Introduction: Water Balloon Mortar

About: I'm Mike, from The Geek Pub. I'm a maker. I love to make things. from woodworking to electronics. Follow along with me!

A water balloon mortar is an awesome thing to have around the house. Its great for summer parties or messing with the neighborhood kids. It even makes a great addition to Halloween setups. So in this Instructable, I'm going to show you how to build one.

Step 1: Watch the Video!

There's a lot of detail to this Instructable. It helps to take a minute to watch this instructional video before moving on. Once you've finished the video, head on over to step 2!

Step 2: Acquire All of the Components

You're going to need a lot of components to make this cannon. You should be able to acquire all of them from your local home improvement center. You can get the balloons at your local big box store, party store, or dollar store. Though the balloons from the dollar store tend to burst a lot and may need to be double wrapped.

Items Needed:

1 2″ SCH 40 Pipe
1 1″ SCH 40 Pipe
2 2″ Caps
2 2″ Couplers
3 2″ to 1″ threaded reducers
3 1″ threaded to 1″ adapter
1 1″ elbow to threaded 1″ elbow
2 1″ Tee 1 1″ threaded sprinkler valve
1 1″ 90 degree elbo 1 1″ ball valve
1 Air compressor quick adapter.
1 2″ Coupler 2 1″ caps
1 Momentary switch
1 25 ft doorbell wire
1 plastic wire wrap
1 Yellow High Gloss
1 Black High Gloss
1 Pipe Primer
1 Pipe Glue

Step 3: Mark and Cut the PVC

Mark out all of the sections of PVC using a measuring tape, making a tick mark with a marker where you'll need to make the cuts. You can make the mortar any size you want, smaller or larger.

You can cut the pipe using a PVC pipe cutter if you have one. A hacksaw or handsaw tends to work well, but you'll need to sand off any burs. I used a compound miter saw with an 80 tooth blade to cut mine down to size and that worked very quickly and left a nice finish. Just remember, PVC is prone to fracturing so cut slow if you use this method.

Step 4: Dry Fit It All Together

Before you touch that glue bottle dry fit all of the components together. If anything doesn't fit or work right at this point it is east to make a new section or replace a component. Once you glue it up it will be a major rework job to fix.

Since there is nothing to hold the pipe together, please do not try to add compressed air at this point.

Step 5: Drill and Install the Air Inlet

To fill the water balloon mortar with air we'll need to connect an air compressor. That's made easy by using an air compressor quick fit connector behind the ball valve.

Drill a hole in the end-cap (behind your off valve) using a drill bit that is slightly smaller than the threads on your quick fitting.

Using a wrench and the quick fitting you can easily thread the hole in the PVC cap. Once that's complete, remove it, wrap the threads with PVC pipe tape and then reinstall it to complete the air fill and make it leak proof.

Step 6: Prime and Glue the PVC Components

Using standard PVC primer and PVC cement, glue all of the components together into the final assembly. It is fine to prime all of the pieces at once and set them aside, but only glue two components together at once. If you glue ahead it is most likely that the glue will dry before you get to the next component.

Some of the larger PVC components will be very hard to press together. A vise will help if you have one. You can also place them on the ground and use a weight or your body to press them together, if needed.

Step 7: Wire Up the Detonator

Wire the detonator using solder and heat-shrink tubing if you have it and are skilled with a soldering iron. If you're not, then at least twist the wires and wrap them in electrical tape.

Drill a hole in the two 1 1/4" caps. One hole will be used for the momentary switch. The other hole is for the lead wires to the sprinkler valve.

Wire one lead of the 9V snap to one lead of the sprinkler valve. Place the momentary switch between the other 9V lead and the other sprinkler valve lead.

Do not glue the detonator together! You'll need to open it to replace the 9V battery in the future.

Step 8: Paint the Components & Assemble It

If you want your water balloon mortar to look cool you need to paint it!

Paint the entire mortar with a single color of your choosing and let that dry overnight. The next day tape off all of the pipe sections leaving only the caps exposed.

Paint the caps with the secondary accent color and let that dry to touch (usually 30 minutes to an hour) and then remove the masking tape.

Once the paint and glue has completely cured (24 hours) reassemble everything using pipe thread tape on all of the threads.

Step 9: Fire Your Water Balloon Mortar

Before you fire the water balloon mortar for the first time you'll want to coat the inside of the barrel with vegetable oil. Do not use a petroleum product as it will cause the latex balloons to burst while they are still inside the barrel!

Fill the mortar up with compressed air. Somewhere between 80 and 100 PSI is just about right.

Fill the water balloons up to where they are just smaller than the barrel diameter and drop them into the mortar.

If they balloons are bursting before they leave the barrel, lower the air pressure or add another balloon layer to increase their strength. If you want to run the mortar up to 120 PSI you'll probably need to wrap four or five balloons around each other.

Well if you liked this project, be sure to check out my other projects here on Instructables. And don't forget to subscribe to my YouTube channel at! You can also check out additional information on all of my projects and videos at my website The Geek Pub!