Surface Preparation Guide for Industrial Coatings
How to Prepare a Surface Before Applying Industrial Coatings
Proper surface preparation is one of the most important stages of any industrial coating project.
Even a high-performance coating can fail prematurely if it is applied to a contaminated, poorly prepared or unsuitable surface. Peeling, blistering, flaking, corrosion and poor adhesion can all occur when the substrate has not been prepared correctly.
Whether you are coating structural steel, machinery, roofing and cladding, concrete floors or other industrial surfaces, the preparation process should be considered before selecting and applying the coating.
New Guard Coatings provides industrial coating solutions and technical information for applications across the UK. This guide explains the key considerations when preparing surfaces for industrial coatings.
Why Is Surface Preparation Important?
Industrial coatings rely on good adhesion to the substrate.
Dust, dirt, grease, oil, rust, loose paint, moisture and other contaminants can prevent the coating from properly bonding to the surface. Applying a new coating over an unsuitable substrate can therefore result in premature coating failure.
Proper preparation can help:
- Improve coating adhesion
- Remove contaminants
- Remove loose or failing coatings
- Reduce the risk of premature coating failure
- Provide a suitable surface profile
- Improve the overall performance of the coating system
- Support a longer-lasting finish
The correct preparation method will depend on the substrate, its existing condition, the previous coating system and the requirements of the new coating.
Step 1: Identify the Substrate
Before beginning preparation, establish what material you are coating.
Common industrial substrates include:
- Mild steel
- Structural steel
- Galvanised steel
- Other metals
- Concrete
- Masonry
- Timber and wood
- Previously painted surfaces
Different substrates require different preparation methods and coating systems.
A preparation method suitable for structural steel may not be appropriate for concrete, galvanised metal or previously coated surfaces.
Step 2: Assess the Existing Surface
Inspect the surface carefully before starting preparation.
Look for:
- Rust and corrosion
- Loose or peeling paint
- Flaking coatings
- Cracking
- Blistering
- Oil and grease
- Dirt and dust
- Chemical contamination
- Moisture
- Surface damage
- Existing coatings
- Areas of poor adhesion
The condition of the existing surface should influence both the preparation method and the coating system selected.
If an existing coating is sound, well adhered and compatible with the proposed system, complete removal may not always be necessary.
However, loose, failing or poorly adhered material should be removed before recoating.
Step 3: Remove Dirt, Grease & Contamination
The surface should be clean before coating.
Oil, grease, dirt and other contaminants can interfere with adhesion and may cause defects in the finished coating.
Cleaning requirements will depend on the substrate and contamination present.
Potential preparation methods can include:
- Degreasing
- Detergent cleaning
- Pressure washing
- Mechanical cleaning
- Solvent cleaning where appropriate
After cleaning, allow the surface to dry appropriately before proceeding.
Particular attention should be given to areas where oil, grease or other contaminants may have accumulated.
Step 4: Remove Rust & Corrosion
Rust and corrosion should be addressed before applying protective coatings to steel and other susceptible metals.
Depending on the condition and specification of the project, preparation can involve mechanical or abrasive methods.
Potential methods include:
- Wire brushing
- Scraping
- Mechanical abrasion
- Power-tool cleaning
- Abrasive blasting
The required level of preparation will depend on the condition of the steel, the intended coating system and the project specification.
Do not simply apply a new coating over loose rust or poorly adhered corrosion products.
Step 5: Remove Loose or Failing Paint
If an existing coating is peeling, blistering, cracking or otherwise poorly adhered, the affected material should be removed.
Loose coating can be removed using appropriate mechanical preparation methods.
Depending on the surface and coating, this may include:
- Scraping
- Wire brushing
- Sanding
- Mechanical abrasion
- Power-tool preparation
- Abrasive blasting
The transition between existing sound coating and prepared areas should be assessed so that the new coating can achieve a suitable finish and level of adhesion.
Step 6: Create the Appropriate Surface Profile
Some coating systems require a prepared surface profile to promote mechanical adhesion.
Abrasive blasting and certain mechanical preparation methods can create a suitable surface profile on metal substrates.
The required profile depends on the coating system and manufacturer's recommendations.
Do not assume that a more aggressive preparation method is always better. The preparation standard should be appropriate for the specified coating system and substrate.
Step 7: Prepare Concrete Surfaces
Concrete requires a different preparation approach from steel and metal.
Before applying a floor or concrete coating, assess the surface for:
- Dust
- Dirt
- Oil and grease
- Moisture
- Cracks
- Weak or friable areas
- Previous coatings
- Surface contamination
- Damage
Concrete should be suitably clean, sound and prepared for the intended coating system.
Mechanical preparation may be required where existing coatings, laitance or other surface contaminants are present.
Potential methods include:
- Mechanical grinding
- Shot blasting
- Abrasion
- Suitable cleaning methods
The specific preparation requirements will depend on the coating system being applied.
Step 8: Prepare Previously Painted Surfaces
Previously painted surfaces require particular attention.
Before recoating, determine:
- What coating is already present?
- Is it firmly adhered?
- Is it compatible with the new coating?
- Is the existing coating damaged?
- Is there corrosion underneath?
- Has the surface been properly cleaned?
A small test area can be useful when coating over an existing system where compatibility is uncertain.
If the existing coating is unsuitable or extensively failed, more extensive removal and preparation may be required.
Step 9: Check for Moisture
Moisture can significantly affect coating application and performance.
Before applying a coating, consider:
- Recent rain
- Condensation
- Damp substrates
- Moisture within concrete
- Humidity
- Surface temperature
- Risk of condensation during application
The coating manufacturer's technical data should always be checked for the required environmental and substrate conditions.
Do not apply a coating to a substrate that does not meet the product's specified requirements.
Step 10: Remove Preparation Residue
Once mechanical or abrasive preparation has been completed, remove dust and loose debris from the surface.
The prepared substrate should be suitably clean before coating.
Particular attention should be given to:
- Dust
- Abrasive residue
- Loose particles
- Cleaning residue
- Oil and grease
- Moisture
Any remaining contamination can interfere with the coating system.
Step 11: Inspect the Prepared Surface
Before applying the coating, carry out a final inspection.
Check that:
- The surface is clean
- Loose material has been removed
- Corrosion has been suitably addressed
- The existing coating is sound where it is being retained
- The substrate is appropriately dry
- Preparation requirements have been achieved
- The environmental conditions are suitable
- The selected coating is compatible with the substrate
This is the final opportunity to identify preparation issues before coating begins.
Surface Preparation for Different Industrial Applications
Steel & Metal
Steel and metal surfaces commonly require cleaning, removal of corrosion and appropriate mechanical or abrasive preparation.
The required preparation level depends on the condition of the substrate and the coating system being specified.
See our guide to Industrial Coatings for Steel Fabrication →
Roofing & Cladding
Metal roofing and cladding should be assessed for corrosion, existing coatings, dirt, weathering and contamination.
Preparation requirements will vary depending on the existing substrate and coating condition.
See our Industrial Coatings for Roofing & Cladding guide →
Industrial Floors
Concrete floors require suitable cleaning and preparation before coating.
Existing coatings, contamination, weak surface material and moisture should all be considered before application.
See our Industrial Floor Coatings guide →
Machinery
Machinery should be assessed for oil, grease, corrosion, existing coatings and other contamination.
The preparation method should be suitable for the machinery substrate and the coating system being applied.
See our Industrial Coatings for Machinery guide →
Common Surface Preparation Mistakes
Painting over rust
Applying a new coating over loose or poorly prepared corrosion can result in premature failure.
Painting over grease or oil
Contamination can prevent proper adhesion between the coating and substrate.
Ignoring existing coatings
An existing coating may be incompatible with the new system or may already be failing.
Applying coatings to damp surfaces
Moisture can affect adhesion and coating performance.
Skipping final cleaning
Dust and preparation residue can become trapped beneath the coating.
Using the wrong preparation method
Different substrates and coating systems require different approaches.
Rushing the preparation stage
Surface preparation often takes significant time, but it is fundamental to the performance of the finished coating system.
Surface Preparation & Coating Selection
Surface preparation and coating selection should be considered together.
The correct preparation method depends partly on the coating system being applied, while the coating system itself depends on the substrate and environment.
When specifying an industrial coating, consider:
- Substrate
- Existing coating
- Surface condition
- Corrosion
- Environmental exposure
- Chemical exposure
- Abrasion
- Temperature
- Moisture
- Required durability
- Application method
- Manufacturer's technical requirements
Where a specific coating system has been specified, follow the manufacturer's technical documentation for preparation and application requirements.
Frequently Asked Questions
What is surface preparation for industrial painting?
Surface preparation is the process of cleaning and preparing a substrate before applying a coating. It can involve removing contaminants, corrosion, loose coatings and other unsuitable material.
Why does surface preparation matter?
Proper preparation helps provide a suitable surface for coating adhesion and can reduce the risk of premature coating failure.
How do you prepare steel before painting?
Steel preparation can involve cleaning, degreasing, removing corrosion and mechanically or abrasively preparing the surface. The required preparation level depends on the substrate and coating system.
Can you paint directly over rust?
Loose rust and corrosion should not simply be coated over. The substrate should be appropriately prepared according to the requirements of the coating system.
Can I paint over existing paint?
Potentially, provided the existing coating is sound, suitably prepared and compatible with the new coating system. Where the existing coating is failing or compatibility is uncertain, additional preparation may be required.
How do you prepare concrete before floor coating?
Concrete should be clean, sound and suitably prepared for the selected coating. Mechanical preparation may be required to remove existing coatings, contaminants or weak surface material.
Does the surface need to be completely dry before painting?
The required substrate condition depends on the coating product. Always check the manufacturer's technical data for specific moisture and environmental requirements before application.
What is the best method of surface preparation?
There is no single preparation method that is suitable for every application. The correct method depends on the substrate, existing coating, surface condition and specified coating system.
Get the Right Coating for Your Surface
Good surface preparation is the foundation of a successful industrial coating project.
Whether you are preparing structural steel, machinery, roofing and cladding, concrete floors or another industrial substrate, the preparation method should be selected according to the surface and coating system.
New Guard Coatings provides industrial coating products, technical information and application guidance for businesses across the UK.
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