SURFACE PREPARATION AND PAINT APPLICATION
There are a lot of myths about waterborne basecoat and its application â€“ many of which arenâ€™t true or are, at best, highly inaccurate â€“ but the basic core message with preparing a surface for painting and applying the paint is care and cleanliness.
Waterborne basecoat is more susceptible to contamination, therefore a two step pre-cleaning process is recommended. This is required as contaminants are either solvent or water (salt residue) soluble. Pre cleaning should be done firstly with a solvent based cleaner followed by the recommended waterbase cleaner. This will ensure all contaminants have been removed, which can impact the waterborne basecoat. This also applies to air quality in the compressor system.
Oil can be present in compressed air, and as is well known, water and oil donâ€™t mix. The presence of oil in your compressed air during the application of waterborne basecoat will result in defects such as â€œfish-eyesâ€ and other imperfections throughout the job. therefore it is vital that you have a quality filtration system on your air supply lines to trap any oil or other contaminants.
Preparation should always be as near as possible to 100 per cent perfect in any paint job, but one issue which requires longer term care is the capacity for waterborne to hide imperfections in the preparation. Solvent based paints, especially silvers, can highlight scratches in poorly prepared surfaces. The capacity for waterborne – with its higher solids content and its non-aggressive nature – to hide imperfections can lead some painters to over apply the product. This approach will cause extended flash-off and if clear coated too early can lead to drop in gloss.
One aspect which does require care is the mixing process. The higher solids content means accurate colour formulation mixing is a must as it will take very little overpour of tinting base to alter the accuracy of a colour. While product usage is reduced consideration should be given to how much tinting base is required to make an actual mix. With most brands of waterborne basecoats 100 per cent tinting base is used during this process, but with Glasurit waterborne 70 per cent of the mix is binder so you use less tinting base in the final job.
Going hand in hand with this is the viscosity of the paint, which relates to the â€œsprayabilityâ€ of the product. This is influenced by ambient air temperature in the booth or area where it is being applied. It is this ambient temperature which governs reduction of the basecoat, not that of the air passing through the spray gun. There is no point mixing paint in a paint room at 18â„ƒ and then spraying it in a booth at 25â„ƒ. Ideally, both areas should be at the same constant temperature. Most systemsâ€™ technical data sheets suggest the ideal spraying viscosity measured at 20â„ƒ. The viscosity will determine the mixing ratio of the paint and the reducer. For most waterborne paints the mixing ratio will be in the order of 10 to 15 per cent of demineralised (distilled) water, but can vary up to as much as 50 per cent with Glasurit, using its special viscosity adjuster.
Next the painter will need to consider relative humidity. Humidity effects the drying of waterborne basecoat. By adjusting spraying conditions with your spray booth, the processing and painting of waterborne basecoat is made simple. Glasurit has two viscosity adjusters used for different climatic conditions.
One issue which will take a little time to get used to is the amount of paint you prepare for each job. Most body shops find that when they start using waterborne they are using more paint than when they used solventborne paint. This is counter to all the publicity, but comes about as a result of uncertainty about the amount of product required.
Most painters, when new to the waterborne system, tend to prepare more paint than they need, and the surplus is wasted, but as they become more efficient with the use of the product and experienced at assessing their needs consumption will lower.
One way around this, as mentioned in the last issue of ABN, is to use a tintable primer, which can be adjusted to suit the colour of the basecoat. This can eliminate the need for a basecoat in a similar colour and eliminate one step of the painting process and the time for it to flash-off. This applies most especially to reds. Tintable primers and waterborne basecoat go hand in hand.
Application techniques for waterborne can vary from brand to brand, and the colour to be used can also have an impact on the way in which you will apply it.
Glasurit 90 Line has been developed to be sprayed in the same manner as a solvent-based paint so that there is very little required for the painter to adapt to their waterborne paint. In that case the application technique is still structured around a cycle of half coat â€“ flash-off, full coat â€“ flash-off â€“ and then a control coat for colour reproduction.
There is some fine tuning around that in relation to how much product is used and how wet a coat should be applied with the full coat or control coat. Thatâ€™s something that will come to the painter with hands-on experience with the product and its use.
â€œBy the time you get to the control coat thereâ€™s very little flash-off time required because of the flash-off which has gone on before,â€ said Glasuritâ€™s Technical and Sales Support Manager Ian Johnson. â€œAnd thereâ€™s very little time required before you start clear coating because of all this.
â€œWith other brands of waterborne, most required to be painted around a cycle of half coat and full wet coat in one application, followed by a full control coat dropped on top then an extended flash off before clearcoating. This is despite some manufacturers promoting the claim that there is no need for intervening flash-off.â€
Whatever the product or process required the important thing is to allow the basecoat to fully flash-off before clearcoating. There is a danger of trapping water which can result in loss of gloss and other problems if you do not get that final big flash-off right.