Filler Primer Sprays

Filler Primer Spray for Automotive Refinishing

Filler primer spray, also known as primer surfacer, is designed to create a buildable intermediate coating that helps refine small sanding marks, scratches and minor surface irregularities before the colour coat is applied.

After suitable drying, a sandable filler primer can be refined to create a smoother, more uniform substrate for subsequent refinishing.

Aerosol application is particularly practical for spot repairs, local bodywork repairs and smaller components where preparing a separate spray gun and compressor is unnecessary.

What Is Filler Primer Used For?

Depending on the individual product, filler primer can be used to:

• refine sanding scratches,
• fill minor surface marks,
• seal and refine repaired filler areas,
• prepare existing coatings for refinishing,
• prime local spot repairs,
• create a uniform substrate before colour application.

Filler primer does not replace body filler. Deep scratches, dents, substantial material loss and major surface defects require suitable repair materials first.

Filler, Primer Surfacer & Spray Putty

The terms filler primer, primer surfacer and spray putty are sometimes used for similar products, but they do not necessarily describe identical film build or filling performance.

A primer surfacer normally provides a sandable intermediate layer for refining minor defects, while products described as spray putty may offer greater build. Actual film thickness and filling ability always depend on the individual product specification.

1K Filler Primer Spray

1K filler primer spray is a single-component, ready-to-use aerosol system. No separate hardener needs to be activated, making it a convenient solution for smaller refinishing repairs.

Individual 1K products can differ considerably in build, drying time, sanding characteristics and substrate compatibility.

2K Filler Primer Spray

2K filler primer spray contains a separate hardener component that is activated before use. Once activated, chemical curing begins and the usable working life of the aerosol becomes limited.

Depending on the formulation, 2K filler systems can provide higher build, faster curing, improved sanding characteristics or enhanced coating performance.

Only activate a 2K aerosol when the substrate is fully prepared and ready to be sprayed.

Filler Primer or Epoxy Primer?

Filler primer and epoxy primer do not necessarily serve the same primary purpose. A filler primer is generally intended to refine the surface and provide build, while epoxy primer is commonly selected for adhesion and corrosion protection.

Some specialist 2K epoxy primers also provide useful filling properties, so certain products can perform more than one function.

Select the system according to the substrate and the complete refinishing process.

Which Substrates Can Filler Primer Be Used On?

Approved substrates vary by product. Depending on its specification, a filler primer can be suitable for:

• polyester body filler,
• sanded existing coatings,
• previously primed surfaces,
• certain bare metals where specifically approved,
• other compatible primer systems.

Not every filler primer can be applied directly to aluminium, galvanised steel, plastics or all bare metals. A separate adhesion, epoxy or corrosion-protection primer may be required.

Filler Primer on Plastic

On raw plastic, filler primer should not automatically be applied as the first coating. Many plastic substrates require a suitable plastic adhesion promoter first.

Where the coating system allows it, a compatible primer surfacer can then be applied over the adhesion promoter to refine the repaired surface.

Preparing the Surface Before Filler Primer

• Clean the substrate thoroughly.
• Degrease using a suitable silicone remover.
• Sand the repair according to the coating system.
• Remove loose or unstable existing coatings.
• Repair deeper defects with suitable body filler where necessary.
• Remove all sanding dust before spraying.

A filler primer cannot compensate for a contaminated or unstable substrate.

How to Apply Filler Primer Spray

1. Prepare and degrease the substrate.
2. Mask surrounding areas.
3. Shake the aerosol thoroughly.
4. Activate the hardener on a 2K product immediately before use.
5. Carry out a test spray.
6. Apply the specified coats using controlled overlapping passes.
7. Observe the required flash-off times.
8. Allow the primer to dry fully before sanding.
9. Sand the surface according to the product instructions.
10. Clean and remove dust before applying subsequent coatings.

The correct spray distance, number of coats, film build, drying time and sanding procedure are product-specific.

How Should Filler Primer Be Sanded?

One of the key characteristics of a sandable filler primer is that the surface can be refined after drying. However, the correct abrasive grade depends on the product, substrate condition and subsequent colour coat.

There is no universal abrasive grade for every filler primer. Follow the sanding recommendations for both the primer and the subsequent refinishing system.

Grey, White or Black Filler Primer?

Filler primers are available in different shades. Selecting an appropriate primer shade can improve colour-coat hiding and reduce the number of colour coats required.

• White or light primer: can be useful beneath light colours.
• Grey primer: a versatile base for many medium colours.
• Dark grey or black primer: can be advantageous beneath darker colours.

Where available, follow the refinishing-system manufacturer's recommended undercoat shade.

Filler Primer vs Body Filler

Body filler is used to repair larger depressions, dents and more substantial surface defects. Filler primer is intended for the finer stage of surface refinement after those repairs have been completed.

A typical repair sequence may therefore include body repair, filler, sanding, suitable primer, filler primer, final sanding, colour and clear coat where required.

When Is Aerosol Filler Primer the Right Choice?

Filler primer spray is particularly convenient for spot repairs, smaller bodywork repairs and individual components where mixing a spray-gun primer surfacer would be unnecessary.

For complete panels or large professional repairs, a spray-gun-applied primer surfacer may provide greater efficiency and control.

Safe Use

Use filler primer aerosols only in the working environment specified by the manufacturer. Provide suitable ventilation and use the respiratory, eye and skin protection required by the product label and safety data sheet.

2K aerosols require particular attention to the specified working environment and respiratory protection.

Frequently Asked Questions About Filler Primer Sprays