Apply stickers without bubbles: how to squeegee on paint, metal and plastic

The company logo sits on the freshly painted steel cabinet. Almost. In the middle a bubble rises, the size of a fingernail. You press it with your thumb and the bubble slides two centimetres further along. Press again and it wanders back.

Applying stickers without bubbles and creases is no black art. You need a squeegee and a clean surface. The rest is doing things in the right order. This article covers paint, metal and plastic. Glass has its own article.

The basis is the application guidelines of the vinyl manufacturers. This guide does not replace the manufacturer's instructions. Where the data sheet for your vinyl, paint or panel differs, follow the data sheet.

Why bubbles and creases form when you apply a sticker

Bubbles are trapped air: the vinyl sticks all the way round, and in between a cushion of air is left with no way out to the edge.

On top of that:

• Dust: a speck under the vinyl stays visible as a small pimple. So work in a dust-free spot.
• Moisture: leftover water, condensation or high humidity under the vinyl lead to bubbles and weak adhesion.
• Solvents and fresh paint: cleaner residue, or paint that has not fully cured, can later form gas bubbles under the vinyl.
• Temperature: in the cold, vinyl and adhesive stiffen and trap air more easily. From a surface temperature of about 30 °C the vinyl grabs too early and can hardly be repositioned.

Creases form when the vinyl is stretched instead of being laid to follow the profile, or when too much heat makes it so soft that it buckles.

The tool: a squeegee, not your thumb

A plastic squeegee presses the vinyl down evenly across its whole width. Ideally it has a felt edge or a fabric sleeve so it does not scratch the vinyl. One manufacturer recommends a fresh felt for the final pass. Replace a squeegee with a nicked edge.

Also have ready: masking tape, adhesive tape for the hinge, a lint-free cloth, water with mild washing-up liquid, isopropyl alcohol and a fine pin.

Before you apply: clean and degrease the surface

Two vinyl manufacturers treat every surface as dirty, even a new one. So you clean immediately before application:

1. Wash with water and mild washing-up liquid free of wax, oil or lotion, then let it dry completely.
2. Remove grease: take off stubborn grease residue with a solvent cleaner. Skip steps 2 and 3 on acrylic glass, and on polycarbonate do them only after a test (see Plastic).
3. Degrease with a mix of 70 % isopropyl alcohol and 30 % water, bought ready-made or mixed from pure isopropyl alcohol, on a lint-free cloth. Wipe dry before the mix evaporates.

Then do the fingernail test: if your nail glides easily over the surface, clean it again. If it drags, the surface is clean.

Test every cleaning product on an inconspicuous spot first, especially on paint and plastic. Cleaners containing ammonia, wax, oil or silicone are off limits.

Safety: isopropyl alcohol is highly flammable. Ventilate, keep flames and sparks away and let the surface air off. Only use the heat gun once nothing smells of alcohol any more, otherwise there is a risk of a flash fire.

Temperature: apply at around 16 to 25 °C, never below the minimum temperature in the data sheet and not in blazing sun. Put the sticker in the room where you will apply it a few hours beforehand.

Applying stickers without bubbles: the squeegee technique step by step

Small stickers: peel back 2 to 3 cm of backing paper along one edge and fold it over. Line the sticker up, press this edge down starting from the middle, then pull the paper out bit by bit and squeegee as you go.

Large stickers go on with the hinge method:

1. Position. Place the sticker, backing paper and all, where you want it and fix it with masking tape.

2. Make the hinge. A continuous strip of tape along one whole edge holds the sticker like a door hinge.

3. Remove the backing paper. Fold the sticker back and peel the paper off in sections of 20 to 30 cm. Pull the paper away from the vinyl, not the other way round, and do not crease anything.

4. Squeegee. Work away from the hinge, each stroke from the centre outwards, firmly and overlapping by about half. That way the air always has a way out. With air-release vinyl, press it down lightly first, then squeegee firmly.

5. Go over the edges again. Remove the hinge, press the edges down, and after 15 to 20 minutes squeegee them firmly once more.

Vinyl letters and logos cut on a plotter come on application tape, which keeps spacing and position. Squeegee both before and after removing the application tape.

According to one manufacturer, the surface should then stay at application temperature for at least 24 hours. Before larger jobs, a test piece is worth it: check its adhesion after 24 hours.

What matters about the surface

Paint

Fresh paint must be fully cured. Wait at least a week, preferably three, and follow the paint manufacturer's instructions. Synthetic resin paint can take up to a month, and two-component paint cures poorly or not at all in the cold. Nano or ceramic coatings weaken adhesion and have to come off first. Matte, heavily textured and dirt-repellent paints are difficult, and so is anti-graffiti coating. On resprayed or damaged areas, paint can come away when the vinyl is removed later.

Metal

Two vinyl manufacturers advise against copper, brass, tin, lead and magnesium as a surface. Bare steel is first de-rusted and primed or painted. Pre-treating bare, tarnished aluminium or stainless steel is a job for a professional. On bare stainless steel, only use vinyl that the data sheet approves for it. Stainless steel stays cold for longer: slightly warmed, the vinyl bonds faster, but only once there is no solvent left in the air. On powder coating, waxes in the coating can reduce adhesion, so do an adhesion test there first.

Plastic

Only apply vinyl to painted or completely smooth parts. Water drop test: if water beads up, leave it alone. If it runs off in a sheet, the vinyl can bond. On rough, textured plastics and on polypropylene and polyethylene the vinyl adheres poorly. Rubber, sealant and trim strips get no vinyl at all. Degrease polycarbonate with isopropyl alcohol after a test, and acrylic glass only with mild soapy water. Never scrape either with a blade. Plastic panels can outgas, so apply a test piece first. No sticker goes on a safety helmet without the helmet manufacturer's approval: vinyl can reduce its strength.

Wet or dry?

On paint, metal and vehicles the vinyl manufacturers recommend dry application. On curved surfaces you can hardly get all the leftover water out. Trapped water weakens adhesion and can freeze in frost.

One manufacturer's wet application instructions with water and washing-up liquid apply explicitly only to glass, polycarbonate and acrylic glass. Another manufacturer allows wet application on vehicles at most for small decals on flat surfaces. Vinyl with air channels is never applied wet. So wet only if the data sheet expressly allows it.

Large areas, curves, rivets: where DIY stops

Larger areas are easier with air-release vinyl: fine grooves in the adhesive lead the air to the edge, so hardly any bubbles remain. Work from the centre outwards, without firm pressure at first, or the channels close up. Do not put peeled-off backing paper back on.

Standard vinyl suits flat and gently curved surfaces. Swage lines, rivets and compound curves need cast vinyl. It follows the profile without tension.

Heat: keep the heat gun moving all the time and measure the temperature. Too much heat scorches the vinyl or makes it so soft that it creases, and you can burn yourself on hot surfaces. Prick bubbles first, otherwise the air expands and damages the vinyl. Post-heating stretched vinyl belongs in professional hands.

One manufacturer only allows vehicle wraps to be applied by trained professionals; another recommends a professional for multiple panels, rivets and corrugated surfaces. This is exactly where our sign-making team takes over the installation. More on this under vehicle graphics. According to one manufacturer, a vehicle with fresh graphics should stay out of the car wash for at least three days, and you should never aim the pressure washer at the edges.

Fixing bubbles and creases

Bubbles: prick the bubble with a fine pin and smooth the air from the edge towards the hole. No craft knife and no blade, or the vinyl may tear. According to one manufacturer, bubbles under 5 mm in vehicle vinyl usually disappear by themselves, depending on temperature within a few days to three weeks.

Dust pimples: a pin will not help here, only prevention.

Creases: the application guidelines give no reliable repair, and that includes peeling off and reapplying. With small stickers, in our view a new one is usually the cleaner choice.

The logo on the sliding door: thumb versus squeegee

A typical case: a trade business applies a small logo itself to a flat area of the van's sliding door, away from any swage lines. In the yard, in the wind, with a thumb, starting from one corner. The result: bubbles and a crease right across the lettering.

Second attempt. The door is washed and degreased until the fingernail drags. The work is done out of the wind and dust. The hinge holds the sticker, the squeegee runs from the centre outwards, and after a quarter of an hour the edges get a second pass. This time the logo lies flat, with no bubble and no crease.

Haste costs more than the vinyl

Patience saves vinyl, it is as simple as that: most bubbles come from rushing, not from the vinyl. Clean the surface and use a squeegee instead of your thumb, and you will rarely need a second sticker.

The limitation belongs here too: on rough plastic, polypropylene or bare steel, technique alone will not save the sticker. There, pre-treatment and adhesive decide, and a test piece comes first. More on choosing materials in Stickers must meet specific requirements and Stickers you can't overlook.

Conclusion: a smooth finish starts before the first stroke of the squeegee

If the surface is degreased, the temperature is right and you squeegee from the centre outwards, the sticker will usually sit flat. Settle three things beforehand. The surface: is the paint cured, the metal painted or professionally pre-treated, the plastic smooth? Then: wet or dry? The data sheet tells you. That leaves size and shape: if curves, swage lines, rivets or several panels are involved, it is better to have it applied.

Rather not apply it yourself? Then we will do the installation. Write to us via Contact and tell us where the sticker is going. You will find lettering under Foil technology, and custom stickers on koeck-print.at.

Frequently asked questions

Can any sticker be applied wet?

No. On paint, metal and vehicles the vinyl manufacturers recommend dry application, because leftover water causes bubbles and weakens adhesion. Only apply wet if the vinyl's data sheet expressly allows it. Vinyl with air channels never goes on wet.

Why does the bubble move around instead of disappearing?

The air is trapped on all sides. Your thumb just pushes it around. It has no way out. Prick the bubble with a fine pin and smooth the air from the edge towards the hole. With the next sticker, squeegee from the centre outwards and the air cushion usually never forms.

What should I do if there are still small bubbles after application?

According to one manufacturer, bubbles under 5 mm in vehicle vinyl usually disappear by themselves, depending on temperature within a few days to three weeks. Check what the data sheet for your vinyl says. If a larger bubble remains, a fine pin helps: prick it and smooth the air towards the hole. A craft knife can tear the vinyl.