Introduction: DIY Aerosol Sprayer - DIY Spray Paint
This is a great way to create your own home made foaming aerosol cleaning products, spray paint, spray oil, etc. Instead of using compressed air as a propellant, this sprayer uses butane, propane, or gas duster i.e. Dust-Off as the propellant. These sprayers are pressurized and sprayed from one valve. They are long-lasting and provide consistent pressure from full to empty without having to be re-pressurized. This project grew out of attempts to improve on the instructable DIY Spray Paint.
Check out the following video demonstrations
- a hacksaw
- 220 grit silicon carbide sandpaper (a-weight is best).
- a couple of light clams or two large binder clips
- a drill or something to melt a hole in the bottle cap (I used an old nut driver and a kitchen torch)
- empty spray can and nozzle.
- Select a can that was originally filled with something similar to what you will fill your sprayer with.
- empty plastic soda bottle, 20 oz. or less
- plastic bottle cap with a tongue seal (See the picture of three different bottle caps).
- medium or thick Cyanoacrylate glue (CA glue). Preferably a rubber toughened one such as Starbond KEG-500
- Polyolefin primer (important!) such as Loctite 770, 3M Scotch-Weld AC77, or Aron Alpha PP Primer
- CA activator
- butane, gas duster (Dust-Off), or a can of propane with a green gas adapter.
- Isopropyl Alcohol or acetone (for prep)
- a clean shop cloth etc. (for prep)
- A large diameter straw or some 1/2" (initial size) heat shrink tubing
Fill Adapter Parts (for spray cans with male valve stems)
- 1/4" ID PEX-B Pipe
- butane fill tips from the cap of the butane can
Step 1: The Valve
release any remaining pressure by Depressing the nozzle of the empty aerosol can, or use a utility knife to poke a small hole in the can . Once all of the pressure has left the can, use a hacksaw to cut the valve off of the top of an aerosol can.
Spray cans that contained water based products use an LDPE inner lining to protect the can against rust and other corrosion. Using cleaning products with a valve that does not have this lining leads to corrosion and bond failure. If you plan on using water based products in your sprayer the make sure to that the underside of the valve has a thin layer of plastic lining.
Step 2: Getting Everything Ready to Prime and Glue
1. Sand the top of the bottlecap and the bottom of the valve.
Note: Many of the aerosol cans have a plastic lining on the inside. This prevents the metal from corroding. Sand, but do not remove the plastic lining from the bottom of the valve.
2. Sand on the inside of the tongue seal. get in every facet. I use high quality flexible 3M 220 grit Silicon Carbide. Go to the hardware store and pick out a few pieces of thin and flexible sandpaper (A-weight paper).
3. Clean the bottlecap/valve (cap-valve) with isopropyl alcohol or acetone, and a clean cloth.
3. Make a hole in the center of the bottlecap — a hair smaller than the diameter of the spout on the bottom of the valve. I like to melt the hole with with a hot tool like an old nut driver. Ideally, the spout should fit snugly inside the hole without distorting the shape of the cap .
4. when the valve has holes where you can see exposed springs etc. Use either heat shrink tubing or a large straw to block the holes (see picture). Lubricate the straw with a few drops of rubbing alcohol or other clean drying lubricant and force it over the holes on the valve. (see picture). After the valve-cap is assembled you can cut down this shield to the glue line for better flow, and to allow any angle spraying.
If you do not sand the parts your sprayer will (probably) fall apart!
It is important to inspect the valve for holes at the top above the one for the spout (see picture). some Rustoleum cans have valves like this with a metal ball in the valve that blocks propellant gas from either the holes or the spout depending on the spray angle. these valves allow you to spray at any angle. If the holes are not partially blocked the inner workings of the valve will fill with the glue and ruin the valve.
Step 3: Assembly
- Apply polyolefin primer to the top of the bottle cap
- Prime the plastic lining and any other plastic parts on the bottom of the valve
- fill the well on the bottom of the valve with CA Glue, enough to fill the gapbetween the valve and bottlecap when they are together.
- holding the valve spout pointing up, slide the cap onto the spout of the valve and the puddle of CA.
- If you got the hole size just right, you may not need to clamp 🎉!
- clamp the valve and the bottlecap.
- clamp lightly, try to not distort the shape of the bottlecap.
CA glue forms a stronger - more flexible bond - if it cures naturally, so wait 15-20 minutes, then Spray the clamped valve-cap with CA Accelerator to cure any of the remaining uncured glue. Wait another two minutes then remove the clamp.
If you do not use polyolefin primer your sprayer will not be able to handle the pressure and will fall apart quickly!
The primer is of prime importance!
bottle caps are made of either polypropylene (PP) or polyethylene (specifically HDPE). Almost all bottle caps made for carbonated beverages are made of HDPE. polyolefin plastics are notoriously difficult to bond due to their low surface energy and resistance to even the strongest organic solvents like acetone or xylene. Polyolefin primer in combination with CA glue allows for very high bond strengths when gluing polyolefins like PP, HDPE, and Teflon (PTFE).
the HDPE bottle cap is flexible and deforms under pressure, so It is preferable to use a rubber toughened CA glue for this step. Rubber toughened formulations of CA glue have superior shock resistance, flexibility, and shear strength. The downside is a reduction in tensile strength and hardness as compared to unadulterated CA. Most rubber toughened CA glue formulations tend to not state that fact. The ones that do mention it tend to be dyed black. Just look for a brand that includes the word "flexible" in the title. I have had good experience with the Starbond KEG-500 glue formulation.
A word of caution. Some CA formulations sacrifice strength for added flexibility, such as Gorilla brand Super Glue. I discouraged you from using these verities. Starbond is a solid well-balanced choice.
DO NOT SUBSTITUTE CA GLUE/PRIMER FOR ANY OTHER GLUE.
- Silicones: absorb propellants/solvents and swell, leading to bond failure
- 2-part epoxies: will not bond pp or pe
- Two-part acrylics. these are often labeled "epoxy" even though they are technically not epoxies and are indicated for plastics. they tend to be opaque and put off a pungent smell (unlike actual epoxy). these dissolve in the solvents and generally do not work on PP or PE anyway.
- Hot glue (both EVA and polyamide formulations). At high enough temperatures (≈400℉) hot melt adhesives (aka hot glue sticks) work very well on polyolefins and ones with a high ethylene monomer content work excellently on both PP and PE. sadly, their flexibility alone is to great and result in bond failure under the high pressures of the sprayer. regardless, their resistance to solvents precludes there use because they are not made of pure PE.
- I have not tested any of them, but my research indicates that there are two part acrylic structural adhesives that would structurally outperform CA glue in the long run. but, as with all acrylics, they do not have the chemical resistance necessary and are very expensive.
- Test the clamps on the valve-cap before you use them. if you cannot find clamps that holds the parts together in proper alignment then you can use two jumbo binder clips, although these tend to distort the shape of the cap.
- Loctite 770 Polyolefin primer glows under UV light. In that case, you can use a UV flashlight to ensure everything is primed. This will also reveal spots you missed while sanding.
Step 4: Forming the Fillet
Forming the Fillet:
- position the glued valve-cap upside-down .
- Apply the Polyolefin primer to the inside of the tongue seal, the lining and any other plastic on the valve.
- Fill the inside of the tongue seal with CA glue in layers. For the first layer wait 5-10 minuets and apply CA activator. Wait for that layer to cure. Additional layers and activator can be applied more rapidly.
- always wait for the previous layer to fully cure before adding another.
- Do not let the glue get outside of the tongue seal, where it will could compromise the threads of the cap and the seal that the cap makes with the bottle.
- Apply CA activator from a distance of 1 ft. from the fillet to prevent the glue from curing too quickly.
- I wait before curing the first layer of the fillet in order to give it time to fill any gaps that may have formed in gluing the valve-cap together in the last step.
- the fillet seals the glue joint away from the sprayer contents to prevent compromising the valve-cap bond.
- The fillet reinforces the cap, so it can handle the high pressure of the propellant without failing.
- the cured CA glue is exceedingly rigid as compared to the bottlecap. without the fillet, the high pressure of the propellant (especially propane) can deform the cap and surpass the flexibility of the CA glue, leading to failure.
- Plain CA glue (nearly pure ethyl-cyanoacrylate e.g. Krazy Glue) is fine for this step because we are not worried about flexibility or shock resistance.
- A bubble may form in the finished fillet. Bubbles in the fillet do not seem to cause any problems.
Step 5: Adapter Assembly (For a Male Valve Stem)
In order to fill the finished sprayer with a stem (male) you need to make a stem-to-stem adapter. The adapter lets you pressurize the sprayer with propellant.
- Select a couple of butane tips that sit well on both the sprayer valve stem and the canister of gas.
- Cut off a 1-1.5" inch piece of 1/4" ID PEX-B pipe
- snap the butane tip into the ends of the piece of pipe
- the adapter can be used to transfer the contents between aerosol cans or to add pressure to an existing aerosol can.
- If you use different materials, It is important to be selective about the tubing. Acrylic was too stiff and HDPE was too flexible. After much experimentation with designs for an adapter, I stumbled upon 1/4" ID PEX-B pipe and got it because I liked it. The butane tips snapped right in like magic!.
My first attempts involved softening a section of 1/8" ID acrylic tubing with a heated steel rod . The old adapter design was a big shortcoming for this project.
Step 6: Pressurizing and Propellant Selection
to pressurize the sprayer you can use:
- propane with a green gas adapter
- Gas duster (dust-off) with the the top removed
place the filled sprayer on a flat surface.
For Female Valve:
- Select a tip from the cap on the butane that fits inside the valve on the cap and test it with the can of propellant to make sure that it opens the valve and gas runs through. Also make sure that seals well with the valve and that it doesn't spew gas where the tip and valve meet.
- fill a soda bottle with your chosen contents.
- screw the valve-cap snugly onto the bottle.
- place the fitting tip on the propellant
- Invert the propellent
- insert the tip in the sprayer valve and pressurize by pressing down on the propellant as you would refill a lighter.
For Male Valve :
- fill a soda bottle with your chosen contents.
- screw the valve-cap snugly onto the bottle.
- put the finished fill adapter on the can of gas.
- while supporting the adapter and can, press down on the propellant can. Be careful to apply pressure directly down, so that the can does not slip and break the fill adapter or the stem on the sprayer.
To avoid the contents from backwashing into the can while pressurizing, either place the sprayer in the fridge or run the can of gas under warm water while shaking it for several seconds. the former feels like a safer option.
Do not depressurize by untwisting the cap. Depressurize using the spray nozzle. It is safer and does not pose a risk of damaging the threads.
Water based Cleaning products work best with butane. do not use spray paint nozzles with water based products, they will never spray the correct pattern.
If you are interested in applying coatings like paint, then you want to use propane. Propane is key to a good coat of spray paint because it provides high pressure and evaporates away before the paint starts to dry, eliminating bubbles in the finished paint. Thin the paint with xylene or naphtha. Do not use acetone, CA Glue is soluble in acetone!
Cooking oil with propane is a store-shelf worthy cooking spray, but it requires a lot of propane because propane is soluble in the oil. I speculate that there is no way around this, so the store bought spray oil probably contains as much propane.
If the sprayer drizzles then add more propellant. For example, Cooking oil, oil based paints or other oily substances may require a lot of propellant as compared to water based substances. Many paint nozzles have atomizers that only produce the correct spray pattern (aerosolize) when there is an abundance of propellant.
► These are the kinds of pressures you can expect for the three propellant options
- 31 psi@70 ° F
- 52 psi@100 ° F
- 125 psi@70 ° F
- 190 psi@100 ° F
Gas duster (Difluoroethane)
- 77 psi@70 ° F
- 124 psi@100 ° F
- valve-caps generally have a long lifespan when pressurized with butane. butane is preferable for making foaming cleaning products.
- Propane provides the greatest pressure and is recommended for paint, for cooking oil, other substances that are miscible with propane and butane.It is the cheapest option. But!
- Propane is the most dangerous option. Bottles may form cracks and bottlecap threads may fail. See (Dealing With Failure)
- Gas duster is the cleanest, the soda bottle handles the pressure well, but it is the most expensive of the three.
- You can combine propellants only from lowest to highest vapor pressure. you can add propane to butane but not vice versa.
- Pressurizing paint with butane tends to cause bubbles to form in the finished paint. The gas does not evaporate quickly enough.
- Use oil based paints.
- Propane may cause slight separation over time or with elevated temperatures. (see §Dealing With Failure)
Usually the first part to fail is the bottle. you should only use the same bottle one time.
the first part of the valve-cap that fails are the threads on the bottle cap but, as long as you respect the bottle cap threads and adequately tighten the valve-cap to the bottle you should not have any problems in the long run
Step 7: Dealing With Failure
- Threads not meshing with bottle correctly:press down as you tighten the valve-cap. Always make sure the cap is tight (within reason).
- Clogging & reduced flow: flush out the clog with a quick burst of propellent.
- Backwashing from sprayer into propellent: refrigerate sprayer or run propellent under hot water before filling
- Separation of valve and cap:
- Do not remove the cap from the pressurized sprayer.
- Apply some polyolefin primer into the crack.
- fill the crack with medium or thin ca glue - wick it into the crack.
- Deterioration of the fillet: Add another layer of CA glue to the fillet.
Testing the valve-cap:
- Screw valve-cap onto an empty bottle or one filled with water.
- Pressurize the sprayer until a little liquid gas stays at the bottom of the bottle (it reaches vapor pressure).
- Set it aside for a week or so.
Important safety information:
- if the bottle doesn't leak, but you see tiny cracks in the top of the soda bottle, throw the bottle away.
- If the bottlecap begins to bulge on the sides to the point of leaking, throw the valve-cap away.
- Some Cleaning products may cause the fillet to deteriorate over time. Test a drop of cured CA glue in the cleaner you want to use before filling the sprayer with it.
- never use anything containing acetone in the sprayer
Step 8: Spray Paint Notes
It has been awhile since I have filled one of these with paint. The first time I tried a water based latex paint. The results were depressing. the paint dried with a bunch of bubbles where the evaporating butane got trapped under curing paint. I was more interested in plasti-dip and got amazing results with propane.
- Buy clear plasti-dip and add the color yourself. Tap Plastics sells opaque pigments that make for a great looking coat.
- Pressurize with propane or
- butane and then propane or
- Only thin with xylene (best option), naphtha, or mineral spirits,
- only use spray paint nozzles
- Before adding more gas, put the sprayer in the freezer for a half hour.
- Wait for it to warm up before you test the pattern.
- Protect the green gas adapter from paint by wrapping it in a cloth while you fill
- Do not engage the sprayer valve before the propane valve or paint can get everywhere.
- Use a lot of propane for the the correct spray pattern. (see pictures)
For all of the pictures above I used flat white rust-oleum oil based protective enamel. I used the thinning instruction on an old prevel sprayer box. I used xylene to thin.
Next time I will weigh it before and after pressurization so I can give some advise about how much propane is best
I have not tried it without thinner, but you may not need to thin at all because the propane itself is so soluble in the paint.
- using a straw to block the holes of an "any angle" valve is crude, possibly heat shrink tubing cut after shrinking to the height of the lip seal would allow any angle spray by only blocking the holes slightly.