Excessive heat comes with finishing problems. Do you know how to prevent them?

Everywhere I hear about the scorching temperatures that are and will be these days. Excessive heat comes with all sorts of problems including those related to painting or varnishing wood. There are large factories where temperature and humidity are controlled, but the vast majority of factories and workshops have to work without such facilities. And that "we stop when the temperatures are very high" doesn't really work when you have contracts with deadlines that, if you don't meet, you can get penalties. So what is to be done? So here's some material on summer finishing.

First of all, I would like to draw the attention of those who work with products that are diluted with petroleum derivatives (white spirit-petrosin, gasoline, diesel) to a very dangerous phenomenon - self-ignition. This includes some waxes, oils or baths, solvent-based outdoor paints and varnishes, which can become dangerous on sunny summer days. If leftovers from use - dirty rags, soggy sponges, brushes, bottles of leftovers, bits of hardened material - are left lying around the workshop and the sun's rays reach them, they self-ignite. The phenomenon is called self-combustionand it's very dangerous. When you are done working put all the scraps in a drum and pour water over them. Never ignore a cloth that you have applied wax with. It can become the source of a fire.

Finishing problems under temperature and humidity conditions occur regardless of the nature of the materials being worked with. Indeed, when products are solvent-based, they are much higher, but excessive heat and humidity also damage waterborne products. Finishing materials are made to work at temperatures of 18-22 grd.C and humidity 50-70%. Outside these ranges they may not behave normally and so problems arise.

The biggest problem of this period is rapid drying of materials. The consequence is film gassingwhen applied by spraying. The varnished surface shows white, rough patches, because some of the varnish particles dry out in the air and fall onto the freshly applied varnish and get stuck to it. The easiest way to avoid this phenomenon is to use a slow thinner, specially formulated for hot summer periods, or to add retardant 5-10% thinner (according to the manufacturer's recommendations) to the spray mixture. Gassing can also occur with waterborne products. It is good to know that special thinners are also available for these materials to slow drying.

High temperatures lead to decrease in the viscosity of finishing materials. For this reason the amount of thinner added will be less. If you follow the recipe without checking the application viscosity with a viscometer cup, you will be surprised by a much more fluid material and you will experience the appearance of run-off on the edges. When you have to apply flowable materials it is best to do it in 2-3 batches, with a 10-15 min. dwell time in between.

When using type A+B materials (polyurethane, acrylic with curing, polyester, etc.) high temperatures can lead to increased reaction speedand faster curing of the product. Reducing the amount of solvent added is no longer a solution because it will accelerate the curing even more. A retardant thinner should be used and the amount of material prepared should be smaller to avoid wastage.

In the case of high-gloss varnishes, rapid drying can result inappearance orange peel and decrease in gloss. The curing time of the film on the surface is too short and the lake does not have time to stretch very well to reflect the light correctly. Using summer thinners or adding retardant thinner solves the problem.

On days when the humidity is also very high, the phenomenon of bleaching of varnish film, especially when working with nitrocellulose lacquers. All the thinner is the solution. In addition to summer thinners or retardants, you can also use a specially formulated thinner for these periods, called 'anti-fog'. Bleaching can also occur due to water splashed on the floor on very hot days. Watering of floors in finishing sections is done to draw dust from the atmosphere. When it is very hot the water evaporates quickly and the humidity in the work area increases.

Appearance of bubbles on the surface of parts is a common fault in hot periods. The reason for this is the very rapid drying of the film on the surface - dust drying, as it is called. The remaining thinner in the varnish film tries to push its way out by pushing into the dried layer and forming bubbles. Avoid them by using slow thinners, applying thinner coats and avoiding drying in direct sunlight.

Sometimes, small holes may appear on the surface finished with solvent-based products as inNeedle pricks. It's because of the appearance of water on the spray paths. Due to the increased humidity the compressors accumulate more water. If it is not removed more often and the spray paths are not fitted with filters, the water gets into the air with which the material is mixed when spraying and is transformed into very fine droplets that appear on the surface as pinpricks. It is recommended to check the compressor very often and to fit high-performance filters on the spray lines up to the gun.

A phenomenon that can occur on hot days with very high humidity is very slow drying of water soluble products. The phenomenon does not only occur in finishing products. On hot summer days, streets can stay wet for a long time after the rain if the wind doesn't blow a little. It happens because water molecules in the atmosphere settle on top of the street preventing water from evaporating (vapour pressure). With a gust of wind they are blown away, making way for the next layer. The same is true of the lake. This is why ventilation is more important than temperature for waterborne products.

Finally, a few recommendations to make this hot summer as trouble-free as possible:

• finish in the morning, when temperatures have not risen very much. Prepare the workshop in the evening (clean, sweep, water) and start finishing in the morning;
• avoid watering on the ground on days with high humidity;
• change the thinner used in winter. Use a summer one;
• dry in separate, well-ventilated areas;
• do not leave wax residues, oils and petrosin-type thinners around the workshop. Always cover them with water.

I wish you all the best for the hot days.