Waterborne Paint: The Beginner’s Guide – Part 3


You learn at your mother’s knee that water dries. Every time you spilt a glass of cordial or watched your mum hang out washing you learned anew that water evaporates, and will dry.
But mum didn’t have to comply with financial constraints or meet bank payments or pay rent from the washing. At least ours never did.
So what makes any body shop which wants to paint with waterborne paints think it can get away without a drying system, especially in colder climates or winter weather, especially if you have to meet the requirements of deadlines or throughput.
Humidity and temperature will have a significant effect on how fast waterborne paint will flash off. This is due to the simple fact that you cannot control the evaporation rate of water. On days which have high humidity, flash off times could be increased,, or in climates where high temperature and very low to no humidity is experienced, such as in Western Australia, it can dry too quickly making blending of difficult colours almost impossible. Glasurit overcame these difficulties by the introduction of a slow viscosity adjuster.
Due to the affect different climatic conditions can have on the painting of more “difficult” colours, such as silver, a body shop may wish to consider arranging day to day work schedules around the monitoring of temperature and humidity. This is not to say that difficult colours cannot be painted in less than perfect conditions, but by doing this the body shop would ensure maximum through-put of work as booth time would be kept to a minimum. By optimising both booth time and climatic conditions you also reduce the risk of exposing the basecoat to dust and other imperfections which will have an impact on the end result.
With the drying of waterborne paints at the very minimum you are going to need an air diffuser or a hand-held blower system to dry the basecoat, simply because water evaporates more slowly than solvent.
There are a number of different options open to you on the market today. These can range from simple hand held blowers to a “tree” with several of these blowers mounted on it, to larger installed systems that will alter the linear air movement within the booth.
It basically comes down to air movement as the necessary component for drying waterborne. Your standard spray booth air flow just doesn’t provide enough air movement to adequately dry paint under sills or beneath body contour lines, or in areas where there is paint overlap.
This is where you have to look at your existing set-up. The “tree” arrangements seem simple and are relatively low cost, but a body shop should ensure its air supply can handle the added demand of air flow.
A set of Junair QADS, for example, will cost you more, but they do a very efficient job of moving air and quickly raising temperature in the booth. The only criticism we have heard of them is that they can move so much air that they can potentially lift dust off the floor and onto the paint job, so care needs to be taken with cleanliness.
The Garmat Accel Cure system of fans, which mounts along the centreline of the spray booth roof, minimises that risk but requires removal every time you want to change ceiling filters in your booth, and this can be a difficult process. Overall, general house keeping must be a high priority with the use of waterborne basecoat.
Spraying of rapid repairs can be undertaken with a hand held blower, which can achieve a quick flash-off time simply by swapping the air line from the gun to the blower, and then back to the gun for the next coat.
A lot of the secret with spraying waterborne revolves around the painter’s approach. On a respray, in the past a painter might start at the rear quarter, then work down one side, across the bonnet, down the other side, across the boot and then finish on the turret. With waterborne, to gain the most efficiency, you need to think of the area which is going to be the slowest to achieve flash-off and then paint that first. This will be the horizontal surfaces, since they are traditionally wetter in painting. Thus, these panels will stay wetter for longer, so it is recommended that you paint these areas first, maybe painting the turret, bonnet and boot lid first, then the vertical panels, so that by the time you have finished you have given those wetter areas longer to flash-off. It’s just a matter of thinking the job through and changing old habits. There’s no more work involved, just a different order of doing things.
If you are doing a front end repair – let’s say a bonnet, front guard and a door – you might like to place your “tree”, if you have one, adjacent to the last panel you are painting. That way the first panels to get paint will have a chance to be flashing-off while the last, and thus wettest, panel will have the assistance of the blower to achieve flash-off. It’s a matter of working smarter, not harder.
Another option is to simply spray air through your gun to assist any wetter areas. It’s not recommended that you blow air over solventborne paint as you run the risk of solvent entrapment. As waterborne basecoat uses water and not solvent to reduce the spray viscosity it’s 100 per cent recommended to blow air over the paint. However, if you don’t dry waterborne properly you can entrap water, as you can with solventborne paints, so you can end up with blistering or a loss of gloss in the clearcoat.
With poor covering colours the normal approach with solventborne is to apply a half coat and then full coats until coverage is achieved, but you are actually putting the paint on heavy and wet. In waterborne this will extend flash-off time since you have a lot of product there. It may be found that it is better to apply several lighter coats before the final full coat, thus achieving the final job in less time because you were getting to flash-off more quickly.
Alternatively, the use of black and white primer or grey shades can eliminate the need for basecoat ground coats resulting in faster drying. Most modern effect colours require the use of coloured ground coats to achieve the correct colour match. For example, a red pearl requires a grey ground coat. If it’s a new panel then mix up a grey wet on wet primer in the same shade of grey and do not use the grey ground coat. Apply your red pearl top coat straight over the wet-on-wet, again reducing the amount of paint used and flash-off time required.
The same can be done with sandable primers. Mix your black and white primer, which your manufacturer’s formulation will give you, and by following this course half the job is already done in the primer process.
The overall picture is that waterborne can be dried as efficiently as any solventborne paints if you approach the job with the right attitude.
The change to waterborne technology requires an open mind. If all employees in a body shop do not have a positive approach to the decision to use waterborne, it is likely to fail. It is vital that both management and the painter technicians are in agreement that waterborne technology is the right step forward and with this in mind, and if you receive the essential correct training on the use of the product the transition to water will be made easy.