Amit Rao

No matter what the surface is, the single most important step in any graphic application is preparing the surface to receive the graphic film. This also is the single most important step affecting the durability of the graphic. Unfortunately this is also the most ignored step.

The surface preparation for different surfaces would be different but there are some common methods. Here’s the recommendation on cleaning methods and surface preparation for different substrates.

Method 1: General cleaning

This method is commonly used to clean painted metal surfaces or plastics and glass. In this, applicators should use an appropriate mixture detergent diluted in water to clean the substrate. Clean the substrate before applying the film. Dust and other contaminants can collect quickly on the substrate and prevent the film from adhering properly. Now, i) Use a mixture detergent and water to clean the substrate and wipe with clean dry lint free cloth. ii) The surface should be allowed to dry naturally. Use a heat gun to dry out any retained moisture, if needed.

For most surfaces: Wipe the substrate with few drops of dish wash detergent mixed in one litre of lukewarm water. Avoid soaps or preparations that contain waxes, oils or lotions. You can also soak the substrate with this solution for some time to remove some contaminants such as bird droppings, etc. Go for the second method, if any other contaminants that cannot be removed. Do not scrub the surface of the substrate as it may cause scratches on the substrate.

But it’s notable that this method is not suitable for cleaning wood, MDF and other porous surfaces. This method works well for substrates like acrylic and glass or other similar substrates. For different substrates you may require different detergents. For example, for cars, you may need to use a detergent that does not affect paint while for glass you can use a dish wash detergent.

Method 2: Iso Propyl Alcohol cleaning

This method uses diluted Iso Propyl Alcohol (IPA) to clean contaminants such as grease and also to remove some difficult contaminants from the surface. It’s always preferred to use a solution of IPA diluted in 1:1 ratio with water. But you can use your own dilution ratio based on your experience and depending on contaminants you are trying to remove.

It’s notable that IPA evaporates quickly and you must wipe the substrate before it evaporates. The evaporation rate increases in warm and/or windy environments. So, i) Saturate a part of clean lint free cloth with IPA. You can dilute the alcohol with one part water, if required. ii) Wipe the substrate before the IPA evaporates. As the cloth becomes dirty, discard it. iii) Make sure the substrate is completely dry. iv) Apply the graphic immediately. Dust and contaminants prevent the adhesive from performing as expected. But it’s notable that this method is best for painted metal surfaces, glass and acrylic. And this method is used to remove contaminants that cannot be removed using Method 1.

Method 3: Dust and dry particle cleaning

In cases of porous substrates where the surface has only dust or other loose particles or debris, you can use this method. Dust and dry cleaning is required to remove loose particles that may contaminate the surface of the adhesive.

For smooth surfaces, Step 1: Use a soft shoe brush or similar brush to gently scrub the surface of the substrate. This will help to dislodge the loose particles from the surface of the substrate. Step 2: Wipe the entire surface using a damp lint free cloth. A damp cloth is recommended because it traps the dust more effectively than a dry cloth. Make sure the cloth is just damp and not wet or dripping water. Carefully note that it will be necessary to discard the cloth frequently as it gathers dust.

Preparation of different substrates for film application

Mild steel and other bare metals

Step 1 (Surface conditioning): Smooth the surface by sanding and removing the rusted or oxidised layers. Clean the surface using Method 1 followed by Method 2, if required.

Step 2 (Surface preparation): Use appropriate filler such as polyester putty and/or sanding for treating dented areas. Allow the filler to dry and then sand to obtain a plain smooth surface

Step 3 (Just before application): Make sure the surface is dry, smooth and ready for application and surrounding area is dust free. Clean the surface using Method 2.

To be noted here is the weld joints in metals are visible though the film. The best way to treat weld joints is to grind them well and apply polyester putty to cover undulations.

Plywood/MDF

Step 1 (Surface conditioning): If painted, strip of all paints from the plywood by sanding. Ensure that all screws and nails are driven into the substrate/removed. If there are multiple panels adjacent to each other, make sure there is no level difference on front surface when panels are butt together. Treat the joints appropriately as recommended by the manufacturer. Apply putty to cover any holes left by the nails and screws.

Step 2 (Surface preparation): i) Lightly sand the surface to remove any loose material from the surface of the plywood. ii) Remove all stickers/labels, etc from the surface of the plywood. iii) Apply one to two coats of oil-based primer and allow it to dry. iv) Apply one to two coats acrylic wall putty to ensure a plain surface and allow it to dry. v) Sand lightly using a 400 grit or more sandpaper to achieve a smooth surface. vi) Apply two coats of oil-based primer and allow surface to dry.

Notable here is that a) If the joints are not treated appropriately the film may lift off the surface of the joint. b) For single panels of MDF/HDF/Wood, one or two coats of wood primer followed by light sanding using 400 grit sandpaper should be enough. To fill in small holes or defects polyester putty could be used. c) Single panels of plywood can be treated with polyester putty to fill surface texture and undulations. No other treatment is required.

Step 3 (Just before application): Make sure the surface is dry, smooth and ready for application and surrounding area is dust free. Sand lightly with 400 grit sandpaper and perform strip test in one or more areas as required to ensure surface is appropriate for application. Clean the surface using Method 3.

Painted metal sheets/aluminium composite panels/powder-coated metal sheets

Step 1 (Surface conditioning): Clean the surface using Method 1. Perform a strip test to determine the adhesion of paint to the substrate. If the paint adhesion is not found to be good, strip off all the paint and prepare surface according to surface preparation guidelines for bare metals.

Step 2 (Surface preparation): Use appropriate filler such as polyester putty and/or sanding for treating dented areas. Allow the filler to dry and then sand to obtain a plain smooth surface.

Step 3 (Just before application): Make sure the surface is dry, smooth and ready for application and surrounding area is dust free. Clean the surface using Method 2.

Gypsum/plasterboard/calcium silicate/cement fibre board

Step 1 (Surface conditioning): Ensure that all screws and nails are driven into the substrate. If there are multiple panels adjacent to each other, make sure there is no level difference on front surface when panels are butt together. Treat the joints as recommended by the manufacturer. Apply putty to cover any holes left by the nails and screws.

Step 2 (Surface preparation): i) Apply one to two coats of oil-based primer and allow it to dry. ii) For surface finish, apply one to two coats acrylic wall putty to ensure a plain surface and allow it to dry. Make sure the areas where two individual panels meet are filled in using material manufacturer’s recommendation. iii) Sand lightly using 150 grit or more sandpaper to achieve a smooth surface. iv) Apply two coats of oil-based primer and allow surface to dry.

It’s notable that for single panels of cement fibre boards, provided the finish is a mirror finish one or two coats of wall primer followed by light sanding, using 400 grit sandpaper should be enough. To fill in small holes or defects polyester putty could be used.

Step 3 (Just before application): Make sure the surface is dry, smooth and ready for application and surrounding area is dust free. Sand lightly with 400 grit sandpaper and perform strip test in one or more areas as required to ensure surface is appropriate for application. Clean the surface using Method 3.

Stainless steel

Step 1 (Surface conditioning): Film application on embossed or textured steel surface is not advised.

Use a Scotch Brite green pad to scrub the entire surface on which film will be applied. And clean the surface using Method 1.

Step 2 (Surface preparation): Use appropriate filler such as polyester putty and/or sanding for treating dented areas. Allow the filler to dry and then sand to obtain a plain smooth surface.

Step 3 (Just before application): Make sure the surface is dry, ready for application and surrounding area is dust free. Clean the surface using Method 2.

And notable point is that the surface finish of stainless steel may be permanently scratched by scrubbing and it may not be possible to restore the original look again.

Glass

Step 1 (Surface conditioning): Scrape the glass to remove any stickers or similar objects. If there is any adhesive residue on the glass remove the residue with the use of an adhesive remover.

Step 2 (Surface preparation): Clean the surface of the glass using Method 1.

Step 3 (Just before application): Make sure the surface is dry, ready for application and surrounding area is dust free. Clean the surface using Method 2.

Common considerations for all surfaces

Notable at this juncture is i) A surface preparation procedure will most likely change many surfaces permanently. ii) A strip test is a destructive test and surfaces may get damaged. Perform this in an inconspicuous area. Repairs to surface may be required after the test. It is essential to carry a thorough pre inspection to determine the extent of work and approximate time required.

To facilitate application, grab rails, handles, emergency lamps, etc will need to be removed. It is not recommended to apply film to the panel housing the switches (switchboards), etc. The finished appearance varies from film to film and also from substrate to substrate. If there is any doubt about the finished graphic appearance, it is recommended that a small area be applied and visual appearance be approved before proceeding to final surface preparation and application.

Checking surface integrity

If you are applying film on a wall, a surface ready for application must be checked thoroughly prior to the application. There are three common tips to be recommended.

Tip 1: Checking plumb level of surface: In many cases, undulations are not visible prior to film application. To ensure that the surface is plumb it is recommended to check the surface with a straight edge in three directions to check for level. Plumb lines can also be used for larger areas. It is always preferred to check the level of the surface specially if the graphic that you are applying has a large area with single colour.

Tip 2: Checking smoothness of surface: To check if the surface is smooth and free from defects, a visual inspection of the entire surface needs to be carried out followed by running your hand across the entire surface to feel for any surface defects.

Tip 3: Checking surface integrity: To check for surface integrity it is recommended to perform a strip test. Prepare the surface as per the appropriate procedure mentioned for different substrates in this document.

i) Cut the film into pieces of approximately 1x10 inch. ii) Apply these pieces to the ready surface and wait for approximately 15 min. iii) If the temperature is below 18oC then gently heat the applied strips using heat gun. iv) Remove the film from the surface at a constant rate of about 2-3 inch per minute. Do not stop once you have commenced removal of the strip. v) After removal check the adhesive side of the film. vi) If the film offers no resistance during removal and the adhesive on the exposed side is not sticky after removal, then the surface needs another coat of primer. vii) If the film has come off with the entire coat of primer and putty then the surface is unsuitable for application and needs to be redone. viii) If the adhesive on the film is intact and feels stick to touch if small bits of primer are seen on the adhesive side of the film, you can safely conclude that the surface is good for application.

It’s always notable that this is a destructive test and may require repairs to surface after the test is performed. The test is recommended to be performed in a number of different areas in a large application. Surface preparation differs from substrate to substrate. In case of doubt, especially while using cleaning chemicals such as Iso Propyl Alcohol, try application on a small inconspicuous area. In many cases the paint may have poor adhesion to the substrate. It is preferred to do a strip test even on painted surfaces.

Hope these surface preparation tips and procedures would be helpful. For any comments, suggestions, feedback or for more information, write in at: rvamit@mmm.com