Haze on new storefront or window glass traces, in National Glass Association bulletins, to the construction site: concrete and masonry runoff, hard water spotting, overspray from sealing masonry, smeared sealants, weld splatter, and glass that got wet in storage. Deposits are a job for a professional window cleaner; etching, corrosion and weld damage have changed the glass itself.
The first kind of haze is something that landed on the glass and dried there. The National Glass Association and the International Window Cleaning Association describe stubborn deposits from concrete and masonry runoff, along with hard water spotting, and trace them to glass stored or left unprotected and to installed glass that was not cleaned promptly during construction.
Concrete is the stubborn one. A glass manufacturer's technical guidance explains that rain running off concrete dissolves silicate, and if that water dries on the glass it leaves "a tenacious, water-insoluble deposit that is chemically bonded to the glass," a bond that forms as the water dries and in mid-winter as readily as in any other season.
NGA says "A large percentage of damaged glass results from non-glass trades working near glass," and lists splashed mortar and cement, smeared silicone sealants, and sealer overspray from masonry waterproofing among conditions that can need more than routine cleaning. NGA adds that protective film left past the manufacturer's recommended date may need aggressive methods to remove.
Some haze will not clean off because the surface itself has changed. The National Glass Association's site protection bulletin describes surface corrosion "often characterized by permanent iridescent or white haze surface staining" in glass that got wet during storage, and chemical attack and surface pitting from overspray and runoff when concrete, masonry or roofing is sealed or cleaned.
A glass manufacturer adds that rain can leach alkaline material out of concrete onto glass and in some instances cause staining and etching. The same bulletin ties hot weld splatter to replacement: it says deep surface scratches, contact by hot weld splatter and edge damage "threaten the structural integrity of glass and may require glass replacement." Grit wiped across dry glass scratches it rather than hazing it; NGA calls for enough water to keep abrasive particles from being trapped under the cleaning tool, and for daylight to evaluate a surface for damage.
The National Glass Association's recommended method is gentle: rinse off heavy dirt, soak the glass with clean water and a mild, non-abrasive glass cleaning solution, and remove all of it right away with a window cleaning squeegee. NGA adds that cleaning solutions "should not include acids" and that "razor blades and metal scrapers should not be part of routine cleaning."
Anything stronger is non-routine work for a professional window cleaner who handles construction cleaning, and NGA warns that "any non-routine cleaning carries a risk of irreparable damage to glass products." Replacement comes into it when the damage is in the glass: weld splatter, deep scratches, severe corrosion, or bonded residue where a glass manufacturer says new glass may prove the only practical remedy. The association's site protection bulletin says the glazing contractor and the glass fabricator or supplier should assess damage that has already occurred.
For a storefront that came out of construction cloudy, ask whether a lite can be restored or must be replaced before anyone tries a stronger method. Accurate Glass & Mirror works on commercial glass, including storefronts and partitions, starting with a free on-site measure and a firm, itemized written quote.
The National Glass Association's gentle cleaning method is the starting point on tempered glass too, and scraping is riskier there. The association says razor blades should be the last possible option, especially on heat-treated glass, and a glass manufacturer says that on tempered glass even a plastic scraper may dislodge tiny debris fused to the surface during heat treating.
Surface haze sits on a face a professional window cleaner can test clean in a small area, while fog or debris inside an insulated unit sits between the panes, where no cleaning reaches. The Fenestration and Glazing Industry Alliance treats fogging inside the unit as an insulating-unit condition, and the storefront glass care guide handles seal failure.
Tell us what the site went through, whether that was concrete work above the glass, welding nearby or film left on too long, and we will look at the glass at a free on-site measure and talk through whether a lite can be restored or must be replaced.
