BMW April 2022

The colder winter weather conditions are unavoidable in South Africa and typical weather in some Highveld areas can deliver freezing conditions to make any painter shiver. This can create many issues when painting a vehicle comes under the microscope.

While the obvious solution is to carry out any respray work in the preferred ideal spray booth where the top ceiling and air arresting filters reside and that can deliver cleaner air than we normally breathe. But not every shop has ideal conditions for refinish.  Low temperature painting is a big challenge because it can produce excessively high film builds which quickly, in many cases, lead to problems of solvent popping (pinholes) which are caused by the top clear or colour coats closing from the top and trapping solvent evaporation and orange peel.

 Final finishes are also a mix of temperature and spray viscosity which will need, if a poor final job is in prospect, to be flattened and again resprayed for a second time. Added to this, every painter must know exactly what hardener and thinner combinations may be needed to avoid the other problem of slower drying times as a car will take much longer to dry in temperatures under 20ºC.

 All manufacturer painting recommendations are based on ideal temperature ranges of around 25ºC but running and many drips or sagging can occur on surfaces in the colder conditions.

 Ideally spray booths must, as a general guide be preheated up to a temperature of 25ºC and then the car should be given a pre-heat period to get to the required metal temperature for repairs to take place in better conditions. 2K materials are extremely toxic and can cause both long-term cancer and severe breathing complications because the isocyanide hardener which is commonly used is a sprayable cyanide and always remains very dangerous to handle. So good ventilation for spraying is a big issue and has to be kept in mind at all times. 

Condensation complications

Thin layers of moisture condensation are easily formed in colder conditions across the whole car body. This will impede or stop the two pack materials from cross linking or curing properly. So, it is vital that surfaces are dry and at room temperature as well as primers and top coats that will need to be kept in heated or at room temperature conditions. 2K Paints in general terms will increase by one second in thickness for every degree that the temperature drops below 25ºC. So, when reduced if they are cold the probability is that the spraying fluid will remain too thick to perform as it should with a remaining high viscosity.

A combination of over four special hardeners from slow up to polar systems is available and in many cases a combination of slow, medium or fast thinners or reducers. Paint makers offer this huge range of refinishing options because a painter with experience in different temperature ranges will determine what combination will work the best to deliver that perfect respray every time.

So, as a general guide, fast thinners when used with a fast hardener will deliver a perfect job in conditions between 12º-20ºC, under that depending on the size of the spray repair an operation may need to move to a polar or extra fast hardener option to make two pack materials cure faster. When painting a vehicle in cold weather conditions always remember that it will take a surface refinish of paint material up to seven days to fully cure from a through hardness perspective. The total drying process is also dependent on temperature conditions so, for success you need to be both a patient and talented painting enthusiast to be successful in colder, adverse painting conditions.