the refractory will take much longer to “seal”.
Fire cement refractory
4 parts Perlite + 1 part fire cement
The fire cement should be rated at 1400 degrees or higher. 1800 degree rating is required for melting brass.
Alternatives for refractory cement
Alternatives for refractory cement include red clay bricks (solid bricks), fire brick (also known as refractory brick or fire clay brick), ankar sandstone (also known as Angkor sandstone or Ankar firebrick), and soapstone.