Time Remaining For Same Day Dispatch -
Time Remaining For Same Day Dispatch -
Paint problems guide - by Andy Potts. First edition 21st August 2017. Edited 13th July 2020.
As Ultrimax are established manufacturers of premium industrial coatings, our field consultants are regularly required to assist and to have a 'hands-on' approach in the paint shop environment. Over the years this valuable experience has helped us to accumulate a library of typical problems & solutions that arise from time to time, so we've collated this 'easy-to-follow' interactive guide to help you quickly isolate any defect, so production throughput is little affected and re-work is kept to a minimum.
The mechanical action of rubbing, scraping, scratching, gauging or erosion.
Abrasion defects happen when a portion of the surface coating is damaged or, in severe cases completely removed exposing the original substrate.
This often occurs through contact with another object, such as the use of metal chains for lifting, cargo scrapes, fenders or even the grounding of a ship.
Sand with 1200 to 2000 grit discs, then compound and polish to restore gloss.
Or sand smooth and refinish.
You can prevent Abrasion with the use of abrasion-resistant coatings formulated with resins and extender pigments which resist abrasion effects. In severe cases of abrasion, the effects may be limited by an abrasion-resistant coating, however impact damage is very difficult to prevent with a coating alone.
Paint Fails to adhere to substrate or underlying coats of paint.
This could be because the surface suffers from contamination or condensation, an incompatibility between coating systems or exceeding the overcoating time.
Remove all coats with poor adhesion. Thoroughly sand and clean the substrate. Repaint using the recommended undercoats and/or topcoats.
By ensuring that the surface is suitably prepared clean, dry and free from contamintation and by using the correct coating specification with recommended overcoating times followed, you can prevent Adhesion Failure.
Very large (macro) crazing/cracking that resembles the skin of an alligator or crocodile. Cracks may penetrate through to the undercoat or down to the substrate.
It's often caused by excessive film thickness and limited paint flexibility. For example, if a hard top paint is coated over a more flexible softer undercoat or the application of a topcoat before the undercoat has dried.
Scrape, sand, use chemical strippers or heat to completely remove the old paint. Apply a good primer that is designed for the material you are planning to paint, then apply the correct topcoat.
Or Remove any loose paint and apply a filling primer that will smoth out the surface and fill most of the cracks. Then, finish with a suitable topcoat.
Alligatoring can be prevented by using the correct coating specification shown in the technical data sheets. It can also be prevented by avoiding excessive film thickness and avoiding application at high ambient temperatures.
Staining of a paint film by diffusion of a soluble coloured substance from the underlying paint to give undesirable discolouration or staining. Often seen where bituminous- or tar-based products are overcoated with topcoats in which the tar or bitumen is soluble. Also occurs with emulsion paints.
Bleen through is generally a full or partial redissolving of the previous coat or an ingredient of a previous coat and can occur when strong solvents are used in the topcoats.
Allow colour to cure, isolate with two pack undercoat(s) and then topcoat.
Or remove original paint film and refinish.
Bleeding can be prevented by using the correct coating specification and materials. By using compatible materials from the same paint system and using appropriate sealer coat is possible.
Dome-shaped projections or blisters in the dry paint film through local loss of adhesion and lifting of the film from the underlying surface. Blisters may contain liquid, vapour, gas or crystals.
There can be many reasons for blistering and is a common coating fault. Many factors can be involved here including osmotic gradients associated with soluble salts, soluble pigments, corosion products, retained solvet and solvents from cargoes etc.
To prevent blistering, ensure that you have the correct surface preparation and application. Apply a suitable coating system after testing for soluble salts with a Positester by DeFelsko.
Consider which of the mentioned blister mechanisms may appear in the environment you are painting in and try to rectify it before painting.
A hazy deposit on the surface of the paint film resembling the bloom on a grape, resulting in a loss of gloss and a dulling of colour.
This could be because the paint fil was exposed to condensation or moisture during curing, especially at low temperature, which is a common phenomenon with amine-cured epoxies. Incorrect solvent blend can also contribute to blooming.
Should blooming occure during application:
a. Apply heat to the affected area
b. Add retarder thinners and apply additional coats.
If the finish has dried, minor blushing may be corrected by compounding or polishing, however severe blushing will require sanding and refinishing.
To prevent blooming apply and cure coating systems under correct environmental conditions (ideally not in heavy moisture) and follow the manufacturer's recommendations.
The covering over of unfilled gaps such as cracks or corners with a film of coating material. This introduces a weakness in the paint film, which may crack or flake off.
Bridging is mainly a human error coating failure. Caused by poor application to the surface, a high-viscosity paint system and failure to brush paint into corners and over welds.
Bridging can be prevented by brush-applying a stripe coat into corners and welds and fill all cracks or weld them prior to application of the full coating system. It is extra work but may prevent costly paint repairs in the future.
Bubbles within a paint film appear as small blisters. These may be intact or broken (leaving a crater). Can be found in excessively think paint films, especially if spray applied, and also with roller application. This should not be confused with blistering.
A probable cause of this trapped air or solvent within the coating that is not released before the surface dries. Air could have become entrapped during the mixing phase or a high ambient temperature during application can also cause significant bubbling.
Sand affected area to a sound substrate and re-coat.
In spray application, bubbling can be prevented by adjusting the viscosity with thinners and following ata sheet requirements for maximum application temperature. Use correct mixing equipement (such as paint shaker) to ensure air is not stirred in during mixing. Apply a mist coat and add defoaming agent to emulsion paints.
Blistering and delamination of a coating system around bare steel areas and coating defects associated with cathodic protection on buried pipelines, immersed structures, and the hulls of ships.
A probable cause is high overvoltage principally from impressed current systems, but also to a lesser extent with sacrifical anodes when the number of anodes is excessive. Factors are incorrect installation, poor monitoring and incompatible coating systems.
To prevent this issue, use a well-designed cathodic protection system, regularly monitored with well-placed reference electrodes, and application of an alkal-resistant coating system will solve any future occurrence.
A friable, powdery layer on the surface of the paint film. A change of colour or fading is also seen. Chalking rates vary with pigment concentration and choice of binder. Chalking is also a known characteristic of certian paints, for example, epoxy paints.
A probable cause of this is disintegration of the paint binder on exposure to weathering and or ultraviolet light which causes a powdery chalk like substance to appear on the surface.
Sand or remove weathered paint film and refinish.
Or compound to remove oxidation and polish to restore gloss.
To prevent Chalking apply a suitable topcoat with high resistance to chalking and with ultraviolet resistance.
Fine cracks that do not penetrate the topcoat of a paint system. Some checking can be so minute that it is impossible to see without magnification.
This is typically caused by a formulation or specification problem, as with cracking, stresses are developed that cause the surface of the paint film to become birttle and crack. Another cause could be limited paint flexibility.
By using a correctly formulated coating system checking can be prevented.
Surface breaks in a wet paint film, where the paint has receded to expose the underlying substrate. The paint is unable to wet-out the substrate. Can be very large.
This can be caused with surface contamination by moisture or a foreign material such as oil, grease, or silicone. Cissing is also common when incorrect solvent blends have been used in the orginial mix.
Sand affected area down to a sound substrate and re-coat.
To prevent this, ensure the surface is clean and free from grease, oil and other contaminants prior to application of a coating.
The production of fine filaments instead of normal atomised particles when some solutions of high-molecular-weight polymers are sprayed. Traditionally when applying chlorinated rubber coatings by conventional spray.
A probable cause could be too high a viscosity with some types of polymers. Cobwebbing will occur with chlorinated rubber paints at almost any viscosity.
By reducing the spraying viscosity, selecting a more suitable solvent blend, and changing the spraying conditions you can prevent cobwebbing from happening.
The splitting of a dry paint film through at least one coat to form visible cracks, which may penetrate down to the substrate. Cracking comes in several forms, from minute cracking to severe cracking.
Cracking is generally a stress-related fialure and can be attributed to surface movement, aging, absorption and desorption of moisture, and general lack of flexibility of the coaitng. The thicker the aint film, the greater the possibility it will crack.
To prevent this, use the correct coating systems, application techniques, and dry-film thickness levels. alternatively, use a more flixible coating system to provide a buffer against cracking.
The formation of small bowl-shaped depressions in the paint film. Not to be confused with cissing.
Cratering is trapped air or solvent bubbles that have burst on the coating surface, leaving small craters as the coating dries. The coating therefore has sufficient time to flow into a uniform film.
To prevent Cratering, improve your spray technique, apply a mist coat, and avoid air entrapment during mixing. You can also add thinners as recommended by the paint supplier to reduce paint viscosity.
Similar to checking but the cracks are generally wider and penetrate deeper into the film
Another common paint problem, crazing most often occurs when application temperature is low or below 5 degrees. It can also be an issue if there is an incompatibility with previous coatings, aging, or if thereis a high film thickness.
To prevent crazing, apply a thinner coat of paint, add slower-drying solvent, check that application and drying conditions are correct for the paint system used, and check compatibility between previous coatings and the new coating.
The development of small wrinkles in the paint film in a pattern resembling a crow's foot.
Usually caused when the surface dry's too quickly and forms a skin, which then wrinkles as solvent slowly evaporates from the soft underlying paint.
Sand the surface down past the cracks and re-coat.
Very similar to crazing in appearance, crows footing can be prevented by applying a thinner coat of paint, adding slower-drying thinners and check that application and drying conditions are correct for the paint system used.
Loss of dhesion between coats of paint.
Provided that compatible paint materials have been used, delaminated defects are generally related to poor surface preparation and application. Contamination between coats, exceeding overcoat times, or application to a glossy surface are the most frequent culprits causing delamination.
Strip to bear substrate and refinish.
Or remove the finish in the affected areas, featheredge and re-finish.
To prevent this, ensure that no contamination occurs between paint coats. Follow the recommended overcoating 'flash' intervals. Lightly abrade and clean glossy surfaces between coats.
Discolouration or gradual decrease in colour of paint when exposed to sunlight/weather. May be accompanied by loss of gloss. In some situations, it may resemble chalking but without the powdery surface. Fading tends to accelerate in the presence of moisture.
This can be caused by incorrect pigmentation, use of non-light-stable organic pigments, atmospheric contamination or porous substrate that leaches away the original colour.
Sand to remove weathered paint fil and refinish.
Or compound to remove oxidation and polish to restore gloss.
To prevent fading, use correct coating systes that resist ultraviolet light and fading. Use a coating with light-stable pigments to retain bright colours.
A form of adhesion where pait flakes from the substrate. A familiar sight on wood substrates and on galvanising.
Flaking is most often caused by using an incorrect paint system, for example, using interior paint on an exterior object ill most likely see flaking soon after drying.
Strip to bear substrate and refinish.
Or remove the finish in the affected area, featheredge and refinish.
Either no or an incorrect pre-treatment used for certain substrates causes flaking, for example nonferrous or galvanised metals. Poor application techniques may also be attributed to differential expansion and contaction of the paint and substrate.
Natural products such as wood, are good examples of surfaces which expand and contract and can cause flaking. It can also be caused as a result of normal aging over time.
To prevent flaking, use the correct coating system and pre-treatment.
The underlying surface is visible through the paint film due to inadequate hiding power of coating material. This is sometimes called grinning-through. Often seen where dark colours are overcoated with lighter colour.
When you can see a previous layer such as a primer showing through the topcoat to the surface, it's known as grinning. It's caused by having a low film thickness of topcoat, poor opacity, covering power of topcoat or possiby even too strong a colour of primer and undercoats.
Apply a further coating.
To prevent grinning, apply adequate dry-film thickness between individual coats, and use opaque coating with good opacity.
Discolouration, detachment and/or blistering, and general degradation of paint film.
High temperature applied to a substrate will cause damage to almost any paint coating with the most likely causes being burning, welding or fire.
Ensure that all welding and burning work is completed prior to painting in order to prevent Heat Damange.
Cracks that radiate from a point of impact.
This is damage caused by an object coming into contact with a paint surface. Most likely to occur with relatively brittle coatings such as on glass fibre reinforced plastics. It also can occur when steel or any other substrate is deformed by impact.
Ensuring your paint coating remains protected is the only defence against impact damage.
The presence of a contaminant between two layers of a multi-coat paint system.
Examples of this issue could be contamination from inadequate washing down of the substrate. Alternatively salt deposits from natural weathering will appear on the surface and if not cleaned before painting can cause paint faults, even foreign deposits like soot from nearby operation can add contamination to a new coating.
Sand paint back to substrate and re-apply primer and topcoat.
To prevent this, carefully inspect and test the surface before paint application, and wash down with fresh water if required.
The dried paint film has the appearance of a dried-out mud flat. The cracks appear as a netwok that can vary in size and amount.
This is generally an over application of heavily pigmented primers such as inorganic zinc silicates or water-based coatings, although the issue can occur with other thick material systems.
A prevention of this is to rigidly stick to recommended coating thickness from technical datasheets and use only recommended application techniques, for example, if a product is spray only, don't apply by brush or roller.
A uniform, pock-marked appearance, in particular of a spray applied coating, in which the surface of the paint film resembles the skin of an orange.
A common problem for automotive sprayers requiring premium finishes.
Orange peel is often caused by the failure of the paint film to flow out, and results in the distinctive orange peel surface. Poor application technique is the most frequent reason for flow issues but an incorrect solvent blend, or too high thixotopy where the material temporarily becomes a fluid then sets to a solid can also cause orange peel.
To prevent this use correct application techniques with suitably formulated products, especially when using 2k paints.
Similar to flaking, although peeling tends to be associated with soft and pliable fresh coatings that can be pulled away from or spontaneously flake away from the substrate or from between coats, due to loss of adhesion.
Peeling is the reduction in bond strength of the paint film due to contamination or incompatibility of coats.
A prevention of this is to use the correct coating system and specification shown on technical documents and only apply coatings to clean, uncontaminated surfaces.
The formation of minute holes in the wet paint film during application and drying, due to air or gas bubbles that burst, giving rise to small craters or holes that fail to coalesce before the film has set.
Solvent vapour or air gets entrapped within a paint film and as these vapours rise through the paint layer, they create a mini volcano effect through the paint coating. It's not only a visual problem, if painting here a waterproof membrane is required pin holes will leach moisture down to the substrate destroying its water proofing.
Sand affected area down to a sound substrate and re-coat.
To prevent getting pinholes in your paint coating, use correct application techniques with suitably formulated products.
Check your datasheets for the correct solvent blends and paint in non-humid environmental conditions. It's also worth checking you are spraying from the correct distance of spray gun to surface and apply a mist coat.
A rippled effect on the surface of the paint.
This can be caused by strong wind blowing across the surface of wet paint causing it to ripple. Where this occurs on the underside, the ripples can hang down in the form of small stalactites. It's also an issue that can be caused by poor application techniques.
Scrape or sand to remove the rippled coating. Make sure the surface is smooth to blend it into the surrounding coating.
Prime Bare areas and use appropriate topcoat.
Prevent rippling by applying paint under clam, dry weather conditions and use professional application equipment.
A narrow downward movement of a coat of paint, often apparent from accumulation of excessive quantities of paint at irregularities such as cracks and holes where the paint continues to flow after the surrounding surface has set.
This is when there is over-application of paint, excessive use of thinners, incorrect or lack of curing agent, or poor workmanship.
Remove the wet paint film with solvent, clean and refinish.
Or, after finish is completely dry. Remove excess paint by block sanding with 1200 to 2000 sanding discs, compound and polish to restore gloss.
Often the runs are caused by applying too much paint to the substrate (otherwise known as human error) so prevent it by using the correct application techniques and always checking your dry film and wet fil thicknesses.
Fine spots of rust that appear on a faint film, often a thin primer coat. The initial spots rapidly spread over the surface, resulting in a film of rust through which the individual spots are difficult to discern. Also, from holidays.
This is when there is over-application of paint, excessive use of thinners, incorrect or lack of curing agent, or poor workmanship.
A prevention of this is to ensure that an adequate thickness of a primer coat is applied to cover the surface profile, and check that the surface profile is not too large.
Individual spots of rust that appear on a paint film and frequently start as localised spotting but rapidly increase in density.
You can identify rust spotting by dried iron salt deposits on a metal surace caused by corrosion. Probable causes of this can be low film thicknesses, voids and holidays.
Steel defects such as laminations and inclusions can also cause spotting as can a high surface profile with a number of peaks in the paint film. another common cause is metallic contamination of a coated surface by grinding dust which then slowly corrodes.
Sand affected area down to a sound substrate and re-coat.
To prevent this, ensure that an adequate thickness of a primer coat is applied to cover the surfce profile, use a thicker coating system or a lower blast profile and protect the coating from grinding dust contamination.
A light staining on the surface of the paint caused by the precipitation of ferrous oxide from adjacent exposed steel.
Rust staining can be caused by water runoff from a rusty surface above a soundly coated surface. Rust staining contaminates water and discolours other items or locations. Usually more of an eyesore than a defect, only stained but in the painting world that is still a problem to solve for the customer.
Sand affected area down to the substrate and re-coat with suitable primer and topcoat.
A prevention on this is to ensure adequate design to stop water run off and suitable maintenance of surrounding substrates.
Sags are caused by the downward movement of a coat of paint that appears soon after application and bfore setting, resulting in an uneven area with a thick lower edge. They are usually apparent on local areas of vertical surface and, in severe situation, may be described as curtains.
When there is an over application of paint, excessive use of thinners, incorrect or lack of curing agent, or poor workmanship its likely you will cause a sagging or sliding of a coating. In extreme circumstances, it could also be a result of a formulation problem.
Remove the wet paint film with solvent, clean and refinish.
Or, after finish is completely dry. Remove excess paint by block sanding with 1200 to 2000 sanding discs, compound and polish to restore.
The only way to repair this kind of damage is to sand back and start from the beginning, so to ensure you prevent Sags, use the correct application techniques with suitably formulated products.
The sedimentation of the solid constituents comprising pigments and extenders from the binder and solvent while standing in a container. Settlement that occurs after mixing and during aplication can result in different shades and performance in different areas.
Settlement is when the paint colouration is not uniform across the whole coating and the inconsistent finish ruins the job. This is a very easily avoidable fault as the most likely caus is a lack of correct mixing at the formulation stage. Always ensure the adequate mixing with a aint mixer to get best results. there are also other possible causes such as old stock or heavily pigmented paint as found with zinc-rich primers.
Sand affected coats and re-coat.
To prevent this use products within shelf life, use adequate mixing procedures, and keep paint mixed or recirculated during spray application.
Eruption of the surface of the paint film. Wrinkling and blistering, which leads to a weak surface and ultimate coating breakdown.
It can be present when incompatible paint systems are being used together or a topcoat with a strong solvent blend reacts with a previous and weaker solvent-blended coating. Overcoating before the previous coat has adequately hardened is also a common cause of solvent lifting.
The best prevention of solvent lifting is to use the correct coating specification, overcoating times, and materials. Conduct compatibility trials with undercoats and topcoats.
Solvent (clear) bubbles on the surface of the paint film soon after application.
An ugly defect like pimples on skin, it's caused by solvent evaporating so quickly from the wet film coat that the resulting void cannot be filled in time and a crater is left behind.
Minor problem: Allow finish to thoroughly dry/cure, sand smooth and refinish. Inspect surface carefully to ensure all craters have been removed.
Major problem: Remove affected film(s). Prime, seal and recoat, as necessary.
Generally incorrect solvent blends, porous surfaces, in-corrected environmental conditions, or high surface temperatures are to blame for solvent popping showing up in a wet film. By using the correct coating specifications, materials, application tecniques and only painting in stable environmental conditions you can prevent Solvent Popping.
Discolouration of a coating system.
When a solid of liquid imparts a discolouration to the coating you tend to be left with a stain.
Sand damaged coatings and re-finish.
To prevent staining, avoid allowing the coating to come into contact with solids that are prone to cause staining or alternatively use dark-coloured coatings where any staining would not be so apparent.
Paint coatings with visible cracks, which may penetrate down to the substrate.
As the name suggests stress cracking can be attributed to surface movement, aging, absorption and desorption of moisture, thermal cycling, and general lack of flexibility of the coating. The thicker the paint film, the greater the possibility that cracking may occur. It often occurs around welds and changes in sections that are difficult to coat accurately.
You can prevent stress cracking by using the correct coating systems and dry-fil thicknesses, or use a more flexible coating system to compensate.
Visual corrosion beneath a paint film, often called creep. Corrosion travels beneath the paint film and lifts the paint from the substrate. Severe cases can show as blistering, flaking, cracks and exposed rust.
It creates an effect that looks like one coating running into another with a thick edge. The most likely cause of this is application of paint to a corroded substrate. You may see rust creep from areas of mechanical damage which results in a missing primer coat. Undercutting often shows in areas of poor design and access, where inadequate preparation and coating thickness was applied. In these same areas maintenance may be difficult which can cause the undercutting to worsen.
To prevent this use adequate coating specifications and maintenance procedures and apply a suitably formulated primer.
The development of wrinkles in the paint film during drying.
It can arise from overcoating before the previous coat has adequately hardened or cured and follow-on effect of one coating layer drying while one is still wet - causes a reaction and wrinkle. Over application of a paint coating can be a cause, particularly with alkyd coatings as these types of material are naturally thicker making it easier to over apply.
If defects are minor: Sand the top surface smooth, allow cure and refnish.
If defect are severe: Remove finish, apply primer/sealer, and repaint.
To prevent wrinkles on your project, use correct coating specifications from your technical datasheet, ensure you mix correctly and apply in thin layers to avoid overcoating. Forced curing with IR heaters will eliminate the risk of applying a layer to a et coating.
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.
