PAINT DEFECTS
Paint defects can be caused by a number of factors. whether that be user error, poor preparation, environmental issues or a paint fault. This guide should help you find a solution to your defect and help rectify it.
Loss of gloss
Water / Moisture
This can cause the clearcoat to become hazy and lose its gloss. Some painters use water on the floor to help eliminate dust and dirt nibs however, when the booth is set to bake this will elevate the moisture levels within the spray booth to a very high level.
Isocyanate that is used in the hardener is very sensitive to moisture in its liquid form. This is the chemical that is mostly affected by moisture.
Storage and can lids
It is advised that the clearcoat and hardener are kept at room temperature at all times a variation in environmental conditions can cause paint defects later on. A can going from a cold workshop floor then to a warm office or mixing room every day can cause condensation on the cans. This can cause moisture related problems over time.
Can lids
It may come to as a surprise but it is not uncommon for painters to leave the can lid off the hardener by accident even for just a few hours or in-between jobs this can cause the hardener to absorb moisture and cause defects later on. We have also been out to bodyshops where the hardener lid has been used on the clearcoat can and vice versa. You may think we are trying to pick fault here but when just one drop of the opposite chemical meets each other this will cause a chemical reaction which will affect the clearcoat over time. This is why we colour code our hardeners to Red lids and other products to black.
Over Application
Over applying the clearcoat means that the film thickness may exceed the recommended levels. When a clearcoat exceeds these recommended levels a few things can happen.
In lower solid clears this will mean that there is a high level of solvent within these films and will take longer to evaporate. When the clearcoat starts curing and the solvents are still left behind in the wet film this can cause the clearcoat to not cure correctly. This will cause the clearcoat to sometimes drop it's gloss as the solvents escape. This can either happen after baking or after a week as the clearcoat crosslinks.
In higher solid clears such as our HS and UHS clears we often say less is more. What we mean by this is as the solvents evaporate in the wet film it will leave a higher percentage of solids behind then that of a lower solids clear. This means less coats of a HS may be equal to that of an MS. increasing the film thickness of a clearcoat with a HS or UHS means that the solvents have a harder time evaporating from the clearcoat and can become trapped in-between the two layers of clear being applied. In this case we recommend leaving a longer flash off time in-between coats and lower the spray room temperature. We want the solvents to evaporate not cure the clear so another coat can be applied on top.
Delamination / Paint peeling off
Paint peeling off or delaminating is caused by poor or no intercoat adhesion in between each paint process. For this section we have split this into 4 sections of the most common paint layers.
Primer peeling from substrate below
Primer is usually applied to a substrate to prepare for basecoat application. The substrate below needs to be that of a 2K nature. Applying a 2K primer over a surface that is soft or that of a 1K nature will cause the layers to not adhere to each other. Also, over time the 1k paint will move when warm and cold unlike the 2k paint which will also cause issues over time. Always ensure that the substrate below has been keyed and cleaned correctly.
Primer peeling from the filler
This is often caused by the filler being incorrectly mixed. Either under cured or over cured. Under cured will keep the filler soft and over cured will cause peroxide to bleach through the layer.
This can also be due to the primer being under cured. if the primer has not been baked and has been left to air dry and heavy coats have been applied the solvent within the primer can struggle to evaporate and although the primer may be hard enough to sand it can still be soft where the primer meets the filler or other substrate below.
Over curing the primer - using the incorrect hardener in primer can cause the primer to cure too fast which also affects the adhesion between the two layers. Some may think that a higher solids hardener is better but this is not the case.
Basecoat peeling from the primer
When basecoat doesn't adhere to the primer this could be due to the primer has absorbed too much moisture either by wet sanding or leaving in a humid environment. Moisture in primer is the primary cause of issues that occur on top of this layer. We recommend dry sanding primer and not leaving longer than 48 hours after being cured to prevent moisture contamination.
Too fine abrasive to sand the primer is another cause of basecoat not adhering to the primer. If the primer has been sanded with a fine abrasive and looks shiny when sanded this is a clue that it is too fine. Abrasives such as P500 are usually adequate enough to give good adhesion and not show any flatting marks above.
Clearcoat peeling from the basecoat
In most cases where the clearcoat has been mixed and applied correctly and still does not adhere to the basecoat it is usually a basecoat fault rather than the clearcoat.
This occurs mostly on solvent based solid basecoat colours which most manufacturers do state that the basecoat when solid should be mixed with 5-10% of the hardener that is going to be used in the clearcoat when applied. What happens when the hardener is mixed with the basecoat is two things, the basecoat slightly crosslinks making it a harder layer. When painting whites for example it is easy for painters to overload the white to make sure it is covered. this can cause a build up of solvents in the basecoat layer and will stay soft underneath. The hardener when mixed with the basecoat will crosslink and make sure the layer becomes harder.
Adding hardener to the basecoat will also increase the solids slightly so when the clearcoat is applied it helps bond the two layers together better. All basecoats contain wax which floats to the surface. With metallics this wax pushes the metallic flakes to the surface rather than the wax itself. When there is no metallic for the wax to push to the surface, the wax itself will float to the surface. When the clearcoat is applied it will sit on top of this surface which of course will not adhere which is why most manufacturers will advise hardener is added because this hardener helps the two layers adhere together.
Usually this is only recommended with good quality HS and UHS clears due to the solid content. Usually MS clearcoats contain more solvent which helps break that waxy surface and allow the clearcoat to adhere however we always recommend looking at the basecoat TDS or speaking with the manufacturer.
Mixing basecoats with a poor quality thinner can also cause delamination because the poor quality thinner usually contains high levels of moisture which gets trapped in the basecoat when applied and then slowly comes out of the basecoat after the clearcoat is applied which is pushed up into the two layers causing delamination.