Don’t drop the ball on your drop coat

The objective is to give that perfect as-new OEM finish. Using these techniques may help overcome the pitfalls of a drop coat.

The objective is to give that perfect as-new OEM finish. Using these techniques may help overcome the pitfalls of a drop coat marred by a mottle effect.

The technical term for a drop coat is a ‘technique coat’ and it’s a crucial part of the refinish process to get right. It’s actually about replicating the effects of the robotic electrostatic bell application technology, typically used on OEM production lines, where the bell spins at high speed to create fine droplets of paint that are designed to fall evenly onto the surface. By mimicking the OEM finish, the main aim of the drop coat is to reduce the risk of the frustrating ‘mottle’ effect in metallic finishes.


As the PPG team works to support painters in a wide variety of collision centres across the country, one of the main issues we see is a lot of painters applying their drop coat very dry. Unfortunately, this typically means that the drop coat is not able to melt into the underlaying basecoat. As well as creating potential mottle issues, this also prevents good adhesion. Generally, the cause stems back to one of three factors – the gun is too far away from the job, application is too fast or the gun air pressure it too high.

Tips and recommendations

Slow down – Because a drop coat is basically a light, mist coat, many painters feel they need to go faster. In fact, you need to resist that temptation and actually go slower. This is particularly important when the temperature soars – it’s the signal to slow down even more.

Watch and feel – Going slower lets you watch the paint going on and monitor the signs that it’s being done correctly. For example, PPG’s Envirobase High Performance waterborne basecoat system needs to go on with a slightly blue tinge, no matter what the actual basecoat colour is. Touch also plays a part – after applying the drop coat and allowing the surface to dry, Envirobase High Performance should feel like a piece of silk, with no feel of dry spray.

Spray gun settings – It’s crucial to follow any recommended spray gun setting and it’s here that PPG has gone one step further. The local PPG technical team has created special spray gun setup guide posters. Designed to be mounted in the paint area where they can easily be seen, they take the guesswork out of the spray gun setup process by providing clear and easily understood guidance. Depending on the application task (including the drop coat), these handy PPG setup guide posters provide recommended nozzles sizes, as well as fluid, fan and air pressure settings and the appropriate distance from the job, in order to optimise gun performance and minimise material usage. 

Tool of trade – Naturally, the spray gun you use has a big impact on achieving a quality drop coat result. Firstly, it should be clean and well adjusted, as well as in good working order. For example, a damaged or worn fluid tip can put the spray pattern out and make the job harder. When it comes to the drop coat, really good atomisation is a must and it’s here that SATA spray guns excel. For example, the latest SATAjet X 5500 is so good it just makes life easy for painters. If you want to try one for yourself, just speak to your PPG Training Manager or Territory Manager.

This tech tip was supplied by Terry Noble – PPG Business Support Manager Australia 

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