Uniform coating is an art

An evenly applied coating is very important. Otherwise an uneven amount of light enters the greenhouse and that can result in a non-uniform crop or problems with the climate control. Gert-Jan van Hattem, of spraying specialist HPW Spuittechnieken, talks about the art of coating.

To achieve an even layer everything has to be just right: the properly mixed amount; the spray pressure, driving speed and the amount released by the nozzles. HPW Spuittechnieken, a partnership between high pressure cleaning company van Hattem, and greenhouse roof cleaners Poot Kasdekreiniging, was set up to apply coatings with machines. Over the course of time it has perfected the art even further. Nowadays a lot of the work is carried out by computer. “But during the actual spraying, there is always a staff member sitting on the machine. You have to constantly keep checking, for example, in case a nozzle becomes clogged. In addition the person sitting on the machine determines the speed it travels and takes into account the spraying pressure which varies depending on the length of the hose between the spraying unit/pump and the spraying machine,” says van Hattem.

Everything has to be right 

The coating is automatically mixed beforehand. The requirements of the customer determine the choice of the concentration. “However, if he asks for an unusual concentration then we double check to make sure that was really what he meant,” he says. Then the computer makes all the calculations, taking into account the amount of fluid, nozzle pressure and driving speed. The nozzles require particular attention. The pressure at the top is different to the pressure underneath: This difference can be regulated by using different types of nozzles. “We’ve had a ten year period in which to optimise this,” says van Hattem. Also the beginning and end of the roof require extra attention because of lower driving speed. “We do our best to ensure that there are no differences in thickness but the coating might be a fraction thicker for a few metres.”

"Applying the coating is only possible in dry weather. If the roof is still wet from the dew, you have to wait until it is dry again."

HPW Spuittechnieken

Only in dry weather 

Applying the coating is only possible in dry weather. If the roof is still wet from the dew, you have to wait until it is dry again. You have to be even more precise with ReduFuse; then it also can’t rain for a few hours after it has been applied. “We always have to pay very good attention to the weather forecast. If we don’t then it’s against our own interests because we’d have to start over again. Therefore, the rule is: When in doubt don’t spray,” he says. 

With the increasing radiation and favourable weather conditions in April the phone at Van Hattem is ringing constantly. All growers want to use his services at the same time. That takes some puzzling with the planning and very long working days. The art is to stay focused, he says. “Only when we do our utmost the customer is satisfied.”
The ever-increasing interest in coatings is leading to more and more work for HPW, also from abroad. By increasing the number of trucks and spraying machines, the company is able to keep up with the growing demand.

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