Glass on site: what damages it before handover
Glass can cope with a lot, but not everything. Most damage happens while building work is still going on: from cement, dust, scrapers and sparks. The majority of it can be avoided.
Most damage happens before handover
Experience shows that glass is most often damaged while building work is in progress, and seldom once the building is finished. Scratches, dull patches and burn marks are usually not a factory fault, but marks left by the site.
Cement, plaster, concrete and lime
This is the most common cause of damage. Fresh cement, plaster and concrete are highly alkaline and etch the glass. Once they have dried and been removed, they leave a dull patch that can no longer be cleaned off.
What to do: rinse it off straight away with plenty of clean water, while it is still wet. Never remove it dry.
Dust and dry wiping
Site dust is sand. Wiping with a dry cloth, or sliding one pane over another, leaves fine scratches.
Dust is removed with plenty of water, never dry.
Scrapers and knives
A blade scratches glass. A scraper (filling knife) is never used across the whole surface of the glass.
On toughened glass, scratches show up more than on ordinary glass, sometimes only after a while.
Sparks from angle grinders and welding
Sparks from angle grinders and welding burn into the glass and stay there for good. Glass close to this kind of work must be covered.
Acids, alkalis and façade cleaners
Products for cleaning brickwork and façades often contain hydrofluoric acid, which permanently etches glass. Neither alkalis nor acids should ever be used on glass.
The wrong silicone or sealant can leave permanent streaks. More in the article Insulating glass units: installation, sealants and storage.
How to protect the glass
Protective film on the glass when the windows go in before plastering and other work.
The contractor tells the other trades that the windows are in and the glass must be protected. The final clean cannot remove everything that has built up over the whole construction period.
How to clean it properly
Plenty of clean water, so that the dirt does not scour the glass.
Soft sponge, cloth, chamois leather, rubber squeegee. One set of tools for the glass, another for the frame and seals.
A mild cleaning agent or an ordinary glass cleaner. Remove grease and silicone residue with alcohol (ethyl alcohol or isopropanol).
Never: alkalis, acids, products containing fluoride, blades, abrasive sponges, polishing machines.
If you notice any damage while cleaning, stop straight away and ask.
Special glass needs even more care
Some glass types have a coating on the outer face: highly reflective solar control glass, anti-reflective glass and self-cleaning glass. A scratch in such a coating is more visible, and at that spot the coating stops working.
Silicone and grease must be kept off self-cleaning glass, and the squeegee must be clean.
In short: cover the glass with film, rinse off cement straight away, nothing dry and nothing sharp.
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