The cutting edge of window scrapers

29th of January 2015
The cutting edge of window scrapers

Torsten Deutzmann of Unger Professional Worldwide reveals why professional window cleaners rely on their scrapers so much.

The word scrape has a number of different meanings, but one of the most appropriate I have found, in terms of window cleaning, is: ‘Move a hard or sharp edge across (a surface) especially to make something smooth’.

Materials used during the construction period, such as cement, grout and paint, can splatter onto glass – and scrapers are the most effective tool to help remove such debris, and other substances that can cause significant problems due to their unsightly appearance or ability to cause physical damage to the façade of a building.

Throwing eggs at buildings can seem like a good practical joke to some but egg can be a stubborn substance to remove once dried on. Scrapers can help in these circumstances, as they can with another big problem when it comes to building maintenance – bird excrement. Bird mess not only has the potential to spread disease and bacteria, its corrosive nature can also cause damage to brickwork and building facades if left for too long. Scrapers can also be useful when dealing with fly-posting or other materials such as stickers.

Toughened safety glass, also known as tempered or safety glass and as ESG in Germany, is extremely common. It is manufactured by a process of extreme heating and rapid cooling, so that the surface area cools much quicker than the inner layer. This makes it stronger than standard glass, and, if the glass does shatter, it breaks into small ‘chunks’ instead of splintering into dangerous, jagged shards.

Extra care needs to be taken when cleaning this type of glass as issues have arisen surrounding ‘fabricating debris’. This takes the form of tiny rough imperfections, sometimes referred to as ‘glass fines’ that are created in the hardening process.

Fabricating debris has been a subject of debate for years, and it prompted the International Window Cleaning Association (IWCA) to publish the IWCA Tempered Glass Informational Bulletin 2004 – Scrapers and Fabricating Debris in 2004. It offers a range of guidance and advice, including:

• Fabricating debris consists mostly of tiny glass chips and glass dust that get baked onto the surface of some tempered glass. These surface defects, also known as glass fines, may create scratches when they are dislodged and trapped by a scraper during window cleaning

• Builders should require suppliers to provide quality tempered glass that can be cleaned without scratching, the same as glass which is not tempered

• There should be a tempered glass scratch liability waiver for all construction window cleaning contracts, and for maintenance contracts when significant scraping will be done. The builder signs a tempered glass scratch liability waiver to assure they will not blame the window cleaner for scratches due to fabricating debris on tempered glass, and will not force the window cleaner to prove that fabricating debris caused scratches on tempered glass.

Check glass

Scrapers should not scratch normal, uncoated glass when used properly, but it is always advisable to check if the glass is scratch resistant before work starts, to follow the manufacturer’s instructions and to perform a test on a hidden area.

One useful way to determine whether glass is safety glass or not is to do the lighter trick. Simply hold a lit flame, from a lighter, match or candle, in front of the glass. If you see a double reflection in the pane it is safety glass. If you see just one flame reflected back at you, then it is normal glass.

When it comes to blades, the material they are made from and the way they have been sharpened are extremely important.

Scrapers are called upon to clear the most tough and stubborn dirt, debris and residue so the steel used should be hardened and corrosion resistant, ensuring that blades stay sharper, and rust-free, for longer. Carbon steel or low/high alloy stainless steels can provide these properties. Carbon steel will produce a stiffer blade, whereas those made from stainless steel are more flexible.

Carbon steel is a hard material, giving the cutting edge greater stability. The blade will stay sharp, but as water and/or cleaning chemicals are often used to lubricate the surface of the window being cleaned, this will have an effect as carbon steel rusts more quickly than stainless steel.

In contrast, stainless steel is more flexible and stays rust-free thanks to its high chrome content, which makes it a more expensive option. Being softer in terms of material means that the finely ground surface will wear down and lose its sharpness quicker than a carbon steel blade.

Dual-sided window cleaning blades made from corrosion resistant 440A grade stainless steel provide excellent edge retention, which means that the blades stay sharp for a long time. These blades benefit greatly from going through a precise honing process, which creates a cutting angle that is sharp and consistent, enhancing the speed and effectiveness of every scraper pass.

Scrapers need to be used with care, the golden rule being never to use one on dry glass. Always wet your window with the correct cleaning solution for the material you are about to remove as this helps to lubricate the blade.

It’s also important to scrape in one direction only, lift the scraper from the surface, and then reapply it. Scraping the blade back and forth across a window increases the chances of dirt being trapped under the blade and causing scratches. Clean your blade regularly in water and always apply an even pressure, holding the blade flat against the glass.

Old, worn-out or damaged blades must be changed regularly to ensure optimum results, and safety is also highly important. When not in use, caps should be placed over blades, or retracted, to minimise the risk of cuts.

The most effective and up-to-date models feature ergonomically designed handles which provide a more comfortable fit in the hand, minimising stresses and strains on hands, arms and shoulders. The latest innovation to hit the scraper market is the ability to change the angle of the scraper head from straight to 30 degrees at the touch of a button. This ensures a smooth and swift transition between manual and pole work.

Blades that are easy to change, using a slider mechanism, are preferable; and it’s also worth investing in a holster that allows you to store your scraper when not in use, but makes it easily accessible when needed. Choose one that has the ability to fit onto a range of tool belts, and has a solid back to protect your leg/body from cuts.

Scrapers have been used by the window cleaning, glass and building industries for years, and they are still the tools to go to when faced with certain types of dirt and debris. As design and technology know-how helps to improve the results they achieve, they can only retain their usefulness for many years to come.


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