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 YouTube.com/c/TheGeekPub! You can also check out additional information on all of my projects and videos at my website The Geek Pub!



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    13 Discussions


    3 years ago on Introduction

    Been thinking about shooting water balloons ever since I made my spud gun. Good to see the idea about barrel lubrication proven, now just to figure out if I can actually fire balloons with a combustion based gun.

    6 replies

    Reply 3 years ago

    This would be possible. The use of some form of obturation (to ensure there is a good seal in the barrel so the gases don't just escape round the edges) will also work to reduce the 'shock' type effect of the more rapid reaction, as well as providing a bit of a heat shield.

    If you use something like corrugated cardboard, this will absorb some of the shock, but would fire out of the end of the cannon too - similar to wadding in old style cannons... If you wanted to recover and re-use, stick a tether to the cardboard, slightly longer than the length of the barrel, and secure the tether to the outside of the barrel.

    The cardboard will then be pushed out of the barrel, along with balloon, balloon (untethered) continues on its merry way, the cardboard gets pulled back by the tether and falls to the ground, ready for resetting :)


    Reply 3 years ago on Introduction

    Yep. I made several different barrel sizes and different balloon sizes. The smaller balloons work far better. The vegetable oil is basically required. But those cheap ass dollar store balloons are hard to keep from bursting on launch. Sometimes even two or three wrapped together burst.


    Reply 3 years ago on Introduction

    I've also been thinking about creating some sort of pad to put under balloon, although the main issue here is making it just shoot the balloon out, not itself.


    Reply 3 years ago

    combustion based design will work. The heat will be absorbed by the water inside the balloon.


    Reply 3 years ago

    The problem here is not in the heat, its the fact that combustion based cannons are an almost instantaneous explosion of energy, while pneumatic valves often take longer to open. Thus, even if it is the same amount of energy, it is over more time.=less chance of breakage. Source: I have made both.


    Reply 3 years ago on Introduction

    The problem again is the rigidity of the balloon. I've had pretty good luck putting the balloon inside a styrofoam or paper cup. That give is a little more protection. But its hard to find big enough cups to scale that up to larger balloons.


    3 years ago

    Crazy idea. I love it and I imagine this thing must be great fun. :-)

    What is the range of this kind of mortar?


    3 years ago

    Isn't this the same thing grant Thompson made on YouTube? It's even the same colors

    1 reply

    Reply 3 years ago on Introduction

    Grant Thompson's is red and black, and his was designed to shoot candy, not water balloon. Sorry to "burst" your bubble. :-)