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Studies have shown that around 95% of all coating failures occur as a results of poor preparation. These failures can appear during application, after drying or curing, or several years later. Correct preparation and application are essential in order to achieve long-term protection. SML Paints and Coatings only sell Jotun products and as a result have the expertise and experience required to provide the right advice helping the applicator to achieve the best possible results.
Below are examples of the more common coating failures and their causes:
Sagging and Running
Sagging occurs when paint has been applied too heavily on a vertical surface or if the paint has been thinned excessively. Runs appear when too much paint has been applied to
one spot. Correct brushing and carefully application in an even and uniform manner will generally prevent this condition.
Sometimes application over a hard glossy surface will cause sagging, but simply sanding the surface prior to application will overcome this situation. If sagging or runs are noticed when the paint is still wet then they should be brushed out. Repairs after drying consist of gently abrading the surface followed by re-coating.
This is one of the most common types of paint failure and is caused by pressure build up under the paint film. This build up in pressure can be caused by a number of factors:
- salt contamination of the substrate. No coatings are 100% waterproof and moisture passing through the paint film will dissolve the salts causing a concentrated solution. This will draw moisture through increasing the pressure until blistering occurs. This phenomenon is called osmosis.
- Solvent entrapment. This can occur when overcoating times are not adhered to or when painting is carried out in direct high temperatures. The extra heat will cause the paint to set too quickly trapping solvent. This is more common when applying darker colours.
To prevent blistering make sure that the surface is clean, dry and free from contamination prior to paint application. Adhere to the overcoating times specified in the data sheets.
Lifting is a raising of the undercoat. It is caused by a strong solvent based paint attacking the previously applied film causing a wrinkled surface. An example is application of a xylene topcoat over a oil-based primer. The xylene in the topcoat will dissolve the primer. In order to prevent this check paint compatibility before application. If lifting has occurred then removal of the affected paint and reapplication is the only option.
Peeling/Loss of Adhesion
Loss of adhesion to the substrate or between coats of paint is, in the majority of cases, due to unsatisfactory surface preparation. Application on oil, dirt, grease and dust will cause loss of adhesion as will a failure to sand glossy surfaces.
To repair the surface abrade to a sound substrate, ensure that the area to paint is clean and dry and then recoat.
Orange peel is a cosmetic defect that causes the paint to take on a dimpled texture similar to that of an orange. This normally occurs during spray application and causes included:
- Improper atomisation due to low air pressure
- Spraying to close to the surface
- Rapid solvent evaporation
If orange peel occurs then abrade down to a smooth surface and repaint if necessary.