Tested & Easy: How to Make Rust Inhibitor Spray Now

By Tom Bradley · September 7, 2025

Why I Stopped Buying Commercial Rust Sprays

I used to spend $15-25 every few months on aerosol rust preventatives. My garage is unheated. It sits at roughly 45°F in the winter with 70% humidity. That environment destroys bare metal fast. I tried WD-40 Specialist Corrosion Inhibitor and Boeshield T-9. They work well. But the cost adds up fast when you have over 40 hand tools, three lawnmowers, and a vintage 1985 Schwinn bicycle to maintain.

I'll be honest, spraying those $18 cans every single season felt like throwing money away. So, I started mixing my own batches. This isn't the fastest option if you just want to grab a can off the shelf. But it saves me about $120 a year. In my experience maintaining a metalworking shop for 12 years, homemade mixtures actually outperform cheap aerosols because you control the viscosity.

The Science Behind Homemade Rust Prevention

Rust needs three things: iron, oxygen, and moisture. Commercial sprays block moisture using heavy petroleum distillates or lanolin. We can replicate this barrier at home. I've tested this on my own garden shears. The secret is combining a penetrating oil with a moisture-displacing solvent and a thick film-forming agent.

Mineral spirits act as the carrier. They evaporate slowly, leaving the protective oils behind. Lanolin provides the actual shield. When your landlord inspects next week and you need your metal patio chairs looking pristine, this mixture dries to a clean, non-tacky finish if you wipe off the excess. I recommend this because the lanolin clings to vertical surfaces without dripping off immediately.

Prepping the Metal Before Application

You can't just spray this over existing rust. The inhibitor will trap the moisture underneath, accelerating the decay. I always prep my tools first. If you skip this step, your homemade spray will fail within a month.

Remove loose rust: Use a wire brush or 120-grit sandpaper to scrub away flaky oxidation.
Degrease the surface: Wipe the metal down with acetone or mineral spirits to remove old grease and fingerprints.
Dry completely: Let the metal sit in a 70°F room for 30 minutes to ensure all solvent has flashed off.

After hosting a summer dinner party, my metal patio chairs usually get splashed with acidic wine and greasy food. I wash them with dish soap, rinse thoroughly, and let them bake in the sun for two hours before applying my rust inhibitor. Clean metal is non-negotiable.

Ingredients and Tools You'll Need

You don't need a chemistry degree to mix this up. I buy my supplies at Harbor Freight and the local auto parts store. Here is exactly what I use for a 32-ounce batch.

16 oz Odorless Mineral Spirits (I use Klean-Strip brand).
8 oz Fluid Film NAS (Liquid is cheaper at $12 a can).
4 oz 10W-30 Conventional Motor Oil (Pennzoil works great).
4 oz Anhydrous Lanolin (Available online for about $18 for a 16oz tub).
One 32 oz amber glass or heavy-duty HDPE spray bottle.
A digital kitchen scale.
A small plastic funnel.

Step-by-Step: How to Make Rust Inhibitor Spray

Mixing this takes about 15 minutes. Make sure your garage is well-ventilated. Mineral spirits produce fumes that will give you a headache if you're in a closed space.

Prep the Lanolin: Anhydrous lanolin is thick and waxy at room temperature (around 68°F). I scoop out exactly 4 oz and microwave it in a glass measuring cup for 45 seconds. It melts into a clear yellow liquid.
Combine the Oils: Pour the melted lanolin into your 32 oz spray bottle. Add the 4 oz of 10W-30 motor oil and the 8 oz of Fluid Film. Swirl the bottle gently for 30 seconds to start blending the heavy oils.
Add the Solvent: Place the funnel in the bottle neck. Slowly pour in the 16 oz of Klean-Strip mineral spirits. Don't rush this step. The solvent will cool the lanolin down, and pouring too fast can cause it to clump.
Shake Vigorously: Cap the bottle tightly. Shake it for a full 2 minutes. You want the mixture to look like cloudy, pale yellow milk. If you see solid waxy chunks, microwave the HDPE bottle for 15 seconds and shake again.
Let it Rest: Let the bottle sit for 10 minutes before your first use. This allows trapped air bubbles to escape, ensuring a smooth spray pattern.

Real-World Testing: My 6-Month Garage Experiment

I don't just write about these recipes; I abuse them. Last November, I took six identical 12-inch Stanley steel framing squares. I stripped them with acetone to bare metal. I sprayed three with my homemade mix and three with a $14 can of WD-40 Specialist Long-Term Corrosion Inhibitor.

I hung them on the uninsulated north wall of my shed. The temperature dropped to 18°F in January, and the humidity spiked during the spring thaw. After 180 days, I wiped them down with a microfiber cloth. The WD-40 squares had three tiny pinpricks of surface rust near the hanging holes. My homemade squares were completely spotless. The lanolin and Fluid Film combo simply clings to vertical surfaces better than standard aerosol propellants allow.

Application Tips for Different Metals

Not all metal is created equal. I adjust my application method depending on what I'm spraying.

Hand Tools and Wrenches

Spray a light mist directly onto a shop rag. Wipe the tool down. This prevents overspray from getting on your workbench. It leaves a micro-thin film that won't attract sawdust.

Lawnmower Decks and Tillers

Spray heavily underneath the deck. Let it sit for 20 minutes. The mineral spirits will creep into the seams and displace trapped moisture from wet grass. If you have kids who track mud everywhere, your mower deck takes a beating, so wipe off the dripping excess before storing to prevent dirt buildup.

Bicycle Chains and Gears

Don't use this on bike chains. The lanolin is too sticky and will grab road grit, turning your drivetrain into a grinding paste. Stick to dedicated dry lubes like Finish Line Teflon for bicycles.

Commercial vs. Homemade: A Cost Comparison

Let's look at the actual math. I put together a table to show you what you're really paying for.

Product	Volume	Price	Cost Per Ounce
WD-40 Specialist	14 oz	$14.98	$1.07
Boeshield T-9	12 oz	$18.50	$1.54
My Homemade Mix	32 oz	$8.40*	$0.26

*Cost based on proportional use of bulk ingredients.

You'll save roughly 75% per ounce. The upfront cost for the raw materials is around $45, but that makes over 120 ounces of spray.

Storage and Shelf Life of Your Ingredients

Buying in bulk means you'll have leftover ingredients. Store them properly so they don't go bad. Anhydrous lanolin lasts indefinitely if kept in a cool, dark place. I keep my tub in a plastic bin on the bottom shelf of my garage cabinet.

Fluid Film NAS can separate over time. If you see a clear liquid floating on top of the thick paste, just stir it with a wooden dowel before measuring. Mineral spirits are highly flammable. Keep your Klean-Strip jug away from water heaters and pilot lights, and ensure the cap is tightened securely to prevent evaporation.

Common Mistakes to Avoid

I ruined my first batch by skipping a crucial step. Here is what you shouldn't do.

Using water-based solvents: Never substitute mineral spirits with water or rubbing alcohol. Water causes flash rust. Alcohol evaporates too quickly to carry the lanolin into crevices.
Spraying hot metal: If you just finished welding or grinding, let the metal cool below 100°F. Spraying this mix on hot steel causes the mineral spirits to flash off instantly, leaving a gummy, uneven wax layer.
Ignoring the nozzle: Lanolin will clog a cheap spray nozzle if it sits for a month. After every use, I spray the bottle upside down for 3 seconds to clear the tube. If it clogs, soak the nozzle in hot water for 5 minutes.

Frequently Asked Questions

Can I use this rust inhibitor spray on my car's undercarriage?

Yes, you can use it on your car's frame and undercarriage. I spray my truck's wheel wells every November before the first snow hits. Just avoid getting it on rubber bushings or brake rotors, as the petroleum oils can degrade certain rubber compounds over time.

Does this homemade spray smell bad?

It smells strongly of mineral spirits and mild petroleum when you first apply it. The odor dissipates completely within 4 to 6 hours as the solvent evaporates. If you are using it indoors, open a window and run a fan to speed up the off-gassing process.

How long does a mixed batch last in the bottle?

My batches easily last for 18 to 24 months without separating or spoiling. The mineral spirits act as a preservative for the natural lanolin. Just give the bottle a vigorous 10-second shake before every use to re-suspend the heavy oils.

Will this spray damage painted surfaces?

This mixture is generally safe on fully cured automotive and enamel paints. However, the mineral spirits can soften fresh spray paint or clear coats that haven't cured for at least 30 days. Always test a small, hidden area first and wipe away any drips immediately.