Introduction: Full Size Haunted Cauldron With Fog

About: There are some things you should just NEVER do.....

Full Size Haunted Cauldron

Nothing better on a Halloween night than to have a huge boiling cauldron around the place! Thing is that cauldrons are hard to find. So to indulge I had to make one!

This cauldron is made from paper mache and expanding rigid polyurethane foam, plywood and boards, along with paper mache logs and an 18 gallon plastic bucket for water. The fog comes from a ultrasonic humidifier (very pricy - but needs no restocking and very little attention) or you can use dry ice in water.

The secret to a great foggy cauldron is to have air being introduced into the fog so that it flows over the edge of the cauldron. This cauldron has a hidden fan pumping air into the mix.

It's lots of fun to play with the fog and it will definitely be the center attention of your Halloween decorations!

Step 1: Materials


~ Three Foot Latex balloon

News Paper

Liquid Starch

2-Part Expanding Rigid Polyurethane Foam (I used 2 lb density)

24" square sheet of 1/2" plywood

24" square sheet of 1/4" plywood

~10' of 1"x4" pine

18 Gallon Plastic Bucket (~16-1/2" tall, ~21-1/2" dia.)

2" PVC Pipe (~12")

3 - 2" PVC Elbows

1 - 2" PVC Coupling

1 - 2" PVC 'T'

Paper Mache powder

Cardboard Tubes - carpet tubes, cling warp, etc.

Vinyl tube for perimeter of cauldron

Hot glue, screws

Spray Paint

'Great Stuff' foam sealant

12-Jet Ultrasonic Water Vaporizer (Mister) and associated power supply

Step 2: Paper Mache Your Balloon

The cauldron is based on the shape of a large (~3ft dia) balloon picked up from a party supply store. The balloon is paper mached with four or five layers of newsprint dipped in liquid starch. Each layer is allowed to dry before applying the next. After the paper mache ball is dry the balloon is popped and the top and bottom are cut off.

The reinforcing structure of the cauldron is based on a 1/2" thick plywood disk on the bottom and a 1/4" thick plywood disk at the top, about 3 inches below the lip of the paper cache cauldron. The disks are spaced apart and held together by 4 uprights composed of 1"x4" pine boards that are spaced around the perimeter of the disks. The boards are fastened to the disks by screws through the plywood.

The bottom disk is approximately 21 inches in diameter with a 15 inch opening cut in it. The top disk is 24 inch diameter with an opening that the plastic bucket will fit through and be supported by the top disk.

Step 3: Add Logs

The logs are made from various cardboard tubes; larger ones are carpet tubes, smaller are various thick walled tubes. The large carpet tubes are cut at an angle to fit against the paper mache cauldron and hot glued in place to the bottom disk and cauldron. Various small tubes are cut at angles and added to the larger carpet tubes to create branches.

All the tubes are covered with paper mache paste to create the illusion of bark and to fill any gaps.

The top edge (lip) of the cauldron was finished and strengthened by taking piece of large diameter vinyl tubing and slitting it down the length so it could fit it over the edge of the rough paper mache lip. The tube was shot full of 'Great Stuff' foam sealant and slipped over the edge of the paper mache and allowed to bond and harden.

Step 4: All Air Duct

As mentioned, the fog needs to have air added to it to keep it flowing over the edge of the cauldron. If there is no added air then the fog just sits in the bucket and does not move much. 2" diameter PVC pipe is used to create an air path from below the bucket up into the side of the bucket. An elbow is also provided inside the bucket so that the air flow entering the bucket is downward. It takes a little bit of finagling to get the bucket with the pipe to fit inside the top disk opening - and that's the goal. The bucket should sit flat on the top disk.

Step 5: Add Fan Assembly

The air for the cauldron fog is provided by a very small computer fan. You don't want the fan very large as you just want a little air to displace the fog and have it slowly flowing over the edge.

The fan is mounted inside a 2" PVC 'T' fitting. The Fan is powered by a plug-in power supply.

The 'T' fitting is needed because the pipe, in addition to carrying air into the cauldron bucket, is bringing out the power lead wire for the ultrasonic humidifier. The cable for the humidifier and the wire for the fan both exit through the side of the 'T' fitting. The opening they exit needs to be covered with tape so that the air from the fan will go up into the bucket. The 'T' fitting resides at the bottom of the cauldron and fits onto the pipe coming down the side of the cauldron.

Step 6: Add Rigid Foam to the Cauldron

The space between the paper mache cauldron body and the plastic bucket is filled with expanding rigid polyurethane foam. This mounts the bucket in place and give the body of the cauldron form and strength.

A board is added across the bottom disk opening to allow a place for the bottom of the bucket to rest.

Step 7: Add Ultrasonic Humidifier - Fog Maker!

The source of the fog is a 12 disk Ultrasonic Humidifier. This is a very pricy item (~$200) but it has lots of benefits in that you don't have to keep adding dry ice to your bucket and the output is constant. The unit does get warn so you do have to add regular ice to keep the water and unit cool, but it is so neat to have fog on demand!

The humidifier disk fits into a float ring that keeps it at the proper depth. The cable from the humidifier goes up through the air pipe to the outside and the supporting humidifier power supply.

You can use the tried and true method of dry ice. It should work just as well. In either case do not put too much water in the bucket. You have to keep the water level below the air duct entrance point and also keep the overall weight of the water to a reasonable value.

Step 8: Dress It Up If You Want!

Who could go wrong by adding a skull?

Well, there are several ridges in my bucket and it allowed me to cut a piece of acrylic that was the same size as the diameter of the bucket and it would support a skull so the skull would be floating in the fog...

How cool!

Adding low voltage lighting can also add a spooky touch.

Note: Please do not use wall outlet (mains) powered lighting as the water and fog creates an electrical shock hazard.

Step 9: Start That Witches Brew...

"Double, double toil and trouble; Fire burn, and caldron bubble." (- William Shakespeare, Macbeth).


PS - See my bubbling goo caldron.

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