Using the spray mechanism found in standard spray cans and some common discarded items you can make your own spray paint. This project uses a bicycle pump to pressurize a small PET pop bottle, and by varying the amount of pressure you pumped into the 'can' and the types of paint added you can produce different effects. The style I got based on the paints I used and the pressure applied is reminiscent of a graffiti mop style.
Enough talk, let's make our own spray paint!
*Inspiration for this project was drawn from the short movie splay
Step 1: Tools + materials
Step 2: Old spray can
Once all the pressurized air has escaped, place the can in a vise and saw around the neck of the can. This will separate the can into the lower housing and the upper nozzle. Keep the upper nozzle and tip out the glass marble found inside the can housing, you can discard the can housing after.
Step 3: Valve
Cut the inner tube on either side of the valve, then trim the rubber around the valve leaving a 12mm (1/2") skirt of rubber.
Next, find a drill bit that is around the same size as the valve you're using. For Schrader valve you'll need a 1/4" bit. Drill into the shoulder of an empty PET bottle. Remove any burrs from the drilled opening, then feed the valve into the neck of the bottle and through the new opening.
Drop a small amount of a rubberized adhesive through the neck of the bottle and onto the rubber skirt around the valve, then pull the valve so that the rubber skirt makes contact with the inside of the PET bottle. You may need to poke your fingers through the neck opening to ensure good contact is made. Allow the adhesive to dry overnight.
Step 4: Nozzle
I tried a few different types of adhesives here and found that the best results were with Sugru. I was able to mold the sugru putty around the opening and join the old spray mechanism with the PET cap. Allow to cure overnight.
After your assembly has dried and cured completely hook it up to a bike pump and test to ensure you have a hermetic seal, if you have any leaks (you'll know) you need to address this with more glue or to re-glue the parts that aren't sealed. This is critical!
Step 5: Fill with old paint
If you are mixing paint make sure you are using like-kinds of paint (latex/acrylic with latex/acrylic and oil paint with oil paint), do not mix oil and latex paints! Mixing dissimilar paints is not advised as it's essentially oil and water. Though, it may produce some interesting results. In fact, ignore my warning, try it. Tell me your results!
Drop your old spray paint marble into the bottle first. then carefully pour your paints into the bottle and fill about 3/4 of the way full. You're going to need a funnel. Since regular paint is quite thick, I diluted my paint with a little water after it was in the bottle. I ad a ratio of about 6:1 paint to water. Experimentation here will produce different results. A thicker paint may not drip as much, but might require more pressure in the bottle (see next step regarding pressurization).
Seal bottle with nozzle cap and shake well to ensure an homogenous mix of paint and water.
Step 6: Pressurize
Hooking the valve to the bike pump I found I had good results at about 20psi. Experimenting here with different pressure may produce different effects. It's important to know that over pressurization will cause your paint bottle to fail, most likely at the nozzle connection. Start with a low psi and gradually work your way up.
Keep an eye on your connection during pressurization to ensure no leaks have spring. I had my bottle up to about 25psi and have yet to notice any leaks. Over-engineering your sealed connections is a good thing here.
Step 7: Spray
My pressurization lasted enough to make the dinosaur shown here and then some, a second pressurization was required to make the buildings. If you're looking to make a larger art installment you'll need to carry your bike pump with you.
Here's a video of my DIY spray paint in action!
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