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When a paint job goes wrong it’s more than a little frustrating; it’s costly. Refinishing a defective product brings labour and material costs that shrink your profit margins. And in some cases, it can even cost you a client.
Over the years, our clients have asked us for advice on all sorts of paint spraying problems. This guide covers the most common issues that we have come across. It will help you to:
PART ONE: Painter mistakes that contribute to a poor finish
PART TWO: Poor adhesion
PART THREE: Poor finish - surface texture
PART FOUR: Poor finish - colour
This little spraying sin is responsible for so many bad paint jobs, especially amongst newbie sprayers. The manufacturer’s technical data sheet contains all the information you need to get the finish right, so do yourself a favour and familiarise yourself with it in advance of using a product. The technical data sheet, details the correct hardener and thinners to be used if applicable as well as spray gun set up, film thickness, drying and re-coat times.
If you don’t leave enough time between coats, your paint finish will suffer. But as any seasoned painter knows, there are many factors that can cause you to misjudge drying times and go in with the second coat too soon.
Cold and humid environments will slow your drying times considerably and can negatively affect your finish in several ways. You can mitigate these issues by:
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This one isn’t rocket science. If you apply a thicker film than the manufacturer states, it will take longer to dry. So always follow the data sheet guidance on film thickness and get yourself a decent film thickness gauge.
Learn about film thickness. |
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Too much solvent or using too fast a solvent will accelerate drying time, resulting in a poor ‘sandpaper’ finish. Read the data sheet and this won’t happen…
Whether you’re a DIYer who is eager to see the end finish or you’re a paint shop sprayer who is behind on a production run, impatience is your enemy. If a product’s data sheet states a 4-hour drying time, 2 hours just won’t cut it.
It can be tempting to guess drying times based on similar products that you have used in the past. Don’t do it! If you get it wrong it will lead to one of two far from ideal scenarios:
Both scenarios will ultimately slow down production and put you behind schedule.
Pimples, blisters, fizz holes, runs and overspray are just a few of the issues that can result from incorrect gun setup or using the wrong size spray tip. Check the product data sheet ahead of setup to avoid running into problems.
You know your pressure is too low for the job on an airless paint sprayer when your pressure is around 100 bar and you experience the following:
However, if you’re at 200 bar and the spray pattern is spotty, you’ve probably got a worn out nozzle.
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It’s a common misconception amongst painters that upping the pressure will speed up the job and achieve a more even finish. In reality, using more pressure than necessary results in:
The key is to work with the lowest pressure needed to achieve an optimal finish. Start with a low pressure of around 100 bar and gradually increase it until you achieve a uniform distribution of material.
Debris in your finish is never a good look. But that’s exactly what you’ll get if you don’t keep your kit clean. A dirty gun, blocked gun filters or clogged extraction filters will always produce a sub-standard end product.
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IDENTIFICATION: Patches of finish that have lifted in ‘feathers’ around the edge of an area that you have repaired.
This defect happens when solvents in the topcoat penetrate through areas of the undercoat.
You can prevent this problem from occurring by using a suitable primer to create a good barrier layer and stable base for the paint repair.
Depending on the extent of the delamination, you will either need to remove the problem area fully and start again or sand it back to a stable surface.
IDENTIFICATION: Areas of topcoat have peeled.
The film hasn’t adhered to the surface beneath it due to insufficient prep and/or using the wrong primer.
Proper surface preparation - thoroughly sand and clean the substrate and then use a suitable primer.
Sand back, start again and give yourself a talking to about skimping on the prep!
IDENTIFICATION: Wrinkling either when applying a new finish or when the finish is drying.
This happens when solvents in your new finish attack the old finish, causing it to become unstable and lift. .
This is a timing issue. Make sure that you recoat within the manufacturer’s stated recoat window so that a mechanical bond can form between layers. If you miss this window, wait for the full curing time stated on the data sheet. The coating will then be hard enough to sand, recoat and achieve a mechanical bond.
Sand back and recoat within the required timeframes.
IDENTIFICATION: Small areas of finish that have lost adhesion to the substrate. The edges of a chip are clean rather than flaking.
Sand back, removing finish from an area that is slightly bigger than the chip, prime and refinish according to the manufacturer’s technical data sheet.
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IDENTIFICATION: Tiny craters in your finish.
Tiny air bubbles have risen to the surface and popped, leaving craters behind.
Make sure your spray gun is adjusted to the correct air pressure setting for the material that you’re spraying and keep the nozzle a suitable distance from the surface that you’re coating.
Sand the affected area with 1200-grit sandpaper and polish it.
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IDENTIFICATION: Your surface finish develops a crackled or spider web appearance.
Before painting, make sure you take the following steps:
Film coat too thick - strip back and refinish using correct film thickness.
Curing - sand back to a flat surface, and recoat after leaving to cure for the correct amount of time.
Cracked surface - strip back to a flat surface or sand back and fill if necessary.
Too much hardener - strip back and refinish using the correct amount of hardener.
Paint reaction - sand back to a bare substrate and start again or sand and apply a barrier paint before refinishing.
IDENTIFICATION: Cracks in your topcoat.
Always refer to the technical data sheet for product film thicknesses, drying times and hardener ratios. Never use a blowtorch to dry things out quickly!
Strip back to a sound surface and redo the job.
IDENTIFICATION: Small pinholes in your paintwork.
Applying primer too thickly or not allowing it to fully dry before recoating.
Check the manufacturer’s technical data sheet sheet for film thickness and drying time requirements.
Sand back to the substrate and reapply the primer in thinner layers.
IDENTIFICATION: A grainy-looking finish.
Spraying from too far away from the substrate. The paint particles atomise and dry before they land.
Spray on a practice piece to gauge the optimal distance.
Grainy - sand back, test distances on a practice piece and then respray.
Paint runs - don’t wipe or mess with the runs. Let them fully cure, sand them out and reapply base and topcoats.
IDENTIFICATION: Crater-like dimples in your paint’s surface that appear during or after spraying.
The substrate is contaminated with wax, grease or oil.
Always clean your substrate with a degreaser at the end of the prep phase before priming or painting.
Sand back to the substrate, degrease and redo the job.
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IDENTIFICATION: Visible foreign particles in your paint/a gritty finish.
Spraying in a dirty or dusty work environment.
Allow the item to cure and then sanding and re-spray.
IDENTIFICATION: Swollen areas in the paint’s surface that appear weeks or months after completing the spray job.
Moisture is trapped under the surface of the paint.
Pimpling is the result of moisture becoming trapped under the surface of the paint. To avoid this, paint in a dry area and use a dehumidifier if you are working in high humidity.
Sand back and start again.
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IDENTIFICATION: Your surface finish has an orange peel texture.
Either the spray gun`s air pressure is too low or the paint has not been thinned sufficiently.
Minor cases of orange peel can be corrected by wet sanding with 1200-grit sandpaper and then buffing. More serious cases will have to be sanded back to an even surface and resprayed.
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IDENTIFICATION: Downward runs of paint on vertical surfaces. Sagging can appear in a local area shortly after spraying or over a long run known as a ‘curtain’.
Most DIYers and junior painters will have experienced this one at some point. They happen when you:
Let the sags fully cure, then sand out and refinish.
IDENTIFICATION: A finish that remains soft once dry, and is susceptible to fingerprints and water marks for days after spraying.
Softness is the result of spraying the undercoat or topcoat too heavily or not allowing enough drying time between coats.
Read the manufacturer’s technical data sheet for film thickness, thinner requirements and drying times.
Remove the offending layers and recoat.
IDENTIFICATION: Shadows or dust in your paintwork.
Static is a common problem when painting plastics. The act of rubbing the panel or “tacking off” creates a static charge that attracts dust in even the cleanest work areas.
Prepare your surface with an anti-static gun. It will remove dust from surfaces and neutralises the static charge to avoid re-attraction.
Sand back to a smooth surface and refinish.
IDENTIFICATION: A cloudy look to the surface of your finish.
Spraying in a humid environment - the “blushing” phenomenon happens when solvents in the paint evaporate and reduce the surface temperature below the dew point, causing moisture to get trapped in the paint layer.
Use a high-quality reducer that is designed for the atmospheric conditions in which you will be painting.
Strip back, add a suitable retarder to the paint and recoat.
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IDENTIFICATION: A yellow stain appears in the topcoat above an area of glazing putty or filler.
This can happen for a few reasons, all of which are to do with the hardener in the filler. In most cases it will be caused by one of the following:
Use a stain-free filler and a sealer coat before applying the colour.
Start over. Sand back, remove the filler and refinish with stain-free filler and sealer.
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IDENTIFICATION: Staining in your colour finish.
Discolouration usually occurs when solvent in the topcoat dissolves soluble pigments in the old finish below.
If you’re painting over an existing finish that may contain soluble pigments, prep it and seal it before adding the new topcoat.
Allow your discoloured finish to fully cure, then seal it and topcoat again.
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IDENTIFICATION: A finish that dulls as it dries.
Dulling can be a symptom of several types of issue, but the most common cause is using the wrong primer or topcoating the primer/undercoat before it has fully cured.
Refer to the undercoat manufacturer’s technical data sheet to establish the correct paint system and curing times and stick to them!
In most cases, you will be able to restore shine with a compound and polish. If the dulling is severe, sand back the topcoat and refinish.
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IDENTIFICATION: Foggy/misty patches in the final finish.
The substrate or paints have been too cold before you spray.
Unless the product’s technical data sheet states otherwise, don’t be tempted to spray if your work area is below ambient room temperature. In cold weather, plan ahead and use a suitable heat source to raise the room temperature.
Sand back, prime and refinish.
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IDENTIFICATION: Streaks in your metallic or transparent finish.
Refer to the product manufacturer’s TDS for instructions on how to correct streaking. This may involve spraying a “control” coat.
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IDENTIFICATION: These streaks or lines are sanding marks that appear through the paint film.
Denib the area and refinish using the recommended paint system.
Most paint spraying problems are avoidable when you:
Although there is almost always a fix for a spray job gone wrong, taking measures to get it right first time will save you time, money and a lot of frustration.
If you can’t find a fix for the issue you’re experiencing or you need more advice, drop us a line and we’ll get your paint job on track.
For further information on Jotun systems or specification products and which you should be using contact us below.
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