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 the highest-performance coating can fail prematurely if it is applied to a surface that is contaminated, poorly prepared, damp or unsuitable for the specified coating system. Peeling, blistering, flaking, corrosion and poor adhesion can all result from inadequate preparation.

Whether you are coating structural steel, machinery, roofing and cladding, concrete floors or other industrial surfaces, the preparation process should be considered before the coating is selected and applied.

This guide explains the key stages of industrial surface preparation, including cleaning, corrosion removal, surface profiling, salt contamination testing and moisture checks.

Why Is Surface Preparation Important?

Industrial coatings rely on strong and consistent adhesion to the substrate.

Dust, dirt, oil, grease, rust, salts, moisture, loose paint and other contaminants can prevent a coating from bonding correctly. Applying a coating over contamination can trap contaminants beneath the coating and contribute to premature failure.

Proper surface preparation can help to:

• Improve coating adhesion

• Remove contaminants

• Remove loose or failing coatings

• Reduce the risk of premature coating failure

• Provide the correct surface profile

• Improve coating performance

• Support longer coating service life

• Improve corrosion protection

The correct preparation method will depend on the substrate, its existing condition, the previous coating system, the environment 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.

A preparation method suitable for structural steel may not be appropriate for concrete, galvanised metal or a previously coated surface.

The coating manufacturer's technical data should always be checked before deciding on the preparation method.

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

• Salt contamination

• 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, firmly adhered and compatible with the proposed coating system, complete removal may not always be necessary.

However, loose, failing, contaminated or poorly adhered material should be removed before recoating.

Step 3: Remove Dirt, Grease & Other Contamination

The surface must be suitably clean before coating.

Oil, grease, dirt, cleaning residues and other contaminants can interfere with adhesion and cause defects in the finished coating.

Depending on the substrate and contamination present, preparation may involve:

• Degreasing

• Detergent cleaning

• Pressure washing

• Mechanical cleaning

• Solvent cleaning where appropriate

Particular attention should be given to areas where oil, grease or other contaminants may have accumulated.

After cleaning, allow the surface to dry appropriately before continuing with preparation.

Don't Forget Salt Contamination

Salt contamination is an important consideration when preparing steel for protective coatings, particularly on structures exposed to marine environments, coastal conditions, de-icing salts or contaminated industrial atmospheres.

Soluble salts can remain on a surface even when it looks visually clean.

If salts remain beneath a coating, they can attract moisture and contribute to problems such as:

• Osmotic blistering

• Loss of adhesion

• Underfilm corrosion

• Premature coating failure

• Corrosion beneath the coating system

For this reason, simply removing visible dirt and rust is not always enough.

Where soluble salt contamination is a potential concern, the surface should be assessed using an appropriate salt contamination test before coating.

How to Remove Salt Contamination

Where salt contamination is identified, the surface should be thoroughly cleaned using a suitable method for the substrate and coating specification.

Fresh water washing or high-pressure water cleaning may be appropriate for removing soluble salts from suitable surfaces.

After washing:

1. Allow the surface to drain and dry.

2. Reinspect the substrate.

3. Retest for soluble salt contamination where required.

4. Repeat cleaning if contamination remains above the specified level.

5. Only proceed with coating once the substrate meets the requirements of the specified coating system.

The required salt contamination level will depend on the coating system, project specification and applicable standard.

Do not assume that a surface is free from salts simply because it appears clean.

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 of the substrate and the coating specification, preparation can involve:

• Wire brushing

• Scraping

• Mechanical abrasion

• Power-tool cleaning

• Abrasive blasting

• High-pressure water jetting

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.

Where a high-performance corrosion protection system is required, a specified blast-cleaning standard may be necessary.

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.

Depending on the surface and coating, this may involve:

• Scraping

• Wire brushing

• Sanding

• Mechanical abrasion

• Power-tool preparation

• Abrasive blasting

The transition between existing sound coating and prepared areas should also be considered so that the new coating can achieve suitable adhesion and a consistent finish.

Where the existing coating is extensively failed or incompatible with the proposed system, complete removal may be required.

Step 6: Create the Correct Surface Profile

Some industrial coating systems require a prepared surface profile to promote mechanical adhesion.

Abrasive blasting and certain mechanical preparation methods can create a suitable profile on metal substrates.

The required profile depends on:

• The coating system

• The substrate

• The preparation method

• The required coating thickness

• The manufacturer's recommendations

• The project specification

Do not assume that more aggressive preparation is always better.

The preparation standard and surface profile should be appropriate for the specified coating system.

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

• Laitance

• Damage

Concrete should be clean, sound, dry and appropriately prepared for the intended coating system.

Mechanical preparation may be required where existing coatings, laitance or other contaminants are present.

Potential preparation methods include:

• Diamond grinding

• Shot blasting

• Mechanical abrasion

• Suitable cleaning methods

Any cracks, holes or damaged areas should be repaired using a suitable repair material before coating.

Step 8: Prepare Galvanised & Difficult Surfaces

Galvanised steel and other smooth or non-ferrous surfaces may require specific preparation before coating.

The surface should be clean and free from:

• Oil

• Grease

• Dirt

• White rust

• Loose material

• Other contamination

Depending on the coating system, light abrasion or another suitable preparation method may be required to provide an appropriate surface for adhesion.

A compatible primer or coating system should then be selected according to the substrate and manufacturer's recommendations.

Step 9: Prepare Previously Painted Surfaces

Previously painted surfaces require particular attention before recoating.

Before proceeding, establish:

1. What coating is already present?

2. Is it firmly adhered?

3. Is it compatible with the new coating?

4. Is the existing coating damaged?

5. Is there corrosion underneath?

6. Has the surface been properly cleaned?

7. Has any soluble salt contamination been addressed?

A small test area can be useful where coating compatibility is uncertain.

If the existing coating is unsuitable, extensively failed or contaminated, more extensive removal and preparation may be required.

Step 10: Check for Moisture & Condensation

Moisture can significantly affect coating application and long-term performance.

Before applying a coating, consider:

• Recent rain

• Condensation

• Damp substrates

• Moisture within concrete

• Relative humidity

• Surface temperature

• Dew point

• Risk of condensation during application

The substrate should be sufficiently dry and meet the environmental requirements specified by the coating manufacturer.

For steelwork, the surface temperature should be assessed in relation to the dew point to reduce the risk of condensation forming on the surface during application.

Do not apply a coating when the substrate or environmental conditions fall outside the product's specified requirements.

Step 11: Remove Preparation Residue

Once mechanical or abrasive preparation has been completed, remove dust, abrasive residue 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

• Salt contamination

• Moisture

Depending on the substrate and specification, suitable methods may include vacuuming, clean dry air or other approved cleaning methods.

Any remaining contamination can interfere with coating adhesion and performance.

Step 12: 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

• Existing coatings are sound or have been removed as required

• The required surface profile has been achieved

• Dust has been removed

• Salt contamination has been addressed where applicable

• The surface is dry

• Environmental conditions are suitable

For larger or high-performance coating projects, inspection and testing should be carried out in accordance with the relevant project specification and applicable standards.

Surface Preparation Standards

The required preparation standard will depend on the coating system and project specification.

For steelwork, abrasive blast-cleaning standards may be specified to define the required level of surface cleanliness.

Where an ISO 12944 coating system is being specified, the preparation requirements should be considered as part of the complete protective coating system rather than as a separate process.

Always follow the preparation requirements stated in the product Technical Data Sheet and project specification.

What Happens If Surface Preparation Is Poor?

Poor surface preparation is one of the most common causes of premature coating failure.

Potential problems include:

Peeling

Contamination or insufficient preparation can prevent the coating from bonding correctly.

Blistering

Moisture, soluble salts and other contamination beneath a coating can contribute to blister formation.

Underfilm Corrosion

Remaining rust, salts or moisture can allow corrosion to continue beneath the coating.

Flaking

Poor adhesion or an unstable existing coating can result in flaking and delamination.

Cracking

An unsuitable coating system, excessive film thickness, movement or poor substrate condition can contribute to cracking.

Premature Coating Failure

Even an expensive high-performance coating cannot compensate for an unsuitable or poorly prepared substrate.

Surface Preparation for Different Industrial Applications

The preparation process should always reflect the application.

Structural Steel

Focus on:

• Rust removal

• Existing coating assessment

• Degreasing

• Salt contamination

• Abrasive blasting or mechanical preparation

• Surface profile

• Dust removal

• Moisture and dew point

Machinery

Focus on:

• Oil and grease removal

• Rust removal

• Existing coating assessment

• Mechanical preparation

• Surface cleanliness

• Compatibility of the new coating

Roofing & Cladding

Focus on:

• Dirt and atmospheric contamination

• Rust

• Chalking

• Existing coating condition

• Pressure washing

• Thorough drying

• Corrosion treatment

Concrete Floors

Focus on:

• Oil and grease

• Dust

• Moisture

• Laitance

• Existing coatings

• Mechanical grinding or shot blasting

• Cracks and surface damage

• Surface profile

Surface Preparation Checklist

Before applying an industrial coating, ask:

☐ Have I identified the substrate?

☐ Have I inspected the existing surface?

☐ Have oil, grease and dirt been removed?

☐ Has rust and corrosion been removed appropriately?

☐ Have loose or failing coatings been removed?

☐ Has soluble salt contamination been considered and tested where necessary?

☐ Has the required surface profile been achieved?

☐ Has preparation residue and dust been removed?

☐ Is the substrate sufficiently dry?

☐ Are temperature, humidity and dew point within the coating manufacturer's requirements?

☐ Is the proposed coating compatible with the prepared substrate?

☐ Has the final surface inspection been completed?

Final Thoughts on Surface Preparation

Surface preparation should never be treated as a quick step before painting.

The performance of an industrial coating system depends heavily on the condition of the substrate beneath it. Correct cleaning, corrosion removal, surface profiling, salt contamination control and moisture management can all contribute to better adhesion and longer coating performance.

There is no single preparation method that is suitable for every industrial coating project.

The substrate, existing coating, environmental exposure, required durability and specified coating system should all be considered before work begins.

Always follow the coating manufacturer's Technical Data Sheet and the requirements of the relevant project specification.

Need Help With Surface Preparation?

Not sure how to prepare a surface before applying an industrial coating?

New Guard Coatings provides technical support on industrial coating selection, surface preparation and application requirements.

Our technical team can help you identify a suitable coating system based on the substrate, environment and required performance.

Contact New Guard Coatings for technical advice on your next industrial coating project.