Surface Preparation Before Bonding and Painting: When to Use Isopropyl Alcohol vs MEK
Surface bonding is a critical part of aircraft structural repair and maintenance, as well as aircraft flight operations in general. When repairs are necessary for the skin, the exterior of the aircraft, such as bonding and painting, the finish has to be perfect.
Before anything is applied to the skin or affected area, it must be clean. This is a non-negotiable. When should you use isopropyl alcohol, and when should you use MEK?
Let's take a look.
Quick Buy: UNIVAR ARPOSOLVE Isopropyl Alcohol & MEK Solvents on GSA Advantage
Why Surface Preparation Matters Before Bonding and Painting
Surface preparation before bonding and painting is one of the most critical steps in achieving reliable adhesion across industrial and aviation applications. Oils, grease, dirt, and other contaminants left on surfaces can interfere with adhesives, contact cement, paint, and coatings, leading to premature failure, rework, or safety issues on aircraft components and industrial materials.
Chemical solvents such as isopropyl alcohol (commonly referred to as rubbing alcohol) and methyl ethyl ketone (MEK) are widely used for effective cleaning, degreasing, and substrate treatment prior to bonding. Selecting the correct solvent directly impacts drying time, residue levels, adhesion strength, and long-term durability.
The Clean–Abrade–Clean Rule for Reliable Adhesion
The best practice in industrial maintenance and aircraft maintenance is the clean-abrade-clean process. This establishes a consistent, high-energy surface that allows structural adhesives, sealants, and bonding compounds to perform as intended.
Initial solvent cleaning removes oils, greases, hydraulic fluid residue, and other surface contaminants that interfere with wet-out and chemical adhesion. Approved solvents, when used in accordance with material data sheets and other technical data, are designed to lift contaminants rather than spread them across the surface.
Isopropyl Alcohol (IPA): General-Purpose Surface Preparation
Isopropyl alcohol, also known as isopropanol or rubbing alcohol, is commonly used as a powerful solvent for surface preparation in industrial and aviation applications.
What Isopropyl Alcohol Is Used For
The isopropyl alcohol that is used for aircraft maintenance is not the same thing that you buy on the shelf of your typical retailer. This is generally 91-99% proof and designed to remove light oils, fingerprints, and dirt from surfaces.
Since it has so little water in the content, it evaporates extremely quickly and lifts these away. Final wipe-downs are recommended before applying adhesives, glues, paints, contact cements, and epoxies, as these will remove oils, fingerprints, and dirt and grime rather than smearing or wiping them away.
Also, they are used to clean sensitive equipment and components where residue must be minimized. Commercial isopropyl alcohol evaporates extremely quickly and leaves no residue, making it an excellent choice so long as it's an approved cleaning agent for the task or components at hand.
IPA is highly effective for degreasing without attacking most plastics, composites, electronics, or painted surfaces. It evaporates quickly, leaving minimal residue that could interfere with bonding or the appearance of the paint.
Aerospace-Grade IPA and Purity Considerations
In aircraft maintenance, high-purity isopropyl alcohol meeting TT-I-735 specifications is commonly required. Higher purity reduces water content, improves drying time, and minimizes the risk of chemical reactions with adhesives and substrates. Aerospace-grade IPA is frequently used on aluminum, composites, and polyethylene surfaces prior to bonding or coating.
Although isopropyl alcohol is found in consumer products such as hand lotions, body rubs, disinfectant sprays, and quick-drying inks, aviation and industrial use demands much higher standards of quality and consistency.
Methyl Ethyl Ketone (MEK): Heavy-Duty Solvent Applications
Methyl ethyl ketone (MEK) is a very effective solvent and is used when isopropyl alcohol is not a strong enough solvent to remove heavy contamination. It also has a high, rapid evaporation rate and strong solvency, making it suitable for demanding aviation and industrial surface preparation tasks.
When MEK Is the Correct Choice
Mek is commonly used to remove heavy greases, waxes, and oils, as well as any other uncured adhesives that resist mild cleaners like isopropyl alcohol. It is specified for stripping or thinning paints, lacquers, and resins when used strictly in accordance with the manufacturer's instructions and approved maintenance processes.
For repainting or rebonding operations, MEK can provide the aggressive final surface treatment that coatings and adhesives need to be properly wetted and adhere to the substrate.
Products such as Aero ARPOSOLVE MEK are commonly used in industrial environments where powerful solvent action is required.
MEK is highly flammable and can be aggressive toward certain plastics and composites. It should only be used with PPE, proper ventilation, and strict adherence to material compatibility guidelines.
IPA vs MEK: Practical Selection for Maintenance and Production
The choice between isopropyl alcohol and methyl ethyl ketone (MEK) depends on:
1. Contamination severity
2. Material compatibility
3. Specific maintenance or production tasks
It is important to remember that MEK is much harder on substrates like plastics and other similar substrates. So keep that in mind and always read the technical data for your aircraft type.
Use Isopropyl Alcohol When:
Performing routine maintenance and surface preparation, cleaning aircraft components, and working with sensitive substrates like composites, plastics, and coated metals.
IPA is perfect for final wipe-downs after abrasion, where residue control, low reactivity, and fast drying time are the most important considerations for consistent bonding and coating.
Use MEK When:
The areas to be prepared have heavy oils, greases, waxes, and uncured adhesive residues after initial cleaning. Also, when thinning paints, coatings, or contact cements for approved procedures is required, use MEK.
MEK's aggressive solvent action is great for demanding industrial and aerospace applications where maximum contaminant removal is required. It is a very powerful but also caustic and inflammable chemical.
Surface Alteration: Promoting Adhesion Beyond Cleaning
Sometimes, cleaning alone is not sufficient. Abrasion is a common technique for treating surfaces by removing weak boundary layers and improving the consistency of bonding. After an abrasive is used, a solvent-soaked wipe with IPA is a great option for removing any remaining dust and residue without spreading it or leaving any behind.
Some materials, such as polyethylene and low-surface-energy plastics, may also require additional treatment or primers to ensure adhesion. But IPA is a great choice on these because it is very sensitive to items like plastics.
Safety and Handling Considerations
Both of these items are flammable solvents and have to be handled and stored correctly. MEK has a higher toxicity risk and requires stricter controls.
Make sure to check the MEK safety data sheet to ensure you are storing it correctly. Also, always follow any other manufacturer directions for storage and your local or service-directed regulations.
Check out the SDS resources for the products listed here:
Procurement and Quality Considerations
One of the biggest challenges you'll face is matching solvent purity, packaging, and quantity to usage requirements. This helps you maintain consistency and cost control, and all but guarantees that you use materials you have rather than sending them to storage and never seeing the light of day.
These products do have a shelf life, so you need to be mindful of it when building your procurement lists. Greenwood Aerospace is the GSA contract holder that you need to partner with. We carry a broad selection of isopropyl alcohol and methyl ethyl ketone solvents to meet whatever surface preparation needs your unit has.
Greenwood Aerospace is Your Trusted Procurement Partner
Greenwood Aerospace has been in the government procurement business for over forty years and has worked with all branches of the military and many federal government agencies to source parts, consumables, and components. We offer a number of the most widely used IPAs on the market via GSA Advantage. We can help you procure IPA in any quantity, whether small or large.
Greenwood Aerospace partners with prime defense contractors to support military and government export programs. We are ITAR-registered, AS9120B-certified, and an approved GSA Schedule contractor.
GSA MAS Contract Number: 47QSMS25D00B8
Compliance & Registration
ITAR DDTC Export Compliant
Cage Code: 2Y735
UEI: KVSUYYSJS174
DUNS: 604006874
NAICS: 488190, 336413, 332722, 336411, 481212, 532411
For large orders or expedited delivery, contact 580-865-6000, 833-GSA-EBUY (833-472-3289), or gsasales@greenwood.aero.
Frequently Asked Questions
What does isopropyl alcohol do to adhesives?
IPA removes surface oils and contaminants without degrading cured adhesive systems.
Is 70% alcohol the same as aerospace IPA?
No. Lower-grade alcohol contains water that can interfere with bonding and paint adhesion.
What is MEK primarily used for?
MEK is used for heavy degreasing, paint thinning, and aggressive solvent cleaning.
Is MEK better than acetone?
Each solvent has different evaporation rates, effectiveness, and material compatibility.
Where should you not use isopropyl alcohol?
Avoid use on uncured coatings or where moisture contamination could cause a reaction.
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